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Home My WebLink AboutReport B - Alaska Coal and Coalbed Methane PotentialU.S. Department of the Interior U.S. Geological Survey Alaska Coal Geology, Resources, and Coalbed Methane Potential By Romeo M. Flores, Gary D. Stricker, and Scott A. Kinney U.S. Geological Survey, Denver, Colorado 80225 DDS–77 U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, Director U.S. Geological Survey, Reston, Virginia: 2004 For sale by U.S. Geological Survey, Information Services Box 25286, Denver Federal Center Denver, CO 80225 For more information about the USGS and its products: Telephone: 1-888-ASK-USGS World Wide Web: http://www.usgs.gov/ Conversion Factors Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) foot (ft.) 0.3048 meter (m) mile (mi.) 1.609 kilometer (km) Area acre 4,047 square meter (m2) acre 0.4047 hectare (ha) acre 0.4047 square hectometer (hm2) acre 0.004047 square kilometer (km2) square foot (ft2) 9,290 square centimeter (cm2) square foot (ft2) 0.0929 square meter (m2) square inch (in2) 6.452 square centimeter (cm2) square mile (mi2) 259.0 hectare (ha) square mile (mi2) 2.590 square kilometer (km2) Weight metric ton 1.10 ton, short (2,000 lb) ton, short (2,000 lb) 0.907 metric ton pound (lb) 453.59 gram (gm) gram (gm) 0.0022 pound (lb) Energy Btu per pound (Btu) 0.0022 mega joules per kilogram Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F= (1.8x°C) +32 Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C= (°F-32)/1.8 III Contents Abstract ..........................................................................................................................................................1 Introduction ...................................................................................................................................................1 Geological Setting ........................................................................................................................................4 Physiographic Regions ...................................................................................................................4 Regional Geology ............................................................................................................................4 Origin of Alaska Coal ....................................................................................................................................6 Coal Metamorphism, Composition, Rank, and Occurrence...................................................................7 Coal Resource Classification ......................................................................................................................8 Distribution of Coal in Alaska....................................................................................................................10 Northern Alaska-Slope Coal Province ....................................................................................................10 Cretaceous Rocks .......................................................................................................................................10 Nanushuk Group............................................................................................................................10 Colville Group .................................................................................................................................13 Cretaceous-Tertiary Rocks........................................................................................................................16 Jago River Formation....................................................................................................................17 Sagavanirktok Formation .............................................................................................................17 Coal Resource Assessment of the Northern Alaska-Slope Coal Province .......................................22 Cretaceous Rocks .........................................................................................................................22 Coal Quality ....................................................................................................................................23 Tertiary Rocks ................................................................................................................................24 Coal Quality ....................................................................................................................................24 Coal Petrology................................................................................................................................24 Central Alaska-Nenana Coal Province ...................................................................................................25 Tertiary Usibelli Group ..................................................................................................................26 Healy Creek Formation .................................................................................................................27 Sanctuary Formation ....................................................................................................................31 Suntrana Formation......................................................................................................................31 Lignite Creek Formation ...............................................................................................................32 Grubstake Formation ....................................................................................................................32 Nenana Gravel ...............................................................................................................................35 Coal Resource Assessment of the Central Alaska-Nenana Coal Province ......................................35 Coal Quality ....................................................................................................................................39 Coal Petrology................................................................................................................................39 Southern Alaska-Cook Inlet Coal Province ............................................................................................40 Tertiary Rocks ................................................................................................................................42 Lower Tertiary Rocks ....................................................................................................................42 Upper Tertiary Kenai Group .........................................................................................................45 Hemlock Conglomerate ................................................................................................................52 Tyonek Formation ..........................................................................................................................54 Beluga Formation ..........................................................................................................................60 IV Sterling Formation .........................................................................................................................65 Coalfields ........................................................................................................................................68 Matanuska Coalfield .....................................................................................................................68 Susitna-Beluga Coalfield .............................................................................................................74 Broad Pass Coalfield ....................................................................................................................75 Kenai Coalfield ...............................................................................................................................75 Coal Resource Assessment in the Southern Alaska-Cook Inlet Coal Province ...............................76 Matanuska Coalfield .....................................................................................................................78 Susitna-Beluga Coalfield .............................................................................................................78 Broad Pass Coalfield....................................................................................................................79 Kenai Coalfield ............................................................................................................................................79 Coal Quality ....................................................................................................................................79 Coal Petrology................................................................................................................................80 Coalbed Methane Potential ......................................................................................................................80 Northern Alaska-Slope Coal Province .......................................................................................81 Central Alaska-Nenana Coal Province ......................................................................................82 Southern Alaska-Cook Inlet Coal Province ...............................................................................82 Summary ....................................................................................................................................................107 Acknowledgments ....................................................................................................................................112 References Cited ......................................................................................................................................117 Figures 1. Map showing coal ranks in coal basins and coal occurrences in Alaska with emphasis on the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces ........................................................................................................................................2 2. Map showing the coal rank and land ownership of Alaska ...........................................................3 3. Map showing the geology and structure of Alaska .........................................................................3 4. Map showing the physiographic regions of Alaska ........................................................................5 5. Map showing general tectonic framework of the Cook Inlet Basin, associated subduction zone, accreted terranes, and volcanic arc.......................................................................................6 6. Stratigraphic column of the Mesozoic and Cenozoic rocks in the Northern Alaska- Slope coal province...............................................................................................................................9 7. Photograph of a coal bed (about 20 feet thick) in the Nanushuk Group ....................................11 8. Map showing net coal thickness map of the Nanushuk Group in the western part of the Northern Alaska-Slope coal province .......................................................................................11 9. Cross section showing the Nanushuk progradation sequences.................................................12 10. Sandstone percentage contour map in the Northern Alaska-Slope coal province .................13 11. Paleogeographic maps showing the depositional environments of the Nanushuk Group in the central Northern Alaska-Slope coal province. (A) early to middle Albian time; (B) middle to late Albian time; (C) late Albian to Cenomanian (?) time; and (D) Cenomanian time (maximum regression)...........................................................................................................................14 V 12. Photograph of interbedded coal, sandstone, siltstone, and mudstone of the Kogosukruk Tongue of the Prince Creek Formation along the lower Colville River downstream from the mouth of the Anaktuvuk River .........................................................16 13. Paleogeographic map showing the depositional environments of the Jago River Formation in the Arctic National Wildlife Refuge area .......................................................17 14. Photograph of a coal bed underlain by a sandstone in the Sagavanirktok Formation ..............................................................................................................................................18 15. Photograph of fluvial-channel sandstone and associated rocks in the Sagavanirktok Formation....................................................................................................................18 16. Stratigraphic cross section of the Tertiary Brookian sequence in the eastern part of the National Petroleum Reserve Alaska ..........................................................................................19 17. West to east stratigraphic cross section showing variations of the coal beds, conglomerates, sandstones, mudstones, and siltstones in the Staines Tongue of the Sagavanirktok Formation between the National Petroleum Reserve in Alaska and Arctic National Wildlife Refuge ........................................................................................................20 18. Maps showing the (A) depth to top of coal-bearing interval and (B) net coal thickness isopach of the Staines Tongue of the Sagavanirktok Formation .................................................21 19. Map showing the coalfields in the Central Alaska-Nenana coal province ...............................25 20. Generalized stratigraphic and lithofacies column of the Usibelli Group in the Central Alaska-Nenana coal province ...........................................................................................................26 21. Stratigraphic cross section showing the variations of the conglomerates, sandstones, siltstones, mudstones, and coal beds in the lower part of the Usibelli Group in the Healy Creek coalfield on the southern part of the Central Alaska-Nenana coal province ................27 22. Paleogeographic maps showing depositional environments of: (A) Healy Creek Formation, (B) Sanctuary Formation, (C) Suntrana Formation, and (D) Lignite Creek Formation ..............................................................................................................................................28 23. Crossbed-orientation measurements in fluvial-channel sandstones in the Healy Creek, Suntrana, and Lignite Creek Formations in Suntrana area ..........................................................28 24. Stratigraphic cross section showing the basal conglomerates and sandstones in the lower part of the Healy Creek Formation east of Suntrana ..........................................................29 25. Photograph of conglomerates (a few inches to 5 feet thick or a few centimeters to 1.5 meters) and sandstones (6 inches to 8 feet thick or 15.2 centimeters to 2.4 meters) deposited by braided streams in the lower part of the Healy Creek Formation in east of Suntrana ...........................................................................................................................................29 26. Stratigraphic cross section showing the middle, coal-bearing part of the Healy Creek Formation east of Suntrana ...............................................................................................................30 27. Stratigraphic cross section of the uppermost part of the Healy Creek Formation showing the fluvial-channel sandstones and F coal bed, and overlying Sanctuary Formation east of Suntrana ...........................................................................................................................................30 28. Photograph of the uppermost part of the Healy Creek Formation, F coal bed, and overlying mudstones of the Sanctuary Formation in the Lignite Creek coalfield .....................31 29. Photograph of the lacustrine mudstone and lenticular limestone units in the Sanctuary Formation in the Lignite Creek coalfield ......................................................................................... 31 VI 30. Stratigraphic cross section of the Suntrana Formation showing the Nos. 2, 3, and 4 coal beds and interbedded fluvial-channel sandstones west of Suntrana........................................32 31. Photograph of the Suntrana showing the thick No. 3 coal bed, clinker bed of No. 4 coal bed, thin No. 5 coal bed, and interbedded fluvial-channel sandstones and clay plug-overbank deposits west of Suntrana .......................................................................................33 32. Photograph of the abandoned fluvial-channel mudstone or clay plug deposit........................33 33. Stratigraphic cross section of the Nos. 3, 4, and 6 coal beds of the Suntrana Formation in the Poker Flats strip mine of Usibelli Coal Mine ........................................................................34 34. Photograph of the Poker Flats strip mine showing the highwall exposing fluvial-channel sandstones and No. 3 coal bed (lower bench) and No. 4 coal bed (upper bench)...................34 35. Thickness map of the No. 6 coal bed of the Suntrana Formation................................................35 36. Stratigraphic cross section of the lower part of the Lignite Creek Formation showing interbedded fluvial-channel sandstones, crevasse splay flood-plain deposits, and thin coal beds west of Suntrana ...............................................................................................................36 37. Photograph of the interbedded fluvial-channel sandstones, flood-plain deposits, and an interbedded thin coal bed of the Lignite Creek Formation west of Suntrana ......................36 38. Photograph of the coarsening-upward mudstone, siltstone, and sandstone sequence overlain by thin coal beds of the Lignite Creek Formation west of Suntrana ............................36 39. Stratigraphic cross section showing variation of minable Healy Creek coal beds and associated sandstones, mudstones, and siltstones in the Jarvis Creek coalfield ...................38 40. Map showing coalfields in the Southern Alaska-Cook Inlet coal province ...............................41 41. Tectonic and volcanic settings of the Cook Inlet Basin .................................................................42 42. Generalized time-transgressive stratigraphy in the Cook Inlet Basin ........................................43 43. Depositional model of the Kenai Group in the Cook Inlet Basin ..................................................44 44. Generalized chronostratigraphic column of the coal-bearing Kenai Group and related rock units in the Southern Alaska-Cook Inlet coal province ........................................................44 45. A generalized stratigraphic column of the Chickaloon and Wishbone Formations in the Matanuska coalfield ............................................................................................................................45 46. Photograph of coal beds of the Chickaloon Formation in the Wishbone Hill coal district ......46 47. Photograph of the lenticular fluvial-channel sandstone (20 feet or 6.1 meters thick) and associated rocks of the Chickaloon Formation in the Wishbone Hill coal district ...................46 48. Photograph of the tabular crevasse splay sandstone and associated flood-plain deposits of the Chickaloon Formation in the Wishbone Hill coal district ...................................47 49. Vertical and lateral lithofacies variations of the Wishbone Formation in the Wishbone Hill coal district ....................................................................................................................................47 50. Photograph of the braided-stream-deposited conglomerates and sandstones in the Wishbone Formation in the Wishbone Hill coal district ................................................................48 51. Stratigraphic cross section of the lower part of the Chickaloon Formation in the Wishbone Hill coal district .................................................................................................................48 VII 52. Photograph of the lower part of the Chickaloon Formation showing the Midway coal zone and adjoining fluvial-channel sandstones in the Wishbone Hill coal district ..................49 53. Stratigraphic cross section of the middle part of the Chickaloon Formation in the Wishbone Hill coal district .................................................................................................................49 54. Photograph of the upper part of the Chickaloon Formation showing the Premier coal zone (50 feet or 15.2 meters thick), Jonesville coal zone (30 feet or 9.1 meters thick), and associated fine-grained sediments in the Wishbone Hill coal district .......................................50 55. Stratigraphic cross section of the upper part of the Chickaloon Formation in the Wishbone Hill coal district .................................................................................................................50 56. Photograph of the upper part of the Chickaloon Formation showing the Jonesville coal zone overlain by fluvial-channel sandstones (>50 feet or >15.2 meters thick) of the Wishbone Formation in the Wishbone Hill coal district ................................................................51 57. Paleogeographic map showing depositional environments of the Chickaloon Formation in the Matanuska coalfield .................................................................................................................51 58. Map showing lines of stratigraphic cross sections of the Kenai Group in the offshore and onshore Cook Inlet Basin. Map also shows areas of cross sections the Kenai Group in the Chuitna area, Capps Glacier area, along the west coast of Kenai Peninsula, and along the north coast of Kachemak Bay .........................................................................................52 59. Offshore north-south cross section (A–A’) of the Kenai Group along the axis of the Cook Inlet Basin .............................................................................................................................................53 60. Offshore (west) to onshore (east) cross section (B–B’) of the Kenai Group across the Cook Inlet Basin ...................................................................................................................................54 61. Onshore north-south cross section (C–C’) of the Kenai Group along the western part of the Kenai Peninsula or eastern margin of the Cook Inlet Basin .................................................55 62. Photograph of conglomerates in the Hemlock Conglomerate in the Katmai National Park ...56 63. Photograph of sandstones in the Hemlock Conglomerate in the Katmai National Park .........56 64. Photograph of thin coal and carbonaceous shale beds in the Hemlock Conglomerate in the Katmai National Park....................................................................................................................57 65. Photograph of braided stream deposits (conglomeratic lower part) in the Hemlock Conglomerate ........................................................................................................................................57 66. Net coal thickness isopach map of the Tyonek Formation in the Cook Inlet Basin ..................58 67. Photograph of coal beds and interbedded fluvial-channel sandstones and mudstones in the Tyonek Formation in the Chuitna River drainage basin ......................................................58 68. Photograph of fluvial-channel sandstones and Chuitna coal bed in the Tyonek Formation in the Chuitna River drainage basin ..................................................................................................58 69. Net sandstone thickness isopach map of the Tyonek Formation in the Cook Inlet Basin .......59 70. Paleogeographic map (block diagram) showing depositional environments of the Tyonek Formation in the Cook Inlet Basin........................................................................................59 71. Generalized stratigraphic column of minable coal beds in the Tyonek Formation in the Chuitna River drainage basin and adjoining areas ........................................................................60 VIII 72. Three-dimensional cross sections (fence diagram) of the Chuitna coal bed and interbedded erosional-based sandstones deposited by braided streams of the Tyonek Formation in the Chuitna River drainage basin ................................................................61 73. Stratigraphic cross section of the coal beds, fluvial-channel sandstones, and intertidal deposits in the Diamond Chuitna lease area east of the Chuitna River drainage basin .........61 74. Stratigraphic lithofacies sequence in the Tyonek Formation showing tidal sandstone flats facies near Wasilla .....................................................................................................................62 75. Stratigraphic cross section of the coal beds and fluvial-channel sandstones in the Diamond Chuitna lease area east of the Chuitna River drainage area ......................................63 76. Vertical lithofacies and associated geophysical logs of minable coal beds (Reds 1, 2, and 3, and Blue) and interbedded fluvial-channel sandstones, and flood plain claystones and siltstones in the Diamond Chuitna lease area east of the Chuitna River drainage area .............................................................................................................................63 77. Vertical lithofacies of coal beds (Reds 1, 2, and 3) and interbedded tidal and intertidal sandstones, siltstones, and mudstones in the Diamond Chuitna lease area east of the Chuitna River drainage area ..............................................................................................................64 78. Photograph of the Capps Glacier coal bed (50 feet or 15.2 meters thick) and overlying fluvial-channel sandstones in the Capps Glacier area..................................................................64 79. Photograph of the coal beds and interbedded flood-plain/crevasse splay deposits in the Capps Glacier area .............................................................................................................................64 80. Structural cross section (north-south) of the Capps Glacier coal bed and associated rocks of the Tyonek Formation in the Capps Glacier area ............................................................64 81. Stratigraphic cross section (northeast-southwest) of the rocks of the Tyonek Formation at Barabara Point showing lenticular conglomerates, sandstone, and coal beds ..................65 82. Stratigraphic (structural) cross section of the Capps Glacier coal bed and associated rocks of the Tyonek Formation in the Capps Glacier area ............................................................65 83. Photograph of the fluvial-channel sandstones (average 60 feet or 18.3 meters thick), flood-plain mudstone and siltstones, and coal beds of the Beluga Formation along the coastal bluffs in west Homer, Kenai Peninsula ...............................................................................66 84. Photograph of a coal bed (3.5 feet or 1.1 meters thick) and crevasse splay deposits of the Beluga Formation along the coastal bluffs west of Homer, Kenai Peninsula ...........................66 85. Stratigraphic cross section of the Beluga Formation showing thick coal beds (for example, Cooper coal bed), fluvial-channel sandstones, and flood-plain mudstone and siltstone along the coastal bluffs west of Homer, Kenai Peninsula ....................................67 86. Stratigraphic cross section of the Beluga Formation showing interbedded thin to thick coal beds (for example, Cooper coal bed), fluvial-channel sandstones, and flood-plain deposits along the coastal bluffs west of Homer, Kenai Peninsula ............................................67 87. Paleogeographic map (block diagram) showing depositional environments of the Beluga Formation in the Cook Inlet Basin .....................................................................................................68 88. Photograph of fluvial-channel sandstones and thin coal of the Sterling Formation along the coastal bluffs in the Clam Gulch area, Kenai Peninsula..............................................69 IX 89. Photograph of fluvial-channel sandstones overlying thin (3 feet [0.9 meter]) to thick (12 feet [3.6 meters]) coal beds of the Sterling Formation along the coastal bluffs between the Clam Gulch and Ninilchik, Kenai Peninsula ..........................................................69 90. Stratigraphic cross sections showing variations in fluvial-channel architecture in the upper part of the Sterling Formation in the Clam Gulch area, Kenai Peninsula: A, Lower part of Clamgulchian type section; B, Middle part of Clamgulchian type section; C, Upper part of Clamgulchian type section ..................................................................70 91. Stratigraphic cross section showing coal beds, fluvial-channel sandstones, and interbedded flood-plain mudstones and siltstones in the lower part of the Sterling Formation between the Clam Gulch area and Ninilchik, Kenai Peninsula ..............................71 92. Photograph of thin to thick coal beds in the lower part of the Sterling Formation.................72 93. Block diagram showing depositional environments of the Sterling Formation in the Cook Inlet Basin .................................................................................................................................72 94. Map showing the geology and coal districts in the Matanuska coalfield ...............................73 95. Cross section of the Premier and Jonesville coal zones of the Chickaloon Formation in the Wishbone Hill coal district ........................................................................................................73 96. Geologic map of the Wishbone Hill coal district showing doubly plunging syncline disrupted by normal faults ................................................................................................................74 97. Photograph of a 4-foot-thick (1.2 meters) coal bed interbedded with fluvial-channel sandstones and flood plain mudstones and siltstones in the Sterling Formation in the Clam Gulch area .................................................................................................................................76 98. Stratigraphic cross section showing interbedded coal beds, fluvial-channel sandstones, and flood-plain mudstones and siltstones in the lowermost part of the Sterling Formation along the north shore of Kachemak Bay east and west of McNeil Canyon ............................76 99. Photograph of a coal bed with tonstein partings and related rocks of the Beluga Formation along the beach bluffs on the northern shore of the Kachemak Bay ....................76 100. Stratigraphic cross section showing interbedded coal beds, fluvial-channel sandstones, and flood-plain mudstones and siltstones in the uppermost part of the Beluga Formation west of McNeil Canyon ....................................................................................................................76 101. Stratigraphic cross section showing interbedded coal beds, fluvial-channel sandstones, and flood-plain mudstones and siltstones in the uppermost part of the Beluga Formation at the mouth of Fritz Creek ...................................................................77 102. Distribution of surface vitrinite reflectance values at sea level in the Northern Alaska-Slope coal province .............................................................................................................83 103. Map of the Northern Alaska-Slope coal province showing distribution of bituminous and subbituminous coals ..................................................................................................................83 104. Map showing surface vitrinite reflectance values in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces ............................................84 105. Vitrinite reflectance values for the Meade Quadrangle, National Petroleum Reserve in Alaska ............................................................................................................................................106 106. Vitrinite reflectance values for the Tunalik No. 1 well, National Petroleum Reserve in Alaska ............................................................................................................................................106 X 107. Stratigraphic cross section of the Nanushuk Group with superimposed vitrinite reflectance values ...........................................................................................................................108 108. Coalbed methane potential in the Nanushuk Group coals based on the thickness and vitrinite reflectance of the nonmarine part of the group in the Northern Alaska-Slope coal province ....................................................................................................................................109 109. Distribution of surface vitrinite reflectance (Ro) values in the Northern Alaska-Slope coal province ....................................................................................................................................109 110. Map of the Cook Inlet Basin showing distribution of oil and gas fields offshore and onshore ..............................................................................................................................................110 111. Facies profile of the lower part of the Sterling Formation and accompanying downhole logs showing horizons of gas accumulation...............................................................................111 112. Facies profile of the upper part of the Beluga Formation and accompanying downhole logs showing horizons of gas-perforated intervals ...................................................................112 113. Location map of the Kenai gas field in the Kenai Peninsula....................................................112 114. Basinwide and vertical variations of vitrinite reflectance (Ro) values in the Cook Inlet Basin ..................................................................................................................................................113 115. Coalbed methane prospect area and depths to vitrinite reflectance values of 0.6 percent superimposed on the thickness isopach of the Tyonek Formation south of the Castle Mountain fault in the northeastern part of the Cook Inlet .....................................113 116. Downhole geophysical logs, hot wire total gas and methane contents, vitrinite reflectance values, and illite diagenetic values in the Edna Mae Walker drill hole ............114 117. Stratigraphic cross section of the Kenai Group in the offshore Cook Inlet Basin with superimposed vitrinite reflectance values .................................................................................115 118. Stratigraphic cross section of the Kenai Group in the onshore Cook Inlet Basin with superimposed vitrinite reflectance values .................................................................................116 Tables 1. Coal resource estimates for Alaska using the classification system of Wood and others (1983)........8 2. Estimates of hypothetical coal resources for the Cretaceous Nanushuk Group and Tertiary Staines Tongue in the Sagavanirktok Formation in the Northern Alaska-Slope coal province .........23 3. (a) Coal quality of coal deposits in the Cretaceous Nanushuk Group in the Northern Alaska-Slope coal province. (b) Coal quality of coal deposits in the Tertiary Staines Tongue in the Sagavanirktok Formation in the Northern Alaska-Slope coal province ..............24 4. Estimates of coal resources for the Tertiary Usibelli Group in the Central Alaska-Nenana coal province ..........................................................................................................................................37 5. Coal quality of coal deposits in the Tertiary Usibelli Group in the Central Alaska-Nenana coal province..........................................................................................................................................40 XI 6. Estimates of coal resources for the Tertiary Kenai Group in the Matanuska, Broad Pass, Susitna, and Kenai coalfields in the Southern Alaska-Cook Inlet coal province .......................78 7. Range (minimum and maximum values) of quality parameters for Tertiary coal deposits in the Matanuska, Broad Pass, Susitna, and Kenai coalfields in the Southern Alaska-Cook Inlet coal province .................................................................................................................................80 8. (a) Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. (b) Vitrinite reflectance values of coals across the surface in the Northern Alaska Slope, Central-Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces ..............(a) 85, (b) 102 9. Properties of sandstone reservoirs and associated gas in the Sterling and Beluga Formations ............................................................................................................................................110 1 Abstract Estimated Alaska coal resources are largely in Creta- ceous and Tertiary rocks distributed in three major provinces. Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet. Cretaceous resources, predominantly bitu- minous coal and lignite, are in the Northern Alaska-Slope coal province. Most of the Tertiary resources, mainly lignite to sub- bituminous coal with minor amounts of bituminous and semi- anthracite coals, are in the other two provinces. The combined measured, indicated, inferred, and hypothetical coal resources in the three areas are estimated to be 5,526 billion short tons (5,012 billion metric tons), which constitutes about 87 percent of Alaskaʼs coal and surpasses the total coal resources of the conterminous United States by 40 percent. Coal mining has been intermittent in the Central Alaskan- Nenana and Southern Alaska-Cook Inlet coal provinces, with only a small fraction of the identified coal resource having been produced from some dozen underground and strip mines in these two provinces. Alaskan coal resources have a lower sulfur content (averaging 0.3 percent) than most coals in the conterminous United States and are within or below the minimum sulfur value mandated by the 1990 Clean Air Act amendments. The identified resources are near existing and planned infrastructure to promote development, transportation, and marketing of this low-sulfur coal. The relatively short distances to countries in the west Pacific Rim make them more exportable to these countries than to the lower 48 States of the United States. Another untapped but potential resource of large mag- nitude is coalbed methane, which has been estimated to total 1,000 trillion cubic feet (28 trillion cubic meters) by T.N. Smith, 1995, Coalbed methane potential for Alaska and drilling results for the upper Cook Inlet Basin: Intergas, May 15 – 19, 1995, Tuscaloosa, University of Alabama, p. 1 – 21. Introduction This report is a synthesis of the largely untapped hypo- thetical coal resources of Alaska, which are estimated to be as much as 5,526 billion short (or 5.5 trillion) tons (5,012 billion metric tons). The last coal resource assessment in 1974 for the conterminous United States (coal remaining in the ground) estimated a total coal resource of 3,968 bil- lion short tons (3,600 billion metric tons) or 4 trillion short tons (Averitt, 1975). Thus, the Alaska coal resource estimate surpasses the total coal resources of the conterminous United States by 40 percent. This report focuses on an assessment of the coal resources of the three major coal provinces in Alaska: Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet and makes up 87 percent of the total coal resources of the State (fig. 1). Also, it will concentrate on the origin, geologic setting, and depositional environments of the coal, as well as coal rank, quality, and petrology and the amount of the resources. In addition, this report will sum- marize the coalbed methane potential and prioritize areas for exploration and development in these major coal provinces. The coal resources of Alaska occur in discrete areas (coalfields) and in isolated, unrelated outcrops (occurrences) (fig. 1). A coalfield may contain coal beds of various ranks, shown in figure 2, and different ages and geologic settings, shown in figure 3. Coal resources and geological settings of minor coalfields not reported here may be found in Stricker (1991) and Wahrhaftig and others (1994). Before the arrival of the European immigrants, native inhabitants used coal in Alaska (Chapman and Sable, 1960, p. 159). The Beechey expedition of 1826–1827 reported the presence of coal in Alaska (Huish, 1836; Dall, 1896). Whal- ing shippers mined coal from near Cape Beaufort, north of the Arctic Circle, before the turn of the twentieth century (Con- well and Triplehorn, 1976). The first coal mine was opened Alaska Coal Geology, Resources, and Coalbed Methane Potential By Romeo M. Flores, Gary D. Stricker, and Scott A. Kinney 2 Alaska Coal Geology, Resources, and Coalbed Methane Potential in 1855 and closed in 1867 at Port Graham (fig. 2) on the southwestern part of the Kenai Peninsula (Martin, 1915). The Russians opened and operated this coal mine before the United States took possession of the Alaska Territory. The U.S. Con- gress passed two significant legislative acts in 1914 that led to development of coal resources of Alaska: (1) the Alaska Coal Leasing Act promoted opening mines in the Alaskan coalfields and (2) the Alaska Railroad Enabling Act authorized con- struction of the railroad from Anchorage to Fairbanks, which encouraged the use of coal by the locomotives and by the gold mining operations to power gold dredges and to fuel steam boilers for thawing the frozen ground. Many coal mines in the Nenana and Matanuska coalfields were active after Congress authorized the construction of the Alaska Railroad, which promoted large-scale production, transportation, and marketing. The first coal-lease sale was held in conjunction with an oil-lease sale in 1983. In 1984, export of Alaskan coal began with shipments to South Korea from Nenana coalfield. Other developments included con- struction of a coal terminal at the deep-water port at Seward, new loading facilities at the Usibelli coal mine, and upgrading of the Alaska Railroad to handle hauling coal to Seward. In 1985, coal production increased by 60 percent over 1984, with a gross value on production of 1.4 × 106 short tons (1.27 × 106 metric tons) valued at $39.7 million (Bundtzen and others, 1986). Coal production for the year 2000 was estimated by Szumigala and Swainbank (2001) at 1,473,000 short tons valued at $38.7 million with 708,000 short tons being exported to Korea. An estimate of total coal in place is 10.4 × 1012 short tons (9.4 × 1012 metric tons), or about 50 percent of total of conterminous U.S. resources. The coal resources of Alaska, have been only minimally exploited or developed. Mined coal is presently utilized for domestic electric power-generating plants, and approximately one-half of the production from the Usibelli mine is shipped to Korea and potentially to other countries bordering the western Pacific Rim. Figure 1. Coal ranks in coal basins and coal occurrences in Alaska with emphasis on the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. Compiled and modified from Merritt and Hawley (1986); Barnes (1967a, 1967b); Magoon and others (1976); Plafker (1987). �� NORTH SLOPE Barrow �� Fairbanks �� Anchorage �� Nome �� GULF OF ALASKA Juneau Angoon ALASKA COALFIELDS AND COAL OCCURRENCES Bituminous Anthracite Subbituminous Lignite �� EXPLANATION �� Alaska Railroad and George Parks Highway Figure 2. Map showing the coal rank and land ownership of Alaska Figure 3. Map showing the geology and structure of Alaska. Modified from S.J. Moll, Scott Bie, Devon Peterson, D.C. Pray, F.H. Wilson, J.M. Schmidt, J.R. Riehle, T.P. Miller (unpublished data, 1997, U.S. Geological Survey, Reston, Virginia) after Beikman (1980). Introduction 3 80 Alaska Coal Geology, Resources, and Coalbed Methane Potential 1.30 percent, and 11.0 to 26.50 percent moisture content from the Kenai coalfield. Coal Petrology The coal petrology of the Tyonek coal beds in the Chuitna River drainage area was investigated by Rao and Smith (1986). Vitrinite (or huminite) is the most abundant maceral and varies from about 66 to 92 percent. Minor liptinite varies from 4 to 18 percent and inertinite from 0 to 9 percent. The woody or huminite maceral is composed mainly of cypress trees (Rao and Smith, 1986). However, oak, beech, hickory, elm, walnut, alder, and birch trees are represented in the peat- forming mires. The huminite maceral is either unevenly dis- tributed vertically throughout the coal beds or it increases in the upper and lower parts of the coal beds. Liptinite macerals in some coal beds increases in the upper part of the coal beds. Inertinite appears to be less preferentially distributed verti- cally in the coal beds than the huminite and liptinite macerals. However, local peak occurrences of inertinite indicate genera- tion of fusinite or charcoal that is formed by forest fires during dry periods. High occurrence of liptinite suggests differential decomposition of the more resistant exinite from vegetal matter. The high concentration of huminite in the lower part of coal beds indicates that the mires were initially vegetated by abundant trees, which evolved into less woody vegetation through time. The high concentration of huminite in the upper part indicates that the mire supported more woody vegetation through time. Coalbed Methane Potential The coal resources of Alaska (about 5,526 billion short tons; see table 1) contain significant potential economic coalbed methane resources. Methane derived from coal, which has migrated and is stored in interbedded sandstone reservoirs in the Cook Inlet Basin, is presently being developed. Coal- bed gas or methane-rich gas is stored (adsorbed) in the coal along fractures, cleats, and pores and (or) within (absorbed) the molecular structure of the coal. Gas is stored in the coal by molecular attraction on the surfaces of the structures of the coal. Methane is a by-product of fermentation during deposi- tion and coalification during burial of peat. The ability of the coal to store gas is a function of rank or grade of coalification (for example, lignite, subbituminous, bituminous) and tem- perature and pressure. Generally, more methane is stored in higher rank coal and at high pressure whereas higher tempera- ture decreases storage capacity. Methane generated in higher rank coal (for example, bituminous) is thermogenic in origin, and methane produced in lower rank coal (lignite and subbitu- minous) is biogenic in origin. Biogenic gas is generated during bacterial activity by methanogens or anaerobes that produced methane as a by-product of their metabolism. In most cases methanogens do this by reducing carbon dioxide with hydro- gen to produce methane. Biogenic gas generated from lignites in Alaska was determined from a 1994 U.S. Geological Survey test well in the Yukon Basin (Flats), where the coal beds are more than 21 ft (6.4 m) thick. A major by-product of development of coalbed meth- ane, especially for subbituminous coal, is coproduced water. Volumes of water produced in major methane-producing Table 7.Range (minimum and maximum values) of quality parameters for Tertiary coal deposits in the Matanuska, Broad Pass, Susitna, and Kenai coalfields in the Southern Alaska-Cook Inlet coal province. [All analyses except Calorific value (Btu) are in percent. Values reported on an as- received basis. Modified from Merritt, 1984] Area Moisture Volatile matter Fixed carbon Ash yield Total sulfur CalorificvalueBtu per pound �� basins in the conterminous United States vary significantly between bituminous and subbituminous coal. The volume of coproduced water from bituminous coal ranges in average from 48 to 240 barrels (7,632 to 38,160 liters) of water per day per well and from the subbituminous coal the average is about 440 barrels (91,600 liters) (Flores, 2000). Hence, the water: gas ratio for the bituminous coal ranges from 0.029 to 0.51 barrel per thousand cubic feet (16.3 to 286 liters per 100 m3) and from the subbituminous coal is 2.88 barrels per thousand cubic feet (21,360 liters per 100 m3) (Flores, 2000). In order to produce the methane from the coal, the reservoir needs to be dewatered, which results in the depressurization of the reser- voir. This water can be disposed of either on the surface, into ponds or existing drainages, or reinjected below the surface. Regulations, quality, and amount of the coproduced water influence the choice of a disposal system. Coproduced water from subbituminous coal of the Tertiary Fort Union Forma- tion being developed in the Powder River Basin of Wyoming is freshwater. It contains concentrations of dissolved solids mainly of bicarbonate, and trace elements and pH values that are generally below and within recommended drinking-water standards (Flores, 2000). Thus gas operators in that basin are permitted to dispose of the coproduced water on the surface; however, the large volume of water being disposed of is affect- ing the environment (for example, biota, ephemeral drainages, ground-water supply). Water-disposal problems may influence potential development in Alaska where the permafrost (for example, Northern Alaska-Slope coal province) is thick (Fer- rians, 1965), and freezing temperatures at the surface for much of the year may curtail surficial disposal by ponding or along preexisting drainages. The quality of water such as concen- tration of total dissolved solids and location of coalbed gas production where recharge areas are juxtaposed to brackish- marine bodies of water (sea, ocean, bay) may prevent surface disposal or reinjection, which may contaminate ground-water supply. Smith (1995) reported that Alaskaʼs in-place coalbed methane resources might be as much as 1,000 trillion cubic feet (tcf) (28 trillion cubic meters [tcm]) based on estimates of the gas content of as much as 245 standard cubic feet per ton (scf/t) for the coals. The high coalbed-methane resource esti- mate of Smith (1995) utilized 200 scf/t for both the subbitumi- nous and bituminous coals in the Northern Alaska-North Slope coal province and 152 scf/t for the subbituminous coal in the offshore area in the Southern Alaska-Cook Inlet coal province. Our investigations of the subbituminous coals in the Powder River coals indicate gas content ranging from 0 to 99 scf/t, averaging 25 scf/t (Stricker and others, 2001). If the Powder River Basin coalbed-methane content is applied for the Alaska subbituminous coal, Smithʼs estimate will be reduced to about one-half the volume. Northern Alaska-Slope Coal Province The voluminous lignite, subbituminous, and bituminous coal of the Northern Alaska-Slope coal province indicates a high potential for large biogenic and thermogenic gas resources. The abundance of bituminous coal with 1,910 bil- lion short tons (1,732 billion metric tons) and subbituminous coal with 1,960 billion short tons (1,778 trillion metric tons) in the Northern Alaska-Slope coal province (fig. 102) indi- cates a high potential for thermogenic and biogenic methane resources. Outcrop and surface-projected mean vitrinite reflectance values in the Northern Alaska-Slope coal province range from 0.31 to 1.71 percent, which corresponds to lignite to low volatile bituminous coal ranks (figs. 103 and 104; table 8a and 8b). Coal rank generally increases southward toward the Brooks Range where the vitrinite reflectance values exceed 1.71 percent (see table 8a and 8b). Thus, the vitrinite reflectance values suggest a range of coal maturation in which coalbed methane, both biogenic and thermogenic, may be gen- erated from subbituminous and bituminous coals, respectively. Tyler and others (2000) and Clough and others (2000) evaluated the potential coalbed methane for the rural com- munities in the Northern Alaska-Slope coal province. They suggested that based on depth, coal thickness, and depositional systems, primary coalbed methane targets and potential explo- ration fairways occur mainly in the Cretaceous Nanushuk Group. These workers identified the area between the east- ern boundary of the National Petroleum Reserve of Alaska (NPRA) to Chukchi Sea (see figs. 8 and 10) as containing the highest coalbed methane potential because of the thickest net coal, which is >300 ft (91 m) (see fig. 8). Potential methane development in this area may be from most of the coal beds that lie at an average depth of 2,000 ft (610 m). Drilling depths for coalbed methane are recommended below the permafrost zone, which is as much as 2,000 ft deep (610 m) (Ferrians, 1965), to 6,000 ft (1,830 m). McKee and others (1986) suggested that permeability is very low below the 6,000-ft (1,825-m) threshold. The Meade Test Well No. 1 and Kaolak Test Well No. 1 have related gas shows with coal beds as much as 30 ft (9.1 m) thick as well as interbedded sandstones at depths between 1,240 and 2,200 ft (378 and 670 m) (Collins, 1959). Here, Barnes (1967a) reported that there are as many as 60 coal beds with a net coal thickness of 350 ft (107 m) within a 4,600-ft (1,400-m) interval. Methane gas shows associated with coal beds in the Nanushuk Group and Corwin Formation were recorded at depths between the surface to about 1,420 ft (430 m) by Husky Oil NPR, Opera- tions, Inc. (1982–83). The presence of high gas content in sub- bituminous coal beds in the Nanushuk and Colville Groups in the NPRA was also reported by Claypool and Magoon (1988). These investigators also noted that the shallow, immature nature of the coal beds make for an unfavorable thermogenic gas source. However, similar subbituminous coal beds of the Fort Union Formation in the Powder River Basin of Wyoming are currently producing coalbed gas from depths of 250– 1,500 ft (76–460 m). Kenai Coalfield 81 82 Alaska Coal Geology, Resources, and Coalbed Methane Potential The vitrinite reflectance values of the Cretaceous coal- bearing rocks (Corwin-Chandler, Grandstand, Torok Forma- tions, the Pebble shale unit, and underlying Jurassic-Devonian rocks) in the Northern Alaska-Slope coal province are shown in figures 105 and 106. The vitrinite reflectance values down to 6,000 ft (1,830 m) range from about 0.30 to 0.66 percent, which corresponds mainly to lignite to subbituminous coal through subordinate high-volatile bituminous C coal (Stach and others, 1982). Vitrinite reflectance values are superim- posed on the cross section of the Nanushuk Group and under- lying rocks (fig. 107). Here, the vitrinite reflectance values of the coal-bearing Corwin-Chandler Formations range from <0.5 to >0.7 percent in the western part (updip) of the North- ern Alaska-Slope coal province and from <0.5 to <0.6 percent in the eastern part (downdip). This indicates that the coal beds may have generated mixed biogenic and thermogenic methane in the western part of the coal province and mainly biogenic methane in the eastern part. The extent of Nanushuk coal beds and the high-potential coalbed methane resources in the western part of the Northern Alaska-Slope coal province is shown in figures 108 and 109. In figure 108, the depths to the vitrinite reflectance value of 0.6 percent are superimposed on the base of Nanushuk Group and the net coal thickness of the Nanushuk Group. When the vitrinite reflectance contours are merged with the extent of the Nanushuk coal and where the Nanushuk coal beds have a net thickness of >400 ft (192 m), the area of highest coalbed methane potential is in the south- western part of the Northern Alaska-Slope coal province. Callahan (1979) suggested that the North Slope gas is biogenic and generated by a microbial activity. Carbon isotopic analyses of near-surface (0–4,920 ft, 0–1,500 m) gas- hydrate- and coal-bearing units by Collett (1993) yielded car- bon isotopic values averaging about –49 permil. This indicates that the methane in near-surface strata is from mixed biogenic and thermogenic origin. However, based on vitrinite reflec- tance values (0.30–0.66), the gas-hydrate and coal-bearing rocks probably were not subjected to high temperatures; thus, the thermogenic gas may have migrated from greater depths. Tyler and others (2000) suggested that in addition to tar- geting coal beds for conventional methane exploration, strati- graphic and structural traps should be explored for coalbed methane potential. Conventional play for thermogenic gas in the coal that migrated updip and was trapped below the perma- frost was also recommended for exploration. The permafrost zone serves as a seal for trapping migrating gas. Stratigraphic traps were suggested by Tyler and others (2000) where coal beds pinch out updip behind progradational shoreline sequences (for example, delta-front, barrier-shoreface sand- stones) in the Nanushuk Group. Structural traps may be found in fault-cored anticlines (for example, Meade and Wainwright arches) (see fig. 8; Tyler and others, 2000). Central Alaska-Nenana Coal Province The coalbed methane potential for the Central Alaska- Nenana coal province is not as high as the Northern Alaska- Slope coal province. The coal beds in this coal province are mainly subbituminous, range from 50 to 66 ft (15 to 20 m) in thickness, and occur to depths of 3,000 ft (910 m). In addi- tion, the Healy Creek Formation is sealed by thick mudstones of the overlying Sanctuary Formation. Exploration targets for potential coalbed methane are along the axes of large synclinal basins such as the Healy Creek and Lignite Creek Basins. In these basins, most of the coal resources in the Healy Creek and Suntrana Formations are thick (as much as 65 ft or 20 m thick) and found from 1,000-to 3,000-ft (305 to 914 m) depths (Wahrhaftig and others, 1994). Although the rank of the Healy Creek, Suntrana, and Lignite Creek coals is mainly subbituminous, Affolter and Stricker (1994) reported heating (calorific) values ranging from 6,130 to 9,210 Btu/lb (3,410 to 5,120 kcal/kg), which correspond to lignite to subbituminous coal. Outcrop and surface-projected vitrinite values of the coal-bearing Usibelli Group in the Central Alaska-Nenana coal province range from 0.21 to 0.48 percent, which corresponds to lignite to subbituminous C coal ranks (fig. 104). Coal ranks generally increase south-southeast toward the Alaska Range, indicating that methane generated in these mainly subbituminous coal deposits is biogenic. The rank and quality (low ash and sulfur) of the Healy Creek, Suntrana, and Lignite Creek coals beds are very similar to the subbituminous coal beds of the Fort Union Formation in the Powder River Basin of Wyoming, which are producing economic biogenic methane at an average of 25 scf/t. In that basin, coalbed methane is produced as close as 1–2 miles (1.6–3.2 km) from coal strip mines (Stricker and others, 2001). However, the strip mining has liberated gas by pressure reduction. Because the Fort Union coal beds have high water saturation, depressurization from dewatering dur- ing strip mining releases and subsequently causes migration of gas by desorption and diffusion through the microstructures in the coal. Thus, success in developing the coalbed methane for the Healy Creek and Suntrana coal beds should probably be focused on areas removed from old underground coal mines and current strip mines. Southern Alaska-Cook Inlet Coal Province The coalbed methane potential for the Southern Alaska- Cook Inlet coal province is high. This resource potential varies from the Kenai, Broad Pass, and Beluga coalfields, which contain lignite and subbituminous coal, to the Matanuska coal- field, which contains bituminous and semianthracite coals. Magoon and Anders (1990) reported that the gas pro- duced from the Kenai Group in the Cook Inlet is biogenic. Gas is mainly derived from the Tyonek and Beluga Forma- tions. This gas is produced primarily from gas-driven–sand- stone reservoirs (table 9) in the Tyonek, Beluga, and Sterling Coalbed Methane Potential 83 BITUMINOUS COAL Barrow B R O O K S R A N G E SUBBITUMINOUS COAL � �� CANADAUNITEDSTATES ALASKA Area of map UNITED STATESALASKA CANADA ARCTI C O C E A N Beaufort Sea �� Figure 103. Distribution of surface vitrinite reflectance values at sea level in the Northern Alaska-Slope coal province. Figure 102. Map of the Northern Alaska-Slope coal province showing distribution of bituminous and sub- bituminous coals. Modified from Sable and Stricker (1987). 84 Alaska Coal Geology, Resources, and Coalbed Methane Potential Formations (Brimberry and others, 1997; Flores and others, 1998). Figure 110 shows the distribution of gas and oil fields in the Cook Inlet Basin producing mainly from the Tyonek, Beluga, and Sterling sandstones. Figures 111 and 112 show the vertical distribution and occurrence of gas in the Sterling and Beluga sandstone reservoirs; gas accumulations in associated coal beds in the Kenai field are shown in figure 113 (Brim- berry and others, 1997; Flores and others, 1998). Since 1958, when gas production from the Cook Inlet was first recorded by the Alaska Department of Natural Resources, Division of Oil and Gas (1997), the total (gross) production from these sandstone reservoirs was about 7,993 billion cubic feet. This gas is thought to be derived from the Tyonek, Beluga, and Sterling coal beds (Kelly, 1968). Coal mines in the Matanuska coalfield have emitted methane from the Chikaloon coal beds, which has caused several mine explosions in 1937 and 1957 (Barnes and Payne, 1956; Smith, 1995). Thirteen out of 18 coal beds in the Tyonek Formation in the upper Cook Inlet Basin (northwest of Wasilla) were determined to contain coalbed methane by Smith (1995). Gas content ranges from 63 ft3 per short ton (1.97 scm3/gm) at stan- dard temperature and pressure (STP) for coal beds at a shallow depth of 500 ft (152 m) to 245 ft3 per short ton (7.6 scm3/gm) at STP for coal beds at a depth of 1,200 ft (366 m). Vitrinite reflectance values range from 0.47 to 0.58 percent and gener- ally increase with depth. The carbon isotope composition of the coalbed gases range from –49.3 to –43.3 permil δ13C with slightly heavier isotope values at depth (Smith, 1995). In general, biogenic methane is isotopically light with methane δ13C values ranging from –55 to –90 permil (Rice and Clay- pool, 1981; Rice, 1993). However, biogenic methane can be as heavy as –40 permil, which can be produced by reduction of isotopically heavy carbon dioxide (Jenden and Kaplan, 1986). Thus, the gas from the Tyonek coal beds may be slightly bio- genic but mostly thermogenic. Chemical composition is 98–99 percent methane with minor amounts of carbon dioxide and nitrogen (see table 9; Flores and others, 1998). Attempts to develop Tyonek coal beds by energy com- panies (Union and Ocean Energy) in the Wasilla area were affected by coproduced water problems. Large amounts of ground water were encountered, which posed production problems in separating the coalbed methane from the copro- duced water as well as water-disposal problems by reinjection. Similar problems were met by gas operators in developing the coal beds of the Fort Union Formation in the Powder River Basin of Wyoming. However, the gas operators in that area are permitted to dispose of coproduced water at the surface. Other targets for coalbed methane development in the Upper ARCTICO C E A N Beaufort Sea 0.1 -0.5 0.51 -0.75 0.76 -0.99 1.0 -1.97 1.98 -4.75 EXPLANATION (Vitrinite reflectance) Anchorage Juneau Barrow ALASKA �� Figure 104. Map showing surface vitrinite reflectance values in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. Coalbed Methane Potential 85 Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. [Modified from Johnsson and others, 1992] Record number Quadrangle scale of 1:250,000 North latitude Westlongitude Formation Mean Ro (%) �� 86 Alaska Coal Geology, Resources, and Coalbed Methane Potential Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation �� Mean Ro (%) Coalbed Methane Potential 87 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 88 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 89 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 90 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 91 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 92 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 93 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 94 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 95 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 96 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 97 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 98 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 99 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 100 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) Coalbed Methane Potential 101 �� Table 8a. Vitrinite reflectance values of coals across the surface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Northlatitude Westlongitude Formation Mean Ro (%) 102 Alaska Coal Geology, Resources, and Coalbed Methane Potential Table 8b. Vitrinite reflectance values of coals across the subsurface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. [Modified from Johnsson and others, 1992] Record number Quadrangle scale of 1:250,000 Well name North latitude West longitude MeanRo (%) �� Coalbed Methane Potential 103 Table 8b. Vitrinite reflectance values of coals across the subsurface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Well name North latitude West longitude �� MeanRo (%) 104 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Table 8b. Vitrinite reflectance values of coals across the subsurface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Well name North latitude West longitude MeanRo (%) Coalbed Methane Potential 105 �� Table 8b. Vitrinite reflectance values of coals across the subsurface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Well name North latitude West longitude MeanRo (%) 106 Alaska Coal Geology, Resources, and Coalbed Methane Potential �� Figure 105. Vitrinite reflectance values for the Meade Quadrangle, National Petroleum Reserve in Alaska. Modified from Magoon and Bird (1988). Figure 106. Vitrinite reflectance values for the Tunalik No. 1 well, National Petroleum Reserve in Alaska. Modified from Magoon and Bird (1988). �� Table 8b. Vitrinite reflectance values of coals across the subsurface in the Northern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces. — Continued Record number Quadrangle scale of 1:250,000 Well name North latitude West longitude MeanRo (%) Coalbed Methane Potential 107 Cook Inlet are in the Tyonek area where the coal beds in the Tyonek are as much as 50 ft (15 m) thick occurring at shallow depths of less than 2,000 ft (610 m). Also, the infrastructure (for example, pipeline) of existing petroleum development is readily available in the area. A basinwide variation in thermal maturity of the Cook Inlet Basin was determined by Johnsson and others (1993) from vitrinite reflectance values of 30 offshore and onshore wells (fig. 114). Reflectance values range from 0.24 to 0.95 percent with high values (0.6–0.8 percent) occurring at increasing depths in the northeastern and southwestern parts of the Cook Inlet Basin (see fig. 114). This indicates that tec- tonic deformation and volcanism along the Aleutian volcanic arc influenced the high reflectance values in the northeastern part of the basin, particularly in the Matanuska Valley. The localized upgrading of the thermal maturity in the Matanuska Valley, based on reflectance values of the Tyonek coal beds, is shown in figure 115 (Smith, 1995). Here, the Tyonek coal beds are mainly subbituminous, but the older coal beds in the east- ern part of the valley range from bituminous to semianthracite. The central part of the basin maintains reflectance values from 0.4 to 0.6 percent, which indicate burial influence by thick sedimentary rock sequences of 12,000–13,000 ft (3,660– 3,960 m) (see figs. 58, 59, and 60) along the basin center. Thermal maturity measured from vitrinite reflectance data is relatively low. Shi-Ming (1996) suggested, in a study of clay mineral diagenesis, that temperatures never exceeded 167°F (75°C) (fig. 116). Rapid rate of subsidence and sedimentation of the Cook Inlet Basin probably controlled the low thermal maturity of the Tyonek, Beluga, and Sterling coal beds. Gener- alized vitrinite reflectance lines are superimposed on the cross sections in figures 117 and 118. Coal beds identified in lithologic logs of the Tyonek and Beluga Formations in the Edna Mae Walker No. 1 well in Kenai Peninsula (see fig. 116) are directly associated with the high gas shows indicated on the mud logs (fig. 116). These coal beds contain as much as 2.5 percent by volume of coalbed methane marked by high gas kicks (see fig. 116). However, based on the downhole hot wire total gas results (see high gas kicks in fig. 116), the coal beds in the upper part of the Tyonek Formation contain by far the most coalbed methane resources. Coal beds in the lower part of the Beluga Formation consist of moderate amounts of coalbed methane resources. Coal beds of the Sterling Formation contain very low coalbed methane concentrations. The difference in the coalbed methane content between the Beluga and Sterling coals may be related to the variation in their rank, beds in the Sterling Formation being mainly lignite and those in the Tyonek and Beluga beds being mainly subbituminous (Barnes and Cobb, 1959). Vitrinite reflectance values of the Sterling Formation coal beds range from 0.32 to 0.44 percent, the Beluga coal beds from 0.42 to 0.58 percent, and the Tyonek Formation coal beds from 0.45 to 0.66 percent; all values increase with depth (fig. 117). These vitrinite reflectance values are closely similar to the subbitu- minous Paleocene Fort Union coal beds (0.31–0.49 percent) in the Powder River Basin of Wyoming and Montana, which have an average gas content of 25 scf/t. Also, the gas content (based on the hot wire total gas and methane in mud logs; see fig. 116) of the Powder River Basin coal beds appears to increase with depth, from below 6,000 ft (1,830 m) to more than 13,000 ft (3,960 m). However, producibility of gas from coal-bed reservoirs at these depths may be negligible due to low permeability below 6,000 ft (1,830 m) (McKee and others, 1986). Thus, by comparison, coal beds of the upper Tyonek and lower Beluga Formations contain the best coalbed methane potential in the Kenai Peninsula, especially reser- voirs less than 6,000 ft (1,830 m) deep. The upper part of the Beluga Formation is mainly exposed along the beach bluffs in the southern Kenai Peninsula. Thus, the targeted coal beds of the lower Beluga and upper Tyonek occur in subcrop and at shallower depths than in the Edna Mae Walker well along the south coast of the Kenai Peninsula. The hypothetical coal resources of the coal-bearing Kenai Group in the Cook Inlet Basin were estimated to be as much as 1.55 trillion short tons (1.45 trillion metric tons) (see table 1). As much as 1.5 trillion short tons (1.36 trillion short tons) of these coal resources is offshore (see table 1). Based on the gas contents of the Tyonek coal beds in the upper Cook Inlet by Smith (1995), which range from 63–245 scf/t (1.97– 7.6 scm3/gm) at STP, the in-place methane resources in that part of the basin may be high. However, based on the sub- bituminous and lignite ranks and the similarity of the vitrinite reflectance values of the Tyonek, Beluga, and Sterling coal beds in the central and southern parts of the basin to those of the Fort Union coal beds in the Powder River Basin, these coals may provide a lower-end estimate of the gas content in the Cook Inlet Basin. Summary Nearly all the coal resources calculated for Alaska are in Cretaceous and Tertiary rocks distributed in three major coal provinces. The Cretaceous coal resources, generally of bituminous and lignite rank, are mainly in the Northern Alaska-Slope coal province with 3,200 billion short tons (2,902 billion metric tons) of hypothetical resources. A minor amount of Tertiary coal resources are in the Northern Alaska- Slope coal province with 670 billion short tons (608 billion short tons) of hypothetical resources. Most of the Tertiary coal resources, mainly lignite to subbituminous with minor bituminous and semianthracite, are in the Central Alaska- Nenana and Southern Alaska-Cook Inlet coal provinces with more than 1,600 billion short tons (1,451 billion metric tons) of combined measured, indicated, inferred, and hypothetical resources. These three coal provinces contain about 87 percent of the total coal resources and represent most of the minable coal beds of Alaska. Combined coal resources (measured, indicated, inferred, and hypothetical resources) in the North- ern Alaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet coal provinces are about 5,526 billion short 108 Alaska Coal Geology, Resources, and Coalbed Methane Potential Pebble shale unitPre-pebble shale45612345SP R111098654321SP RSP R123456SP R1234SP R12312345621 SP RSP R345SP R67SP R123Dominantly nonmarine faciesEXPLANATIONDominantly shallow marinesandstone and shaleBottomsets of westerly derived Torok deposited onbottomset turbidite facies of southerly derivedTorok and Fortress Mountain Formations at some horizon belowForesets projected fromseismic line 68E-77in syncline to southBottomsets (basinal)Base of pebble shale unit fromwell and seismic data andadjusted for tectonic thickening of Torok FormationPre-pebble shale unitFormationKukpowrukFormationCorwin Formation1,700-ft Torok removedto account for tectonicthickeningTopsets (shelf)Arbitary location of nomenclature changeGrandstand FormationNanushuk Group NinulukFormationSeabee Formation , Colville Group Chandler FormationNanushuk GroupGR TT1234567891011SP R13456Foresets(slope)????6.7°6°??WESTTunalikNo. 1KaolakNo. 143 km107 km MeadeNo. 162 kmOumalikNo. 118kmEastOumalikNo. 157 kmTitalukNo. 140 kmWolf CreekNo. 346 kmUmiatNo. 1UmiatNo. 2McCullochCol. U. 2GubikNo. 110km9km18km35 kmEASTB.P. ItkillikNo. 1Torok Pebble shale unitTorok-SeabeeFormations, undivided550 ft of fault repetition removed760 ft of fault repetition removed Torok Formation2°1.8°GR = Gamma raySP = Spontaneous potentialR = Resistivity.70.61.57.62.56.54.57360 (.57)488429 (.37)460(.43).60.57.52.60.65.64.700.50.60.52.63.62.75.62.60.7.60.66.57.49.45.55.66.75.69.63.56.58.71.63.55.56.59.64.52.53.60.49.52.65.47.52.58.62.58.60.58.63.60.73.61.53.58.53.51.51.49.73.82.86.450.70Foreset (slope)Figure 107. Stratigraphic cross section of the Nanushuk Group with superimposed vitrinite reflectance values. See figure 8 for location of cross section. Summary 109 Figure 108. Coalbed methane potential in the Nanushuk Group coals based on the thickness and vitrinite reflectance of the nonmarine part of the group in the Northern Alaska-Slope coal province. Adopted from Smith (1995). Figure 109. Distribution of surface vitrinite reflectance (Ro) values in the Northern Alaska-Slope coal province. 110 Alaska Coal Geology, Resources, and Coalbed Methane Potential Figure 110. Map of the Cook Inlet Basin showing distribution of oil and gas fields offshore and onshore. CBM #1 is the well studied by Smith (1995). Table 9. Properties of sandstone reservoirs and associated gas in the Sterling and Beluga Formations. Modified from Brimberry and others (1997). Reservoir data of Kenai field �� tons (5,012 billion metric tons). Of this total, 13.5 billion short tons (13.2 billion metric tons) are identified coal resources mainly from the Central Alaska-Nenana and Southern Alaska- Cook Inlet coal provinces. Thus, only a small fraction of the total coal resources of Alaska is known, and a large amount is undiscovered. Coal mining has been intermittently attempted in the Central Alaskan-Nenana and Southern Alaska-Cook Inlet coal provinces. A dozen or more underground and strip mines in these two coal provinces have produced over 40 million short tons (36 million metric tons). Thus, only a small fraction of the identified resources has been produced of the more than 13.5 billion short tons (billion metric tons) that are estimated to occur in these coal provinces. Alaskan coal resources have low sulfur content (averaging 0.2–0.4 percent) compared to the coal in the conterminous United States. This low-sulfur coal is within or below the minimum value mandated by the 1990 Clean Air Act amendments. The extremely large identified coal resources are located near existing infrastructure, which should aid in their development, transportation, and market- ing. The short distance of these resources to countries in the western Pacific would appear to make them more marketable there than in the conterminous United States. An untapped resource is coalbed methane. With more than 5,500 billion short tons (5,012 billion metric tons) of combined coal resources of Alaska coal, the in-place gas resource is an exceedingly large volume. A large part of the measured, indicated, inferred, and hypothetical coal resources, about 5,482 billion short tons (4,972 billion metric tons), is in the Northern Alaska-Slope and Southern Alaska-Cook Inlet coal provinces where in-place and planned infrastructure (pipelines, highways, and so on) can assist in the transporta- tion and marketability of coalbed gas. The shallow depths to a large portion of the methane-bearing coal beds in onshore areas make the gas more accessible for future development. Summary 111 �� Figure 111. Facies profile of the lower part of the Sterling Formation and accompanying downhole logs showing horizons of gas accumulation. The Sterling facies include fluvial-channel sandstones and flood-plain mudstones and siltstones. 112 Alaska Coal Geology, Resources, and Coalbed Methane Potential Acknowledgments The authors acknowledge Heather Mitchell, Dean Han- cock, Jennifer Goldsmith, and Steve Dunn for their assistance in generation of the digital illustrations for this paper. The data for this study were collected from 1988 to 2002 with the help of numerous geologists, too many to mention here, from the U.S. Geological Survey, Alaska Department of Natural Resources Division of Oil and Gas and Division of Geological and Geophysical Surveys, Alaska Geologic Materials Center, and Bureau of Land Management. Funding for part of this study from the Division of Oil and Gas is very much appreci- ated. Finally, we thank the Usibelli Coal Mine Inc., Beluga, Diamond Alaska, and Placer Dome coal companies, ARCO Alaska Inc. and International ARCO, and Marathon Oil Com- pany, Anchorage, Alaska and Littleton, Colorado, for sharing information and permission to describe their core data. �� Figure 112. Facies profile of the upper part of the Beluga Formation and accompanying downhole logs showing horizons of gas-perforated intervals. �� CANADA UNITED STATES ALASKA Area of map CANADA �� Kenai�� CookInlet��R i v e r � ��Figure 113. Location map of the Kenai gas field in the Kenai Peninsula. Gas accumulations in the Beluga and Sterling Formations occur on a doubly-plunging anticline. KTU 43- 6X is the well described in figures 110 and 111. Acknowledgments 113 Anchorage Seward �� 0.2 -0.3 0.3 -0.4 0.4 -0.5 0.5 -0.6 0.6 -0.7 0.7 -0.8 Cook Inlet Basin Subsurface perspective Mean Ro (%) EXPLANATION Oil well Fault Castle MountainFaultBruinBayFault Border RangeFault CANADA UNITEDSTATES ALASKA Area of map CANADAFigure 114. Basinwide and vertical variations of vitrinite reflectance (Ro) values in the Cook Inlet Basin. Modified from Johnsson and others (1993). �� SusitnaRiverAnchorage Palmer Depth to 0.6 vitrinite reflectance in thousands of feet (km) Tyonek Formation isopach in thousands of feet (km) Tyonek Formation Chickaloon Formation EXPLANATION �� C in thousands of feet (kilometers) �� Tyonek Formation Prospective area Figure 115. Coalbed methane prospect area and depths to vitrinite reflectance values of 0.6 percent superimposed on the thickness isopach of the Tyonek Forma- tion south of the Castle Mountain fault in the northeastern part of the Cook Inlet. Adopted from Smith (1995). CANADACANADA UNITED STATES ALASKA Area of map CANADA 114 Alaska Coal Geology, Resources, and Coalbed Methane Potential Figure 116. Downhole geophysical logs, hot wire total gas and methane contents, vitrinite reflectance values, and illite diagenetic values in the Edna Mae Walker drill hole. SP=spontaneous potential; mV=millivolt; SN=sonic; Ro=vitrinite reflectance; %=percent. Ipf=illite peak profile at 10 angstroms; Ic= illite crystallinity. Modified from Shi-Ming (1996). �� Acknowledgments 1150.40.31,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,000SP(mV)-10025SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)SP(mV)SN(ohmm)-25100OLD MANS BAY No 11,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,00013,00014000-1250-25150KALGIN ISLAND1,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,00013,00014,000-10025-25300REDOUBT SHOALS No 11,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,000-10025-25200KUSTATAN No 11,0002,0003,0004,0005,0006,0007,0008,0009,00010,000-15025-25300GRAYLING No 1-A10002000300040005000600070008000900010000-1750-25225McARTHUR POINT No 1100020003000400050006000700080009000100001100012000-1250-25150TYONEK STATE No 1100020003000400050006000700080009000100001100012000-15025-25175TOWER No 1?????????10002000300040005000600070008000900010000-12500200TRADING BAY No 1A SOUTHA' NORTHEXPLANATION0.60.50.60.50.4Sterling FormationBeluga FormationTyonek Formation Hemlock ConglomeratePre-Hemlock FormationFigure 117. Stratigraphic cross section of the Kenai Group in the offshore Cook Inlet Basin with superimposed vitrinite reflectance values. See figure 58 for location. 116 Alaska Coal Geology, Resources, and Coalbed Methane Potential (ft)Depth(ft)Depth(ft)(ft)1,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,000SP(mV)-100 25SN(ohmm)SP (mV)SN(ohmm)SP (mV)SN (ohmm)SP (mV)SN(ohmm)SP (mV)SN (ohmm)-25 100OLD MANS BAY No 11,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,00013,00014,000-100 75-25 225NINILCHIK No 1-125 25-25 27501,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,00013,00014,000DEEP CREEK No 12001,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00012,00013,00014,00015,00016,000-125750EDNA MAE WALKER No 1-25 300-150 001,0002,0003,0004,0005,0006,000ANCHOR RIVER No 1SECTION B TO B' (WEST TO EAST SOUTH PART OF STUDY AREA)B (WEST)B' (EAST)DepthSterling FormationBeluga FormationTyonek FormationHemlock Formation Pre-Hemlock 0.60.50.40.30.30.40.50.6Depth(ft)DepthEXPLANATIONFigure 118. Stratigraphic cross section of the Kenai Group in the onshore Cook Inlet Basin with superimposed vitrinite reflectance values. See figure 58 for location.