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HomeMy WebLinkAboutDrilling and Reservoir Engineering Analysis of Pilgrim Hot Springs 1982PLL OOZ ee AILLING: AND RESERVOIR ENGINEERING ANALYSIS OF PILGRIM HOT SPRINGS, ALASKA of UAF PETROLEUM ENGINEERING A Report Submitted to the State of Alaska a Department of Commerce & Economic Development e Division of Energy & Power Development William Sheffield, Governor Richard Lyon, Commissioner William Beardsley, Director a DEPD Report 83-514-2 December, 1982 | re be = AN-EVALUATION OF THE DRILLING AND vo==—"RESERVOIR ENGINEERING ANALYSIS DONE AT PILGRIM HOT. SPRINGS, ALASKA IN THE SUMMER OF 1982 By Michael J. Economides Petroleum Engineering Department University of Alaska, Fairbanks Consultant’s Report This document is a final report on the Reimbursable Services Agreement between the Division of Energy and Power Development of the State of Alaska and the University of Alaska: Michael J. Economides, Principal Investigator, and titled Pilgrim Geothermal Drilling Project. o The report consists of a technical interpretation of the drilling and reservoir engineering data obtained in the Spmmer of 1982. The University of Alaska acted as the technical consultant to the D.E.P.D. while Woodward-Clyde Consultants (W.C.C.) acted as the Principal Contractors. The project, as done by W.C.C., was an unqualified success. The amount of drilled footage negotiated both at the beginning and during the project is remarkable, considering the extremely short budget. The contractor and the subcontractor, EXSCO of Anchorage, performed well in the field. The drilling and data gathering were quite adequate and the solutions to the heavy logistical problems were competent and favorable to the State’s budget. While the operation of the project is rated as excellent, the actual reservoir identified is lackluster. The shallow reservoir described in the technical portion of this report is well delineated and it can produce a significant hot water flow rate. However, the distance between the reservoir and any population center makes its utilization quite questionable. The fluid cannot sustain power generation. A deeper reservoir, virtually certain at approximately 5000 ft, could become the next target in the area if the economics of fluid transportation were proven favorable. In general, based on worldwide experiences, the distance between Pilgrim Springs and Nome is approximately twice the allowable distance. If a power plant were constructed at Pilgrim Springs, the closest major consumer of that electricity would be the community of Nome. One possible route for powerlines would be westward from Pilgrim Springs to the Cobblestone River Valley, crossing the Kigluaik Mountains at Mosquito Pass, and then south to Jensens Camp and along the road to Nome. This distance is roughly 55 miles. The next closest significant settlement is at Teller, which would be a distance of 45 miles. Electric power transmission, although technically feasible, cannot be evaluated without drilling and reservoir engineering data at depth. Such a verdict is beyond the scope of the project. Funding, several times that allocated already, must be secured prior to the next phase. Deep drilling (to 6000 ft) is strongly recommended for the assessment of the deep reservoir potential. ho TECHNICAL INTRODUCTION In an attempt-to identify the geothermal potential of the Pilgrin Springs area in the Seward Peninsula, Alaska, exploratory drilling was undertaken in the Summer of 1982. A total of four wells were drilled through a State appropriation. The Division of Energy and Power Development acted as the Project Manager while Woodward-Clyde Consultants were selected as the principal contractor. Two other shallow wells were drilled in 1979. The six wells were completed to tap various depths ranging from approximately 60 ft to 1000 ft. The drilling activity followed an extensive geological and geophysical assessment done by Forbes et al. (1979), Turner and Forbes (1980) and Wescott and Turner (1981). Their work indicated the existence of an extensive, liquid dominated, shallow geothermal reservoir in the area. The shallow reservoir, copfirmed by the 1979 drilling, was delineated within a 1 to 1.5 km“ area, bounded by permafrost at least 350 ft thick. The results of the 1979 drilling were presented by Kline (1981). Table 1 is a summary of the well completion data. Figure 1 shows the well locations. Wells PS1 and PS2 were. drilled to 150 ft. Air-lifted flowrates were estimated at 200 GPM and 350 GPM, respectively, with a flowing wellhead temperature of 91°c. The wells were cemented, filled with mud and left unperforated until 1982 when they were reopened. The mud settled at 105 ft in both wells, making them inaccessible below that depth. They were perforated using shape charges at the interval 70-100 ft (PS1) and 60-90 ft (PS2). The unaided flowrate never exceeded 30 GPM in PS1 and 65 GPM in PS2. The first well, drilled in 1982 was PS3 at a total depth of 260 ft. A 3-inch slotted liner was installed between 155 and 255 ft. The completed interval produced 60 GPM at over 65°C. Wells PS4 and PS5 were attempts to test an intermediate depth. They were drilled to 881 ft and 1001 ft respectively. Well PS4 is an open hole completion from 186 ft to 881 ft. A flowrate of 100 GPM and a wellhead temperature of 46°C were recorded. Well PS5 was completed below 540 ft with a 3" slotted liner. This interval presented siginificant problems during drilling. The formations encountered were often very hard materials. The total flowrate in Well PS5 was only 10 GPM, with a temperature of 35°C. A sixth well, MI1, was drilled on public land designated as Mary’s Igloo Native Selection Land. It was completed between 227 and (307 (f¢ ‘using 73" ‘slotted liner. The flowrate was 120 GPM at 25°C). The successively lower flowing temperatures observed in the. deeper completions _were later explained by the data from temperature versus depth surveys. Interpretation of the temperature surveys will be discussed in detail in this article. -3- Table 1 WELL-COMPLETION SUMMARY, PILGRIM SPRINGS, ALASKA Welt Drilling Drilled Remarks Date Depth PS-1 Fall’79 “150 Cemented from 1979-1982. Perforated in 1982 between 60-90 ft. PS-2 Fall ‘79 150 Cemented from 1979-1982. Perforated in 1982 between 70-100 ft. PS-3 Sum. ’ 82 260 Static head 12 ft. above land surface. Artesian flow at 60 GPM PS=4 Sum. ‘82 881 76 feet of drill stem stuck in bottom. Static Head of 12 ft. Latest artesian flow- 250 GPM at 46°F. : PS-5 Sum.’ 82 1001 Latest artesian flow: 10 GPM at 37°F MI-1 Sum.’ 82 307 Static head at ll ft. above land surface. Latest artesian flow: 100 GPM at 26°F very soft, sweet REGIONAL GEOLOGY The thermal activity at Pilgrim Springs is located in the Pilgrim River Valley, a tectonic depression (graben) bounded by Precambrian amphibolites and Mesozoic plutons. In some areas it is overlain and overthrust by Paleozoic carbonates. Potassiun- Argon dating done by Turner and Swanson (1981) indicated a cooling age of 84 m.y. suggesting igneous intrusive activity in mid-Cretaceous time. .Gravity surveys conducted in the region by Kienle and Lockhart (1980) suggest that Pilgrim Springs is near the intersection of two possible fault zones which form the corner of a downdropped basement block. Other faults in the area have been verified by seismic data and geologic mapping, and one or more of these faults could provide a deep conduit for the geothermal anomaly. “~~ The possible existance of a major rift system is of significance for the regional geothermal potential. A helium survey was conducted to test this rift model, and nine out of eleven helium anomalies occur near the proposed rift segments and suggest abnormally high heat flow in these areas. Furthermore, extensive basaltic fields north of Pilgrim Springs area have been interpreted as resulting from eruption in a zone of crustal weakness produced by the general north-south extension (Turner and Swanson, 1981). The amount of separation along this proposed rift is less than the widths of the Quaternary depressions which have probably been enlarged by normal faulting and marginal subsidence, along with rifting. Potassium-argon dating indicates that volcanism which was associated with rifting began in the Upper Miocene (Turner and Swanson, 1981). Finally, a permafrost boundary, enclosing a 1 to 1.5 kn2 area has been identified. The thickness of the permafrost is over 350 ft. TEMPERATURE DATA INTERPRETATION Previous temperature data were limited to shallow depth, (4.5 meters) by Wescott and Turner (1981), soil Helium surveys by Turner and Forbes (1980), and geothermometry by Motyka et al. (1980) Motyka’s estimate for the source water temperature using Na-K-Ca as the temperature indicator was 150°C + 10°C. The data of Wescott and Turner indicated a regional geothermal anomaly and suggested that the well sites chosen for PS3, PS4 and PS5 were likely locations for the source fluid. ‘The temperature data for this study were taken from temperature versus depth data recorded in the wells drilled in the Pilgrims Springs region. Two months after completion of the last well, temperature surveys were run in all six wells. The temperature versus depth profiles for all wells were identical in shape, as shown in Fig. 2. All showed a trend toward a maximum temperature at depths from -40 to 100 feet, .followed by a sharp decrease in temperature with depth from 100 to 250 ft, followed by a constant geothermal gradient ranging from 1.8°C to 2.1°C per 100 ft that was recorded down to 900 ft in the deepest well. The two wells, drilled deep enough to determine the geothermal gradient at depth (PS4 and PS5) show temperature trends that would intersect at about 155°C at a depth of 4875 ft. Hence, the geothermometer temperature estimate of 150°C is corroborated by the latest findings. In addition, and more importantly, the data suggest that all of the wells overlay the source reservoir at the 4875 ft depth. Figure 3 is a schematic representation of the temperature versus depth profile that would be expected at a well (A) near the vertical conduit that allows hot water from the deep zone to the shallow zone. Well B, further away from the source, shows a lower maximum temperature in the shallow zone which grades to a lower temperature at the base of the shallow temperature anomaly and results in a higher geothermal gradient to reach the source temperature at depth. The shallow temperature anomaly observed in all the wells suggests that somewhere in the immediate region, water from the hot source at depth is flowing upwards through a fissure or fault which extends vertically from a depth of about 50 feet to the 4875 foot depth identified as the source depth. Aerial variations in the maximum recorded temperature for the six wells are contoured in Figure 4. These data suggest that the hot source fluid enters the shallow formation at some point to the north of the six well sites. The fluid then flows radially and laterally away from the fissure source towards springs such as the Pilgrim Springs or perhaps in the surrounding stream beds, thus creating a steady state flow pattern for the shallow hot | water zones Locating the hot water source for the shallow zone is relatively unimportant, since the fluid at depth provides a -7- “4 oo rn TEMPERATURE (DEGREES CENTIGRADE) 0 0 COLOC(ité«C SSCL THO %.00 «106.00 a ee + —+ — 4 8 “sy — St 8 Es Na é TT = 8 RL t , ' BLS 8 \ Ss $4 eT Ww be. 8 z= a Be SYMBOL WELL NO, 5 a Ps] “ PS2 Z + Ps3 % PS4 g QQ PSS § > MII to Temperature Versus Depth Profiles of the Pilgrim Springs Wells SURFACE TEMPERATURE SHALLOW RESERVOIR GEOTHERMAL = be 0 GRADIENTS & SOURCE TEMPERATURE ! | | | | | | | ~|I50°C I | | fr RCE DEPTH TEMPERATURE Figure 3. Conceptual Representation of the Shallow and Deep Reservoirs at Pilgrim Springs. 0 100 200m @ 1982 WELLS PILGRIM 6 1979 WELLS SPRINGS Figure 4. Temperature Contours in the Shallow Reservoir. -10- high temperature source formation extending aerially at least as far as the total area drilled. The temperature data provide a most compelling justification for deeper drilling in the area. -1l- SHALLOW FORMATION PROPERTIES Core samples were taken from the 87 to 95 foot depth interval in Well PS4. Three plugs were taken and analyzed for porosity and permeability. The uppermost sample was a large- grained, poorly cemented, primarily quartz sandstone with a porosity of 40% and air permeability in excess of 4 Darcys. This sample is believed to be representative of the shallow hot water zone. The middle sample was a fine grained, well cemented, quartz sandstone with a porosity of 28% and exceptionally low permeability. The deepest sample was a loose conglomerate with a porosity of 24%. The permeability of this sample could not be determined. The middle sample could represent the impermeable base for the shallow hot water zone. Data from an interference well test are shown in Table 2. Shut-in pressures were recorded in PS2 while PSl1 was flowing at a rate of 30-35 GPM. A log-log graph of the drawdown pressures in Well PS2 versus time was analyzed by type curve matching with the line source solution, as shown in Fig. 5- From the pressure match, the permeability is estimated at 4.5 Darcys. The time patch gives_a porosity compressiblity product of 5.4 x 107° psi- » which results in an estimate of 14 x 10 psi for the compressibility, if the porosity is assumed to be 40%. The results of the interference test agree with the core analysis data from Well PS4 and suggest that the shallow hot water zone has similar properties throughout the region of the six wells. CONCLUSIONS The wells drilled in the region of the geothermal anomaly near Pilgrim Springs provide considerable insight into the general characteristics of the geothermal system. Previous work, including resistivity studies and geothermometry are corroborated by the temperature profiles observed in the, six wells. The existence of a hot water zone of about 150°C and at a depth of around 5000 feet is now virtually certain. The shallow reservoir, using the existing wells will produce over 300 GPM of unaided production at 90°C. With pumping, the flow rate would be increased significantly. The very high permeability would offer little resistance to flow. The longevity of the reservoir is unknown since the geometry of the deep reservoir is not defined. Experience elsewhere, with similar geologic settings point towards a longevity spanning several decades. el Dee Table 2 Pressure Interference Data Between Wells PS1l and PS2 PS1 (flowing), q = 30-35 GPM PS2 (wellhead pressures recorded) Time(min) p(psig) Time(min) p(psig) 0 3.5 20 1.4 8 2.9 22 1.5 12 2.4 24 1.3 14 2.3 27 1.1 16 2.1 29 1.9 17 2.0 30 9.9 18 1.9 31 0.8 Distance between wells = 269 ft Water viscosity = 1 ep Reservoir porosity = 40% Reservoir thickness = 60 ft -i3- -4I- Figure 5. ap (psi) 10 100 t (minutes) 7 lo 10 Type-Curve Matching of the Pressure Interference Data Between Wells PS1 and PS2. REFERENCES Forbes, R.3., Wescott, E.M., Turner, D.L., Kienle, J., Ostercamp, T., Hawkins, D.B.,Kline, J.T., Swanson, S., Reger, R.D. and Harrison, W sr "A Geological and Geophysical Assessment of the Geothermal -Retential of Pilgrim Springs, Alaska", Geophysical Institute, UAF and Alaska D.G.G.S. Preliminary Rept-, 39 pp., 1979. Kienle, J. and Lockhart, A. in Turner, D.L. and Forbes, R.B. (Eds), 1980. Kline, J.T.: "Surficial Geology of the Lower Pilgrim Valley and Vicinity, Western Seward Peninsula, Alaska", Alaska D.G.G.S., AOF-140, 1981. Motyka, R., Moorman, M. and Forbes, R.B. in Turner, D.L. and Forbes, R.B. (Eds), 1980. Turner, D.L. and Forbes, R.B. (Eds): "A Geological and Geophysical Study of the Geothermal Energy Potential of Pilgrim Springs, Alaska", Geophysical Institute, UAF, Report UAG R-271, 166 pp.-, 1980. Turner, D.L. and Swanson, S.E. in Wescott, E.«M. and Turner, D-L. (Eds), 1981. Turner, D.L. (and 13 other authors): "Summary of Results of a Geological and Geophysical Investigation of the Geothermal Energy Potential of the Pilgrim Springs KGRA, Alaska," Geothermal Resources Council, Trans. v.4, pp. 93-95, 1980. Wescott, E.M. and Turner, D.L. (Eds): "Geothermal Reconnaissance Survey of the Central Seward Peninsula, Alaska", Geophysical Institute, UAF, Report UAG. R-284, 123 pp., 1981. -15- APPENDIX SUMMER 1982 DRILLING REPORT The drilling program at Pilgrim Springs this past summer began 3 weeks behind schedule for several reasons. First, the ice on Norton Sound was late to break-up. Secondly, the barge on which the drilling materials were to be transported was the last barge to arrive at Nome, instead of the firt as originally expected. Finally, the procurement of the drilling materials, once off loaded in Nome, was held up because of the lighterage company’s unwillingness to give the State project priority over local firms and villages. Drilling, finally, commenced on June 25 with the spudding of well PS3 that afternoon. Temperatures around 77°C =—were encountered at just 17 feet below ground surface. However, this high geothermal gradient was not maintained and the temperature rose slowly after that. Drilling—near the surface was hampered by the presence of a high water table. Water was hit at just 4 feet below ground level and its presence caused severe sloughing of the hole below ground. In fact, the cavity formed, attained a diameter of approximately 4 feet while the auger bit was ‘only 20 inches in diameter. Surface casing (16 inches) was set when the auger encountered sandstone at just over 17 feet of depth. On the evening of June 26, an attempt was made to run 10 inch “casing to 70 feet. However, the hole was too crooked and the next morning the casing was pulled out. At noontime the casing was run back in, after several hours were expended in cleaning the hole. Finally that evening, it was landed at 50 feet and cementing was performed. , Drilling recommenced at 1:00 p.m. on June 28 and proceeded without major problems for two days. Down time did occur in this period for the purpose of replacing a bit and some minor repairs on the rig. Then the drill got stuck on June 30 and it’ took approximately 10 hours before it was freed. It should be noted that several of the hours were spent in repairing parts of the drill rig. The drill was finally extracted just after midnight of July l. That day was spent conditioning the hole by tripping back in and circulating and then trying to get 8 inch casing in. The 8 iach casing would not go any further than 78 feet because of the crookedness of the hole, so it was decided to take it out. Once out, conditioning was performed and the hole was logged by David Kirchner using a geophysical logger provided by the drilling firm. The logging probe would only go to 78 feet so the drill string was tripped back in to 198 feet. -16- At 3:00 am, July 2, running in of 6 inch casing began. Considerable difficulty was encountered in getting the casing down and further problems with the rig resulted in considerable time delays. Casing was eventually set at 167 feet and cemented on July 3. That evening drilling began to 260 feet final depth and reached bottom the following morning at 4:20 am. Some loss of water was encountered while drilling this last section. Also, some sloughing was experiened. Casing was set at 254 feet, using 3 inch slotted liner, during the afternoon of July 4. That evening, the rig was moved to the site of PS4 which was selected because of the high helium content of the soil. Surface casing was set with no problems. Drilling with 14- 3/4 inch bit and a stabilizer that had been air freighted from Anchorage to Nome commenced at 4:50 pm on July 5. The depth reached 90 feet within 5 hours and casing was set at 86 feet. While waiting on cement, a core sample was obtained. This required a core barrel that was air freighted out of Anchorage. Two cores were taken, each about 3 feet in length, from about 84’ to 90’. Drilling continued without problems from 90 feet at 1:00 am, July 7, to 515 feet at 3:15 am, July 8. Multiple trips were made for conditioning until noontime, July 8, when a geophysical log was taken. Casing began at 4:00 pm and was abandoned at 187 feet into hole at 8:30 am the following morning, July 9. Casing was cemented and drilling started the morning of July 10. From 640 to 670 feet, it was noticed that the formation was taking considerable water. In the early morning hours of July ll, a test trip out was made and difficulties were encountered. It was decided to trip all the way out and this was completed at 3:50 pm, after suffering a down time for a broken chain con the drawworks. A stabilizer/reamer was constructed on site and tripped in that night. At 445 feet it was necessary to stop in order to weld the rig-freme—back together. Reaming resumed after spending an hour repairing the rig. This was at 3:45 am, July 12. On bottom at 827 feet in the morning and drilling with no problems except for some lost circulation. At noon time the driller pulled 3 feet off the bottom, left the mud pumps going and went to lunch, thus leaving the rig completely unattended. Upon returning from lunch, it was found that the ‘formation had taken up almost all the mud in the tanks. Whether mud circulation was completely lost is a point that was argued about. Also, it was found that one of the mud punps had failed but it is unknown exactly when. Throughout the night, and into the next morning, attempts were made to free the stuck drill pipe but’ to no avail. At noon, circulation was stopped in order to run a temperature log through the drill pipe. The logging was done using two maximum reading thermometers taped to the geophysical probe. The probe was -17- lowered down to 850 feet. After waiting for a few minutes, David Kirchner began to bring the probe back up. Unfortunately, he did it too fast and broke the cable. The next day, July 14, a hemp rope arrived from Nome to use on the cat head for hammering the drillpipe. Hammering seemed to move the drill pipe somewhat but it was never enough to break the drill’ loose. With the geophysical probe lost inside the drill pipe, cirewtarion was impossible. It was noticed that hammering caused -an—inerease in the temperature of the flow from PS4. On the morning of July 15, a decision was made to move the rig to the site chosen for the Mary’s Igloo well (MI-1). PS&4 at this time was flowing at 100 GPM and 46°C. The water was quite soft and drinkable. That afternoon, the surface casing (16 inch) for MI-l was set and cemented. A temperature of 71 °c was encountered at the 20 foot level. Drilling from 20 feet to 235 feet with the 14 3/4 fiich bit was smooth and took only 17 hours. A combination of 6 inch and 8 inch casing was run to 233 feet. Plugs of cement were spotted at the bottom, 60 to 70 feet, and from about 55 feet to surface. Just after midnight on July 18, TD was reached at 307 feet. The bottom portion of the well was cased, using 84 feet of 3 inch slotted liner. . : Most of the day was spent moving the rig back to PS4 to try again at freeing the stuck drill pipe and performing some needed repairs. The first order of business was trying to fish out the geophysical probe. For this, some small drill pipe (OD about 1 1/4 inches) was air freighted from Anchorage to Nome. Several attempts were made but none were successful. On the evening of July 19, dynamite was placed inside the stuck drill pipe at about 800 feet and was set off. This route was chosen following this State’s decision to drill PS5, a well not originally planned for. The rig moved to PSS on July 21 from midnight to 8:00 am and PS5 was spudded at 1:30 pm. For surface casing, some old, thin walled 16 inch pipe was located in Nome and flown out. Te amounted to two 5 foot long pieces. These were welded together and cemented in place. The original seam welds broke 3 feet below ground level so it had to be dug out and rewelded. More cement was pumped around the top to seal the casing. Because ?S5 was unplanned, many materials were in short supply. In lieu of bentonite mud, a synthetic type called "clear mud" was used. This type was tried because of its very small volume and weight in shipping yet producing large volumes of anwhen mixed on site with water. Its performance was adequate. The drillers had no previous experience with this mud. Drilling proceeded without problems to about 116 feet. At that depth, a cement plug was set in a 4 foot thick sloughing zone. This partially healed the sloughing. Drilling went well ~18- until 185 feet was “reached. At this point the chain on the breakout table broke again and it was decided that casing should be run." : By noontize, July 23, casing had been set at 178 feet and cemented. Drilling started just after midnight with hard drilling being encountered. At 5:00 am it was decided to trip out and look over the bit and stabilizer. The bit was changed and drilling proceeded through the day with no problems. The drill reached 456 feet and tripping out began so that repairs could be made. Repairs were completed and drilling proceeded further. It reacned 588 feet by 1:00 pm on July 25 and tripping out began so that casing could be run. While waiting on cement, general cleanup started. On the next day, drilling proceeded with few problems except for some occasional hard drilling. Then at 2:00 am on July 27, a failure on the rig caused a shutdown. When this was repaired, the drill string was found to be stuck. Changing back to the “clear mud" knocked the pipe free. T.D. was reached at 1001 on 11:35 am, July 27. By early afternoon the bit was out and casing began using 3 inch slotted liner. Casing was set and demobilization started.