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Home My WebLink AboutCO 238Conservation Order Cover Page XHVZE This page is required for administrative purposes in managing the scanning process. It marks the extent of scanning and identifies certain actions that have been taken. Please insure that it retains it's current location in this file. Conservation Order Category Identifier Organizing RESCAN DIGITAL DATA OVERSIZED (Scannable with large plotter/scanner) [] Color items: [] Diskettes, No. [] Maps: [] Grayscale items: [] Other, No/Type [] Other items [] Poor Quality Originals: OVERSIZED (Not suitable for [] Other: plotter/scanner, may work with 'log' scanner) [] Logs of various kinds [] Other NOTES: BY: ~ MARIA Scanning Preparation Production Scanning Stage 1 PAGE COUNT FROM SCANNED DOCUMENT: PAGE COUNT MATCHES NUMBER IN SCANNING PREPARATION' ? YES ~ NO BY: Stage 2 IF NO IN STAGE 1~ PAGE(S) DISCREPANCIES WERE FOUND: __ YES NO (SCANNING IS COMPLETE AT THIS POINT UNLESS SPECIAL ATTENTION IS REQUIRED ON AN INDIVIDUAL PAGE BASIS DUE TO QUALITY, GRAYSCALE OR COLOR IMAGES) General Notes or Comments about this Document: 5/21/03 ConservOrdCvrPg.wpd STATE OF ALASKA ALASKA OIL AND GAS CONSERVATION COMMISSION 3001 Porcupine Drive Anchorage, Alaska 99501-3192 Re: THE APPLICATION OF ARCO ) ALASKA, INC requesting ) amendments to Rule 3 of ) Conservation Order No. 145.) Conservation Order No. 238 Prudhoe Bay Field Prudhoe Oil Pool November 22, 1988 IT APPEARING THAT: I · ARCO Alaska, Inc, by letters dated November 7, 1986; April 21, 1987; November 23, 1987; and October 24, 1988, requested amendments to Rule 3 of Conservation Order No. 145. · Notice of public hearing was published in the Anchorage Daily News November 27, 1986. 3. No protests were filed with the Commission. FINDINGS: · , Rigid, high density polyurethane foam can be used as an alternate to cement for securing the conductor pipe. Surface casing has been set at depths to 5000' in the Prudhoe Bay Field. · The maximum strains measured in the casing joints in a 5-spot thaw test well, representative of a Prudhoe Oil Pool producing oil well, were 0.13% in compression and 0.08% in tension. · The worst-case strains calculated for a representative Prudhoe Oil Pool producing well are 0.7% in compression and 0.5% in tension. These worst-case strains were predicted by a mathe- matical model which was developed to match field test results. 5. Thaw-subsidence and freeze-back produces static loads. CONCLUSIONS: I · Conductor casing can be adequately secured by filling the annulus behind the pipe to the surface with cement or rigid foam. · Surface casing can be safely set at depths to 5000' in the Prudhoe Bay Field. Conservation Order No. 238 November 22, 1988 Page 2 · Casing designs should provide minimum axial strain properties equal to the worst-case strains, calculated to be 0.7% in compression and 0.5% in tension. NOW, THEREFORE, IT IS ORDERED THAT Rule 3 of CO 145 is amended to read: Rule 3 Casing and Cementing Requirements a) Conductor casing shall be set at least 75 feet below the surface and sufficient cement shall be used to fill the annulus behind the pipe to the surface. Rigid high density polyurethane foam may be used as an alternate to cement, upon approval by the Commission. The Commission may also admini- stratively approve other sealing materials upon application and presentation of data which show the alternate is appro- priate based on accepted engineering principles. b) Surface casing to provide proper anchorage for equipment, to prevent uncontrolled flow, to withstand anticipated internal pressure, and to protect the well from the effects of perma- frost thaw-subsidence or freeze-back loadings shall be set at least 500 feet, measured depth, below the base of the perma- frost but not below 5000 feet true vertical depth. Sufficient cement shall be used to fill the annulus behind the casing to the surface. The surface casing shall have minimum axial strain properties of 0.5% in tension and 0.7% in compression. c) Alternate casing programs may be administratively approved by the Commission upon application and presentation of data which show the alternatives are appropriate, based upon accepted engineering principles. DONE at Anchorage, Alaska, and dated November 22, 1988. ~ 1Va s ~ha~a~ .ti ~ r atn°~' Ga-~s ~rn~sa~-/rva t i on C ommi s s ion ,/'' ~L ~'Sm±th, Comm±ss±~ner Alaska 05_1 and Gas Cortservat±on Comm±ssion ARCO Alaska, Inc. ?osi Oifice October 24, 1988 Mr. C. V. Chatterton Commissioner State of Alaska Alaska Oil and Gas Conservation Commission 3001 Porcupine Drive Anchorage, Alaska 99501 Subject: Proposed Change to Field Rule 3 or Conservation Order No. 145 Dear Chat' The purpose of this letter is to replace the three previous proposals to change Prudhoe Bay Field Rule 3 dating November 7, 1986, April 21, 1987 and November 23, 1987 with one comprehensive change to Field Rule 3 and to transmit the attached report on surface casing requirements for Prudhoe Bay wells. As discussed in our March meeting, it was felt that combining these related proposals would help clarify ARCO's position and simplify the Commission's approval process. The attached proposed Rule 3 updates Prudhoe Bay Field Rules and combines all previously approved surface casings with additions which are supported in the attached report into one listing. The following is a list of the proposed changes. 1) Replace Rule 3A, 3B and portions of 3C with Rule 4A and 4B of the Lisburne Field Rules. This will essentially update Prudhoe Bay Field Rules. 2) Eliminate the 1.8 design factor as applied to required post-yield strains for surface casing. Rule 3C currently requires that surface casing in Prudhoe must have minimum post-yield strain capacities of .9% in tension and 1.26% in compression. Elimination of the 1.8 design factor would reduce this requirement to .5% in tension and .7% in compression. See attached Background. RBG/53.1 ARCO AOsska, ~nc. is ~ Subsidiary of At~anlicRich~iefldCon~panV REEEIVED OCT 2 7 Oil & Gas Cons, Commissim.~ ~ A~chorage Mr. C. V. Chatterton October 24, 1988 Page 2 There are three reasons why this change should be made and they are as fol 1 ows' A) The present factors can result in over design. The original strain minimums of 0.9% in tension and 1.26% in compression were arrived at by applying a 1.8 design factor to a calculated worst-case strain of 0.7% in compression and 0.5% in tension. This 1.8 design factor is only applicable when dynamic loading conditions exist. ARCO Alaska, Inc. currently uses this 1.8 design factor on casing joint strength to allow for the tremendous impact loads which exist while running casing into the hole. Thaw subsidence is a static condition and does not require this large 1.8 design factor. Thaw subsidence design factors should be more in line with those used for the static conditions of burst and collapse which are 1.1 and 1.0, respectively. It should be noted that a casing failure caused by burst and collapse would be far more catastrophic than a surface casing failure due to thaw subsidence. Therefore, a 1.0 design factor should be utilized for thaw subsidence. B) The worst-case thaw subsidence strain calculations are very conserva- tive and already have built in design factors. The worst-case study strains are more than five times greater than those measured in the 5-spot thaw test which represented a producing period of 20 years. (Reference 1). This difference between measured and calculated strains is a good example of the magnitude of the "built in" design factors. C) More realistic design factors could result in considerable cost savings. Until recently, the field rules have not caused any incon- venience because all proposed surface casings have met the field rule requirements. Currently, alternate casing designs are being considered as part of our on-going effort to reduce drilling costs. Unnecessary additional design factors result in increased casing costs which are a signficiant percent of the total drilling cost. These costs not only impact drilling in current fields but also the feasibility of future marginal fields. (Reference 1: T. K. Perkins; J. A. Rochon; R. A. Ruedrich; F. J. Schuh; and G. R. Wooley, Prudhoe Ba~v Field Permafrost Casin9 and Well Design for Thaw Subsidence Protection, Atlantic Richfield Co., North American Producing Division, May, 1975). RBG/53.2 Mr. C. V. Chatterton October 12, 1988 Page 3 3) Replace the balance of Rule 3 with a comprehensive list of all previously approved surface casings and a list of the evidence to be submitted to the Commission to approve additional types and grades of surface casing. In support of the additions made to the proposed listing is the attached copy of "Surface Casing Requirements for Prudhoe Bay Well". This is a report prepared for the State of Alaska Oil and Gas Conservation Commission by ARCO Alaska, Inc., Standard Alaska Production Company and Exxon Company, U.S.A. These recent studies have provided additional insight on predicted surface casing performance and expected casing strains due to permafrost thaw under the closest projected wellhead spacing scenarios at Prudhoe Bay (i.e., wells spaced every 30' in rows 175' apart). If you have any questions or would like to discuss this matter further, please contact Rich Gremley at 265-1635. Sincerely, R. A. Ruedrich Drilling Manager RAR:RBG:hf Concur: Ro M Standard Alaska Production Co. Attachment RBG/53.3 BACKGROUND Shortly after the discovery of the Prudhoe Bay Field, the industry became concerned with the possibility of casing and well damage as a result of permafrost thaw subsidence. In an effort to more fully evaluate thaw subsidence problems, the industry performed numerous laboratory, field and engineering studies. In 1973, Atlantic Richfield and Exxon started thawing the permafrost in a closely spaced 5-spot well pattern. This thaw test was designed to simulate the thaw that would result from 15-20 years of produc- tion. The largest strains measured in the casing in this test are 0.13% in compression and 0.08% in tension. In conjunction with the 5-spot thaw test, a computer model was developed to predict worst-case strains. These computed strains are the highest compressive and tensile strains that would result from the worst possible combination and relative thickness of sand and silt layers. The maximum thaw subsidence casing strains calculated by the model are 0.7% in compression and 0.5% in tension. A design factor of 1.8 was applied to these worst-case strains resulting in the current conser- vation order strains requirements of 1.26% in compression and 0.9% in ten- sion. The following table compares the above mentioned strains. Design Factor Compression Over Measured Tension Design Factor Over Measured Measured 0.13% 0.08% Worst-case .7% 5.4 0.5% 6.3 Conservation Order 1.26% 9.7 0.9% 11.3 wi th 1.8 design factor 10/12/88 RBG/53a PROPOSED FIELD RULES CHANGES FOR PRUDHOE BAY Rule - CASING AND CEMENTING a) A conductor casing shall be set at least 75 feet below the surface and sufficient cement shall be used to fill the annulus behind the pipe to the surface. Rigid high density polyurethane foam may be used as an alternate to cement, upon approval by the Commission. The Commission may also administratively approve other sealing materials which are supported by sound engineering principles and performance data. b) Surface casing to provide proper anchorage for equipment to prevent uncontrolled flow, to withstand anticipated internal pressure and to protect the well from the effects of permafrost thaw-subsidence or freeze-back loadings shall be set at least 500 feet, measured depth, below the base of the permafrost but not below 5000 feet true vertical depth. Sufficient cement shall be used to fill the annulus behind the casing to the surface. The surface casing shall have minimum post-yield strain properties of .5% in tension and .7% in compression. c) Surface casing types and grades approved for use through the permafrost interval include: 1. 13-3/8", 68#/ft, L-80, API BTC or (shouldered connection)1 2. 13-3/8", 72#/ft, L-80, API BTC or (shouldered connection)1 3. 13-3/8", 72#/ft, N-80, API BTC 4. 13-3/8" 68#/ft, NT-80, CYHE, ERW, API BTC 5. 10-3/4"', 45.5#/ft, L-80 (shouldered connection)1 6. 10-3/4", 45.5#/ft, K-55, API BTC 7. 10-3/4", 45.5#/ft, J-55 API BTC or (shouldere~l connection)1 8 9-5/8", 47#/ft, L-80 (shouldered connection)~ 9. 9-5/8", 40#/ft, J-55, API BTC 10. 9-5/8", 36#/ft, K-55, API BTC 11. 9-5/8", 40#/ft, J-55, API BTC 12. 9-5/8", 36#/ft, K-55, API BTC These surface casing types are approved for wells spaced every 30 feet or more. NOTES: 1. Shouldered connections: A shouldered connection is a coupled connection using a tapered Buttress-type thread and an internal shoulder which acts as a positive make up stop. 10/24/88 RBG/53b.1 2. CYN-80 (controlled yield N-80) and MN-80 (Mannesmann's N-80) are both the same as L-80 and have been deleted from the list. 3. 30' spacing was the worst case spacing calculated base~'~Cc~~D model i rig. OCT2i ,;" -2- d) 4. HF-ERW Arctic grade J-55 is an ARCO Alaska, Inc. specification. It meets all the API specification for J-55 plus additional ARCO specification which reduce weld defects and improve cold weather properties. Both J-55 and HF-ERW Arctic grade J-55 have been modeled and meet the Commission's requirements. To avoid confusion and to simplify the list of casing, only J-55 has been listed. The Commission may administratively approve additional types and grades of surface casing through the permafrost interval upon a showing that the proposed casing and connection can withstand .5% in tension and .7% in compression. Evidence submitted to the Commission shall include: 1. Full scale tension and compression testing or 2. Finite element model studies outlined in "Surface Casing Require- ments for Prudhoe BaS Wells" or 3. Other types of finite element model studies acceptable to the Commi ss i on. **"Surface Casing Requirements for Prudhoe BaS Wells" report prepared for State of Alaska Oil and Gas Conservation Commission, by ARCO Alaska, Inc., Standard Alaska Production Company and Exxon Company, U.S.A., April, 1987. 10/24/88 RBG/53b.2 PROPOSED FIELD RULES CHANGES FOR PRUDHOE BAY Rule - CASING AND CEMENTING a) A conductor casing shall be set at least 75 feet below the surface and sufficient cement shall be used to fill the annulus behind the pipe to the surface. Rigid high density polyurethane foam may be used as an alternate to cement, upon approval by the Commission. The Commission may also administratively approve other sealing materials which are supported by sound engineering principles and performance data. Surface casing to provide proper anchorage for equipment to prevent uncontrolled flow, to withstand anticipated internal pressure and to protect the well from the effects of permafrost thaw-subsidence or freeze-back loadings shall be set at least 500 feet, measured depth, below the base of the permafrost but not below 5000 feet true vertical' ~depth. Sufficient cement shall be used to fill the annulus behind the ~casing to the surface. The surface casing sh~ll have minimum ~post-yield strain properties of .5% in tension and .7% in compression. , Surface casing types and grades approved for use through the permafrost interval include' i 13-3/8", 68#/ft, L-80, API BTC or (shouldered connection)1 21 1~-3/8", 72~/ft, L-80, ApI BTC or (shouldered connection)1 3. 13-3/8", 72#/ft, N-80, API BTC .:~ . '~i3~_..3../...8_']_.,__.6._8j./~..f._t__,..._N.Z._-_80_O~_CYHE, ERW, AP I BTC · .~0,3Z_4..__,__~5_._...#/ft,. L~._8_~_)(shouldered connection) 1 6. 10-3/4", 45,5#/'ft"~:~:Z'~-~ API BTC 7 10-3/4", 45.5#/ft, J-55 API BTC or (shouldere~ connection)1 8~ 9-5/8", 47#/ft, L-80 (shouldered connection) 9. 9-5/8", 40#/ft, bT,-55, API BTC 10. 9-5/8", 36#/ft, K-55, API BTC 11. 9-5/8", 40#/ft, J-55, API BTC 12. 9-5/8", 36#/ft, ~-55, API BTC-~-~ These surface casing types are approved for wells spaced every 30 feet or more. NOTES' 1. Shouldered connections' A shouldered connection is a coupled connection using a tapered Buttress-type thread and an internal shoulder which acts as a positive make up stop. 10/24/88 RBG/53b.1 2. CYN-80 (controlled yield N-80) and MN-80 (Mannesmann's N-80) are both the same as L-80 and have been deleted from the list. 3. 30' spacing was the worst case spacing calculated bas~ model i ng. OCl'2 2 Alaska Oil.& Gas Cons. Commi~,.'sim] ~ Anchorage 9 s/e' ~ 7~ ~- ~ ~rc " ARCO Alaska, Inc. {' Post Office Box 100360 COMM SR EfJG [ Anchorage, Alaska 99510-0360 Telephone 907 276 1215 April 21, 1987 State of Alaska Alaska Oil and Gas Conse~ation Co~ission 3001 Porcupine Drive ~chorage, Alaska 99501 Subject: Use of the following casings in Prudhoe Bay for the closest projected wellhead spacing of 30 feet in rows of 175 feet apart: 13-3/8", 68 lb/ft, L-80 API BTC 13-3/8", 72 lb/ft, L-80 API BTC 13-3/8", 72 lb/ft, N-80 API BTC '10-3/4", 45.5 lb/ft, L-80 (shouldered connection) 10-3/4", 45.5 lb/ft, J-55 (shouldered connection) 9-5/8", 47 lb/ft, L-80 (shouldered connection) Dear Mr. Chatterton: The purpose of this letter is to transmit the attached report on the request to change existing field rules for the Prudhoe Oil Pool. The Prudhoe Bay field rules should be updated to consider current technology and practice, to allow further environmental imPact reductions and cost-reducing improvements in the foreseeable future. Recent studies have provided additional insight on predicted surface casing performance and expected casing strains due to permafrost thaw under the closest projected wellhead spacing scenarios at Prudhoe Bay (i.e., wells spaced every 30 feet in rows 175 feet apart). The allowable and expected casing strains as functions of depth are provided in Figure 1 of the report. Based on these results, the following casings should be approved for use at Prudhoe Bay. · 2. 3. 4. 5. 6. 13-3/8", 68 lb/ft, L-80 AP1 buttress thread connection 13-3/8", 72 lb/ft, L-80 API buttress thread connection 13-3/8", 72 lb/ft, N-80 API buttress thread connection 10-3/4", 45.5 lb/ft, L-80 shouldered connection 10-.3/4", 45.5 lb/ft, J-55 shouldered connection 9-5/8", 47 lb/ft, L-80 shouldered connection ARCO Alaska, Inc, is a Subsidiary of AtlanticRichfieldCompany :::' 2 z 1987 ~L.'; [. ~ , ./ Alask~t 0il & Gas Cons. Cornmisslon Anchorage Mr.-C. V. Chatterton . April 21, 1987 Page -2- In conclusion, ARCO Alaska, Inc, Standard Alaska Production Co., and Exxon Co., U.S.A. request the administrative approval of the report as a document for future design criteria and revise the present Prudhoe Bay Field Rules accordingly. If you have any questions on this transmittal please contact me at 263-4614. Sincerely, R. A. Ruedrich Drilling Manager RAR/VM: klp Attachment cc: Mr. R. H. Reiley Standard Alaska Production Company P.O. Box 196612 Anchorage, Alaska 99519-6612 Mr. W. D. Smith Exxon Company, U.S.A. Production Department Alaska Interest P.O. Box 2180 Houston, Texas 77252-2180 ARCO Alaska, Inc. Post Office Bd~, ,00360 Anchorage. Alaska 99510-0360 Telephone 907 276 1215 November 23, 1987 Mr. C. V. Chatterton Commissioner State of Alaska Alaska Oil and Gas Conservation Commission 3001 Porcupine Drive Anchorage, Alaska 99501 Subject: Use of the following casings in Prudhoe Bay for the closest projected wellhead spacing of 30' in rows of 175' apart: 13-3/8", 68#/ft, L-80 API BTC or (shouldered connection) 13-3/8", 72#/ft, L-80 API BTC or (shouldered connection) 13-3/8", 72#/ft, N-80 API BTC 10-3/4", 45.5#/ft, L-80 (shouldered connection) 10-3/4", 45.5#/ft, J-55 API BTC or (shouldered connection) 9-5/8", 47#/ft, L-80 (shouldered connection) Dear' Mr. Chatterton: The purpose of this letter is to transmit the attached report on the request to change existing field rules for the Prudhoe Oil Pool. The Prudhoe Bay Field Rules should be updated to consider current technology and practice, to allow further environmental impact reductions and cost-reducing improve- ments in the foreseeable future. Recent studies have provided additional insight on predicted surface casing performance and expected casing strains due to permafrost thaw under the closest projected wellhead spacing scenarios at Prudhoe Bay (i.e., wells spaced every 30' in rows 175' apart). The allowable and expected casing strains as functions of depth are provided in Figure I of the report. Based on these results, the following casings should be approved for use at Prudhoe Bay. ARCO Alaska, Inc. I$ a Subsidiary of AtlanticRIchfleldCompany Mr. C.V. Chatterton November 23, 1987 Page 2 1) 13-3/8", 68#/ft, L-80 API BTC or (shouldered connection) 2) 13-3/8", 72#/ft, L-80 API BTC or (shouldered connection) 3) 13-3/8", 72#/ft, N-80 API BTC 4) 10-3/4", 45.5#/ft, L-80 (shouldered connection) 5) 10-3/4", 45.5#/ft, J-55 BTC or (shouldered connection) 6) 9-5/8", 47#/ft, L-80 (shouldered connection) In conclusion, ARCO Alaska, Inc., Standard Alaska Production Company and Exxon Company, U.S.A., request the administrative approval of the report as a document for future design criteria and revise the present Prudhoe Bay Field Rules accordingly. If you have any questions on this transmittal, please contact me at 263-4614. Sincerely, R. A. Ruedrich Dri 11 i ng Manager RAR: RBG: pk . RBG/18 Attachment cc: Mr. R. H. Reiley Standard Alaska Production Company P.O. Box 196612 Anchorage, Alaska 99519-6612 Mr. W. D. Smith Exxon Company, U.S.A. Production Department Alaska Interest P.O. Box 2180 Houston, Texas 77252-2180 . . ~ NOTICE TO PUBLISHER STATE OF ALASKA ' . '~' ,:~ : ADVERTISING ORDER NO. NG ORDER NO., CERTIFIED AFFIDAVIT OF PUBLICATION (PART vnu~;;n 2 OF THIS FORM) WITH ATTACHED COPY OF ADVERTISE- /~J= 08-5576 , , ~- , .~,- MENT MUST BE SUBMITTED WITH INVOICE. _ ~ ...... ~ -- [DATE OF A.D. .;'. Anchorage Daily News . ' ' Calyn Evans ~ November 25, 1986 '" P. O. B~X 1490'01 '" . PHONE ' Anchorage, Alaska 99514-9001 (9o7) 279-1433 DATES ADVERTISEMENT REQUIRED: Ti P U B L I S FI E R Alaska Oil & Gas Conservation Conmission 3001 Porcupine Drive Anchorage, Alaska 99501 November 27, 1986 THE MATERIAL BETWEEN THE DOUBLE LINES MUST BE PRINTED IN ITS ENTIRETY ON THE DATES SHOWN. SPECIAL INSTRUCTIONS: Type of Advertisement: ~ Legal , [] Display [] Classified [] Other (Specify): Notice of Public Hearing STATE OF ALASKA Alaska Oil and Gas Conservation Commission Re.. The application of ARCO Alaska, Inc. for a change in the minhm~ strain properties of surface casing used in the Prudhoe Bay Field. The Alaska Oil and Gas Conservation Commission has been requeSted, by letter dated November 7, 1986, to issue an order to anmnd Rule 3(c) of Conservation Order No. 145 to change the mininum strain requirements for the surface casing. A person who my be harmed if the requested order is issued, my file a written pro- test, prior to December 12, 1986, with the Alaska Oil and Gas Conservation Conmission, 3001 Porcupine Drive, Anchorage, Alaska 99501 and request a hearing on the matter. If the Pconmirotest is filed timely and raises a substantial and mterial issue crucial to the ssion's detennination~ a 'hearing on the rotter will be held at' the above' address at 9..00 AM on January 7, 1987, in conforinance with 20 AAC 25.540. If a hearing is to be held, interested Parties may confirm this bY calling 'the C0nmission's office, (907) 279-1433, REF 1 2 3 4 AMOUNT DATE R 08030 _ , , 01 08,,5sv4 TOTAL OF ALL PAGES COMMENTS 86-11-25 Notice of Public Hearing FIN AMOUNT LC 1 3 4 hE~uISITIONED BY: ISY ] CC 87 0846200]. ,2-901 (Rev. 6-85) .IQ PUBLISHER ARCO Alaska, Inc. i,,' Post Office B6 ,00360 Anchorage, Alaska 99510-0360 Telephone 907 276 1215 November 7, 1986 Mr C V Chatterton g(o~ Commi s s i oner ~,,~ State of Alaska Alaska Oil & Gas Conservation' Commission 3001 Porcupine Drive Anchorage, AK 99501 SUBJECT' Proposed change to Field Rule 3c of~C'o-fise-~FiJ[t/{'6~ ,.Ordeff~'NO'~'145'and Field Rule 4d of Conservation Order No. 173 Dear Mr. Chatterton: The purpose of this letter is to request changes in the following Prudhoe Bay and Kuparuk River Field rules; Rule 3c of Conservation Order No. 145 and Rule 4d of Conservation Order No. 173. Cur- rently, these rules require that surface casing in Prudhoe and Kuparuk must., have minimum post-yield strain capacities of 0.9% in tension and 1.26%'in compression. ARCO proposes that these strain capacities should be changed to 0.5% in tension and 0.7% in compression. The forces that cause these strains are a direct result of permafrost thaw subsidence. See attachment for back- ground. There are three reasons why these changes should be made and they are as follows: 1. The present factors can result in over design. The original strain minimums of 0.9% in tension and 1.26% in compression were arrived at by applying a 1.8 design factor to a calcu- lated worst-case strain of 0.7% in compression and 0.5% in tension. This 1.8 design factor is only applicable when dynamic loading conditions exist. ARCO currently uses this 1.8 design factor on casing joint.strength to allow for the tremendous impact loads which exist while running casing into the hole. Thaw subsidence is a static condition and does not require this large 1.8 design factor. Thaw subsidence design factors should be more in line with those used for the static conditions of burst and collapse which are 1.1 and 1.0 respec- tively. It should be noted that a casing failure caused by burst and collapse would be far more catastrophic than a surface casing failure due to thaw subsidence. Therefore, a 1.0 design factor should be utilized for thaw subsidence. RECEIVED NOV 1 9 1986 ARCO Alaska, Inc. Is a Subsidiary o! AtlantlcRIchfieldCompany Alaska 0il & 6as Cons. Commission Anchorage Page Two 'i'~ Field Rule'~ 3c & 4d November 7, 1986 2. The worst-case thaw subsidence strain calculations are very conservative and already have built-in design factors. The worst-case study strains are more than five times greater than those measured in the 5-spot thaw test which represented a producing period of 15 years. (Reference 1) This difference between measured and calculated strains is a good example of the magnitude of the "built-in" design factors. 3. More realistic design factors could result in considerable cost savings. Until recently, the field rules have not caused any inconvenience because all proposed surface casings have met the field rule requirements. Currently, alternate casing designs are being considered as part of our on-going effort to reduce drilling costs. Unnecessary additional design factors result in increased casing costs which are a significant percent of the' total drilling cost. These costs not only impact drilling in current fields but also the feasibility of future marginal fields. In conclusion, ARCO Alaska, Inc. requests the administrative approval of the'~'proposed field rule change which would eliminate the 1.8 design factor as applied to required post-yield strains for surface casing. ~ If you have any questions or would like to discuss this matter further, please contact Rich Gremley at 265-1635. Sincerely, R. A. Ruedrich Drilling Manager RAR/RBG/dmr misc:90 Reference 1. T. K. Perkins; J. A. Rochon; R. A. Ruedrich; F. J. 5chuh; and G. R. Wooley; Prudhoe BaS Field Permafrost Casin9 and Well Design for Thaw Subsidence Protection, Atlantic Richfield Co., North American Producing Division, May 1975. RE£E VED 1,40V 1 9 1986 Alaska Oil & Gas Cons. Commission Anchorage BACKGROUND Shortly after the discovery of the Prudhoe Bay Fi61d, the industry became concerned with the possibility of casing and well damage as a result of permafrost thaw subsidence. In an effort to more fully evaluate thaw subsidence problems, the industry performed numerous laboratory, field and engineering studies. In 1973 Atlantic Rich- field and Exxon started thawing the permafrost in a closely spaced 5-spot well pattern. This thaw test was designed to simulate the thaw that would result from 15-20 years of production. The largest strains measured in the casing in this test are 0.13% in compres- sion and 0.08% in tension. In conjunction with the 5-spot thaw test, a computer model was deVeloped to predict worst-case strains. These computed strains are the highest compressive and tensile strains that would result from the worst possible combination, and relative thickness of sand and silt layers. The maximum thaw subsidence casing strains calculated by the model are 0.7% in compression and 0.5% in tension. A design factor of 1.8 was applied to these worst-case strains resulting in the current conservation order strains requirements of 1.26% in compression and 0.9% in tension. The following table compares the above mentioned strains. Compressi on Tens i on Measured 0.13% 0.08% Worst-case '~ ' .7% 0.5% Conservation Order 1.26% 0.9% RECEIVED NOV 1 9 1986 Alaska Oil & Gas Cons. Commission Anchorage PROPOSED FIELD RULES CHANGES FOR PRUDHOE BAY RULE ~'. CASING AND CEMENTING c) Surface casing types and grades approved for use through the permafrost interval include' 1. 13-3/8", 68#/ft, L-80, API BTC or (shouldered connection)* 2. 13-3/8", 72#/ft, L-80, API BTC or (shouldered connection)* 3. 13-3/8", 72#/ft, N-80, API BTC 4. 10-3/4", 45.5#/ft, L-80 (shouldered connection)* 5. 10-3/4", 45.5#/ft, J-55 API BTC or (shouldered connection)* 6. 9-5/8", 47#/ft, L-80 (shouldered connection)* These surface casing types are approved for wells spaced every 30 feet or more. *Shoul oered connections' A shouldered connection is a coupled connection using a tapered Buttress-type thread and an internal shoulder which acts as a positive make up stop. Examples of shouldered connection include Mannesmann's BDS, Interlock's Seal-Lock, Nippon's NSCC, Vallourec's VAM and New VAM and Tuboscope's TKC connections. The Commission may administratively approve additional types and grades of surface casing through the permafrost interval upon a showing that the proposed casing and connection can withstand the permafrost thaw subsidence and freeze back loadings which may be experienced. Evidence submitted to the Commission shall include: L~ ~~.~_7 1. Full scale tension and compression testing or 2. Finite element model studies outlined in "Surface...Casing Require- ments for Pr.udhoe Bay Wells" or 3. Other types of finite element model studies acceptable to the Commi s s i on. **"Sur.face Casing .Requirements for Prudhoe Bay.....Wells" report prepared for State of AlaSka Oil and Gas Conservation Commission, by ARCO Alaska, Inc., Standard Alaska Production Company, and Exxon Company, U.S.A., April, 1987. o .. RBG/23