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Home My WebLink AboutCO 206Index Conservation Order 206 Milne Point Field 1. November 1, 1984 Conoco’s request for an exception 2. November 6, 1984 Notice of Hearing and Affidavit of Publication STATE OF ALASKA ALASKA OIL AND GAS CONSERVATION COMMISSION 3001 Porcupine Drive Anchorage, Alaska 99501 Re: THE APPLICATION OF CONOCO ) INC. for an order granting ) an exception to Rule 4(c) ) of Conservation Order No. ) 173 for wells to be drilled ) from eight drill pads in ) the Kuparuk River Field. ) Conservation Order No. 206 Kuparuk River Field Kuparuk River Oil Pool November 16, 1984 IT APPEARING THAT: 1. Conoco Inc., by letter dated November 1, 1984, requested the Alaska Oil and Gas Conservation Commission to issue an order granting an exception to Rule 4(c) of Conservation Order No. 173 to allow surface casing to be set as deep as 5000 feet true vertical depth in development wells on Milne Point Unit drilling pads A, B, C, D, E, F, L, and Central Facilities. 2. Notice of public hearing was published in the Anchorage Times on November 6, 1984. 3. There were no protests filed to the application. FINDINGS: 1. ~The Ugnu sands and the West Sak sands are hydrocarbon-bearing and potential reservoirs in some areas of the Kuparuk River Field. 2. The West Sak sands are hydrocarbon-bearing in the area of drilling pads A, B, C, D, E, F, L, and Central Facilities. 3. The oil in the West Sak sands has a low solution GOR and has no known gas-oil contact. 4. In the area of the eight referenced drilling pads, the West Sak sands are structurally located so as to be at or below the maximum surface casing setting depth of 2700 feet true vertical depth prescribed in Rule 4(c) of Conservation Order No. 173. 5. The West Sak Reservoir is currently being investigated in the West Sak Sands Section 35 Project to determine the feasibility and method of reservoir-wide exploitation. 6. The West Sak sands will be better protected in the area of the eight drilling pads if they are cemented above the shoe of the surface casing rather than several thousand feet above the shoe of the production casing in the Kuparuk River Oil Pool wells that are to be drilled on the pads. Conservation Or~' No. 206 Page 2 November 16, 1984 7. Conservation Orders No. 190, 193, and 203 granted an exception to Rule 4(c) of Conservation Order No. 173 for wells to be drilled on 18 drilling pads and the information and experience gained from setting the surface casing deeper than 2700 feet true vertical depth indicates that the West Sak reservoir can be drilled safely with a conductor/diverter system and a minimum 9.0 pounds per gallon drilling fluid. CONCLUSIONS: 1. A surface casing string setting depth deeper than prescribed by Rule 4(c) of Conservation Order No. 173 is safe and will protect the permafrost in the area of the eight drill pads. 2. Development wells to be drilled to the Kuparuk River Oil Pool on the referenced eight pads can be safely drilled to 5000 feet true vertical depth using a conductor casing, a diverter system and no less than 9.0 pounds per gallon drilling fluid. 3. The West Sak Reservoir will be better protected from damage if it is cemented behind the surface casing. NOW THEREFORE, IT IS ORDERED THAT: Milne Point Unit development wells to be drilled to the Kuparuk~River Oil Pool on drilling pads A, B, C, D, E, F, L, and Central Facilities may be drilled to a maximum 5000 feet true vertical depth before surface casing is set provided that conductor casing is set and cemented in accord with Conservation Order No. 173, a diverter system is used in accord with 20 AAC 25. 035(b)(1) and a drilling fluid of at least 9.0 pounds per gallon is used in the drilling. DONE at Anchorage, Alaska and dated November 16, 1984. V. Chatte , Alaska Oil and Gas Conservation Commission Harry W. ~ugler, Com~fissioner Alaska O~il and G~Conservation Commission Lonnie C. Smith, Commissioner Alaska Oil and Gas Conservation Commission Notice of Public Hearing STATE OF ALASKA Alaska Oil and Gas Conservation Commission Re: The application of CONOCO, INC. for a conservation order granting an exception to Rule 4(c) of Conservation Order No. 173. Notice is hereby given that Conoco, Inc. has requested the Alaska Oil and Gas Conservation Commission to issue an order granting an exception to Rule 4(c) of Conservation Order No. 173 for development wells to be drilled from pads A, B, C, D, E, F, L, and the Central Facilities Pad.in the Milne Point Unit area of the Kuparuk River Field. The exception is requested in order to cement surface casing below the West Sak Sands in the area of the field where the potentially productive Sands will be better protected and isolated than under current rules. A deeper surface casing depth has already been proved to be a safe prac- tice in many wells in the Kuparuk River Field. Parties who may be aggrieved if the referenced order is issued granting the referenced request are allowed 10 days from the date of this publication in which to file a protest, in writing, stating in detail the nature of their aggrievement and their request for a hearing. The place of filing is the Alaska Oil and Gas Conservation Commission, 3001 Porcupine Drive, Anchorage, Alaska 99501. If such a protest is timely filed, a hearing on the matter will be held at the above address at 9:00 AM on November 16, 1984 at which time protestants and others may be heard. If no such protest is timely filed, the Commission will consider the issuance of the order without a hearing. Harry ~. Kugler / Commi s s ioner Alaska Oil & Gas Conservation Commission ] 0 0 1 P i..'~ ~. C U ,P i i..~' [~i '"" T~'i.AT SH~ IS ~.'~B I,E:G~L CL~.,RK 13 STATe Cfi .AbAS~, ~',~[) TE~A'I: THE; 5544 1 1 /0 6 ! 8 4, NOTICE OF PUBLIC HEARING STATE OF ALASKA . ". Alaska Oil and Go, s Conservation Commission Re The application of CONOCO, INC. for o' conservation order granting on exception to Rule 4(c) of Conservation Order. No. Notice is hereby given that that Conoco Inc. has requested the Alaska Oil and Gas Conservation .Commission t0 issue an.order granting an exception to-Rule 4(.c) O'f Conservation Order N6. 173 for deve opment wells to be drilled from pads A, B, C, D, E, F, L, and the Central Foci lilies. Pad in t~e Milne PoinLunit area bf the. Kuparuk River F e d The exception is requested In orde~ to ce- ment Surface casing,below the,West Sak Sands in the area"Of the field Where the potentially productive .Sands Will be, I~etter. pro- tected and isolated than under current .ru.les.. A deeper surface casing depth 'has already been approved to:b~ a .~s0feli~ractice in many wells in the Kupar,uk River Field.. ' ,.. POtties who may be'aggrieved if the referenced orde, ri's:lssued. granting the reference request'are 3":..-.;' ~ '0 d;:. Of this publication in Which to file: :;, 3'~..f ,~' .'." n,.'~ ...'m,,:~ ... detail the' nature of their aggrlev¢,m~' ' ' 3,"~J 1,',¢,.,' 3001 'Porcul~lne Drive, Anchorage, ~3..'k.' 9.;5( i ~- ..';;ch i~ c' cie.:' is timely f ed, a hearing'on the mc"...;" .-. I address at.9:00'AM on November '~. ' :.3- ',~ ...,'.i:'" '."'"e i~-o'e:'- ants and others may be heard. If- ;; ~.~'.." i-,'clu~l 'the commission will consider the ,~, .~.m"c:, ?.~ ,-r. :;~ mcr '..;'.0J' :: hearing. . . .. ' ..... ,, '~,i,,,,Horry,,W,. Kugler , · 'C'om'mlssloner , ' I" ' ' ' , A aska 011 & Gas Conservation corn'i~l'isZ I i I, sion ,, , ', ,, ,, PUb: NovemDer 6, 1984 PO: Aa-08 55441 · TF~'E; S. IZg OF TH:IS AD i~:A8............ 74, i.,It'~ES SIGNE:[).......... S 22.,. 2O 19~,5~99 i. hl.S.................., n7 I)AY r',f' NOV ,1.984 ~ ~C~i V~D TO BEF'ORE X,E "~'" ....... ,(~"0 ~' ~lask~ Oil &~Gas Cons. .......... L,, ~: 'f f~. 8 A '1' ~: 0 t~' [,, A, 8 K' A anchorage CommisMo~ log November 1, ]984 Alaska Oil and Gas Conservation Commission. State of Alaska 3001 Porcupine Drive Anchorage, Alaska 99501 Conoco Inc. 2525 C Street Suite 100 Anchorage, Alaska 99503 RECEIVED Alaska Oil & Gas Cows. ornmlssion Anchorage C ' Gentlemen: Conoco Inc. hereby applies for an Order granting exceptions to Rule 4(c) of Conservation Order No. 173, and Rule 20 AAC 25.536 of Register 74, for all wells to be dri].led in the Milne Point Unit from the "A", "B", "C", "D", "E", "F", Central Facilities and "L" PadS. RE: Rule 20 AAC 25.536 of ReRister 74 We are confident that there is adequate data available from existing wells in areas surrounding well pads for the Upper Cretaceous (Wast Sak and Ugnu sands) reservoir evaluRtion. This request for exception would apply only to wells drilled from pads where open hole log information is available from preceding wells. In ali. other cases, we wi].], be pro- posing a log run(s) below conductor. RE: Rule 4(c) of Conservation Order No. 173 We have elected to go with a deeper surface casing program in order to ensure a competent cement across the Upper Cretaceous (West Sak and Ugnu) formations to protect and preserve for future development. We propose that surface casing be set a minimum of 250 feet below the base of the Upper Cretaceous (West Sak) sands with a maximum allowable depth of 5000 feet TVD. Several alternatives were considered, inclt~ding stage collars and foam cement. Stage collars have been used in previous wells to cement the Upper Cretaceous but they present several problems: i · The stage collar is generally set just below the sands, then cement is circulated through the too]. to 500 feet above the shallowest hydrocarbon sand (as per State regulations). This involves placing 2100± feet of cement within 500± feet of the surface casing shoe. Severe channeling can result in having cement into the surface casing that could prevent the downsqueeze of the Arctic Pak slurry. 2. The casing can not be reciprocated while cementing through the stage collar. Potential for a quality cement job is thus greatly diminished. Be Stage collars are closed by applying a differential pressure across the tool. If the external hydrostatic pressure is much higher than anticipated, due to severe channeling or formation sloughing, the tool may not close. There is also the potential for seal failure. In either situation, a cement squeeze would be required. Past experience has proven that the Upper Cretaceous sands are extremely difficult to squeeze successfully. 4· The stage collar is not difficult to drill out but there will always be an abrasive restriction at that point in the casing string. In the high angle wells being drilled on the Slope, the restriction represents a potential problem of hanging-up packers, and production seals protruding below a completion assembly can be severely damaged. Nitrogen (foam) cement was considered to be a viable alternative for the stage collar. We considered the feasibility of a large volume of the light weight nitrogen cement as a lead slurry pumped down the production casing, followed by a second stage of conventional Class "G". The objective would be to place the lightweight slurry across the Upper Cretaceous sands and the conventional slurry would be set across the Kuparuk formations. Using the lightweight slurry in the top 3,000 feet (TVD) of the hole should minimize the potential of partial lost returns while cementing. Nitrogen cement is a good mud displacement fluid due to its rheology properties and it can also be mixed at weights as low as ~10.5 ppg and still obtain reasonably good. compressive strength, over the long term. Economically, the n~.trogen cement would reduce well costs by an estimated $70,000 to $80,00 per well as compared to using a stage collar. There are, however, several drawbacks to the nitrogen cement: It is uncertain how we].], the cement slurry would displace the dril].ing mud when the fluid weights are nearly equal. If displace- ment were not as expected (channeling), the slurry would be conta- minated. This would result in a poor cement bond, a reduced cement strength and a potential for cement into surface casing. · Another complication of using the lightweight slurry is the evalua- tion. Several techniques are available to make a qual~.tative analysis but the nitrogen in the s].urry coupled with the lower compressive strengths makes it d~.fficult to obtain a reliable quantitative analysis. Setting surface casing below the Upper Cretaceous sands is obviously superior to the two alternatives mentioned, for providing a dependable isolation of all the shallow oil sands. We are very conscious of the minima], support offered by the conductor set at 80 feet (below surface) but we are a].so confident that the operation can be done safely and with no significant risk. Only the lower sands (referred to as the "N" and "O" sands) are capable of flowing to the surface. However, these formations have an Equivalent Mud Weight Pore Pressure of only 8.6 ppg with a GOR of 200 SCF/BBL. Net pay of the two sands is estimated at roughly 60 feet spread out over a gross interval of 246 feet. As the attached calculations indicate, a base mud weight of 9.~ ppg is more than adequate to control the formations and the gas from the sands wi].], have a neglibib]e influence on the hydrostatic. And, based on past experience, this weight mud system can be used confidently without fear of breaking down formations and losing returns. During drilling operations, we will maintain a quality mud system with adequate fluid loss control for good filter cakes and a mud weight of at least 9.0 ppg. We will be prepared to safe].y handle the cuttings gas at the surface and will closely monitor the volumes and weights of the mud. In the extreme case of lost circulation resulting in a gas kick, the kick will be diverted to the reserve pit to protect the conductor shoe. Very truly yours, /Manager of Alaskan Operations DRG/kr I ECEIVED Mud Weigh~_Reduction While Dri~n~ the Upper Cretaceous Sands Assumptions: ROP - 300'/hour After drilling the kelly down, circulate to clear collars plus 100' before picking up. Circulation Rate = 400 gpm Vel. (D.P.) = 1.24 fps Vel. (D.C.) = 2.67 (200') ECD = 9.6 (9.A MW) Therefore, we would drill 30' in 6 minutes, then pick-up and circulate for 3 minutes. The net pay in the "N" and "0" sands were estimated at 60', the overall length was 246' for a 40° incline, these figures will be 78' and 321'. - Assuming a 12.5" hole, the 246' will recover 210 f3 (vol..). - Assuming an average porosity of 35% Water saturation of 100% in shale Water saturation of 30% in sands GOR of 210 f3/BBL Base Oil Volume = 78'(0.85 fs/f) x 0.35 x (1-0.30) + 5.614 fS/bbl = 2.90 bbl This volume would be drilled in (246 + 30)(9) = 74 Minutes With an annular velocity of 1.24 fps, the returns would be distributed over 74 x 60 x 1.24 = 5490'. This would indicate that the first of the oil would be to the surface while still drilling the sands. Therefore, use the average depth for gradient calculations. At the surface GOR = 210 SCF/BBL 210 x 2.9 = 609 f~ of methane ~(609~ = P V~ ~(Assume avg. temperature approximately 60°) P2V~st' P2 = 9 6 x 2200' x .052 = 1098 V2 = 8 f~ (overall vol. for average gradient) The 8 f3 would be distributed evenly throughout the well 8/4400' = 0.0018 f~/f RECEIVED ~,tasXa Oi~ a Gas Cons. Commisslor~ Anchorage Mud Weight Reduction While Drilling the Upper Cretaceous Sands Through the "0" and "N" sands, the gross interval is 246' with a net pay of 60'. In. a deviated well, these values will, of course, be higher. Therefore, clay content = 246 = 80% (2~6+60) Sandstone = 20% Assuming a matrix density = 2.65 g/cl 100% water saturation in clays, water gravity = 1.0 g/cc 30% water saturation in sands, oil gravity = 0.9 g/cc For a representative value, we will assume that every foot drilled is 80% clay and 20% sand. At a depth of 5,000' with a circulation rate of 400 gpm, the bottoms-up time would be 66 minutes. We would thus drill an estimated 220'. Therfore, a worst case (minimum increase of mud weight) would be with the backside returns (from shallow sands) extending from surface to bit. Average density of clay formation (including water) would be: (2.65 g/cc x 0.70) + (1.0 g/cc x 0.30) = 2.15 g/cc In the sandstone formations: (2.65 g/cc x 0.70) + [(1.0 g/cc x 0.30) + (0.90 g/cc x (1-0.30))] x 0.30 = 2.13 g/cc Average density value would thus be: 2.15 g/cc (0.80) + 2.13 g/cc (0.20) = 2.146 g/cc 2.146 g/cc x 62.43 P/CF = 134.0 P/CF g/cc Based on the estimated penetration rate of 300'/hr with an estimated hole size of 12.5", we would drill 0.85 CF of formation (1.0 linear foot) in 10.2 seconds. At a pump rate of 400 gpm, the cutting will be added to 400 gpm x (1/60 sec/min) x (1/7.48 gal/CF) = 0.89 CF/S Therefore, 0.89 CF of mud will carry (0.85 CF/10.2 sec) = 0.08 CF of formation. Annulus contains [0.89/(0.89 + 0.08)] = 92% mud and [100-92] = 8% drilled solids/fluids. The gradient of drilling mud (9.4 ppg) is 0.489 psi/ft, while the gradient of the drilled solids/fluids would be [134 P/CF x (1/7.48 G/CF)] = 17.9 ppg = 0.931 psi/ft. The resultant gradient ~.n the annulus would thus be estimated at: (0.92 x 0.489 psi/f) + (0.08 x 0.93 psi/f) = 0.524 psi/ft 0.524 psi/ft = 10.1 ppg (This does not take into account the actual ECD which will be approximately 0.2 ppg higher) Each linear foot contains 0.85 f3 of 9.4 ppg (0.4888 psi/ft) mud. If the mud volume is reduced by the gas volume, the resultant weight would be: .85 f3 = 6.358 gallons x 9.4 ppg = 59.76 lbs/f w/gas .0018 = .013 gallons 6.358 - 0.013 = 6.344 x 9.4 =.49'.64 lbs/f 59.64/6.358 = 9.38 ppg This minimum reduction would be more than covered by the increase in weight from solids.