The Tanner Field, located in Section 30 and 31 of Township 51N and Range 70W in Campbell County, Wyoming was operated by Citation Oil and Gas.Discovered in 1991, Tanner produces a 21o API gravity crude oil with a viscosity of 11 cp at the reservoir temperature of 175oF from the Minnelusa B sandstone at a depth of 8,915 ft with an average porosity of 20% and an average permeability of 200 mD.Average thickness is 25 ft.Like Cambridge, Tanner is interpreted to be a preserved remnant of a highly dissected coastal Eolian dune complex.
Tanner is a small field consisting of one injection well (Tanner Unit 21-31) and two production wells, north (Tanner Unit 24-30) and south (Tanner Unit 22-31) of the injector.A net pay isopach is shown to the left.Swept or floodable pore volume is 2,560 Mbbls distributed equally with 1,280 Mbbls north of the injection well and 1,280 Mbbls south of the injection well.Original oil in place is 2,000 Mbbls or 80% oil saturation.Bo is 1.02.The floodable pore volume and original oil in place represents about half the total field, as seen in the figure on the left.
Primary production from April 1991 to September 1997 was 381,696 barrels of oil.Primary oil recovery from the floodable pore volume was calculated by adding 100% of the production from 21-31 to 50% of the production from 24-30 and 50% of the production from 22-31.Alkaline-surfactant-polymer flood floodable area primary production was estimated to be 241,463 bbls or 11.8% OOIP.Water injection began in October 1997 and continued through April 2000.Waterflood production from October 1997 to April 2000 was 265,515 barrels of oil or 13.0% OOIP. All oil production beyond primary oil production was assumed to be from the alkaline-surfactant-polymer flood area.Total primary plus waterflood oil recovery from the alkaline-surfactant-polymer flood area is 506,968 bbls or 24.8% OOIP.Cumulative water injection was 588,420 bbls or 0.245 pore volume.Water break through occurred after injection of 388,307 bbls or 0.151 pore volume.Ultimate primary plus waterflood recovery from the floodable pore volume is predicted to be 48% OOIP.Oil production and oil cut are shown as a function of time in the figure above.Primary production in the figure above includes production from outside the alkaline-surfactant-polymer floodable area. The table below summarizes all production through 11-30-08.
ASP injection was initiated when the oil production was at a 43% oil cut after injecting 0.245 pore volume water through April 2000.The single injection well and two production wells project spacing is roughly 40 acres.Injected chemical solution was 1.0 wt% sodium hydroxide plus 0.1 wt% active ORS-41 (surfactant) plus 1000 mg/L Alcoflood 1275A (polymer).Alcoflood 1275A is a partially hydrolyzed polyacrylamide polymer with approximate molecular weight of 18 x 106 Daltons and 25% degree of hydrolysis.ORS-41 is an alkyl aryl sulfonates with an approximate molecular weight of 410 Daltons.Injection sequence was 0.251 pore volume (642,700 bbls) of ASP solution followed by 0.252 pore volume (644,685 bbls) of a tapered concentration polymer slug that began in July 2002.The subsequent water drive began February 2005.A total of 0.406 pore volumes (1,039,224 bbls) of water have been injected subsequent to the polymer flush through November 2008.
Response to alkaline-surfactant-polymer injection can be seen after six months of injection.Oil cut in October 2000 diverges from the established waterflood decline as shown in the figure to the right.Incremental oil is established from divergence from continuation of the waterflood oil cut beginning fall 2000.Incremental oil produced through November 2008 is 12.6% OOIP (252,645 bbls).ASP injection is predicted to recover 17% OOIP or 340,000 bbls of oil for a cumulative ultimate oil recovery of 65% OOIP.As of October 2008 a total of 1,105,180 bbls of oil have been produced from all wells by primary, waterflood, and chemical flood.Current oil cut is 9.0%.Predicted waterflood performance matches coreflood and field performance with ultimate field oil recovery forecast to be 48% OOIP.
The north portion of the Tanner Field is performing differently than the south portion.The figure to the left depicts oil cut versus cumulative oil production after injection begins and compares it with the Cambridge Field.The north portion of the Tanner Field production equals the production of the Cambridge Field at similar oil cut.The south portion of the Tanner Field has produced about half the volume of the Cambridge Field and the north portion of the Tanner field but the oil cut is still high at 46%.Also note in this figure that the extension of the waterflood decline parallels the average of eight Minnelusa waterfloods.
Chemical and incremental plant costs were $1,430,000.Incremental operating costs were assumed to be negligible since an economic waterflood would have operated through out chemical injection.Current chemical, facilities, and fluid design cost per incremental barrel is at $5.66.
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