The Cambridge field1, located in Section 28 of township 53N and Range 68W in Crook County, Wyoming was operated initially by Barrett Resources and completed by Hunt Petroleum.The field produces from the Permian Minnelusa Upper B sand at about 7,108 ft.The field is interpreted to be a preserved remnant of a highly dissected coastal Eolian dune complex.Structural contours on top of the Upper B sand porosity indicates a slight northeast-southwest trending dip; the top of structure being in the northeast.The figure to the left depicts a net pay isopach.A non-active water leg exists to the southwest, which is not shown in the isopach.
The Cambridge Field is defined as 7,117 Mbbls pore volume with 4,875 STMB of original oil in place.The figure to the left shows the single injection well, 32-28, and the six production wells.It was discovered in 1989 with Federal 31-28.The field produces 31 cp crude oil.Peak primary oil production was 489 BOPD.Within a year, the production rate had declined to 37 BOPD as is typical of Minnelusa reservoirs.Federal 21-28 and 32-28 began production in June 1990 with peak production of 69 and 292 BOPD, respectively.The Federal 23-28 started production in October 1990 with peak production occurring in November 1990 of 212 BOPD of oil and 18 BWPD of water.Primary production totaled 217.7 STMB of oil or 4.5% OOIP and 23.8 MBW water from December 1989 to December 1992.
An alkaline-surfactant-polymer flood was applied to the field in a secondary mode, beginning in February 1993.This eliminated duplicating the operating cost of the waterflood during alkaline-surfactant-polymer injection.The swept area of the Cambridge Field is 5,827 Mbbls pore volume with 4,072 Mbbls of original oil in place.The injected alkaline-surfactant-polymer solution consists of 1.25% sodium carbonate plus 0.1% Petrostep B-100 (surfactant) plus 0.15% Alcoflood 1275 (polymer).1,745 Mbbls of ASP solution was injected.Polymer injection as a mobility control buffer began in October 1996.The final water drive started in February 2000.Oil recovery through November 2008 is 2,211.5 MSTB or 54.3% OOIP of the swept area at an oil cut of 2.7%.Numerical simulation predicted 1,337 MSTB or 32.8% OOIP for a waterflood from the swept area and 2,289 MSTB or 56.2% OOIP for the alkaline-surfactant-polymer flood.Total field actual production is 2,291 MSTB or 56.3% OOIP.Total field numerical simulation waterflood prediction is 1,388 MSTB or 28.5% OOIP.
Current incremental alkaline-surfactant-polymer oil is 903 MSTB or 22.2% OOIP, equal to the ultimate estimated incremental oil predicted from the simulation. The figure above shows the production history. The figure to the right depicts the cumulative oil produced after injection was initiated as a function of oil cut. Swept area production in pore volume of the Cambridge field is about double that of an average of eight Minneulsa waterfloods and the waterflood of the Mellott Ranch field. Not only is the Cambridge production double that of the average Minnelusa field, the oil was produced in 15 years, 1993 to 2008, instead of the 20 to 25 years for the average waterflood. The net present value of the Cambridge oil therefore is significantly enhanced.
The total cost for the plant, chemicals, and incremental operating is $2,767,000 for a current incremental barrel cost of $3.06.
1 Vargo, Jay, Turner, Jim, Vergnani, Bob, Pitts, Malcolm J., Wyatt, Kon, Surkalo, Harry, and Patterson, David: "Alkaline‑Surfactant‑Polymer Flooding of the Cambridge Minnelusa Field",SPE Reservoir Evaluation and Engineering, vol 3 number 6, December 2000, pages 552-558.Originally SPE 55633, presented at the 1999 Rocky Mtn Regional Meeting in Gillette Wyoming.
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