Abstract

An alkaline-surfactant-polymer flood was implemented in the Tanner Field, Campbell County, WY, after waterflooding to a 43% oil cut. Tanner is a Minnelusa B sand with one injection well and two production wells. Primary production began in April 1991 with a waterflood starting in October 1997. Peak waterflood production reached 19,000 bbls oil per month in February 1999. Waterflood continued through April 2000 at which time oil production had declined to 9,500 oil bbls per month at an oil cut of 43%. In May 2000, an alkaline-surfactant-polymer solution was injected. A solution of 1.0 wt% sodium hydroxide plus 0.1 wt% active ORS-41HF plus 1000 mg/L Alcoflood 1275A dissolved in Fox Hills water was injected through January 2005. A tapered concentration polymer drive began in February 2005. Oil recovery through December 2005 is 1,013,944 bbls from the total field and 874,490 bbls from the floodable pore volume or 44% OOIP. Incremental oil to date is 199,670 bbls or 10% OOIP. Projected ultimate oil recovery is 65% OOIP. Ultimate waterflood oil recovery was calculated to be 48% OOIP. This paper will discuss all aspects of alkaline-surfactant-polymer flood implementation from the laboratory evaluations to the field.

Chemical Enhanced Oil Recovery in the Minnelusa

Minnelusa fields in the Powder River Basin have been chemical flooded for over 30 years. Polymer flooding began in the Minnelusa trend in 1972 at Stewart Ranch.[1,2] Mobility control, profile modification, and combination mobility control-profile modification floods have been applied to the Minnelusa fields in secondary and tertiary modes..[3,4,5,6] Alkaline-surfactant-polymer flooding began with a secondary application at the West Keihl field in 1988.[7,8] The Cambridge alkaline-surfactant-polymer flood was the second Minnelusa alkaline-surfactant-polymer flood also performed as a secondary application.[9] Other Minnelusa floods such as Mellott Ranch and Driscoll Creek implemented an alkaline-surfactant-polymer flood in a tertiary mode after years of waterflood. Tanner is unique in that alkaline-surfactant-polymer injection began after a short waterflood when the oil cut was 43%.

Reservoir Description

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 8915 ft with an average porosity of 20% and an average permeability of 200 md. Average thickness is 25 ft.

Tanner is a small field consisting one injection well and two production wells, north and south of the injector. A net pay Isopach is shown in Fig. 1. 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 toal field, as seen in Fig. 1.

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