Steam Drive as a Supplemental Recovery Process In an Intermediate-Viscosity Reservoir, Mount Poso Field, California
Authors: Stokes D.D. , Brew J.R. , Whitten D.G. , Wooden L.W. 
Published: December 2007

This paper describes field pilots and laboratory model studies used to design a full-scale, steam-drive project in the Mount Posofield, California. Actual field results are compared with model predictions. Performance indicates that the field will equal model-prediction recovery Performance indicates that the field will equal model-prediction recovery efficiency, but at a reduced oil-steam ratio.

Introduction

The Mount Poso field is located in the San Joaquin Valley approximately 14 miles north of Bakersfield, Calif. (Fig. 1). The productive area of the field constitutes some 2, 100 acres, with Shell Oil Co. owning approximately 97 percent of the total acreage, The field was discovered in percent of the total acreage, The field was discovered in 1926 and was developed in three major stages with 104 wells drilled from 1926 to 1930, 115 wells from 1934 to 1936, and 72 wells from 1941 to 1943. Only scattered infill drilling has occurred since 1943. A maximum production rate of 19,700 BOPD with 82-percent water cut production rate of 19,700 BOPD with 82-percent water cut was reached in 1943.

The structure in the main area of the Mount Poso field is an easterly rising homocline with a dip of approximately 6 deg. (Fig. 2). Closure to the east and north is provided by the Mount Poso fault, a normal fault with provided by the Mount Poso fault, a normal fault with displacement of approximately 400 ft along the east and 200 ft along the north. Production is obtained from four separate horizons of Lower Miocene age. The Upper Vedder is the shallowest of the four zones and the largest in terms of productive area and volume. The top of the Upper Vedder sand ranges from 1,600 A deep updip to 2,000 ft deep at the oil-water contact.

Cumulative oil production through 1970 from the Upper Vedder zone in the main area of Mount Poso is estimated at 90 a million bbl, or approximately 35 percent of the original stock-tank oil in place. This relatively low recovery efficiency under strong water-drive conditions provided a significant target for a supplemental recovery provided a significant target for a supplemental recovery process. process. Geologic and Reservoir Properties

The Upper Vedder is a lower coarse to medium-grained, well-sorted, subrounded, unconsolidated sand with an average gross thickness of 75 ft throughout the main area of the field. The sand is of excellent reservoir quality and has good lateral continuity with no major shale breaks. Interbedded, thin, fine-grained silt stringers are present in the Upper Vedder and show a reduction in reservoir quality and higher water saturation. These stringers are not continuous throughout the field but are correlatable only in small areas. The poorer quality of these units could inhibit vertical fluid flow in the Upper Vedder. A typical electric log of the Vedder sands is shown in Fig. 3.

Some minor faulting occurs downdip in the central portion of the Upper Vedder reservoir. Sand-to-sand portion of the Upper Vedder reservoir. Sand-to-sand contact is present across these faults because displacement is only 10 to 40 ft. Data from pressure measurements indicate a pressure discontinuity exists across these faults; however, this does not present a barrier to fluid movement. Migration of radioactive tracer material across the downdip fault in Section 9 was observed during tests conducted in 1972, and more importantly, oil production response has been observed updip across this fault resulting from steam injection on the downdip side.

The Upper Vedder reservoir has an average porosity of 33 percent and an absolute permeability of 20 darcies. Gross thickness of the Upper Vedder averages 75 ft with 55 ft of net pay.

JPT

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