Wilmington Field, California, Polymer Flood A Case History
Authors: Krebs H.J. 
Published: December 2007

The failure of the Ranger Zone Fault Block V polymer flood in the Wilmington field is discussed. The apparent poor results indicate the need for better reservoir information and improved knowledge of polymers and their behavior underfield and reservoir conditions.

Introduction

The ever-increasing world demand for crude oil, combined with dwindling reserves and the need to improve efficiencies of waterflood operations, resulted in laboratory studies and field tests of recovery processes that would improve the mobility ratio. It has long been recognized that improved mobility ratios should bring about increased displacement efficiencies, thereby resulting in greater oil recovery.

When added to injection water, the Dow Pusher chemicals, which are high molecular-weight, water-soluble polymers, decrease the water mobility in porous media polymers, decrease the water mobility in porous media many times more than would be expected from the increased viscosity of the injected brine.

In early 1967 Dow approached the unit operator of the Fault Block V Unit, Wilmington oil field, with a proposal to add polymer to the existing waterflood. A portion of the unitized area of the Ranger Zone was designed for a Pusher flood with injection beginning in July 1969. Pusher flood with injection beginning in July 1969. Initial polymer concentration was 150 ppm, which was increased to the designed concentration of 250 ppm later in the life of the flood.

The Pusher flood area, the pattern of injection wells, and the producers included in this study are shown in Fig. 1.

Geology and Reservoir Characteristics

The Wilmington oil field, as shown in Fig. 2, is located in Long Beach, Calif.; about 30 miles south of Los Angeles. Development of the seven oil-bearing zones began in 1937. Full-scale waterflooding on the south flank of the Ranger Zone was started in 1958, in the later stages of primary depletion.

The field is cut by a system of north-south faults that divides the producing zones into a series of "fault block" reservoirs. The Ranger Zone reservoir in Fault Block V is bounded by the Harbor Entrance fault on the west and the Golden Avenue-Daisy Avenue faults on the east, as shown in Fig. 3. This pool is unitized between the Harbor Entrance fault and the Los Angeles County flood control channel. The eastern third of the pool is operated under a cooperative agreement with Standard Oil Co. of California. Pay zones are found from about 2.200 to more than 7,500 ft. The vertical pay intervals are divided into seven zones, more or less depending on edge-water profiles. The Ranger zone, found at depths ranging from about 2,500 to 4,000 ft. has the greatest areal extent and spans the Pliocene-Miocene contact.

The Ranger Zone sands are arkosic (composed of feldspars. quartz. micas, heavy minerals, and some interstitial clays). They are generally loose to friable and range from thin interbeds to beds that are 10 to 5O ft thick. The sand units are blanket-type insofar as the over-all zone is concerned, although individual members are extremely lenticular within the zone.

Because of their unconsolidated nature, core porosities (30 to 40 percent) measured at surface pressure are high. Recent studies indicate considerably lower reservoir porosities and higher connate water saturation than were porosities and higher connate water saturation than were measured at the initiation of the Ranger Zone flood. Permeabilities are generally high and run into the darcies. Permeabilities are generally high and run into the darcies. JPT

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