Introduction

This extended abstract, in support of a poster session, describes the use of the concept of Pattern Size Reduction (PSR) to improve waterflood recovery. This concept incorporates infill drilling, producer-to-injector conversions and peripheral waterflood expansion. Waterflood recovery is primarily improved by creating smaller patterns, improving pattern geometry, increasing the rate of injection throughput and ultimate throughput volume.

Screening Study

A parametric study was conducted in early 1991 which correlated ultimate recovery with controllable field operating variables1 . This study clearly showed that patterns with tighter well spacing, higher ultimate injection throughput and optimum pressure maintenance had higher recoveries. It also indicated that more symmetrical patterns have higher recoveries. This study was used to identify areas within the various Prudhoe Bay Unit (PBU) waterfloods where waterflood optimization can improve recovery. These areas were subsequently studied in greater detail and re-development plans created.

The two example given below characterize the analysis techniques used and the results obtained.

Analysis Example – "A" Pad

The parametric study identified the "A" pad area of the WPWZ waterflood as having a lower than average projected ultimate recovery. This pad also had the largest pattern size and well spacing of any PBU waterflood. A multi-company development team, composed of staff from reservoir engineering, production engineering, geosciences and facility engineering, was created and challenged to come up with a re-development plan which would improve "A" pad recovery.

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