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Geological Society, London, Special Publications; 1995; v. 84; p. 165-173;
DOI: 10.1144/GSL.SP.1995.084.01.17
© 1995 Geological Society of London

Water and Gas Injection Methods

Prudhoe Bay: infill drilling in gravity dominated WAG floods

T. C. Wilcox1, M. W. Polzin2, S. S. Kuo2 & K. J. Humphrey1

1 BP Exploration (Alaska) Inc., PO Box 196612, Anchorage, Alaska 99519, USA
2 BP Exploration Inc., PO Box 4587, Houston, Texas 77210, USA

Many horizontal miscible gas floods experience relatively low vertical sweep efficiency due to gravity segregation of the injected solvent and reservoir liquids. This is true for the Prudhoe Bay Miscible Gas Project (PBMGP) in which the enriched-hydrocarbon miscible injectant (MI) is expected to sweep only approximately 300f the reservoir volume in the project areas. The Prudhoe Bay reservoir has a relatively thick oil column, high inter-sand vertical permeability, high net-gross, and is generally developed on 80 acre (324 = 103 m2) well spacing.

An infill drilling project was implemented in the Northwest Fault Block (NWFB) area of Prudhoe Bay (Fig. 1) to improve solvent sweep efficiency and increase EOR reserves. This project differs from many EOR infill drilling projects in that most of the additional recovery is attributable to EOR, with minimal improvement in waterflood recovery.

The infill project is feasible because the reservoir is relatively thick, and sufficient EOR reserves are obtained from miscible displacement around new injectors. A significant increase in flood rate can also occur, resulting in production acceleration. Results of the project will guide analysis of infill drilling in other EOR areas at Prudhoe. The Prudhoe Bay Miscible Gas Project is the world’s largest enriched-hydrocarbon miscible gas flood, and is located in northern Alaska, USA.