A case history of the Hemlock Reservoir of the McArthur River Field in Cook Inlet, Alaska demonstrates continued water injection during an extended production shut-in resulted in higher oil rates once production was resumed. With volcanic eruptions of Mt. Redoubt, located 30 miles to the south, production was shut-in for over three months during 1990 due to interruption of oil shipping and storage operations. This paper describes the results of effective waterflood management and the benefits of data gathering through pressure mapping and static tracer surveys during the production shut-in.

Maintaining water injection during the 1990 shut-in raised the average reservoir pressure by 230 psig and resulted in higher oil rates upon the resumption of production. Previous extended production shut-ins during 1976 and 1985 were followed by oil rate declines of up to 25%.

Reservoir pressures were monitored during continued water injection while the production was shut-in to define areas of lower pressure and poor reservoir conformance. Pressure mapping and static tracer surveys significatly improved the Hemlock reservoir description. Based on this data, infill drilling and waterflood conformance projects are being designed to increase recovery through improved vertical and areal sweep efficiency.

The waterflood management decisions and reservoir analysis techniques discussed in this paper provide useful insights to increase oil rate and reserves in future waterflood applications.

This case history describes waterflood surveillance and analysis which may be implemented during extended production shut-ins to improve reservoir description and define recovery enhancement projects.

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