Production of Gas from Tight Naturally-fractured Reservoirs with Active Water

ABSTRACT

There are numerous examples of tight naturally fractured gas reservoirs with active water in the foothills of Alberta and northeastern British Columbia. Examples include the Pincher Creek field in Alberta and the Bucking Horse, Pocketknife, Sikanni and Grassy fields in British Columbia. Recovery factor is typically low from this type of reservoir due to water production. The problem is frequently attributed to coning, but coning may actually playa minor role. In fact, the gas/water contact in the fracture system may be relatively flat Initial gas recovery com.. prises gas displaced from fractures plus pressure depletion from the matrix. The amount of pressure depletion in the matrix is a function of structural relief above the original gas/water contact Subsequent gas recovery is an imbibition process, which may be very slow. Laboratory work, conducted at the TIPM Laboratory on behalf of Husky, demonstrates that water will continue to imbibe into tight matrix rock submerged under water for months. This work implies that the best operating strategy may be to produce the wells at the highest rates possible until water breakthrough, followed by a shut-in period of perhaps several years to allow gas to re-accumulate.

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