ABSTRACT

The Jean Marie Member of the Redknife Formation in northeast British Columbia (NTS 94-I and 94-P) is a unique, gas-bearing silty limestone. A detailed evaluation of fluids and pressures from over 200 wells illustrates the presence of anomalously low fluid potential. Pressure/depth ratios range from 8.0 to 4.4 kPa/m. A comparison with water gradients from adjacent aquifers illustrates that pressures are 30 to 3000 kPa below regional pore pressures and 2000 to 7000 kPa below normal pore pressures. Formation damage is common on drill-stem tests because of the large pressure differentials between formation pressure and hydrostatic drilling fluid pressure.

Very few wells have produced water during testing or production. Examination of chemical analyses of "water" samples indicates that most of the samples were of mud filtrate. It is gas, not water that forms the continuous reservoir phase of the Jean Marie Member.

Recent pressure tests are commonly several hundred kPa below regional pressure trends. These tests are from pools where there is gas production. The removal of gas can cause a lowering of formation pressures several kilometres from the producing well.

Numerous hypotheses exist to explain the subnormal fluid pressures. All require the existence of "seals" or low permeability strata. Regional trends in the Jean Marie Member are interpreted in terms of these hypotheses. The regional investigation of fluids and pressures has identified considerable potential for additional gas discoveries.

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