There are numerous examples of tight naturally fractured gas reservoirs wit
h active water in the foothills of Alberta and north- eastern British Colum
bia. Examples include the Pincher Creek field in Alberta and the Bucking Ho
rse, Pocketknife, Sikanni and Grassy fields in British Columbia. Recovery f
actor is typically low from this type of reservoir due to water production.
The problem is frequently attributed to coning, but coning may actually pl
ay a minor role. In fact, the gas/water contact in the fracture system may
be relatively flat. Initial gas recovery comprises gas displaced from fract
ures plus pressure depletion from the matrix. The amount of pressure deplet
ion 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 ope
rating strategy may be to produce the wells at the highest rates possible u
ntil water breakthrough, followed by a shut-in period of perhaps several ye
ars to allow gas to re-accumulate.