Pressure buildup behavior in deformable medium formation

Based on the fact that formation properties of deep high pressure reservoirs, low permeability tight reservoirs, and naturally fractured reservoirs are trend to be affected by the variation of effective stress, a buildup test model is established for deformable medium reservoir. By defining a pseudo function, the formulations of the model are linearized partially, and numerical method is used to solve the problems. Typical curves of pressure transient tests are obtained and analyzed on double logarithm plots. Both pressure curves and pressure derivative curves of deformable medium formation are significantly different between drawdown and buildup cases. During radial flow period, the pressure derivative curves of drawdown test goes upwards gradually with the duration of production, and the greater is the permeability modulus, the shorter is the distance between the pressure curves and the pressure derivative curves. While as for buildup test, the pressure derivative curves goes downwards gradually with duration of shut-in, and the greater is the permeability modulus, the greater is the distance between the pressure curves and the pressure derivative curves. The difference between pressure drawdown and pressure buildup curves becomes more obvious as production time increasing. Thus, the principle of superposition cannot be used to pressure buildup analysis in deformable formation.