Productivity analysis method for gas-water wells in abnormal overpressure gas reservoirs

Abstract A productivity analysis for gas-water wells in abnormal overpressure gas reservoirs, considering seepage capability changes of gas-water two phases, elastic drive energy of reservoirs and fluids, physical property changes caused by stress sensitivity of reservoir etc, is proposed, and the influences of various factors on gas production rate are analyzed by practical examples. Based on generalized Darcy formula and the law of conservation of mass, mathematical models of steady-state and unsteady-state seepage considering stress sensitivity of reservoirs and seepage capability changes of gas-water two phases are established, then, corresponding formulas of gas production rate are deduced. Results of practical example analysis show that: the increase of reservoir water content causes decrease of seepage capability of gas phase, and thus declining the gas production rate, so the influence of seepage capability changes of gas-water two phases on gas production rate cannot be ignored in the process of productivity evaluation for gas-water wells; gas production rate has smaller variations with the increase of stress sensitivity when production pressure drop is small, while gas production rate decreases significantly with the increase of stress sensitivity when production pressure drop is large. Therefore, the production pressure drop of gas wells at the beginning of the development should not be too high for gas reservoirs with high stress sensitivity.