Dynamic prediction and influencing factors analysis of gas and water co-production stage in tight sandstone reservoir

Abstract

Tight gas reserves account for a large portion of unconventional gas resources. At the stage of multiphase production of gas and water, gas productivity can be severely reduced because of water accumulation at the bottom of wellbore. This study investigates the effects of multiphase flow on bottomhole-pressure (BHP) estimation and productivity forecast for tight gas wells. The Beggs-Brill method is modified to calculate BHP by considering the phase changes of water in wellbore. The modified Beggs-Brill method is demonstrated with a relatively high accuracy (relative error <5%) in BHP calculation though comparing it against measured values. This study also establishes a new productivity model which mainly combines the water blockage effect caused by multiphase flow in the reservoir. The new model is further validated against field measurements. The results also suggest the relative permeability of gas and the mass ratio of gas and water follows a power-law relationship in the water-blockage area, and the gas productivity can be severely reduced once water blockage occurs for the tight gas wells.