Numerical Study on Co-production Characteristics of “Three Gases” in Coal-Measure Strata

Abstract

AbstractChina is rich in coal-bearing gas resources, but the strata of coalbed methane, shale gas and tight sandstone gas (tight gases called as three gases) are often stacked together. Multilayer co-production of different types of tight gases presents different gas production characteristics and interlayer interference phenomena, which brings difficulty for efficient exploitation in coal-bearing strata. In this study, a reservoir numerical simulation model for co-production of three gases was established based on the analysis of the difference of reservoir properties and gas production mechanisms between three gases. The production characteristics and interlayer interference of different combinations of tight gas layers were analyzed. A co-production gas well from Ordos Basin was selected for a case study. The results show that the tight sandstone gas has a high rate at the beginning of production, while the release of the productivity of coalbed methane is usually lagged behind, and the release of shale gas productivity can last a long time. When the fluids in the three layers flow into the same wellbore, it can affect each other. The main behavior is that the long-time water production in the upper coalbed can cause water loading in the wellbore, which will restrain the production of sandstone gas and shale gas in the lower layers. Similarly, the sandstone gas and shale gas produced in the lower layers may also invade the upper coalbed and cause the decline of coalbed methane production. The simulation results are consistent with the field case. The obtained results have a certain guiding significance for the efficient exploitation of multi-layer in coal-bearing.KeywordsCoal-bearing strataCo-production of three gasesNumerical simulationInterlayer interferenceCase study