Study on Co-production compatibility evaluation method of multilayer tight gas reservoir

Tight sandstone gas reservoir normally has a poor pore connectivity and a low productivity of single layer production, and the multilayer co-production technique has received increasing attention to improve its recovery in recent years. However, the range and impact of geological conditions are still unclear, leading to a challenging comprehensive evaluation of multilayer co-production compatibility. In this study, the impact of a series of factors on multilayer tight gas production is discussed by numerical simulation in detail, and their compatibility thresholds are determined. The variable weight based fuzzy comprehensive evaluation (VW-FCE) method is constructed, and a co-production compatibility index (CCI) is further proposed for multilayer tight gas reservoir co-production evaluation, with an application to Daning-jixian tight gas reservoirs for verification. The results show that thickness, permeability, reservoir pressure, and gas saturation are the key factors affecting the co-production, and the 10-year cumulative gas production contribution of the lower sandstone increases with the increase of each parameter ratio between the lower and the upper sandstones. When the properties of two co-production layers are similar, their compatibility is mainly impacted by the formation pressure and gas saturation variations. Otherwise, their compatibility is controlled by the formation thickness and permeability. The CCI values for multilayer co-production is 0.6–1, and the gas production capacity shows a positive exponential relationship with the evaluation index. The proposed method is verified by comparing with the actual production data from typical wells of tight sandstone gas co-production in the Daning-Jixian area, which indicates that the CCI is appropriate to evaluate the co-production compatibility of multiplayer tight gas reservoir, and provide theoretical supports for tight gas co-production.