Study on recovery factor and interlayer interference mechanism of multilayer co-production in tight gas reservoir with high heterogeneity and multi-pressure systems

Abstract

The coupling effects of complex pore structure and poor reservoir properties generally lead to relatively low production of single layer in tight gas reservoir. The multilayer or multilayer co-production increasingly gain popularity in exploitation of tight gas reservoirs to achieve high recovery factor and economic profit. The multilayer co-production of tight gas reservoir with high heterogeneity or multi-pressure systems is more complex than that of the single-layer production. It is still not very clear about the mechanism of co-production. To fill this gap, a set of numerical simulations are intentionally designed and implemented in this paper to systematically understand production characteristics, interlayer interference, and recovery factor of multilayer co-production in tight gas reservoirs. Based on the established numerical gas reservoir simulation model, sensitivity analysis of influencing parameters of interlayer interference and recovery factor, including interlayer permeability contrast, interlayer pressure difference, thickness of gas layer, gas saturation, and producing rate, has been carried out. Subsequently, a type of machine-learning method, i.e., random forest method (RFM), is use to quantitatively characterize the main influencing parameters on interlayer interference and recovery factor. In the end, the predicted models of recovery factor and interference time are proposed by using the linear correlation and nonlinear correlation. The numerical experiment results reveal that the gas of high-pressure layer will flow back to the low-pressure layer in the multilayer co-production scenario and the influencing parameters have a great effect on daily gas production, recovery factor, backflow time, formation pressure and contribution rate of each layer. The thickness of gas layer and producing rate have the strongest and weakest influences on the gas recovery, respectively. However, the influence of interlayer pressure difference on interlayer interference is highest and the gas saturation has a lower effect on interference time than other parameters. The recovery factor and interference time of multilayer co-production is about 54.09%–63.82% and 55–565 days respectively. The correlation results of recovery factor and interference time have a good agreement with the results of numerical simulation, and the uncertainties are controlled within 10%. The research results of numerical simulation, RFM and predicted model are applied to a gas well of the tight gas and the validity and practicability of the results are verified, which can provide a solid foundation for the exploitation of tight gas reservoirs with high heterogeneity and multi-pressure systems.