煤层气藏缝网压裂直井生产动态规律

体积压裂技术在煤层气藏开发中已得到广泛应用,针对体积压裂形成的裂缝网络(SRV),矩形边界复合模型相比于传统的径向复合模型能够更加准确合理地描述流体的渗流规律。解析或半解析函数方法无法对考虑SRV的矩形复合模型进行求解,而应用线性流模型对其求解则又会产生较大的误差。为此,利用双重介质模型对煤层气藏体积压裂区进行描述,综合考虑煤层气的吸附与解吸、扩散、渗流等多重运移机制,建立了基于非稳态扩散的煤层气藏矩形复合压裂井试井模型。结合Laplace变换、Stehfest数值反演以及计算机编程技术,采用边界元方法对模型进行求解,得到了煤层气藏生产动态变化的规律。对试井典型曲线进行了流动阶段划分,并分析了气藏边界尺寸、体积压裂区渗透率、吸附气含量、储层渗透率以及SRV尺寸等参数对生产动态规律变化的影响,实现了对体积压裂改造后的煤层气藏更为准确合理的描述。该项研究成果为深入认识煤层气运移规律和高效合理评价及开发煤层气藏提供了理论依据。

Production performance laws of vertical wells by volume fracturing in CBM gas reservoirs

Volume fracturing technology has been widely applied in the development of coalbed methane (CBM) reservoirs. As for thesimulated reservoir volume (SRV) created by volume fracturing, the seepage laws of fluids are described more accurately and rationallyin the rectangular composite model than in the traditional radial composite model. However, the rectangular composite model consideringSRV cannot be solved by using the analytical or semi-analytical function method, and its solution from the linear flow model has largererrors. In view of this, volume fracturing areas of CBM reservoirs were described by means of dual-medium model in this paper. Thecomplex CBM migration mechanisms were investigated comprehensively, including adsorption, desorption, diffusion and seepage. A welltesting model for rectangular composite fracturing wells in CBM reservoirs based on unsteady-state diffusion was built and solved by usingthe boundary element method combined with Laplace transformation, Stehfest numerical inversion and computer programming technology.Thus, production performance laws of CBM reservoirs were clarified. The flow regimes of typical well testing curves were dividedand the effects on change laws of production performance from the boundary size of gas reservoirs, permeability of volume fracturedareas, adsorption content, reservoir permeability and SRV size were analyzed. Eventually, CBM reservoirs after the volume fracturingstimulation were described more accurately and rationally. This study provides a theoretical basis for a better understanding of the CBMmigration laws and an approach to evaluating and developing CBM reservoirs efficiently and rationally.