考虑应力敏感和水力裂缝方位角的页岩产能模型

Shale Productivity Model Considering Stress Sensitivity and Hydraulic Fracture Azimuth

产能预测对页岩气的高效合理开发有着重要的作用,而目前国内外对于页岩气分段压裂水平井产能的研究没有同时考虑到天然裂缝应力敏感和水力裂缝形态及渗流特征对产能的影响。为此,根据双重介质渗流理论,综合考虑了页岩储层的吸附解吸、扩散运移、天然裂缝的应力敏感效应,建立了页岩储层渗流模型;同时考虑水力裂缝的有限导流能力、裂缝方位角等因素,利用点源函数方法将裂缝离散,之后叠加建立水力裂缝模型,最后将两种模型耦合得到页岩气藏压力水平井不稳定渗流模型和产能模型。根据已建立的页岩气压裂水平井产能模型,编程计算出产能特征曲线;通过对比模拟结果分析出,与实例类似的页岩气压裂水平井的最优水力裂缝导流能为15-18 D·cm,最优缝长分布方式为外高内低的U型,最优水力裂缝间距分布为等间距分布;模拟结果与页岩气井的现场数据的对比,也验证了该模型的准确性。该研究对页岩气开发有着重要的指导意义。

The productivity prediction plays an important role in the efficient and rational development of shale gas reservoirs.At present,the researches on the productivity of multi-stage fracturing horizontal wells in shale gas reservoirs at home and abroad does not take into account stress-sensitive effects of natural fractures and hydraulic fracture morphology and seepage characteristics on productivity.Therefore,based on dual medium seepage theory,considering the adsorption,desorption and diffusion mechanisms(pseudo-steady state and transient diffusion)of shale gas in reservoirs and stress-sensitive effects of natural fractures,the shale gas reservoir seepage model is established.The limited conductivity of hydraulic fractures and hydraulic fracture azimuth are considered into the hydraulic fracture model.The source function method is used to discretize the crack,and then the hydraulic fracture model is superimposed.Finally,the two models are coupled to obtain the unstable seepage model and productivity model of the multi-stage fracturing horizontal well in the shale gas reservoir.According to the established shale gas fracturing horizontal well productivity model,the productivity characteristic curve is calculated by programming.The comparative hydraulic simulation results show that the optimal hydraulic fracture conductivity of the shale gas fractured horizontal well which is similar to the example is 15-18 D·cm,the optimal distribution mode of seam length is u-shaped with outer high and inner low,and the optimal fracture spacing distribution is equidistant.The comparison between the simulation results and the field data of shale gas wells also verifies the accuracy of the model.This research is of significance to shale gas development.