页岩气水平井增产改造体积评价模型及其应用

目前,已有的水力压裂储层增产改造体积(SRV)评价方法主要包括微地震监测法、倾斜仪测量法以及数学模型计算法,其中,直接测量方法都存在着成本高、可复制性差的不足,而理论模型计算SRV可以降低成本,提高计算的速度和结果的准确性、可靠性。为此,在分析目前SRV评价模型局限性的前提下,基于水平井分段分簇压裂裂缝扩展理论、岩石力学理论和渗流力学理论,考虑页岩气水平井分段分簇压裂裂缝扩展过程中流体扩散渗流场和裂缝诱导应力场同时改变对页岩体天然裂缝的触发破坏机制,针对页岩气储层水平井分段分簇缝网压裂建立了一套SRV数值评价模型(以下简称新模型),并据此对分簇裂缝延伸行为、水力裂缝诱导应力场变化、水力压裂储层压力场抬升以及天然裂缝破坏区域的扩展进行数值模拟与表征,计算储层改造总体积,并在涪陵国家级页岩气示范区X1-HF井对新模型进行了矿场应用验证。结果表明:(1)新模型的计算方法与页岩压裂过程储层SRV实际物理演化机制相一致,可实现对SRV更准确地计算和定量表征;(2)新模型模拟所得SRV与现场微地震监测结果较为吻合;(3)示范区内水平井分段压裂形成的SRV能够满足页岩气高效开发的要求,压裂增产效果明显。结论认为,新模型具有较高的准确性和可靠性,对于涪陵页岩气示范区后期页岩气缝网压裂优化设计、井间距调整和加密井部署设计等都具有重要的指导作用,值得大规模推广应用。

A stimulated reservoir volume (SRV) evaluation model and its application to shale gas well productivity enhancement

At present, existing evaluation methods for stimulated reservoir volume (SRV) of hydraulic fracturing mainly include microseismic monitoring method, tiltmeter measurement method and mathematical model calculation method, However, the direct measurement methods have the defects of high cost and poor repeatability. And if the theoretical model is used to calculate SRV, the calculation cost can be reduced, the calculation speed can be increased and the accuracy and reliability of calculation results can be improved. In this paper, the restrictions of existing SRV evaluation models were analyzed. Then, based on the fracture propagation theory of horizontal well multistage and multicluster fracturing, the rock mechanics theory and the seepage mechanics theory, the inducing and damage mechanisms to the natural fractures in shale by the simultaneous change of fluid diffusion seepage field and fracture induced stress field in fracture propagation by horizontal well multistage and multicluster fracturing were studied, and a SRV numerical evaluation model (hereinafter "new model" for short) was established correspondingly. Based on this, the propagation behavior of fracture cluster, the change of induced stress field of hydraulic fracture, the uplift of reservoir pressure field of hydraulic fracturing and the extension of natural fracture damage area were numerically simulated and characterized, and the total stimulated reservoir volume was calculated. Finally, this new model was applied and verified on site at Well X1-HF in the Fuling National Shale Gas Demonstration Area. And the following research results were obtained. First, the calculation method of this new model is consistent with the actual physical evolution mechanism of reservoir SRV in shale fracturing, so it can calculate SRV more accurately and characterize it quantitatively. Second, the SRV simulation result of this new model is line with the field microseismic monitoring result. Third, the SRV contributed by the horizontal well multistage fracturing in the demonstration area can satisfy the requirement of efficient shale gas development and its stimulation effect is remarkable. In conclusion, this new model is of high accuracy and reliability, and it can be used to guide the fracturing design optimization of shale gas fracture network, well spacing adjustment and infill well deployment in the later development stage of the Fuling National Shale Gas Demonstration Area, so it is worth popularizing and applying extensively.