页岩气藏多级压裂水平井流动特征及产能评价方法研究

Shale gas attracts wide attention after the large scale successful exploitation in America with its advantage in huge reserves and low pollution. China has shown great determination of developing the burgeoning strategic resources with the Equivalent shale gas recoverable resource and the large energy demand. Due to complexity of pore type, polytrope of gas migration and advanced techniques of development measures，there is barely any adaptive evaluation method for shale gas development. The reason lies in a deficient knowledge of microscopic mechanism of shale gas migration. In this research, pore structure characteristics of shale matrix is analyzed first, based on the results of experiments, combined with productive law of shale gas, a general mathematical expression of gas migration process in pores of different scales (matrix pores, natural fractures, artificial fractures) is established; mathematical expression of gas artificial fracture and intrinsic fracture is established based on the analysis of production datas and fracture stress sensitivity, and coupled mathematical expressions of pores of different scales and network of fracture in shale gas reservoir are established, adaptive mathematical method is applied to solve the model, and shale gas productivity evaluation method is established. Therefore, the model can serve as predicting tool of shale gas productivity, and provide reference basis for shale gas horizontal well fracturing optimization design.

页岩气以其巨大的资源量和低污染等优势、及美国的成功开发应用，引起世界广泛关注。中美页岩气可采资源量相当，且随着中国对能源需求的增长、能源结构调整的需要，预示着页岩气资源的开发利用对中国意义重大。由于页岩孔隙类型复杂、气体运移方式多样、开发措施先进，导致常规产能评价方法在页岩气藏中难以适应，究其原因是对不同尺度流动空间中气体微观渗流机理认识严重不足。本研究基于广泛实验研究成果，结合页岩气生产规律，建立页岩中不同尺度流动空间（不同尺度的基质孔隙、天然裂缝、人工裂缝等）的气体运移的运动表达式，并形成页岩气储层不同尺度孔隙、裂缝系统及水平井井筒流动的耦合数学模型；采用适用的数学方法求解，发展创新页岩气开发的产能评价技术，从而为页岩气开发设计和产量变化规律预测提供工具，为页岩气水平井压裂优化设计提供依据。

页岩气以其储量大的优势成为能源领域的重要组成部分，但极低的渗透率决定了其采用多级压裂水平井开发的必然性，而储层改造存在高成本与低效益的矛盾，因此需在页岩气井钻、完井前进行气井产能评价。本次研究围绕页岩气藏多级压裂水平井的产能评价展开，首先对页岩气藏吸附、解吸过程进行了实验研究，揭示了各类因素对页岩气吸附、解吸情况的影响规律，并根据实验结论和理论建模分析对传统的Langmuir模型进行修正；对水力裂缝的应力敏感效应进行实验研究，并形成考虑有限导流能力和应力敏感效应的水力裂缝表征方法；对页岩气在基质内的渗流机理进行试验分析，明确气体在页岩中的赋存方式和流动机理，建立了考虑气体溶解、吸附、含水、滑脱等因素的多重介质页岩气藏多级压裂水平井产量预测模型，利用解析法求解模型后，对产能的影响因素进行了敏感性分析；最后提出了一种在纳米-微米孔内分别处理体相气体和表面吸附气体的数值模拟方法，并编制了基于非结构网格的页岩气数值模拟程序。开发的模拟器能够准确预测页岩气的产能，对实际的页岩气生产具有指导意义。