页岩气藏开采基础研究

Widely distributed shale gas reservoirs have large reserves but low abundance, so segmented fracturing horizontal wells are required to develop commercially. Characteristics of shale gas reservoirs: ① Dense: nanoscale pore throat, permeability is very low; ② Containing large amounts of organic matter with low maturity, and gas resolution among crystals is accompanied while production; ③ Big crispness: fractures propagate randomly including lots of microcracks. So, Shale media has nanometer pore throat, micron cracks and meter-scale fractures, so the flow in shale is a multi-scale problems. To develop efficiently, the scientific research on micro-nano scale transport, crack propagation and multi-scale flow should be carried out. Main content and methods: ① Reconstruct digital core of shale based on CT or SEM / FIB image, simulate gas-water two-phase flow using Lattice Boltzmann Method (LBM) considering desorption of organic matter, and develop transport properties calculation methods, which establish foundation for macro flow simulations. ② Based on the dynamic fracture mechanics and experimental results, relationship between brittleness and crack will be studied to reveal the fracture propagation mechanism under fluid-solid coupling effect, and the corresponding numerical simulation method will be also established. ③ Construct multi-scale network flow model combining discrete fracture network model (DFN) and continuous multiple media model, and establish simulation theory on fluid flow in segmentation fractured horizontal wells in shale reservoirs, which lay the foundation for the engineering analysis.

页岩气藏分布广，储量大但丰度低，需应用分段压裂水平井开采才具有商业价值。其特点：①致密：纳米级孔喉，渗透率极低；②含大量有机质：成熟度低，开采时伴随晶间气体解析；③脆度大：压裂缝扩展随机性强，且微裂隙发育。因此，页岩介质具有纳米级孔喉、微米级裂隙和米级压裂缝，其运移属多尺度流动问题。为高效开采，需对微纳观运移、裂缝扩展、多尺度缝网流动等科学问题开展研究。主要内容和方法：①基于CT或SEM/FIB图像构建纳米级数字岩芯，考虑有机质解吸基于格子波尔兹曼(LBM)方法开展气水两相流动模拟，形成运移传输性质的计算方法，为宏观缝网流动模拟奠定基础；②基于断裂动力学和实验，研究脆度与断裂的关系，揭示流固耦合作用下的裂缝扩展机制，建立数值模拟方法；③有机组合离散裂缝网络模型(DFN)和连续多重介质模型，构建多尺度缝网流动模型，建立页岩气藏分段压裂水平井的流动模拟理论，为工程分析奠定基础。

页岩介质具有纳米级孔喉、微米级裂隙和米级压裂缝，其运移属多尺度流动问题。本项目针对微纳观运移、裂缝扩展、多尺度缝网流动等页岩气藏高效开采的关键科学问题开展研究，取得了以下创新成果：（1）分子尺度上，形成了基于分子模拟的页岩气吸附解吸及运移机理研究方法，揭示了页岩气在干酪梗、黏土等页岩中的吸附过程以及在多相环境下吸附和解吸行为；（2）孔隙尺度上，建立了一套多尺度数字岩心构建方法及孔网模型提取分析方法，形成了考虑微尺度效应、气体高压影响和有机质吸附的影响基于孔隙网络模型和格子Boltzmann方法的页岩气/气水两相流动模拟方法，揭示了页岩气单相及气水两相孔隙尺度渗流规律；（3）油藏尺度上，建立了考虑天然裂缝影响的应力场—渗流场—缝内流场三场耦合的裂缝扩展数值模拟方法，从细观力学试验到宏观模拟揭示了页岩破裂和分段压裂水平井缝网扩展规律；基于均化理论，建立了考虑有机质分布和微观运移机理的页岩气宏观数学模型，形成了双重介质和嵌入式离散裂缝耦合的页岩气多尺度流动模拟方法；编制了页岩气藏压裂优化及产能评价一体化方法，形成了页岩气藏分段压裂水平井油藏工程参数优化方法，为页岩气藏的高效开发提供理论基础和技术支撑。相关成果在德国应用化学等期刊发表论文108篇，出版学术专著1部，申请国家发明专利18项、软件著作权4件，获教育部高等学校科学研究优秀成果奖自然科学一等奖1项、中国石油和化学工业联合会科技进步二等奖1项。