基于边界元法的页岩气藏缝网多段压裂水平井不稳定渗流理论研究

Horizontal wells incorporated with massive hydraulic fracturing are becoming the key technologies to develop shale gas reservoirs efficiently. In view of the gas multi-transport mechanisms and the induced fracture network in multi-scaled shale gas reservoir, there have some drawback and disadvantage for existed models and methods to study the transient percolation models for multi-fractured horizontal well(MFHW) with stimulated reservoir volume (SRV). This project intends to reveal the gas percolation law in multi-scaled reservoir space by exploring the coupling mechanisms of gas ad-/de-sorption, diffusion, percolation, slippage, and stress sensitive on the basis of microscopic pore structure of the Weiyuan-Changning national shale development demonstration area. According to the monitoring results of micro seismic on fractured well and its induced complex fracture network, we will establish a comprehensive physical and mathematical models for MFHW to incorporate the shapes of SRV, hydraulic fractures, horizontal well and the characteristics of reservoir formation. Thereafter, the boundary element method (BEM) is used to deeply study the transient well testing and production performance of MFHW which existed complex fracture network in SRV and multi-transport mechanisms gas flow for gas flow in these models. Through the analysis of above, we want to form a new percolation theory based on BEM for MFHW in multi-scaled shale reservoir with multi-transport mechanism and complex fracture network. Research results will have important significance for the optimization of hydraulic fracturing parameters, the evaluation of post-fracturing, and the confirmation of in-situ reservoir properties, which have an important theoretical and practical value to guide the economy and scale development of shale gas reservoir.

水平井加体积压裂已经成为页岩气藏经济规模开发的关键技术。针对页岩气在多尺度储渗空间中存在多重输运机理以及体积压裂形成的复杂缝网，现有模型和方法在研究储层缝网多段压裂水平井不稳定渗流时存在缺点和不足。本项目拟在对威远-长宁国家页岩开发示范区储层微观孔隙结构研究的基础上，探究气体吸附-解吸、扩散、渗流、滑脱和介质变形的相互耦合机理，揭示气体在多尺度储渗空间中的流动规律。根据微地震监测结果，合理描述气藏体积压裂后形成的复杂裂缝网络；耦合考虑缝网形态、压裂裂缝、水平井筒和储层，建立页岩气藏考虑多重输运机理和复杂缝网的多段压裂水平井物理和渗流数学模型，采用边界元法对气井不稳定试井和产量动态进行深入研究，形成基于边界元法的页岩气藏缝网多段压裂水平井不稳定渗流理论。研究成果对于优化压裂参数、评估压后效果、确定储层原地物性参数和指导页岩气藏经济、规模开发具有重要的理论和应用价值。

页岩气作为一种非常规天然气资源，在我国分布广泛、资源量巨大。经过近十年的技术引进与消化吸收，我国已经成为继北美之后第二个实现页岩气商业化开采的国家。根据规划，页岩气将成为今后我国天然气上产的主力，对于保证我国能源安全和经济社会发展至关重要。. 页岩气藏储层微纳尺度孔隙发育，具有明显的多尺度性；页岩气特殊的成藏方式，导致气体赋存方式多样，主要以吸附气和游离气状态赋存。此外，水平井加体积压裂已经成为页岩气藏经济规模开发的关键技术。因此，如何针对页岩气在多尺度储渗空间中存在多重输运机理以及体积压裂形成的复杂缝网，现有模型和方法在研究储层缝网多段压裂水平井不稳定渗流时存在缺点和不足。项目以威远-长宁国家页岩开发示范区储层为研究背景，采用室内实验与理论研究相结合的方式，开展了真实页岩储层孔隙结构、吸附与扩散性能、应力敏感等实验研究，明确了页岩储层微观孔隙结构和传质扩散规律。在此基础上，探究了气体吸附-解吸、扩散、渗流、滑脱和介质变形的相互耦合机理，揭示了气体在多尺度储渗空间中的流动规律。在微地震监测结果和缝网扩展模拟的基础上，描述了气藏体积压裂后形成的复杂裂缝网络；耦合考虑缝网形态、压裂裂缝、水平井筒和储层，建立了页岩气藏考虑多重输运机理和复杂缝网的多段压裂水平井物理和渗流数学模型，采用边界元法与源函数等方法对气井不稳定试井和产量动态进行了研究，形成一套基于边界元和源函数法的页岩气藏缝网多段压裂水平井不稳定渗流理论。研究成果对于优化压裂参数、评估压后效果、确定储层原地物性参数和指导页岩气藏经济、规模开发具有重要的理论和应用价值。. 相关研究成果发表SCI期刊论文12篇，出版专著1部，授权发明专利1件。依托该项目，培养硕博士研究生6人，成果在示范区得到现场应用，成果作为重要支撑荣获省部级科技进步一等奖2项。