页岩气体积压裂缝网模型分析及应用

Analysis and application of fracture network models of volume fracturing in shale gas reservoirs

对低渗透页岩储层进行体积压裂改造以形成复杂裂缝网络是获得页岩气经济产能的关键,压裂改造体积和缝网导流能力是评价体积压裂施工效果的关键指标,同时对压裂优化设计、压后产能预测及经济评价也具有重要意义。为此,在分析页岩气体积压裂特点的基础上,对两种主要页岩气体积压裂缝网模型的假设、数学方程及参数优化方法进行了比较分析,并结合美国Marcellus页岩区块现场参数对页岩储层压裂方案进行了优选。结果表明:离散化缝网模型及线网模型均能有效表征复杂缝网几何特征,模拟缝网的扩展规律和缝网中压裂液流动及支撑剂运移,获得缝网几何形态参数,可优选压裂施工方案;天然裂缝发育的页岩层是体积压裂改造的重点,水平地应力差越小则越易形成复杂缝网,施工排量越大,压裂液泵入总量越大,则储层改造体积范围越大,缝网导流能力越高,页岩气产能就越高。

Volume fracturing in low-permeability shale gas reservoirs which aims to induce a complicated fracture network is a key measure to acquire commercial productivity of shale gas. Stimulated reservoir volume and fracture network conductivity are important criteria of evaluating volume fracturing treatment effect and essential for fracturing optimization, production prediction after fractu ring, and economic evaluation. Based on the analysis of volume fracturing characteristics of shale gas, a comparative analysis was made of the two dominant shale gas volume fracturing network models in terms of modeling assumptions, mathematical equations, and parameter optimization methods. In addition, we also selected an optimal shale reservoir fracturing plan in combination with field parameters of the Marcellus Shale Block in the USA. It shows that both discrete fracture network model and wiremesh model can not only describe geometrical characteristics of a complicated fracture network, but simulate the extending rule of a fracture network and fracturing fluid flow patterns and proppant transport methodologies in a fracture network, thereby to acquire geometrical parameters of a fracture network and optimize a fracturing scheme. In terms of a shale gas reservoir with a natural fracture system, it is a key factor of volume fracturing and easy to induce a complicated fracture network with a small horizontal crustal stress difference. Be sides, the larger the pumping rate and fracturing fluid volume, the greater the stimulated reservoir volume, fracture network con- ductivity as well as shale gas productivity.