页岩气水平井重复压裂产能数值模拟

Numerical simulation on productivity when shale-gas horizontal-well refracturing

产能模拟是页岩气水平井重复压裂优化设计的重要环节。对于页岩气水平井而言,初次压裂形成的复杂网络以及随生产进行而被扰动的储层应力场和压力场使得重复压裂产能模拟更加困难。根据页岩储层压后多重孔隙介质特征,考虑页岩气在开采过程中“有机质干酪根—无机质纳米孔隙—天然裂缝”的多尺度空间流动行为以及储层参数和水力裂缝导流能力随生产的动态变化,建立页岩气水平井重复压裂产能预测的数学模型。基于矿场生产数据的历史拟合验证该模型的可靠性,探讨气井初次压裂后有效应力和水力裂缝渗透率变化规律,为重复压裂时间节点优化提供参考。重复压裂模拟结果表明,重复压裂通过增加原有水力裂缝的导流能力,再次为页岩气的流动提供快速通道,提高页岩储层吸附气的采出程度。

When shale-gas horizontal-well refracturing, productivity simulation is an important link in its design optimization. As for these wells, the complex fracture network formed during the first fracturing, and the disturbed stress and pressure fields in reservoirs make this simulation more difficult. So, a mathematical model to predict the productivity was established for shale-gas horizontal-well refracturing based on some characteristics of multiple porous media after fracturing, combined with multi-scale spatial-flow behaviors of “organic kerogen-inorganic nanometer pore-natural fracture”, and the dynamic variation of reservoir parameters and hydraulic-fracture conductivity. Moreover, its reliability was verified based on history matching. In addition, the variation laws of both effective stress and hydraulic-fracture permeability after the first fracturing were summarized to provide some reference for optimizing refracturing time node. Results show that refracturing rebuilds high-speed channels for shale-gas flow by increasing the conductivity of original hydraulic fractures, so as to improve recovery degree of adsorbed gas in these reservoirs.