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页岩气藏一般具有低孔隙、低渗透等特征,对其实施缝网压裂是高效开发页岩气的最佳途径。采用位移不连续法建立线弹性二维均质地层诱导应力场分布数学模型,通过水平应力差异系数对顺序压裂和交替压裂的裂缝间距进行优化研究。结果表明,水平应力差异系数受到裂缝净压力、裂缝缝长、原地应力场等因素的影响;裂缝净压力越大、缝长越长,水平应力差异系数越小;随着与裂缝距离的增加,水平应力差异系数呈现先减小后增加的趋势,因此,存在后续裂缝形成复杂网络的最佳裂缝间距;顺序压裂裂缝间距不宜过大,且后续压裂裂缝间距应适当减小;交替压裂裂缝间距最优时,缝间水平应力差异系数最小,对中间裂缝形成缝网最有利。
Shale gas reservoirs are generally characterized by low porosity and low permeability. The implementation of seam network fracturing is the best way to develop shale gas efficiently. Displacement discontinuous method was used to establish the mathematical model of induced stress field distribution in linear elastic two-dimensional homogeneous strata. The fractal spacing between sequential fractures and alternate fractures was optimized through the horizontal stress difference coefficient. The results show that the coefficient of horizontal stress difference is affected by such factors as net fracture pressure, crack length and in situ stress field. The larger the net fracture pressure and the longer the fracture length, the smaller the horizontal stress difference coefficient. With the increase of the distance to the fracture , The difference coefficient of horizontal stress firstly decreases and then increases. Therefore, the optimal crack spacing of complex networks with subsequent cracks exists; the interval of sequential fracturing cracks should not be too large, and the spacing of subsequent fractures should be appropriately reduced; and the alternating pressure When the crack spacing is the best, the difference coefficient of the horizontal stress in the seam is the smallest, which is most favorable to the formation of the crack in the middle crack.