致密油水平井多簇裂缝扩展数值模拟研究

Numerical simulation studies on multi-cluster fracture propagation in tight-oil horizontal wells

大庆油田致密油水平井近年来主要采用密切割布缝进行压裂改造,多簇裂缝扩展将产生诱导应力,从而导致各簇裂缝延伸均匀程度不一致。为此,采用有限元软件ABAQUS建立了大庆油田致密油水平井多簇裂缝扩展数值模型,采用扩展有限元(XFEM)模拟方法,研究了2个布缝参数(簇距、段内簇数)、3个压裂施工参数(压裂工艺、施工排量及液体黏度)对裂缝扩展的影响。同时对比分析模拟结果与矿场实际光纤测试的各簇产能贡献结果,发现模拟的各簇裂缝长度与各簇的产油贡献具有很好的一致性,证实了模拟结果的正确性。模拟结果表明:当簇距缩小至5m时,各簇应力干扰明显,不利于裂缝扩展,当簇距达到10m及以上时,平均单簇裂缝半长变化不明显,合理簇距约为10m。平均单簇裂缝半长随段内簇数的增加呈增大趋势,但非均匀延伸程度也随之增大;与桥塞段内多簇同时改造相比,连续油管单簇依次改造模式更有利于裂缝延伸;平均单簇裂缝半长随施工排量的升高呈增大趋势,提高施工排量还能促进裂缝均匀延伸。平均单簇裂缝半长随液体黏度的升高呈增大趋势,可适当提高高黏液体比例。

In recent years,tight oil horizontal wells in Daqing oilfield are mainly fractured by close cutting.However,the multicluster fracture propagation generates induced stress,which leads to uneven fracture extension in each cluster.To this end,the finite element software ABAQUS was used to establish the numerical model of multi-cluster fracture propagation in horizontal wells in Daqing tight-oil reservoir.The effects of two fracture parameters(cluster spacing,clusters within one fracturing stage)and three construction parameters(fracturing processes,construction displacement,and liquid viscosity)on fracture propagation were studied by the extended finite element(XFEM)simulation method.At the same time,it is found that there is a good consistency between the simulated fracture length of each cluster and the oil production contribution of each cluster when the simulated result is compared with the capacity contribution result of each cluster tested by actual optical fiber in the field.This confirms the correctness of the simulation results.The simulation results show that the stress interference of each cluster is obvious when the cluster spacing is reduced to 5 m,which is not conducive to fracture propagation.The mean fracture half-length of a single cluster does not change significantly when the cluster spacing reaches 10 m or more,and the reasonable cluster distance is about 10 m.The fracture halflength increases with increased clusters within one fracturing stage,but the non-uniform extension also becomes obvious.Compared with the simultaneous stimulation of multiple clusters in the bridge plug stage,the coiled tubing single-cluster stimulation mode is more favorable to fracture propagation.The average half-length of single cluster fractures increases with the rise of the construction displacement,and the uniform extension of fractures can be promoted by increasing the construction displacement.The average fracture half-length of a single cluster rises with the increase of liquid viscosity,and the proportion of high viscous liquid can be increased appropriately.