Numerical simulation studies on multi-cluster fracture propagation in tight-oil horizontal wells
In recent years,tight oil horizontal wells in Daqing oilfield are mainly fractured by close cutting.However,the multi-cluster 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 stud-ied by the extended finite element(XFEM)simulation method.At the same time,it is found that there is a good consistency be-tween 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 half-length increases with increased clusters within one fracturing stage,but the non-uniform extension also becomes obvious.Com-pared 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 con-struction displacement,and the uniform extension of fractures can be promoted by increasing the construction displacement.The av-erage 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.
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