大斜度井多簇水力压裂裂缝扩展数值模拟

Numerical Simulation of Multi-cluster Hydraulic Fracture Propagation in Highly Deviated Wells

大斜度井多簇水力压裂技术是开发低渗透油气田的有效手段,但压裂过程中出现的裂缝转向、应力干扰问题使得裂缝扩展形态十分复杂。基于全局黏聚区模型建立大斜度井3簇裂缝同时扩展的有限元数值模拟,对不同井斜角、原位应力差条件下的裂缝注入点压力、裂缝形态进行研究。结果表明:当井斜角由20°增大至80°时,裂缝起裂逐渐变难,起裂压力增幅达47.38%,且中缝受边缝的干扰程度降低;裂缝形态由初始沿射孔方向延伸逐渐转向至沿垂向应力方向,且当井斜角等于60°时3簇裂缝合并成1条主裂缝。当地应力差由0增大至5 MPa时,3簇裂缝的起裂压力逐渐降低,且中缝受边缝应力干扰程度增加;裂缝形态由沿着3簇初始射孔方向延伸不发生明显裂缝转向,到起裂于初始损伤区之后迅速发生裂缝转向。该有限元计算模型可对现场大斜度井多簇水力压裂施工提供一定参考。

Multi-cluster hydraulic fracturing technology with highly deviated wells is an effective method for stimulating low-permeability hydrocarbon reservoirs.However,facture geometries are very complicated because of fracture turning and stress interference.Based on the global cohesive zone model,the finite element numerical simulation of three fractures simultaneous propagation in highly deviated wells was established to study the injection point pressure and fracture geometries in different well deviated angles and different in-situ stresses.Results show that when the well deviated angle increases from 20°to 80°,fracture initiation gradually becomes difficult,the fracture initiation pressure increases by 47.38%,while the interference degree of the middle fracture by the side fractures decreases.The fracture geometries gradually turns from the initial direction along the perforation to the direction along the vertical stress,and when the deviated angle is 60°,three fractures merge into one main fracture.When the in-situ stress difference increases from 0 MPa to 5 MPa,the initiation pressure of the three fractures gradually decreases,and the stress interference degree of the middle fracture by the side fractures increases.The three fracture geometries changes from propagating along the initial perforation directions without obvious fracture turning to the fracture turning rapidly after propagating away from the initial damage area.This finite element model can provide some references for the application of multi-cluster hydraulic fracturing in highly deviated wells.