东海低渗区压裂诱导应力分析及施工参数优化

Analysis of fracturing induced stress and optimization of construction parameters in low permeability area of the East China Sea

考虑地层弹性模量、泊松比、地应力等参数,基于位移不连续理论、弹性理论,建立了诱导应力场数学模型,以东海低渗21-X井为例,开展了Abaqus数值模拟,分析了射孔角度、射孔排量、簇间距对裂缝转向扩展和诱导应力的影响,结果表明:随着簇间距的增大诱导应力增大,增大幅度呈平缓趋势,推荐簇间距为30~60 m;随着射孔排量增大,诱导应力差异系数范围逐渐增大,推荐射孔排量为5~6 m^(3)/min;当射孔角度为0°时,裂缝长度最长,随着射孔角度增大,裂缝逐渐形成双翼型转向裂缝,且转向特征逐渐明显,推荐射孔角度为0°~30°;当水力裂缝偏转角<90°或天然裂缝偏转角≤45°时,水力裂缝尖端诱导应力差较小,甚至为负,从而阻碍裂缝转向作用力较小,有利于形成复杂缝网,达到增产上储的目的。

A mathematical model of induced stress field was established based on displacement discontinuity theory and elastic theory,considering formation elastic modulus,Poisson's ratio and in-situ stress.Taking the low-permeability well 21-X in the East China Sea as an example,Abaqus numerical simulation was carried out to analyze the effects of perforation angle,perforation displacement and cluster spacing on fracture turning propagation and induced stress.The results showed that,the induced stress increases with the increase of cluster spacing,and the increment range is not large.The optimal data between clusters is 30~60 m.With the increase of perforation displacement,the range of induced stress difference coefficient gradually increases,and the optimal perforation displacement is 5~6 m^(3)/min.When the perforation angle is 0°,the fracture length is the longest.With the increasing of the perforation angle,the fracture gradually forms a double airfoil steering fracture,and the steering characteristics are gradually obvious.The optimal perforation angle is 0°~30°.When the deflection angle of hydraulic fracture is less than 90°or the deflection angle of natural fracture is less than 45°,the induced stress difference of hydraulic fracture tip is small or even negative,and the effect of preventing fracture steering is small,which is conducive to the formation of complex fracture network,so as to achieve the purpose of increasing production and reservoir.