水力压裂诱发断层滑移对套管的剪切作用研究

Shear Effect of Fault Slip Induced by Hydraulic Fracturing on the Casing

国内某平台出现的压裂过程中的套管变形损坏问题频发,现场蚂蚁体测试结果显示该区块储层天然裂缝及断层发育,因此推断水力压裂诱发断层激活滑移导致套管受剪切变形。首先建立了包含上部盖层、含有断层的储层以及下部隔层的断层滑移地质力学模型,对断层面间相互作用关系进行推导,运用黏聚接触方法对其进行表征,模拟计算了压裂液进入断层后断层激活滑移的距离。随后建立了含有断层的三维水平井套管—水泥环—地层力学耦合模型,计算分析了压裂诱发的断层滑移量及其对套管所受外载荷、应力及变形的影响。结果表明,水力压裂流体进入后降低了断层胶结物胶结强度与断层面摩擦强度,使得断层系统力学平衡被破坏,导致断层激活滑移;断层滑移的剪切作用会给穿越断层的套管施加强度高且非均匀性强的外载荷,造成套管变形失效。研究验证了现场对于套管变形是由于压裂流体激活天然裂缝及断层滑移剪切套管所致的猜想,并提出了相应的预防措施,对现场实际作业具有一定的指导意义。

Casing deformation and damage frequently occurred during the fracturing process of well X on a platform in China.The results of the on-site ant test showed that natural fractures and faults are developed in the reservoir in this block.It was inferred that hydraulic fracturing induced fault slip had caused casing deformation by shear.Firstly,a geomechanical model of fault slip including the upper cap rock,fault-containing reservoir,and lower interlayer was established,and the interaction relationship between the actual fault planes was deduced,characterized by the cohesive contact method,and the pressure was simulated and the distance of fault slip after fracturing fluid enters the fault was calculated.A three-dimensional horizontal well casing-cement sheath-formation mechanical coupling model with faults was established,and the fault slippage induced by fracturing and the external load,stress,and deformation on the casing were calculated and analyzed.The results show that the entry of hydraulic fracturing fluid reduces the joint strength of the fault cement and the friction strength of the fault plane,which destroys the mechanical balance of the fault system and causes fault reactivation slip;the shearing effect of fault slip will exert high and non-uniform external loads on the casing passing through the fault result in casing deformation and failure.The research verifies the conjecture that the casing deformation is caused by fracturing fluid activation of natural fractures and fault slip shearing the casing,and puts forward corresponding preventive measures,which have certain guiding significance for field operations.