重复压裂前的地应力场分析

Analysis of stress field before refracture treatment

重复压裂是低渗透油藏增产稳产的重要措施之一,井眼周围和初次压裂裂缝附近的应力场分布对重复压裂裂缝的起裂和延伸有重要的影响。运用弹性力学和流固耦合理论,建立了原始地应力作用下的垂直井围岩应力、初次压裂裂缝诱导应力和孔隙压力诱导应力计算模型,实现了对重复压裂前井眼和裂缝附近地应力的定量研究;通过计算,得出了应力场和孔隙压力随空间和时间的变化特征。研究认为:孔隙压力变化和初次压裂裂缝在2个水平主应力方向产生的诱导应力,将改变初次压裂后井周的应力分布,并可能引起2个水平主应力的重定向;2个水平主应力的初始差值是决定应力是否发生重定向以及应力反转发生时间的关键因素。

Refracture treatment is an important measure for enhancing or stabilizing well productivity in the low-permeability reservoir. Stress fiehl around the well bore and near the fracture formed by previous fracturing has an important influence on determining cranny split and stretch. Based on elastic mechanics and fluid-solid coupling theory, calculation models were established about initial stress around a vertical well and the stress induced by initial cracks and pore pressure variation. A quantitative study was carried out on stress field around the well and the cracks before refracture treatment. The variation feature of stress field and pore pressure with space and time have been indicated through calculation. The sludy shows that the stresses induced by pore pressure variation and initial cracks will cause redistribution of stress field. Thus, two horizontal principal stresses may be reoriented during this process. Initial difference between the maximum and minimum principal stresses is the key factor which decides the stress reorientation and the time of stress reversal.