重复压裂气井诱导应力场模拟研究

重复压裂是低渗透油气田开发中后期增产挖潜和稳产的重要技术措施。重复压裂新裂缝的重新定向分析是具有相当难度和应用价值的核心问题，也是制约重复压裂优化设计的关键。重复压裂产生的裂缝方向取决于地应力状态，因此，垂直裂缝气井重复压裂前储层中的应力分布，尤其是水平主应力方向控制着重复压裂裂缝的起裂方位和延伸方向。系统研究了垂直裂缝井重复压裂前应力场的分布特征及其影响重复压裂气井应力大小和方向变化的主要因素。应用弹性力学和流．固耦合等理论建立了重复压裂气井的诱导应力场的数学模型，开发了相应的计算模拟程序，实现了垂直裂缝气井重复压裂前应力场的定量分析与模拟。研究表明，垂直裂缝气井中初始水力裂缝产生的诱导应力和气井生产过程中孔隙压力变化产生的诱导应力能够改变气井周围的应力场分布，并导致气井中的应力场发生重新定向。新场气田的实际运用结果也表明，重复压裂气井中的初始应力差和生产时间是决定应力重新定向的关键因素．

SIMULATION STUDY OF INDUCED STRESS FIELD IN REFRACTURING GAS WELL

Refracturing is an important technique for enhancing or stabilizing well productivity in the low-permeability oilfield. The reorientation of refracture is fairly difficult and most important in refracturing. The refracture orientation depends on the stress field in vertically-fractured gas well. The stress field,especially the orientation of horizontal principal stress in vertically-fractured gas well,determines the azimuth of refracture creation and refracture propagation. The stress characteristics of vertically-fractured gas well and the main factors affecting the change of stress value and the stress orientation are studied systematically. It is proved that the induced stress resulting from the initial hydraulic fracture and the variation of pore pressure resulting from production can change the distribution of stress field of the gas well and lead to the reorientation of stress field. Using the theory of elasticity and fluid-solid coupling,the mathematical model of induced stress of refracturing gas well is set up and the software is developed to quantitatively analyze and simulate the stress filed before refracturing for vertically-fractured gas well. The application to Xinchang gas field shows that the initial differential stress and production time are the key factors to determine the stress reorientation in refracturing gas well.