疏松砂岩应力损害分析评价

Numerical Simulation of Stress-Induced Wellbore Damage in Unconsolidated Sandstone Reservoirs

疏松砂岩为应力敏感介质,完井、开采过程中储集层易产生膨胀/压实变形,造成应力损害,影响油井产能。以疏松砂岩介质的力学性能及其在孔隙流体作用下的动态应力演化过程为基础,综合考虑流体渗流、储层变形和破坏等因素,建立了流固耦合形式的疏松砂岩应力损害定量评价模型,并采用有限元数值模拟方法求解。采用该模型对胜利油田某裸眼油井疏松砂岩油藏进行了应力损害定量评价,结果表明:近井壁储集层沿最大主应力方向剪切膨胀,孔隙度、渗透率相应提高,而沿最小主应力方向区域塑性压实,孔隙度、渗透率均下降;开采过程中油藏压力衰竭导致储集层骨架有效应力增加,储层孔隙度和渗透率下降,随生产压差增大,储层渗透性能将进一步降低,生产过程中应采取必要措施以消除应力损害。

The unconsolidated sandstone reservoirs are sensitive to stress variations. The formation of these reservoirs can be easily compressed or swelled during drilling and production process and cause formation damage and impact oil production. Based on the mechanics properties of unconsolidated sandstone and dynamic stress evolution under porous fluid, a formation stress damage evaluation model was created which couples fluid flow and solid considering the porous flow, formation deformation and damage, and the model was solved using finite element method. This model was used to evaluate the formation damage in an open hole well in Shengli Oilfield. The analysis result indicates that, the porosity and permeability was increased along the maximum shear stress direction due to the expansion, and the porosity and permeability was decreased along the minimum shear stress direction due to compaction. The effective stress increases due to reservoir pressure declining in production, and the porosity and permeability decreases. With the increased of production pressure difference, the permeability of formation decreased further. Efforts should be used to eliminate the stress damage. The results of finite element numerical simulation indicated that drilling and drawdown pressure has significant influence on reservoirs transmissibility, efforts should be made to reduce stress-induced damage and improve completion longevity and optimize well productivity.