水井反冲洗地层三维弹塑性固结分析

Three dimensional elastoplastic consolidation analysis of water-injecting well backwash

注水井反冲洗工艺是抽油机井维持正常生产的重要措施之一,反冲洗压力是决定反冲洗效率的主要因素。反冲洗过程涉及到地层与套管在水压作用下的相互耦合作用,鉴于目前对洗井压力的制定以套管抗挤压强度为依据,运用ABAQUS-6.5软件,对油藏岩石-套管进行了三维弹塑性固结有限元分析,建立了流-固耦合数学模型,研究了注水井反冲洗过程中套管、地层和流体的瞬态响应,实现了套管、地层和流体间的耦合作用,得到了套管应力随洗井时间的变化规律。计算结果表明,洗井地层的地应力分布状态和地层性质对洗井压力影响较大,主要受到地层弹性模量、渗透性能和地层水平地应力的影响。洗井压力的制定应综合考虑套管和地层状况,与单纯考虑套管的承载能力相比,其研究结果可为洗井工艺的制定提供更为准确的理论基础。

Water injecting well backwash is one of the important measures to maintain normal production;backwash pressure is the main factor determining the efficiency of backwash well.Backwash process involves the coupling function of formation and casing under water pressure.In view of the backwash well pressure is based on compressive strength of casing.Three dimensional elastoplastic consolidation of rock and casing is analyzed by ABAQUS-6.5 finite element software.A fluid-solid coupling model is established to research transient responses of casing,formation and fluid during backwash,the coupling between casing and formation and fluid is realized;the change regulation of casing stress with anti-cleanup’s time is obtained.Numerical results indicate that the distribution of in-situ stress and formation property have significant impact on backwash pressure,which include formation elastic modulus,penetrating quality and horizontal in-situ stress.Casing and formation conditions should be taken into account for backwash pressure decision.Compared with the in-situ stress only considering the bearing capacity of the casing,the study results provide a more accurate theoretical basis.