Abstract: 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.

Key words: formation, backwash, fluid-solid coupling, elastoplasticity, finite elements