Strength assessment for water shut-off baffles in a fractured medium

The paper proposes a mathematical model for estimating the strength of two-layered water shut-off baffle adjacent to a wellbore after pumping the cured synthetic resin into a fractured or fractured-porous water-saturated media. The mathematical model is based on the solution to the Lame problem of three-layered pipe, the solution to the problem of isotropic elastic half-space with a cavity, and the von Mises yield criterion for ideal-plastic body. For the outer layer of resinfractured rock barrier, the elastic moduli of equivalent homogeneous isotropic medium are calculated using the differential self-consistent method for needle-like inclusions. The proposed model allows one to account for both the stress relaxation in the rock to a hydrostatic stress state in geological times and the possible tectonic stresses in the rock. In a three-dimensional space of parameters “resin strength - Poisson's ratio for resin - bottomhole pressure after water shut-off in a well”, the strength and yield areas for inner and outer layers of two-layered water shut-off baffle are calculated using some fixed parameters. It is shown that in many cases involving the real elastic and strength properties of the cured synthetic resins, especially under stresses in the reservoir conditions, the water shut-off baffle will be destroyed in any production well operation. It is also proved that the water shut-off operation efficiency does not increase with an increase in the injected synthetic resin volume.

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