Abstract
Water injection in oilfield may break initial balance of reservoir and lead to re-distribute of stress and deformation of strata. For further research of the evolution characteristics of in-situ field by water injection, the influence on reservoir by water injection was analyzed and different variables were set to study the effects of depth, injection-withdraw ratio and elastic modulus on strain and stress of strata based on fluid-solid coupling theory. Research shows that: As the water injection, the formation pressure around injection well is greater than that of the production well and the effective stress around injection well is less than that of production well. The deeper the formation is, the smaller the normal strain and vertical displacement are. Besides, the largest shear strain is on the top of reservoir, while the smallest is in central reservoir and different injection-withdraw ratios have significant influence on formation pressure. Elastic modulus mainly influences the deformation of the formation and deformation size is negatively related to the elastic modulus. This study provides a reference for casing damage under the effect of water injection.
Highlights
To maintain the reservoir pressure and improve recovery rate of crude oil, water injection is applied in oil field
The initial pressure of reservoir in equilibrium is broken by the water injection with high pressure in the injection well and the pressure relief in the oil well, resulting in the re-distribution of formation pressure
It can be seen that the influence degree of pore pressure affected by injection is positively correlated with the strata depth and the spatial pressure distribution is in a pyramid shape, that is, the degree is larger in the lower part
Summary
To maintain the reservoir pressure and improve recovery rate of crude oil, water injection is applied in oil field. With the help of multi field coupling method, using reservoircap rock model, Rutqvist et al (2009) studied the stress change of reservoir in the process of injection, gave focus on the influence of liquid migration on stress changes and analyzed the tensile failure and shear failure mechanism. In order to further study about the influence of water injection on stress and deformation, according to the production conditions of oil field, this paper first analyzed the overall effect of water injection on reservoir based on the fluid solid coupling theory. According to the formation depth, production control and rocks’ strength parameter, three different variables, depth, Injection-Withdraw Ratio (IWR) and elastic modulus, were set respectively to study the stress and deformation response.
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