Abstract
The natural microdefects of shale and the expansion of microcracks under hydration and overlying rock loadings are important for the wellbore stability. According to the conservation of energy, the force of the microdefects and microcracks under finite deformation is studied by the method of configuration force through the migrating control volume in the spatial observer. Under the hydration stress and rock pressure, the equation of hydration stress and its work in reference configuration has been obtained, and the equations of configuration forces and configuration moment have been established as a consequence of invariance under changes. The relationship between the configuration and deformation forces is determined by the second law. The energy dissipation equation of the crack tip has been deduced, which shows that the projection of the concentrated internal configuration body force at the crack tip in the opposite direction of the crack is equal to the energy dissipation of the crack tip per unit length. The inertial and internal parts of the concentrated configuration body force at the crack tip have been derived; it is indicated that the internal configuration force plays a leading role in the irreversible fracture process. Moreover, the energy release rate of shale under hydration is proved to depend on constitutive responses and hydration stress. In the theoretical system of configuration force, the migrating control volume at the crack tip contains inclusions, microcracks, microvoids, and heterogeneity of the rock itself. We use the configuration force theory to solve the problem of rock crack propagation and rock fracture. The factors considered are more comprehensive, which can better reflect the actual situation and provide a theoretical basis for the study of wellbore stability.
Highlights
Academic Editor: Jianguo Wang e natural microdefects of shale and the expansion of microcracks under hydration and overlying rock loadings are important for the wellbore stability
E relationship between the configuration and deformation forces is determined by the second law. e energy dissipation equation of the crack tip has been deduced, which shows that the projection of the concentrated internal configuration body force at the crack tip in the opposite direction of the crack is equal to the energy dissipation of the crack tip per unit length. e inertial and internal parts of the concentrated configuration body force at the crack tip have been derived; it is indicated that the internal configuration force plays a leading role in the irreversible fracture process
We use the configuration force theory to solve the problem of rock crack propagation and rock fracture. e factors considered are more comprehensive, which can better reflect the actual situation and provide a theoretical basis for the study of wellbore stability
Summary
The points’ position X X (ξ1, ξ2, t) of the control volume boundary zR(t) in the current configuration is y y⌢(X (ξ1, ξ2, t), t) On this basis, we can define the interface deformation velocity caused by the migrating control volume. E crack propagation velocity describes the position change of the crack tip in the reference configuration E deformation velocity of crack tip v(t) and the deformation velocity of migrating control volume interface u are similar Both of them are not the material points’ velocity; they are the position changes of the different material points in special structures or defects in the current configuration
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