Pore pressure and stress distribution analysis around an inclined wellbore in a transversely isotropic formation based on the fully coupled chemo-thermo-poroelastic theory

Abstract

a b s t r a c tWellbore instability is a widespread problem when drilling in shale formations, particularly with waterbased drilling fluid. The main reason for the occurrence of wellbore instability is that stress concentration and pore pressure redistribution occur around the wellbore once a hole is drilled; current studies show that the drilling fluid temperature and solute mass fraction play important roles during the process. In this work, a non-linear fully coupled chemo-thermo-poroelastic finite element model is developed to quantitatively access thermal and chemical effects on time-dependent pore pressure and effective stresses; in addition, material constant sensitivity analysis of an inclined well drilled in a transversely isotropic formation is presented. The results reveal the following: fluid transfer is greatly affected by thermal and chemical osmosis, the lower temperature and higher solute mass fraction of the drilling fluid contribute to decreasing the pore pressure and are beneficial for wellbore stability, and thermal parameters (such as thermal osmosis coefficient and thermal diffusivity) and chemical parameters (such as reflection coefficient and solute diffusion coefficient) have high effects on the pore pressure and effective stresses. Anisotropy ratio analysis of the material constants indicates that the pore pressure and effective stresses are very sensitive to Young's modulus and the permeability ratio, but are not sensitive to Poisson's ratio. Therefore, the developed coupled chemo-thermo-poroelastic theory illustrates that optimization of the reduction of the drilling fluid temperature while maintaining a high solute mass fraction could enhance wellbore stability.

Three-dimensional quasi-static general solution for isotropic chemoelastic materials and their application

“…Problems involving coupled chemical and mechanical fields are common in engineering. The finite element method (FEM) is commonly used to solve such problems [16][17][18][19][20], primarily due to the rapid advancements in finite element software in recent years. Various materials, such as shale [17][18][19][20], polymer colloid [21], and hydrogel [16], are capable of reacting to chemical stimuli.…”

“…The finite element method (FEM) is commonly used to solve such problems [16][17][18][19][20], primarily due to the rapid advancements in finite element software in recent years. Various materials, such as shale [17][18][19][20], polymer colloid [21], and hydrogel [16], are capable of reacting to chemical stimuli. Yang et al [16] developed a fully coupled multi-field finite element formulation based on the governing equations of thermal conduction, electric flow, ionic diffusion, and momentum balance to analyze the impacts of coupled fields on thermo-electro-chemo-elastic materials.…”

Analysis and Application of Transversely Isotropic Chemical Poroelastic Media Subjected to Point Liquid and Chemical Sources

“…Zhou et al [29] developed a chemo-thermo-poroelastic FEM model used to solve the coupled problems of wellbore in shale. In another work, Cao et al [30] extended the chemothermo-poroelastic FEM model into the nonlinearity of shale with penetration, thermal and chemical effects.…”

Numerical Simulation on Borehole Instability Based on Disturbance State Concept

“…Zou et al established a stress-strain model of hydrated soil with the DSC method to describe the process of the failure of the cement structure [24]. The application of the DCS method in borehole stability is still not reported [25][26][27].…”