Study on the Seepage Force-Induced Stress and Poroelastic Stress by Flow Through Porous Media Around a Vertical Wellbore

Abstract

Fluid flowing through reservoir pores not only generates poroelastic stress but also exerts seepage force on rock skeleton. However, the mechanism of seepage force is not clear. Traditional methods of analyzing wellbore stability and hydraulic fracture initiation are mainly focused on the poroelastic stress without the effects of seepage force. Based on the linear elasticity and consolidation theory, this paper analyzed the mechanism of seepage force and poroelastic stress, and presented an analytical solution for seepage force-induced stress around a vertical wellbore. It also introduced how to calculate poroelastic stress by exerting hypothetical body force and surface force. Through comparison and superposition of stress fields, this paper studied the change characteristics of the poroelastic and seepage force-induced stress under different borehole pressures and the effects of seepage force on the wellbore tensile failure. Numerical simulation results show that when fluid flows through the rock, using traditional models without considering, the effect of seepage force to calculate the borehole pressure-induced stress will result in lower calculation results. Compared with the traditional model, seepage force-induced circumferential tensile stress is larger, and the seepage force significantly reduces the formation breakdown pressure. Rocks near the borehole wall with lower permeability and larger Poisson’s ratio have a greater action of seepage force. When fluid flows through the reservoir, the effects of seepage forces cannot be ignored in the analysis of hydraulic fracturing and wellbore stability.

Mechanistic study on the effect of seepage force on hydraulic fracture initiation

“…The flow of fracturing fluids in pore throats with circular cross-sections can be assumed as the laminar flow of viscous incompressible fluids, that is, Poiseuille flow. 15 The seepage of non-Newtonian fluids in rock pores is not within the scope of this paper. Under Poiseuille flow conditions, the velocity u(r) of the fluid flowing in the xdirection in the circular pipe is 41 :…”

“…The flow of fracturing fluids in pore throats with circular cross‐sections can be assumed as the laminar flow of viscous incompressible fluids, that is, Poiseuille flow 15 . The seepage of non‐Newtonian fluids in rock pores is not within the scope of this paper.…”

“…The results indicated that the larger the value of the gradient ratio is, the smaller the magnitude of the bearing capacity coefficients is. Wang et al 15 presented an analytical solution that enables the evaluation of the stress field induced by SFs in steady seepage conditions. By conducting simulations to analyze the stress distribution around the wellbore, they discovered that the SF significantly affects the effective stress field surrounding the wellbore and has a notable impact on the formation breakdown pressure.…”

Research on Fluid–Solid Coupling Mechanism around Openhole Wellbore under Transient Seepage Conditions

“…(Note that in this paper, positive values are assigned to compressive stress, while negative values represent tensile stress.) For an open-hole wellbore, the stress equilibrium equation and stress boundary conditions satisfied by the surrounding rock when fluid seepage enters the rock pores are as follows [23]:…”

“…To establish a finite difference format, the first step is to create a stress function Φ to characterize the radial stress σ'r and circumferential stress σ'θ: For an open-hole wellbore, the stress equilibrium equation and stress boundary conditions satisfied by the surrounding rock when fluid seepage enters the rock pores are as follows [23]:…”