Numerical simulation on the effect of pore pressure gradient on the rules of hydraulic fracture propagation

Weiyong Lu,Changchun He

doi:10.1177/01445987211009389

Abstract

To clarify the influence of pore pressure gradient on hydraulic fracture propagation, the stress distribution in and around the borehole is explained by theoretical analysis method in this paper. A mechanical model of hydraulic fracture initiation under the action of pore pressure gradient is established. Then coupled seepage-stress-damage software is used to simulate the initiation and propagation of hydraulic fractures in rock samples under the action of pore pressure gradient. Finally, the influence of the number and spatial position of the induction holes on the initiation and propagation of hydraulic fractures is analyzed. It is shown that: (1) Pore pressure gradient can effectively reduce the initiation pressure of hydraulic fractures. (2) The greater the pore pressure gradient is, the easier the hydraulic fracture is to spread to the region with high pore pressure. (3) With the action of pore pressure gradient, the hydraulic fracture is shaped as ‘丨’, ‘丿’ and ‘S’ types and can be represented by the four abstract conceptual models.

Highlights

Many rocks of oil and gas reservoir, characterized with both pores and fractures, are dualporosity and typical low-permeability medium (Cordero et al, 2019; Wang, 2018; Wang et al, 2018)
RFPA2D-Flow software, a seepage-stress coupling analysis system for rock fracture instability, is used to the influence of pore pressure gradient on hydraulic fracture propagation based on the damage mechanics theory, in which both tensile and shear failure criteria of the rock are chosen
With the increase of the water pressure in the induction hole, the deflection amplitude of the hydraulic fracture becomes larger and larger (Lu et al, 2016). This is consistent with the experimental results of Lu et al Both numerical calculation and physical test results (Figure 3) show that the non-uniform pore pressure field formed by the induction hole affects the propagation of hydraulic fractures

Summary

Introduction

Many rocks of oil and gas reservoir, characterized with both pores and fractures, are dualporosity and typical low-permeability medium (Cordero et al, 2019; Wang, 2018; Wang et al, 2018). It was found by the through rock plate rupture test that the initiation pressure and direction of hydraulic fracture was affected by the stress difference at the tip of hydraulic fracture and affected by the size and gradient of the pore pressure.

Results

Conclusion