Simulation of tectonic stress field and prediction of fracture distribution in shale reservoir

Wenlong Ding,Ruyue Wang,Zhe Wang,Yaxiong Sun,Xinghua Wang,Kai Jiu,Weite Zeng

doi:10.21285/2686-9993-2021-44-4-397-407

Abstract

In this paper, a finite element-based fracture prediction method for shale reservoirs was proposed using geostress field simulations, uniaxial and triaxial compression deformation tests, and acoustic emission geostress tests. Given the characteristics of tensile and shear fractures mainly developed in organic-rich shales, Griffith and Coulomb – Mohr criteria were used to calculate shale reservoirs' tensile and shear fracture rates. Furthermore, the total fracture rate of shale reservoirs was calculated based on the ratio of tension and shear fractures to the total number of fractures. This method has been effectively applied in predicting fracture distribution in the Lower Silurian Longmaxi Formation shale reservoir in southeastern Chongqing, China. This method provides a new way for shale gas sweet spot optimization. The simulation results have a significant reference value for the design of shale gas horizontal wells and fracturing reconstruction programs.

Highlights

For low-porosity and low-permeability shale reservoirs, the nano-scale pores in the matrix have basically no seepage capability
The natural gas productivity in the organic-rich marine shale reservoirs of the Lower Paleozoic in the Sichuan Basin of China is positively correlated with the degree of fracture development [17–19]
It can be seen from the simulation results of the tectonic stress field (Fig. 3) that the maximum principal stresses of the Longmaxi Formation shale reservoir in southeastern Chongqing were concentrated between -217.404 and -4.109 MPa

Summary

Introduction

For low-porosity and low-permeability shale reservoirs, the nano-scale pores in the matrix have basically no seepage capability. The great success of the marine organic-rich shale gas industry in North America shows that natural fractures can promote the large-scale accumulation of hydrocarbons in shale reservoirs [4–6]. The natural gas productivity in the organic-rich marine shale reservoirs of the Lower Paleozoic in the Sichuan Basin of China is positively correlated with the degree of fracture development [17–19]. A finite element-based fracture prediction method for shale reservoirs was proposed using geostress field simulations, uniaxial and triaxial compression deformation tests, and acoustic emission geostress tests. This technology has achieved good application effects in the prediction of fracture distribution in the Lower Silurian Longmaxi Formation shale reservoir in southeastern Chongqing, China. It provides a new way for shale gas sweet spot optimization, and the simulation results have important reference value for the design of shale gas horizontal wells and fracturing reconstruction programs

Methods

Results

Conclusion