Lattice Numerical Simulations of Hydraulic Fracture Propagation and Their Geometry Evolution in Transversely Isotropic Formations

Dezhi Qiu,Rui Huang,Yinhe Lin,Vamegh Rasouli,Jun Zhang,Jinchuan Liu,Branko Damjanac,Minou Rabiei

doi:10.3389/feart.2021.787736

Abstract

Accurate prediction of the fracture geometry before the operation of a hydraulic fracture (HF) job is important for the treatment design. Simplified planar fracture models, which may be applicable to predict the fracture geometry in homogeneous and continuous formations, fail in case of fractured reservoirs and laminated formations such as shales. To gain a better understanding of the fracture propagation mechanism in laminated formations and their vertical geometry to be specific, a series of numerical models were run using XSite, a lattice-based simulator. The results were studied to understand the impact of the mechanical properties of caprock and injection parameters on HF propagation. The tensile and shear stimulated areas were used to determine the ability of HF to propagate vertically and horizontally. The results indicated that larger caprock Young’s modulus increases the stimulated area (SA) in both vertical and horizontal directions, whereas it reduces the fracture aperture. Also, larger vertical stress anisotropy and tensile strength of caprock and natural interfaces inhibit the horizontal fracture propagation with an inconsiderable effect in vertical propagation, which collectively reduces the total SA. It was also observed that an increased fluid injection rate suppresses vertical fracture propagation with an insignificant effect on horizontal propagation. The dimensionless parameters defined in this study were used to characterize the transition of HF propagation behavior between horizontal and vertical HFs.

Highlights

Hydraulic fracturing is a widely used stimulation technology in unconventional reservoirs
The shear stimulated area (SSA) may represent the area along the natural interface that is stimulated by hydraulic fracture (HF)
The elastic modulus was defined as the ratio of the modulus in the caprock layer to the modulus of the reservoir, denoted as effective Young’s modulus (EE); the ratio of the tensile strength of the natural interface and caprock layer to the tensile strength of the reservoir formation was denoted as effective tensile strength (TE); the effective stress anisotropy (SE) was defined as the ratio of the vertical to the minimum horizontal principal stresses; and the effective injection rate (QE) was defined as the ratio of the injection rate to the minimum value used in each case

Summary

Introduction

Hydraulic fracturing is a widely used stimulation technology in unconventional reservoirs. Due to the sedimentation process, the reservoirs and the over- and underlying formations are formed in a laminated form, which is known as the transverse isotropic medium. Sediments are horizontal layers, with the axis of symmetry perpendicular to the lamination; they are referred to as a vertical transversely isotropic medium (VTI or TIV). Hydraulic Fracture Propagation Geometry formations is a function of stress anisotropy, the contrast between the mechanical properties of the reservoir formation and caprocks, and, to some extent, the operational aspects, such as the injection rate and fluid properties (Zhou et al, 2016; Li et al, 2017; Zeng et al, 2018; Aimene et al, 2019; Dou et al, 2019). Understanding hydraulic fracture (HF) propagation in laminated reservoirs is important to accurately predict the fracture geometry for the treatment design

Results

Discussion

Conclusion