Numerical Investigation of Influence of In-Situ Stress Ratio, Injection Rate and Fluid Viscosity on Hydraulic Fracture Propagation Using a Distinct Element Approach

Abstract

Numerical simulation is very useful for understanding the hydraulic fracturing mechanism. In this paper, we simulate the hydraulic fracturing using the distinct element approach, to investigate the effect of some critical parameters on hydraulic fracturing characteristics. The breakdown pressure obtained by the distinct element approach is consistent with the analytical solution. This indicates that the distinct element approach is feasible on modeling the hydraulic fracturing. We independently examine the influence of in-situ stress ratio, injection rate and fluid viscosity on hydraulic fracturing. We further emphasize the relationship between these three factors and their contributions to the hydraulic fracturing. With the increase of stress ratio, the fracture aperture increases almost linearly; with the increase of injection rate and fluid viscosity, the fracture aperture and breakdown pressure increase obviously. A low value of product of injection rate and fluid viscosity (i.e., Qµ) will lead to narrow fracture aperture, low breakdown pressure, and complex or dispersional hydraulic fractures. A high value of Qµ would lead wide fracture aperture, high breakdown pressure, and simple hydraulic fractures (e.g., straight or wing shape). With low viscosity fluid, the hydraulic fracture geometry is not sensitive to stress ratio, and thus becomes a complex fracture network.

Numerical Modeling and Investigation of Fluid-Driven Fracture Propagation in Reservoirs Based on a Modified Fluid-Mechanically Coupled Model in Two-Dimensional Particle Flow Code

“…Then, after the crack extended to a certain length, the bond failure at the other side of the borehole is initiated. These processes are different from the results of Zhang et al [11], where the cracks developed symmetrically.…”

“…Then, after the crack extended to a certain length, the bond failure at the other side of the borehole is initiated. These processes are different from the results of Zhang et al [11], where the cracks developed symmetrically. When assuming that the fluid injection rate was 1.0 × 10 −4 m 3 /s, Figure 10 shows that when SH:Sh = 20:20, there are three main fractures developing in three different directions, while with SH:Sh = 20:15, there are only two main fractures, which initially extend deviating from the direction of maximum principle stress and then along it.…”

“…This ensures that fluid can still migrate in a model even without cracks. As the normal force at a contact increases, the aperture related to force can be given as: e = e inf + (e 0 − e inf )exp(−0.15σ n ) (11) where σ n is the effective normal stress at the contact (in MPa). When σ n tends to infinity, the aperture decreases asymptotically to e inf .…”

“…The stress in the x-direction (S H ) is always 20 MPa, while the stress in the y-direction (S h ) is varied between 12, 15 and 20 MPa, respectively. Under the assumption that the hydraulic apertures of fluid flow pipes conform to Equation (11), the average initial apertures in these models are 5.33 × 10 −7 , 4.98 × 10 −7 and 4.55 × 10 −7 m, respectively. With increasing fluid pressure in the domains, the aperture can reach 1.03 × 10 −6 m when the bonding stress condition between particles is tension.…”

“…Today, fracturing of oil and gas reservoirs, using a mixture of viscous hydraulic fluids and sorted sand, is the most commonly used reservoir stimulation technique [3][4][5]. Other applications of hydraulic fracturing include the disposal of radioactive waste drill cuttings underground [6], heat production from hot dry rock geothermal reservoirs [7,8], as well as the measurement of in situ stresses [9][10][11].…”