Hydraulic fracturing process by using a modified two-dimensional particle flow code - case study

Abstract

By using a modified PFC 2D model, the authors conducted a series of simulations to examine the influences of in-situ stress ratio, fluid injection rate, anisotropy of laminated rocks, and perforation parameters on hydraulic fracturing process. The simulations indicated that: 1) larger in-situ stress ratio will induce smaller breakdown pressures and faster propagation, and hydraulic fractures will extend along the direction of the maximum principal stress or approach to this preferred path; 2) smaller difference of in-situ stresses or faster fluid injection rate is helpful for creation of complex fracture network; 3) weak layers are preferred locations and directions for fracture initiation and propagation in the laminated rocks; 4) hydraulic fractures initiate easily at the bottoms of perforation channels, and propagate generally along or approaching to the direction of maximum principal stress.Keywords: a modified PFC 2D model; isotropic medium; the laminated rock; in-situ stress ratio; fluid injection rate; dip angle of bedding planes.Reference to this paper should be made as follows: Zhang, L., Zhou, J. and Han, Z. (2017) 'Hydraulic fracturing process by using a modified two-dimensional particle flow code -case study

Numerical simulation of hydraulic fracturing in transversely isotropic rock masses based on PFC-2D

“…As we know, faster fluid injection implied a higher strength similar to compressive tests of rock specimens applied with dynamic loads in the laboratory. Because stress in the solid skeleton induced by the injection borehole could not immediately adjust, higher fluid injection rate would lead to larger breakdown pressure in hydraulic fracturing [22]. What is more, when the injection rate reached to a large value (such as 5.0×10 -4 m 3 /s, shown in Fig.…”

“…The remaining microscopic parameters of BPM and SJM were the same as Table 1 and Table 2. With references of the previous research [21][22][23][24][25], the microscopic parameters in the fluid calculation were shown in Table 4. In order to verify the numerical model of hydraulic fracturing, hydraulic fracturing tests were carried out under different initial in-situ stresses.…”

“…This may not achieve the desired purpose of hydraulic fracturing. On the other hand, with the excessively fast injection rate, crack initiation and propagation along multiple orientations were easily formed around the injection borehole [22]. Meanwhile, excessively fast injection rate would cause the situation that the original cracks were not widened and grown yet while the new crack initiation.…”

“…Thus, the DEM can simulate the crack initiation, propagation and penetration more realistically. The particle discrete element method, which is a distinct element-based model [15], has been widely used in rock fracture research [14,[16][17] and hydraulic fracturing [18][19][20][21][22][23][24][25]. Since unconventional oil and gas reservoirs, such as shale, have the distinct layered structure, the bedding planes will affect the initiation and propagation of the hydraulic fractures.…”

Influence of Grain Size Heterogeneity and In-Situ Stress on the Hydraulic Fracturing Process by PFC2D Modeling

“…Hence, a large amount of research has been carried out to figure out the mechanism of hydraulic fracturing by means of experiments, simulations, and theoretical analysis. Various studies have shown that the main factors influencing hydraulic fracturing include external factors [5][6][7][8], such as in-situ stress, fluid viscosity and injection rate, and wellbore geometry, and internal factors [9][10][11][12][13], such as rock strength, natural fracture features, and rock anisotropy and heterogeneity.…”