Confining Stress Response to Hydraulic Fracturing Volumetric Opening on the Representative Volume Element (RVE) Scale

Abstract

Confining stress response is considered an accompanying behavior of hydraulic fracturing. Along these lines, an evaluation model of confining stress response was presented in this work. It was established on a rock representative volume element (RVE) and based on the hydraulic volumetric opening model, which stems from the theories of poroelasticity, breakdown damage, and hydraulic fracture mechanics. From the extracted outcomes, it was demonstrated that the confinement of the stress response depends on the matching among the characteristic parameters (εb,εs,m) of the rock breakdown, the volumetric opening, and channel flow regimes of the fracturing fluid. Examples in four limiting fracturing regimes show that (1) the confinement of the stress response is strongly determined by the existence of various fracturing regimes and takes place in a different manner during fracture initiation and opening. More specifically, during fracturing initiation, the ratio of the confining stress response to the far-field stress (Pcmax/σh) is 2.0500 in the M regime, 1.9600 in the M˜ regime, 2.7126 in the K regime, and 1.7448 in the K˜ regime, while when the fracture is opened, these values (PC/σh) are 1.8994, 1.8314, 1.6378, and 1.2846, respectively. (2) The impact of the confined stress response to the fluid pressure is also affected by the fracturing regimes; e.g., in both M and M˜ regimes, the peak confinement stress responses lag behind peak pore pressures, but in the K and K˜ regimes, lag off disappears. (3) The pore volumetric opening (Vpe) leads to an increase in the confining stress response, while the fracture opening (Vpd) leads to a reduction in the confining stress response.