Distribution of induced stress by high energy gas fracturing in wellbore

Key words:  high principal stress discrepancy reservoir  high energy gas fracturing  induced stress distribution  complex fracture networks

Abstract:

High energy gas fracturing (HEGF) can generate several radial fractures with random azimuths, and the principle horizontal in-situ stress distribution will be disturbed by the pre-fracturing, which will promote hydraulic fracturing to activate more natural fissures with various angles. In this study, a new horizontal stress perturbation model with random azimuths of pre-fractures was proposed based on the Sneddon elastic model of induced stress and combined with radial and circumferential stress distribution models in high pressure wellbore. The induced stress distribution with single or multiple fractures during HEGF was analyzed, and the effects of different parameters were investigated, including fracture length, fracture number, fracture azimuths, fracture net pressure and the discrepancy of primitive in-situ stress. The results indicate that, due to the HEGF induced pre-fractures, the discrepancy of the principle stress can occur in three significant areas, including the increasing area, the mitigating area and inversing area. The inversing area will expand with the fracture length prolonging, the fracture net pressure increasing, and the primitive in-situ stress difference decreasing. The stress inversing area will appear in both sides out of the fractures tips with lower angle azimuths, and can occur in both sides along the fractures with higher angle azimuths, which also demonstrate that the jamming capability of the fractures with high angle azimuths is superior to the lower angle azimuths. The multiple fractures will disturb with each other, and the optimal combination is to overlay two pairs of pre-fractures parallel to the minimum and maximum primitive principle in-situ stress.