Analysis of the hydraulic fracturing mechanism and fracture propagation law with a new extended finite element model for the silty hydrate reservoir in the South China Sea

Abstract

The existing hydrate exploitation technology is characterized by low gas production in single wells and a small exploitation range, owing to the low porosity and low permeability of submarine hydrate reservoirs; therefore, commercial exploitation is difficult to achieve. There is an urgent need to improve exploitation efficiency by means of reservoir reconstruction. Hydraulic fracturing technology may be useful for low-permeability reservoirs such as silty hydrate reservoirs in the South China Sea (SCS). In this study, we established a new hydraulic fracturing model of a horizontal single well for gas-hydrate-bearing-sediments (GHBS) using the cohesive zone method (CZM) based on the extended finite element method (XFEM). To this end, we utilized field measured data of GHBS at site GMGS3-W19. The effect of fluid-solid coupling was considered, and the fracture propagation criterion was set as the maximum principal stress criterion to analyze the hydraulic fracture propagation law of hydrate reservoirs in the SCS. First, we illustrated the effectiveness of the CZM based on XFEM in simulating the fracture morphology of GHBS hydraulic fracturing. A Parametric study showed that the hydrate saturation, horizontal geo-stress coefficient, perforation angle, and injection rate play crucial roles in the fracture propagation path and characteristic parameters of GHBS hydraulic fractures. The fracture development pattern and propagation law of a silty hydrate reservoir within the SCS were theoretically obtained. The results of the present study partly provide theoretical support for hydrate exploitation engineering in the SCS.