Analysis of 3D Hydraulic Fracture Morphology and Fracture Critical Parameters in Hydrate-Bearing Sediments in the South China Sea Using Extended Finite Elements
Jinxin Liu, Yongping Yu, Bing Li, Youhong Sun
Abstract
Hydraulic fracturing is a technology used to improve the fluid flow performance of hydrate-bearing sediments (HBSs). It enhances the pore structure of HBSs and increases the porosity and permeability, thereby improving the exploitation efficiency of natural gas hydrates. However, most of the analytical models are two-dimensional, and there is an obvious gap between the critical parameters of cracks and the experimental results. In this study, a new single-cluster model of hydraulic fracturing for the horizontal well is established with available data from site GMGS3-W19 of the South China Sea (SCS) based on the three-dimensional (3D) extended finite element method (XFEM). The hydraulic fracturing behavior of HBSs for different perforation angles, hydrate saturation, horizontal in situ geo-stress coefficient, and injection rate is investigated, and the initiation and propagation mechanism of hydraulic fractures is revealed in a three-dimensional scale. The results showed that with the increase of hydrate saturation, the ability of hydrate to connect the sediment skeleton is enhanced, and the HBSs have a more vital ability to resist fluid pressure. The remaining pores in the HBSs are filled; the degree of pressure holding in the fracture increases; the fracture development is hindered; and the difficulty of fracture initiation increases.