Modelling hydraulic fracturing in a complex-fracture-network reservoir with the DDM and graph theory

Shale gas reservoirs usually contain complex natural fracture (NF) networks. Numerical simulations of NF networks in an infinite, discontinuous medium require large computational resources to store the coordinates, intersections and paths of the fractures. To reduce the computational time and save computer memory, NF networks and the expected hydraulic fracture (HF) networks are both mapped into graphs based on graph theory. A modified displacement discontinuity method (DDM) is used to simulate the deformation and propagation of HFs. The results show that the HF networks are affected primarily by the NF networks, the in situ stress and the fracturing parameters. A higher net pressure leads to a wider but shorter band of HF networks, and a greater stress contrast leads to a longer but narrower band of HF networks. A dimensional parameter ψ is defined by the combination of the net pressure and the stress contrast. As ψ increases, the stimulated reservoir volume (SRV) increases. The stress interaction among HFs in a fractured medium is similar to that in an isotropic homogeneous medium but is more complex because of the influence of NFs.