Complementary hydro-mechanical coupled finite/discrete element and microseismic modelling to predict hydraulic fracture propagation in tight shale reservoirs

Abstract

This paper presents a novel approach to predict the propagation of hydraulic fractures in tight shale reservoirs. Many hydraulic fracture modelling schemes assume that the fracture direction is pre-seeded in the problem domain discretization. This is a severe limitation as the reservoir often contains large numbers of pre-existing fractures that strongly influence the direction of the propagating fracture. To circumvent these shortcomings a new fracture modelling treatment is proposed where the introduction of discrete fracture surfaces is based on new and dynamically updated geometrical entities rather than the topology of the underlying spatial discretization. Hydraulic fracturing is an inherently coupled engineering problem with interactions between fluid flow and fracturing when the stress state of the reservoir rock attains a failure criterion. This work follows a staggered hydro-mechanical coupled finite/discrete element approach to capture the key interplay between fluid pressure and fracture growth. In field practice the fracture growth is hidden from the design engineer and microseismicity is often used to infer hydraulic fracture lengths and directions. Microsesimic output can also be computed from changes of the effective stress in the geomechanical model and compared against field microseismicity. A number of hydraulic fracture numerical examples are presented to illustrate the new technology.

Numerical methods for hydraulic fracture propagation: A review of recent trends

“…A local remeshing approach (i.e. limited only to the surrounding of the fracture front) has been developed in 3D and coupled to fluid flow in a staggered way with limited testing of the different hydraulic fracture propagation regimes (Profit et al, 2015(Profit et al, , 2016a.…”

Adaptive Finite Element‐Discrete Element Analysis for Microseismic Modelling of Hydraulic Fracture Propagation of Perforation in Horizontal Well considering Pre‐Existing Fractures

“…The update of the mechanical stresses satisfies the momentum balance equation, with the assumption that fluid acceleration relative to the solid and the convective terms can be ignored. The mechanical governing equation is given by the following [35]:…”

“…In seismology, a low -value, around 1, is indicative of an earthquake. In hydraulic fracturing situations, the -value is expected to be higher and the occurrence of a low -value is an indication of reactivation [35,37]. The -value calculation can be calculated from the magnitude of each event.…”

“…Discrete fracture networks (DFNs) can be generated serving as pre-existing fractures to explore the effects of a number of different natural fractures on the same domain [35,37]. For each DFN, the following data is specified:…”

“…For investigating the hydrofracturing cracks in heterogeneous media, the authors of this paper developed the continuum-based discrete element method (CDEM) [34]. The conventional FEM has limitations to deal with the fracture propagation; furthermore, the mesh refinements have to be adopted [35]. The coupled finite element-(FE-) discrete element (DE) method makes the cracks flexibly propagate between the elements; the adaptive analysis and remeshing strategy could conquer the problems in solving fracture propagation by conventional FEM [36].…”