Modeling of Fluid Transfer from Shale Matrix to Fracture Network

Abstract

The objective of this paper is to incorporate a more detailed description of flow in shale matrix to improve modeling of production from fractured shale-gas reservoirs. Currently, most modeling approaches for shale-gas and -oil production are based on the dominance of Darcy flow in both natural fractures and matrix. We improve the description of matrix flow by considering diffusive (Knudsen) flow in nanopores. In our dual-mechanism approach, when Darcy flow becomes insignificant due to nanodarcy matrix permeability, Knudsen flow takes over and contributes, substantially, to the transfer of fluids from matrix to fracture network. Furthermore, we consider stress-dependent permeability in the fracture network. Therefore, incorporating Darcy and diffusive flows in the matrix and stress-dependent permeability in the fractures, we develop a dual-mechanism dual-porosity naturally fractured reservoir formulation and derive a new transfer function for fractured shale-gas reservoirs. The dual-mechanism dualporosity formulation presented in this paper can be used for numerical or analytical modeling purposes. We use the new formulation of matrix to fracture fluid transfer with an analytical model and demonstrate the differences from the conventional formulation.

Numerical Simulation of Natural Gas Flow in Anisotropic Shale Reservoirs

“…A comprehensive understanding with regard to the complex flow processes as mentioned earlier is certainly required to build a correct mathematical model for shale gas flow. In tight formations like shale gas, the traditional Darcy flow becomes invalid because of the nanodarcy matrix permeability (Ozkan et al 2010). At nanoscale permeability, Knudsen diffusion becomes the dominant mechanism that drives the gas flow from the matrix to the fracture network.…”

A multi-linear flow model for multistage fractured horizontal wells in shale reservoirs

“…The shale gas reservoir is isothermal.ˆThere are the no-flow boundaries parallel to the hydraulic fractures at the middle of two fractures in closed reservoir.˜Wellbore storage effect is taken into account. Flow in every region is assumed to be linear similar to the model proposed by Ozkan et al (2010) and is shown in Fig. 2.…”

“…Considering the limited width of the simulated region, five-region model was defined to simulate the SRV to extend the trilinear model (Stalgorova and Mattar 2012b). Dehghanpour and Shirdel (2011) improved the Ozkan's dual-porosity model (Ozkan et al 2010) to explain the unexpected high gas production in shale gas reservoirs based on the pseudo-steady model of Warren and Root (Warren and Root 1963). Then, equivalent flow model (Ketineni S and Ertekin 2012) was used to describe the SRV and solved the elliptical flow problem by Mathieu modified functions.…”

“…These studies mainly focused on vertical well or horizontal well and few about the MFHW. Although Ozkan et al (2010) and Brown et al (2009) developed a trilinear flow model to simplify the complex process and get good results in unconventional gas reservoirs, desorption and adsorption mechanism, which is the key mechanism of shale gas reservoirs, was ignored. Sang et al (2014) presented a new mathematical model considering adsorption and desorption process, which made up the disadvantage of the trilinear flow model for MFHW in shale gas reservoirs.…”

An Analysis for the Influences of Fracture Network System on Multi-Stage Fractured Horizontal Well Productivity in Shale Gas Reservoirs

“…The results show that the slip flow and transitional flow are the typical flow regime in shale, which is different from the linear flow equation of conventional gas reservoirs. Ozkan et al (2010) studied the flow mechanisms in shale matrix and micro fracture system [19], and developed a dual-mechanisms model by coupling diffusion with Darcy flow to describe the gas flow in shale matrix. [20].…”