Physics-Based Fluid-Flow Modeling of Liquids-Rich Shale Reservoirs Using a 3D Three-Phase Multiporosity Numerical-Simulation Model

Abstract

Summary Production from liquids–rich shale reservoirs in the US and Canada has increased significantly during the past few years. However, a rigorous understanding of shale rocks and fluid flow through them is still limited and remains a challenge. Thus, the objective of our research is developing a 3D physics–based model for simulating fluid flow through these types of multiporosity rocks. This is important given the recent spread of these types of reservoirs throughout the world. Simulation of liquids–rich shale reservoirs is performed with the construction of an original fully implicit 3D multiphase modified black–oil finite–difference numerical formulation, which uses a multiporosity approach as well as diffusion from solid kerogen. The multiporosity system includes adsorbed porosity, organic porosity, inorganic porosity, natural–fracture porosity, and hydraulic–fracture porosity. A numerical model is developed with capabilities to handle dissolved gas in the solid part of the organic matter, adsorption/desorption from the organic pore walls, viscous– and non–Darcy–flow mechanisms (slip flow and Knudsen diffusion), and stress–dependent properties of natural and hydraulic fractures. Examples of simulated results are presented as crossplots of pressure, production rates, and cumulative production vs. time. These plots are used to show the contributions of free gas, adsorbed gas, and dissolved gas to fluid production from liquids–rich shale reservoirs. Results indicate that both desorption and gas diffusion positively affect shale performance. Simulation results demonstrate that not taking into account desorption and diffusion from solid kerogen leads to underestimating production from liquids–rich shale reservoirs. Furthermore, the simulation study shows that long periods of time are required for the effects of these two mechanisms to be manifested. This helps to explain why shales have been produced over long periods of time (several decades), such as in the case of Devonian wells in the Appalachian Basin. The type of 3D simulation model for multiporosity liquids–rich shale reservoirs developed in this paper is not currently available in the literature. The approach implemented in this paper provides a novel and important foundation for simulating complex shale reservoirs.