Design and Examination of Requirements for a Rigorous Shale-Gas Reservoir Simulator Compared to Current Shale-Gas Simulators

Abstract

The development of shale plays in North America has achieved great success in satisfying increased energy demand. With the advances in experimental approaches, investigation of microstructures in organic-rich shale has identified several different pore types and the abundance of pores from the nanometer to the micron scale. Yet current modeling work for such reservoirs is mainly performed with dual porosity models based on Darcy's law. In addition, a great discrepancy between simulation results and production data persists. Because flow regimes in porous media are quite sensitive to pore size, the flow mechanisms in shale reservoirs are considerably more complex than Darcy flow and the feasibility of conventional models has been frequently challenged. This work presents an integration of realistic multi-porosity and multi-mechanistic treatments to resolve the conundrum of fluid flow in shale.Based on a unique reservoir simulator, a micro-scale multiple-porosity model for gas flow in shale reservoirs is presented in this paper. The model consists of three separate porosity systems: kerogen, inorganic minerals, and natural fractures. Inorganic and organic portions of the shale matrix are represented by sub-continua with different characteristics considering pore structures, fluid storage and flow mechanisms. In the kerogen gas desorption, diffusion and Darcy flow occur simultaneously. Through considering the different pore families in the kerogen, the effects of nanopores and microporosity are incorporated into the model. In addition, a novel gridding scheme has been specially designed to recognize the complex structures. To accomplish this, the grid incorporates randomly distributed kerogen in the shale matrix and different continua are tied to each other via arbitrary connectivities. Through changing the properties of both matrix and fracture, a unified concept of dynamic apparent permeability of shale matrix is proposed. The derived concept allows the design and function of the Micro-Scale Model to be extended to the reservoir scale model containing hydraulic fractures. The more realistic gas production forecasts using the workflow presented in this paper indicate significant differences from that of conventional models. The ability to more accurately simulate the complex flow mechanisms using the proposed techniques will allow operators to better predict and enhance ultimate recovery from shale reservoirs.

Quad-porosity shale systems – a review

“…Knudson diffusion and slip flow were taken into account through the incorporation of apparent permeability. In their work, a shale reservoir was represented by the quadruple-porosity system which was first introduced by Aguilera (2010) and Andrade et al (2010Andrade et al ( , 2011, namely, as organic and inorganic matrix and natural and hydraulic fractures. Hudson (2011) analyzed the gas transport in shale reservoirs with an explicit differential model.…”

Understanding Complex Source Rock Petroleum Systems to Achieve Success in Shale Developments

“…Reservoir simulation tools (Shabro 2011, Andrade 2011 are only now starting to incorporate some of these more complex flow models and the multi-component characteristics of these source rocks. Much of this knowledge is gained through a much deeper understanding of the basin modeling and source rock modeling disciplines.…”

Flexible and Efficient N-Porosity, Full-Featured Simulator Design, and Application

“…More recently, Fung et al (2011) have demonstrated applications with Middle Eastern carbonates of up to three porosity types within their generalized multi-porosity scheme. Moreover, interest in the simultaneous simulation of four porosity types for unconventional gas reservoirs is now under active study (Andrade et al 2011). This paper presents the design of our simulator with respect to the challenges of modeling multiple porosity types.…”