Development of a Multi-Continuum Multi-Component Model for Enhanced Gas Recovery and CO2 Storage in Fractured Shale Gas Reservoirs

Abstract

Shale gas reservoirs have been proposed as feasible choices of location for injection of CO2 and/or N2 because this method could enhance recovery of natural gas resources, while at the same time sequester CO2 underground. In this paper, a fully coupled multi-continuum multi-component simulator which incorporates several transport/storage mechanisms is developed. To accurately capture physics behind the transport process in shale nanopores, Kundsen diffusion and gas slippage are included in the flow model. An extended Langmuir isotherm is used to describe the adsorption/desorption behavior of different gas components and the displacement process of methane as free gas. Pressure-dependent permeability (due to rock deformation) of natural fractures induced by hydraulic fracturing is also considered in the simulator. In addition, modeling of complex fracture networks is very crucial for simulating production of shale gas reservoirs because there exists various scales of fractures with multiple orientations after the fracturing treatment for horizontal well. In this work, a hierarchical approach which integrates EDFM with dual-continuum concept is adopted. The hybrid model includes three domains: matrix, major hydraulic fractures and large-scale natural fractures (described by EDFM), and micro-fractures in SRV region which are modeled by dual-continuum approach. Embedded Discrete Fractures Model (EDFM) is an efficient approach for explicitly simulating large-scale fractures in Cartesian grid instead of complicated unstructured grid. Moreover, a nested-grid refinement method is used to capture the fluids transfer from matrix to fractures. Fully implicit scheme is applied for discretizing fluid equations, and the corresponding Jacobian matrix is evaluated by Automatic Differentiation with Expression Templates Library (ADETL). The AD-Library framework allows wide flexibility in the choice of variable sets and provides generic representations of discretized expressions for gridblocks. Several simulations and sensitivity analysis are performed with the developed research code for determining the key factors affecting shale gas recovery. Modeling studies indicate that the properties of fracture networks could greatly influence methane production. Different injection strategies including huff-n-puff scenario are also evaluated to provide insights for optimizing production of multi-fractured horizontal well. Results show that CO2/N2 injection can be an effective approach with great application potential for enhancing shale gas recovery.

A new analytical method based on pressure transient analysis to estimate carbon storage capacity of depleted shales: A case study

“…Many researchers found that the permeability of natural fractures is sensitive to pressure change (Jiang et al, 2014;Wu et al, 2013). Therefore, the pressure effect of the natural fracture is considered.…”

“…Only few people, till recently, have attempted to transform shale formations into repositories (Jiang et al, 2014;Tao and Clarens, 2013). It is pointed out in many published works that, kerogen contained in shale could result in a significant gas adsorption amount (Akkutlu and Fathi, 2011;Ambrose et al, 2010;Kang et al, 2010;Loucks et al, 2009;Sondergeld et al, 2010;Wang and Reed, 2009).…”

“…A series of numerical simulation studies were also performed on in-house or commercial simulation simulators to appraise the http (Dahaghi, 2010;Godec et al, 2013;Sun et al, 2013;Jiang et al, 2014;Schepers et al, 2009;Liu et al, 2013). With this numerical method, more accurate and convincing results can be obtained.…”

Performance of horizontal wells with fracture networks in shale gas formation

“…The state equation of SG is given as pM ZRT 11 g ρ = ( ) Many researchers found that the stress-sensitivity effect should be considered in low-permeability reservoir (Jiang et al, 2014;Wu et al, 2013). To simulate the stress-sensitivity effect, a practical equation with respect to pressure is applied (Pedrosa, 1986),…”

A multi-continuum multi-phase parallel simulator for large-scale conventional and unconventional reservoirs

“…In , a hybrid multiple-continuum-medium modeling approach is developed to describe different types of fractures, including hydraulic fractures, natural fracture network, and micro fractures. In (Moinfar et al, 2013;Jiang et al, 2014), explicit fracture models are coupled with MINC model for the simulation of unconventional reservoirs. A unified framework model is developed in , which is able to incorporate known mechanisms and processes (gas adsorption and desorption, geomechanics effect, Klinkenberg or gas-slippage effect and non-Darcy flow) and use a hybrid fracturemodeling approach to simulate the unconventional gas reservoirs.…”