Dynamic Permeability Models in Dual-Porosity System for Unconventional Reservoirs: Case Studies and Sensitivity Analysis

Abstract

Dynamic Permeability is one of the most important key features for unconventional reservoir. The production of unconventional reservoirs, such as shale oil and gas, tight oil and gas, coal bed methane etc., heavily depends on the effective permeability of fracture. However, its permeability changes nonlinearly due to dual-porosity system, which affects the accuracy of unconventional reservoir simulation. This paper investigates two commonly accepted dynamic permeability models in details, S&D model and G&W model. Furthermore, these models are compared and applied in field cases. This study can help us understand the physics behind dynamic permeability in dual porosity system, and facilitate applying dynamic permeability model from core scale to field scale. Firstly, unconventional oil and gas recovery process in dual porosity system is analyzed to determine the key petrophysical controlling factors. In particular, the relation between permeability and fracture porosity is analyzed and discussed in details. Then the most popular two models, S&D model and G&W model, are compared and analyzed. The advantages and disadvantages of those models are discussed, including gas desorption effect, matrix shrinkage effect, micropososity change effect. In addition, the models are applied to several field cases, and the results of these two models are discussed and compared with each other. Finally, the models are applied to pressure transient analysis, to test their feasibility in unconventional reservoir simulation. By analyzing the model, the important role of fracture porosity in permeability prediction is addressed. The results of cases study validate the accuracy of G&W model, which can give a better prediction of dynamic permeability, and perfectly describe rebounding pressure phenomenon as pore pressure decreases. For different models, the sensitivities of several parameters in geomechanical equations and Langmuir isothermal equation are analyzed by Monte Carlo method, and these key sensitive parameters have impact on the simulation results for unconventional reservoirs. From geomechanical perspective, the effects of fracture porosity on permeability change are investigated and discussed in details, which is critical in dual porosity system. The field cases and relevant sensitivity analyses are essential in understanding the physics behind the problem. By comparison and applications of the models, it is concluded that dynamic permeability models can be applied to unconventional reservoir simulation.

Insights, Trends and Challenges Associated with Measuring Coal Relative Permeability

“…Even though flow through fractures is well studied, the poroelasticity and adsorption/ desorption mechanics of coal add complexity when trying to understand relative permeability behaviour. Under increasing effective stress loads not only do the fractures change widths, the matrix itself also deforms (Lu et al, 2018;Liang et al, 2017). If methane is introduced into the coal matrix and pore pressure is increased then the matrix will adsorb methane and swell.…”

Investigation of the Effect of Natural Fractures on Multiple Shale-Gas Well Performance Using Non-Intrusive EDFM Technology

“…Although there are many analytical or semi-analytical models to simulate shale-gas reservoirs [20][21][22][23], numerical reservoir simulation is needed to accurately model multiple shale-gas well production due to complexity of natural and hydraulic fracture configurations and complex two-phase flow physics [24][25][26][27]. The traditional local grid refinement (LGR) method with structured grids is difficult to model complex fractures explicitly [28,29].…”

Rayleigh fractionation in high-Rayleigh-number solutal convection in porous media

“…This subject has received renewed interest due to its potential impact on geological carbon dioxide (CO 2 ) storage. The injection of supercritical CO 2 into deep saline aquifers for long-term storage is the only technology that allows large reductions of CO 2 emissions from fossil fuel-based electricity generation [4][5][6][7][8]. Dissolution of CO 2 into the brine eliminates the risk of upward leakage [9][10][11], because it increases the density of the brine and forms a stable stratification [12].…”