Abstract
Fluid flow in the dual-medium carbonate gas reservoir is characterized by stress sensitivity and non-Darcy flow effect. In order to accurately describe the unsteady flow of gas and water in the dual-medium gas reservoir, a two-phase flow model of gas and water is built. First, reservoir space and fluid flow characteristics of carbonate gas reservoirs are investigated, and the flow model that considers both the stress sensitivity and non-Darcy flow is built based on the fundamental flow theory, after fully investigating the reservoir space and fluid flow characteristics of carbonate gas reservoirs. Then, the perturbation theory is introduced, and the model is solved in the Laplace space, after which the obtained Laplace space analytical solution is converted into the real-space solution. Finally, the productivity evaluation model for the dual-medium gas reservoir with the gas-water two-phase flow is built, based on the flowing material balance method and Newton iteration. The presented productivity evaluation model is applied to analyze the effects of stress sensitivity and non-Darcy flow on the two-phase flow model of gas and water for the dual-medium gas reservoir and the reservoir productivity. The results indicate that a higher stress sensitivity coefficient is demonstrated to indicate higher stress sensitivity and accelerated production decline of the reservoir, while a lower non-Darcy flow effect coefficient represents a stronger non-Darcy effect and boosted drop of initial production of the reservoir. Hence, it is not reasonable to neglect the effects of stress sensitivity and non-Darcy flow during the evaluation of the productivity of a dual-medium carbonate gas reservoir. The model presented in this research provides important references for improving the recovery performance of dual-medium gas reservoirs.
Highlights
Carbonate reservoirs are important targets for hydrocarbon exploration and exploitation, because they contain abundant oil and gas resources (Xu et al, 2007)
This study aims and manages to build a gas-water two-phase flow model of carbonate gas reservoirs, incorporating both stress sensitivity and non-Darcy flow
1) The dual-medium carbonate gas reservoir is grealtly different from the conventional gas reservoir, in terms of the storage space and fluid flow characteristics
Summary
Carbonate reservoirs are important targets for hydrocarbon exploration and exploitation, because they contain abundant oil and gas resources (Xu et al, 2007). Carbonate Gas Seepage and Productivity characterized by stress sensitivity, non-Darcy effect, and unique relative gas-water permeability relationship. Most research only considers the effects of a single factor, and rare studies have been reported to investigate the joint impacts of stress sensitivity, non-Darcy flow, and two-phase relative permeability of gas and water on carbonate gas reservoirs. This study aims and manages to build a gas-water two-phase flow model of carbonate gas reservoirs, incorporating both stress sensitivity and non-Darcy flow. Dual-medium carbonate gas reservoirs are different from conventional reservoirs, and they are composed of matrix and fracture systems (Li et al, 2017)—the low-porosity, FIGURE 1 | Relationship between core permeability and overburden pressure. Substituting Eqs 53–55 into Eq 50 yields: FIGURE 4 | Productivity prediction workflow based on the semi-analytic model for two-phase flow of gas and water
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