Real Gas Effect and Bulk Diffusion Characteristics of Shale Mixed Gas Transport in Microscale Fractures

Abstract

Shale gas reservoirs are rich in microscale fractures. In this paper, the characteristics of gas percolation in microscale fractures are taken as the research object. By coupling the actual gas equation, the multi-component gas equation, and the bulk gas diffusion equation, analytical solutions of the comprehensive percolation equation are obtained. Through mathematical model research, the following conclusions are obtained: (a) after considering the slip flow of the solid surface, the mass flow rate of multi-component gas under different pressure conditions increases by about 20−10,000%. (b) Different from continuous flow and slip flow, the mass flow rate of bulk gas diffusion decreases with pressure increase. (c) The intersection pressure is 31 MPa. When the pressure increases from 0.5 MPa to the pressure at the intersection point, the mass flow rate of integrated flow increases with decrease of the methane content. (d) When the pressure continues to increase from the intersection point pressure, the mass flow rate of integrated flow decreases with decrease of the methane content.

Study on the Solution and Variation Law of Diffusion Coefficient Based on the Numerical Simulation Optimization Method

“…Diffusion mainly refers to the process in which molecules of a substance transfer from a high concentration to a low concentration under the action of the concentration gradient until the concentration is uniformly distributed. , The rate of diffusion is proportional to the concentration gradient of the substance. Since the diffusion coefficient is a key parameter to characterize the diffusion rate of methane molecules, its measurement and solution has always been research hotspot. , The diffusion coefficient of gas from the coal seam generally lies in the range of 10 –15 –10 –7 m 2 /s. , It is normally calculated by the coal particle desorption method which is to solve the diffusion coefficient by fitting the analytical solution of the diffusion theoretical model on the basis of desorption data. − According to different assumptions, diffusion theoretical models are divided into the single-pore diffusion model , and the double-pore diffusion model. , In accordance with different solution conditions, diffusion theoretical solution can be classified as constant pressure solution and constant volume solution. − Crank, Yang, and Nie et al have derived approximate analytical solutions under constant-pressure condition based on the Fick’s law of diffusion. Analytical solutions are generally derived in the form of infinite series under specific assumptions and boundary conditions.…”

“…11 , 12 It is normally calculated by the coal particle desorption method which is to solve the diffusion coefficient by fitting the analytical solution of the diffusion theoretical model on the basis of desorption data. 13 − 17 According to different assumptions, diffusion theoretical models are divided into the single-pore diffusion model 18 , 19 and the double-pore diffusion model. 20 , 21 In accordance with different solution conditions, diffusion theoretical solution can be classified as constant pressure solution and constant volume solution.…”

Desorption Characteristics of CH4–C2H6 Mixed Gas in Heavy Hydrocarbon-Rich Coal Seams

“…Although coal is the stabilizer and ballast of energy security, coal and gas protrusions in the mining process seriously restrict the safe production of coal mines and endanger the occupational safety and health of workers. − In the prevention and control of coal and gas herniation, the gas content of the coal seam is a critical indicator of gas outflow from mines. The gas content enables predictions of areas at risk of coal and gas herniation, along with effectiveness evaluations of antidisruptive measures. − Moreover, the safety requirements are tightening with the increasing depth of coal mining, and the reliability and accuracy of the coal bed methane content measurement results are paramount.…”

“…The gas content enables predictions of areas at risk of coal and gas herniation, along with effectiveness evaluations of antidisruptive measures. 4 − 6 Moreover, the safety requirements are tightening with the increasing depth of coal mining, and the reliability and accuracy of the coal bed methane content measurement results are paramount.…”

Research Progress on the Microfracture of Shale: Experimental Methods, Microfracture Propagation, Simulations, and Perspectives

“…Therefore, an in-depth exploration of the causes, characteristics, and propagation patterns of the microfractures generated during the process of hydraulic fracturing in shale holds urgent engineering practicality and significant research value. In addition to its practical significance in enhancing shale gas recovery [13], the investigation of microfracturing in rocks holds equal importance for the development of rock fracture theories. The theory of structural control in rock masses posits that the influence of rock mass structure on rock fracturing is significantly greater than that of rock materials, serving as a fundamental theory in rock mechanics.…”