Laboratory Measurements of the Relative Permeability of Coal: A Review

Abstract

The relative permeability of coal to gas and water is an essential parameter for characterizing coalbed methane (CBM) reservoirs and predicting coal seam gas production, particularly in numerical simulations. Although a variety of studies related to the relative permeability of coals have been conducted, the results hardly meet the needs of practical engineering applications. To track the dynamic development of relative permeability measurements in the laboratory, discover the deficiencies, and discuss further work in this field, this paper investigates the relative permeability measurement preparation work and laboratory methods and summarizes the development of techniques used to determine the water saturation during experimentation. The previously determined relative permeability curves are also assembled and classified according to coal rank and the absolute permeability. It is found that the general operations in the relative permeability measurement process are still not standardized. The techniques applied to determine the water saturation of coal in experiments have been refined to some extent, but no optimal technique has been recognized yet. New techniques, such as the incorporation of high-precision differential pressure gauges, can be used to determine the water production during relative permeability measurement. In addition, the existing relative permeability data are limited, and no study has focused on supercritical carbon dioxide-water and mixed gas (methane and carbon dioxide)-water relative permeability measurements. To meet the requirements of actual projects, further research on this topic must be conducted.

A novel method for determining water saturation of porous media in relative permeability measurement using DPT

“…The relative permeability curve shows a narrow two-phase span, high irreducible water saturation and lower water relative permeability characteristics. These characteristics are consistent with the high-rank coal (with a permeability less than 0.1 mD) relative permeability curve reported by Shen et al [29]. To evaluate the reliability of the relative permeability measurement using this self-developed device, we compared the measurement results with Sun et al [16].…”

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

“…According to the previous experience, the sum of relative permeability for gas and water is less than one under most conditions. ,,− This indicates that the fluid flow capability is reduced due to the appearance of two-phase flow. The term permeability loss was introduced by Song et al to quantify the loss magnitude caused by the two-phase flow, as shown in eq . where k rl is the relative permeability loss.…”

Stress-Dependent Fractal Model for Predicting the Relative Permeability of Rocks Based on Equivalent Capillaries

“…Nowadays, there are some commonly used experimental methods for two-phase flow studies, such as the steady-state method and the unsteady-state method. 16,17 The steady-state method can measure the relative permeability over a wide range of saturation levels with high reliability. However, this method takes a long time to reach saturation equilibrium.…”

“…Although most existing studies on relative permeability have been carried out based on laboratory experiments, there is currently no standard method for measuring relative permeability. Nowadays, there are some commonly used experimental methods for two-phase flow studies, such as the steady-state method and the unsteady-state method. , The steady-state method can measure the relative permeability over a wide range of saturation levels with high reliability. However, this method takes a long time to reach saturation equilibrium.…”