Location
Rolla, Missouri
Session Dates
11 Jun 1999 - 17 Jun 1999
Keywords and Phrases
Gas Diffusion; Counter Diffusion; Transient Technique; Gas Flow in Coal
Abstract
This paper describes a new experimental technique developed to measure the diffusion coefficient (D) for a coal-methane system using the transient flow mechanism, and examine its dependency on factors that change with continued flow – pressure and gas concentration. Although developed primarily for coalbed methane reservoirs and coal in the gob regions, it also has application in situations where a second gas is injected in coal since it utilizes the principle of counter-diffusion. The results show that there is a continuous decrease in the value of D with decreasing mean concentration of methane in coal. The logarithm of D varies directly with the pressure. Two effects may be responsible for this decrease. The first is a possible change in the flow mechanism with decreasing methane concentration due to the existence of varying pore sizes in coal. The other is the volumetric strain of solid coal matrix induced by desorption of gas, the so called ‘shrinkage effect’. This matrix shrinkage may be resulting in reduced pore sizes, and consequently, a decrease in the value of D.
Department(s)
Mining Engineering
Meeting Name
8th U.S. Mine Ventilation Symposium
Publisher
University of Missouri--Rolla
Document Version
Final Version
Document Type
Article - Conference proceedings
File Type
text
Language
English
Recommended Citation
Harpalani, Satya and Ouyang, Shaofan, "A New Laboratory Technique to Estimate Gas Diffusion Characteristics of Coal" (1999). U.S. Mine Ventilation Symposium. 4.
https://scholarsmine.mst.edu/usmvs/8usmvs/8usmvs-theme3/4
A New Laboratory Technique to Estimate Gas Diffusion Characteristics of Coal
Rolla, Missouri
This paper describes a new experimental technique developed to measure the diffusion coefficient (D) for a coal-methane system using the transient flow mechanism, and examine its dependency on factors that change with continued flow – pressure and gas concentration. Although developed primarily for coalbed methane reservoirs and coal in the gob regions, it also has application in situations where a second gas is injected in coal since it utilizes the principle of counter-diffusion. The results show that there is a continuous decrease in the value of D with decreasing mean concentration of methane in coal. The logarithm of D varies directly with the pressure. Two effects may be responsible for this decrease. The first is a possible change in the flow mechanism with decreasing methane concentration due to the existence of varying pore sizes in coal. The other is the volumetric strain of solid coal matrix induced by desorption of gas, the so called ‘shrinkage effect’. This matrix shrinkage may be resulting in reduced pore sizes, and consequently, a decrease in the value of D.
