Location

Rolla, MO

Session Start Date

6-11-1999

Session End Date

6-17-1999

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 and Nuclear Engineering

Appears In

U.S. Mine Ventilation Symposium

Meeting Name

8th U.S. Mine Ventilation Symposium

Publisher

University of Missouri--Rolla

Publication Date

6-11-1999

Document Version

Final Version

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Jun 11th, 12:00 AM Jun 17th, 12:00 AM

A New Laboratory Technique to Estimate Gas Diffusion Characteristics of Coal

Rolla, MO

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.