Bulk Density Logs Estimate Coalbed Methane Adsorbed, Desorbed and Producible Gas Volumes

Bowler, Jack¹, Steven A. Tedesco^2 
1 Bowler Petrophysics, Inc, Denver, CO 
² Dorado Gas Resources LLC, Englewood, CO

Wireline bulk density logs are used to identify coals and estimate coal thickness. This information is needed to help determine the economic viability of a coalbed methane project. Coals have a low bulk density (RHOB) and are easily identified. 

Studies conducted on cored high volatile "B" and "A" bituminous coal samples in the Illinois Basin, Illinois, and Forest City Basin, Kansas, show that both methane gas desorption and adsorption laboratory measurements can be correlated to RHOB. The authors find that desorption=a*RHOB^-b and adsorption=c - d*RHOB. These simple models enable one to make an estimate of both adsorbed and desorbed gas volumes in place. 

A study conducted on high volatile "A" bituminous Rowe coals deeper than 1,000 feet in the Cherokee Basin, Oklahoma, reveals a correlation between RHOB and gas production. Produced gas volume=e - f*RHOB. 

The results of these studies show RHOB can be used to do more than identify coals and their thickness. RHOB can estimate gas reserves and save time and money.