Method to quantify total raw coalbed desorbed gas volume from geophysical logs

#This invention relates to a use of geophysical logs to determine total raw coalbed gas desorbed from coal seams penetrated by a plurality of well bores.

#This invention relates to the drilling of coalbed methane wells into the ground in order to intersect coal bearing formations and seams. Most coal seams contain methane adsorbed to the coal surfaces. Methane gas will desorb from the coals and enter the well bore after the well bore pressure is reduced. This gas can then be delivered from the well bore to the surface and sold as a natural gas energy supply. It is necessary to determine how much gas can be desorbed from the coals before proceeding with further expenditures. There must be enough methane gas adsorbed to the coals that can be desorbed for the operator to make a profit. This invention rapidly calculates desorbed gas volumes in place from geophysical logs recorded in well bores. Computer software yields the fastest results but calculations can be made by hand, calculator, computer spreadsheet, and by other means.

#This invention minimizes the use of a lengthy and expensive laboratory desorption method to determine project viability and gas reserves calculation. This invention calculates continuous total raw gas desorption (gas volume)/(weight of coal) from geophysical logs after calibrating to laboratory derived desorption. This invention rapidly calculates gas reserves from geophysical logs which are already available. Calculations are very fast when this method is incorporated in a computer software program.

#FIG. 1. is a logarithmic plot of total raw laboratory desorbed coal gas (labDES) against geophysical log bulk density (RHOB).

#A common means of determining total raw desorbed coalbed gas consists of:

#1. Cutting a core in a coal seam during the drilling of the well.

#2. Removing the core from the well and placing it in a sealed container (also known as a canister) at reservoir temperature.