Reservoir characterization of a coalbed methane openhole cavity completion using production and pressure transient data

Abstract

This dissertation presents the development of a coalbed methane reservoir description from the analysis of production and pressure transient data for a producing openhole cavity well and two observation wells completed in the Fruitland Formation in the San Juan Basin, Colorado. A major objective of the work was to identify a method that can be used to obtain a reservoir description in a coalbed methane reservoir. The methods proposed in the literature for estimating properties of coalbed methane reservoirs were evaluated. A more specific objective was to validate the method chosen for coalbed methane reservoir description in a specific geologic location. A good reservoir description may help quantify an increase in the effective permeability of the coal natural fracture system. This will help us to understand the reservoir conditions where cavitation may be a suitable stimulation technique for coalbed methane reservoirs. As a result of this research, several observations about coalbed methane wells have been made. This research indicates that (1) cavitation alone cannot account for all the increased gas production, (2) the use of a reservoir simulator is necessary to obtain a reservoir description, (3) the cavitation process forms an altered zone, (4) existing analytical solutions do not accurately characterize the complicated flow of a coal reservoir, (5) interference tests should not be analyzed using conventional or pseudopressure methods to estimate permeability between coalbed methane wells because of gas saturation gradients, and (6) lab relative permeability data should not be used for the Fruitland Formation coal sample.