Measuring CO₂ in Coalbed Reservoirs

Steven MacDonald. WellDog, Inc., 1482 Commerce Drive, Suite T, Laramie, WY  82070  [email protected]

CO₂, whether natural occurring or introduced, can have significant effects on the production and subsequent handling of gas from coalbed reservoirs. CO₂ has greater affinity for absorption onto coal than methane and thus displaces methane. This displacement, with naturally occurring CO₂, will result in a reduction of the capacity of the coal to hold methane, and if not considered, will result in lower than predicted SCF/ton of methane storage. In systems of introduced CO₂, such as flooding or enhanced recovery, the greater affinity of CO₂ for the surface of the coal is used to drive off the methane and thus increase the production rate. In both cases, knowledge of the amount of CO₂ in the system can affect the economics and operational procedures of producing the reservoir.  Raman spectroscopy, a laser-based spectroscopy used for chemical analysis, has been adapted to quantify and identify the chemical forms of CO₂ in reservoir fluids.