Investigation of feasibility of injecting power plant waste gases for enhanced coalbed methane recovery from low rank coals in Texas

摘要

Greenhouse gases such as carbon dioxide (CO2) may be to blame for a gradual rise in the average global temperature. The state of Texas emits more CO2 than any other state in the U.S., and a large fraction of emissions are from point sources such as power plants. CO2 emissions can be offset by sequestration of produced CO2 in natural reservoirs such as coal seams, which may initially contain methane. Production of coalbed methane can be enhanced through CO2 injection, providing an opportunity to offset the rather high cost of sequestration. Texas has large coal resources. Although they have been studied there is not enough information available on these coals to reliably predict coalbed methane production and CO2 sequestration potential.The goal of the work was to determine if sequestration of CO2 in low rank coals is an economically feasible option for CO2 emissions reduction. Additionally, reasonable CO2 injection and methane production rates were to be estimated, and the importance of different reservoir parameters investigated. A data set was compiled for use in simulating the injection of CO2 for enhanced coalbed methane production from Texas coals. Simulation showed that Texas coals could potentially produce commercial volumes of methane if production is enhanced by CO2 injection. The efficiency of the CO2 in sweeping the methane from the reservoir is very high, resulting in high recovery factors and CO2 storage. The simulation work also showed that certain reservoir parameters, such as Langmuir volumes for CO2 and methane, coal seam permeability, and Langmuir pressure, need to be determined more accurately. An economic model of Texas coalbed methane operations was built. Production and injection activities were consistent with simulation results. The economic model showed that CO2 sequestration for enhanced coalbed methane recovery is not commercially feasible at this time because of the extremely high cost of separating, capturing, and compressing the CO2. However, should government mandated carbon sequestration credits or a CO2 emissions tax on the order of $10/ton become a reality, CO2 sequestration projects could become economic at gas prices of $4/Mscf.