Vol 2 Chapter 14: CO2 Storage in Coalbeds: CO2/N2 Injection and Outcrop Seepage Modeling
Shaochang Wo and Jenn-Tai Liang
Abstract: Methane (CH4) production from coalbeds can be enhanced by injection of carbon dioxide (CO2), nitrogen (N2), or a mixture of both (flue gas) to accelerate methane production at sustained or increased pressures. Coal has the capacity to adsorb considerably more CO2 than either methane or nitrogen. However, the actual field performance of enhanced methane recovery processes, wherein CO2 is concurrently stored, is largely dictated by how effectively injected gases contact and interact with coalbeds over the active project lifetime. By history matching the early nitrogen breakthrough time and nitrogen cuts in BP’s Tiffany Unit, simulation indicated that the injected N2 may only contact a small portion of the total available pay, which was evidenced by the spinner surveys conducted in some of the N2 injectors. As a possible explanation, the elevated pressure affected by N2 injection may expand the coal fractures on the preferential permeability trends in the Tiffany Unit. Simulation prediction of CO2–N2 mixed gas injections was performed following the history matching in the pilot area. Methane seepage has already been observed from many locations along the north and west Fruitland outcrops in the San Juan Basin. The concern is that injected CO2 could likely follow the methane seepage paths and leak from the outcrops. Based on the geological setting of the Fruitland coal outcrop, a representative seepage model was used to simulate the effects of CO2 contact volume (net pay interval) in coal and the injection distance from the outcrop on methane and CO2 seepage. Under certain conditions, simulation predicted that a large volume of methane and CO2 breakthrough could occur if the CO2 injection wells are placed too close to the outcrop.
Carbon Dioxide Capture for Storage in Deep Geologic Formations – Results from the CO2 Capture
Project Geologic Storage of Carbon Dioxide with Monitoring and Verification - Volume 2
Edited by: Sally M. Benson, Lawrence Berkeley Laboratory, Berkeley, CA, USA
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