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    June, 2005

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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