Techbits: Coalbed-Methane Recovery and CO2 Sequestration Raise Economic, Injectivity Concerns

Abstract

Representing Australia, the U.S., Canada, and Europe, 40 engineers and geologists attended an SPE Applied Technology Workshop (ATW) focused on the viability of enhanced coalbed-methane (ECBM) recovery and CO2 sequestration in coalbeds. The workshop “Enhanced Coalbed-Methane Recovery and CO2 Sequestration,” held in Denver from 27–29 October 2004, was led by Scott Reeves, Executive Vice President of Advanced Resources Intl., and the program committee included Bill Gunter, Research Officer of the Alberta Research Council; Mike McGovern, Senior Staff Engineer of Burlington Resources; Henk Pagnier, Program Manager-SUS Energy, TNO-Netherlands Inst. of Applied Geosciences; and Pablo Tejera Cuesta, Reservoir Engineer for Shell Intl. E&P. The ATW featured six sessions focusing on different aspects of ECBM recovery and CO2 sequestration, providing an excellent snap-shot of research and pilot programs in this topic area. Session 1, moderated by Reeves, introduced the workshop and reviewed the state of ECBM-recovery technology. During his introduction, Reeves noted that ongoing work in ECBM recovery is very research oriented and is driven by CO2 sequestration. Cuesta continued the session with an introduction to ECBM-recovery technology, stating that coalbed methane is a significant part of the global hydrocarbon resource base. He reviewed the reservoir characteristics of coal (classified as a continuous-type reservoir) in which gas storage is dominated by adsorption. Major points of discussion highlighted economic considerations, including the cost of injectant required for ECBM-recovery operations as well as the separation, capture, and storage of CO2. Lessons Learned Gunter moderated Session 2, focusing on pilot projects and emphasizing results and lessons learned and noting that experience with ECBM recovery and CO2 sequestration in coal includes one large-scale project in the Allison Unit of the San Juan basin and a series of single-well micropilots in Canada, Poland, and China. These pilot programs have focused on coal of bituminous-through-anthracite rank, and major issues being addressed include geomechanics, permeability, matrix swelling, and fracture porosity. McGovern presented the results of CO2 flooding in the Allison Unit, motivated by the desire to recycle CO2 produced from Fruitland coal while enhancing CBM production. Within the Allison Unit, CO2 was injected continuously for more than 5 years. During the project, approximately 4.7 Bcf of CO2 was injected, and approximately 4.2 Bcf of CO2 was sequestered. Incremental methane recovery during the project was approximately 1.5 Bcf, and the ratio of CO2 injected to methane produced was approximately 3.1:1.0. David Law of the Alberta Research Council presented results of micropilot programs in Mannville coal of the Western Canada sedimentary basin and the No. 3 coal of China’s Qinshui basin. In the pilot areas, Mannville coal is of highly volatile B bituminous rank, and the No. 3 coal is of anthracite rank. Well testing in these micropilots included multiple production and injection-falloff tests. The Mannville micropilot is notable because a variety of gases were injected, including pure CO2, flue gas, pure N2, and CO2-enriched flue gas. The Qinshui basin contains the first pattern of commercial CBM wells drilled in China and contains the highest-rank coal developed for CBM to date. Well testing in the Qinshui basin confirms that sequestration potential exists in anthracite and that permeability can exceed 12 md.