THE COAL-SEQ PROJECT: KEY RESULTS FROM FIELD, LABORATORY, AND MODELING STUDIES

摘要

In October 2000, a multi-year government-industry R&D collaboration known as the Coal-Seq project was launched in the United States. Participants in the project include the U.S. Department of Energy as the project sponsor, Advanced Resources International, Burlington Resources, and BP America. The project objectives are to evaluate the feasibility of CO_2 sequestration in deep, unmineable coalseams using enhanced coalbed methane (ECBM) recovery technology. The Coal-Seq project is achieving its objectives via reservoir simulation studies of existing ECBM pilot projects in the San Juan basin, laboratory modeling studies of coal behavior, technical and economic sensitivity studies, and assessments of the potential and economic performance for ECBM recovery and CO_2 sequestration in deep, unmineable coals. Since its inception, and now in its final year, many important findings have emerged from the project, some of the more notable being: 1. CO_2 injection into coal can significantly improve methane recovery. At the Allison Unit CO_2-ECBM pilot in the San Juan basin, methane recovery was improved from 77% to 95% of original gas in place within the central pilot area. 2. Coal permeability and CO_2 injectivity was substantially reduced with CO_2 injection (by up to an order of magnitude near the wells, and extending to an estimated 1,000 ft from the wellbores). This has a detrimental effect to ECBM/sequestration economics. 3. While existing reservoir simulation models yield essentially similar results, the theoretical models they are based upon for multi-component sorption, diffusion and phase behavior may not accurately replicate actual reservoir behavior. Specifically, coal swelling cannot be adequately modeled in a dynamic fashion. 4. N_2-ECBM appears more economically favorable than CO_2-ECBM. However, from a carbon sequestration perspective, a gas comprising of mostly CO_2 appears the most favorable. 5. A technical/economic sensitivity has shed light on the most favorable coal conditions for sequestration. These include deep, high-rank coals with low permeability and that have not been previously developed for conventional coalbed methane production. However, this assumes technology is developed to overcome reduced injectivity due to matrix swelling. 6. An assessment of CO_2-ECBM/sequestration potential in the U.S. suggests a potential resource of 150 Tcf of gas and a sequestration capacity of 90 Gt of CO_2 exists.