Evaluation of the Technical and Economic Feasibility of CO 2Sequestration and Enhanced Coalbed Methane Recovery in Texas Low-Rank Coals

Abstract

Carbon dioxide (CO 2) from energy consumption is a primary anthropogenic greenhouse gas. Injection of CO 2in coalbeds is a plausible method of reducing atmospheric emissions, and it can have the additional benefit of enhancing methane recovery from coal. Most previous studies have evaluated the merits of CO 2disposal in high-rank coals. The objective of this research is to determine the technical and economic feasibility of CO 2sequestration in, and enhanced coalbed methane (ECBM) recovery from, low-rank coals in the Texas Gulf Coast area. Our research included an extensive coal characterization program, deterministic and probabilistic simulation studies, and economic evaluations. We evaluated both CO 2and flue-gas injection scenarios.

In this study, coal-core samples and well pressure transient test data were obtained for characterization of Texas low-rank coals. Simulation studies evaluated the effects of well spacing, injectant fluid composition, injection rate, and dewatering on CO 2sequestration and ECBM recovery.

Probabilistic simulation of 100% CO 2injection in an 80-ac five-spot pattern indicates that Wilcox Group coals can store 1.27–2.25 bcf of CO 2at depths of 6200 ft (1890 m), with an ECBM recovery of 0.48–0.85 bcf. Simulation results of 50% CO 2–50% N 2injection in the same 80-ac five-spot pattern indicate that these coals can store 0.86–1.52 bcf of CO 2, with an ECBM recovery of 0.62–1.10 bcf. Simulation results of flue-gas injection (87% N 2–13% CO 2) indicate that these same coals can store 0.34–0.59 bcf of CO 2with an ECBM recovery of 0.68–1.20 bcf.

Economic modeling of CO 2sequestration and ECBM recovery for 100% CO 2injection indicates predominantly negative economic indicators for the reservoir depths and well spacings investigated, using natural gas prices ranging from $2 to $12/mscf and CO 2credits based on carbon market prices ranging from $0.05 to $1.58/mscf CO 2($1.00 to $30.00/ton CO 2). Injection of flue gas (87% N 2–13% CO 2) results in better economic performance than injection of 100% CO 2.

Moderate increases in either gas prices or carbon credits could generate attractive economic conditions that, combined with the close proximity of many CO 2point sources near unminable coalbeds, could generate significant CO 2sequestration and ECBM potential in Texas low-rank coals.