Carbon dioxide (CO₂) from energy consumption is a primary anthropogenic greenhouse gas. Injection of CO₂ in 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 CO₂ disposal in high-rank coals. The objective of this research is to determine the technical and economic feasibility of CO₂ sequestration 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 CO₂ and 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 CO₂ sequestration and ECBM recovery.

Probabilistic simulation of 100% CO₂ injection in an 80-ac five-spot pattern indicates that Wilcox Group coals can store 1.27–2.25 bcf of CO₂ at depths of 6200 ft (1890 m), with an ECBM recovery of 0.48–0.85 bcf. Simulation results of 50% CO₂–50% N₂ injection in the same 80-ac five-spot pattern indicate that these coals can store 0.86–1.52 bcf of CO₂, with an ECBM recovery of 0.62–1.10 bcf. Simulation results of flue-gas injection (87% N₂–13% CO₂) indicate that these same coals can store 0.34–0.59 bcf of CO₂ with an ECBM recovery of 0.68–1.20 bcf.

Economic modeling of CO₂ sequestration and ECBM recovery for 100% CO₂ injection indicates predominantly negative economic indicators for the reservoir depths and well spacings investigated, using natural gas prices ranging from $2 to $12/mscf and CO₂ credits based on carbon market prices ranging from $0.05 to $1.58/mscf CO₂ ($1.00 to $30.00/ton CO₂). Injection of flue gas (87% N₂–13% CO₂) results in better economic performance than injection of 100% CO₂.

Moderate increases in either gas prices or carbon credits could generate attractive economic conditions that, combined with the close proximity of many CO₂ point sources near unminable coalbeds, could generate significant CO₂ sequestration and ECBM potential in Texas low-rank coals.