CO2 Sequestration Potential of Texas Low-Rank Coals
Injection of CO{sub 2} in coalbeds is a plausible method of reducing atmospheric emissions of CO{sub 2}, and it can have the additional benefit of enhancing methane recovery from coal. Most previous studies have evaluated the merits of CO{sub 2} disposal in high-rank coals. The objective of this research was to determine the technical and economic feasibility of CO{sub 2} 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, including acquisition and analysis of coal core samples and well transient test data. We conducted deterministic and probabilistic reservoir simulation and economic studies to evaluate the effects of injectant fluid composition (pure CO{sub 2} and flue gas), well spacing, injection rate, and dewatering on CO{sub 2} sequestration and ECBM recovery in low-rank coals of the Calvert Bluff formation of the Texas Wilcox Group. Shallow and deep Calvert Bluff coals occur in two, distinct, coalbed gas petroleum systems that are separated by a transition zone. Calvert Bluff coals < 3,500 ft deep are part of a biogenic coalbed gas system. They have low gas content and are part of a freshwater aquifer. In contrast, Wilcox coals deeper than 3,500 ft are part of a thermogenic coalbed gas system. They have high gas content and are part of a saline aquifer. CO{sub 2} sequestration and ECBM projects in Calvert Bluff low-rank coals of East-Central Texas must be located in the deeper, unmineable coals, because shallow Wilcox coals are part of a protected freshwater aquifer. Probabilistic simulation of 100% CO{sub 2} injection into 20 feet of Calvert Bluff coal in an 80-acre 5-spot pattern indicates that these coals can store 1.27 to 2.25 Bcf of CO{sub 2} at depths of 6,200 ft, with an ECBM recovery of 0.48 to 0.85 Bcf. Simulation results of flue gas injection (87% N{sub 2}-13% CO{sub 2}) indicate that these same coals can store 0.34 to 0.59 Bcf of CO{sub 2} with an ECBM recovery of 0.68 to 1.20 Bcf. Economic modeling of CO{sub 2} sequestration and ECBM recovery indicates predominantly negative economic indicators for the reservoir depths (4,000 to 6,200 ft) and well spacings investigated, using natural gas prices ranging from $2 to $$12 per Mscf and CO{sub 2} credits based on carbon market prices ranging from $$0.05 to $$1.58 per Mscf CO{sub 2} ($$1.00 to $30.00 per ton CO{sub 2}). Injection of flue gas (87% N{sub 2} - 13% CO{sub 2}) results in better economic performance than injection of 100% CO{sub 2}. CO{sub 2} sequestration potential and methane resources in low-rank coals of the Lower Calvert Bluff formation in East-Central Texas are significant. The potential CO{sub 2} sequestration capacity of the coals ranges between 27.2 and 49.2 Tcf (1.57 and 2.69 billion tons), with a mean value of 38 Tcf (2.2 billion tons), assuming a 72.4% injection efficiency. Estimates of recoverable methane resources range between 6.3 and 13.6 Tcf, with a mean of 9.8 Tcf, assuming a 71.3% recovery factor. Moderate increases in gas prices and/or carbon credits could generate attractive economic conditions that, combined with the close proximity of many CO{sub 2} point sources near unmineable coalbeds, could enable commercial CO{sub 2} sequestration and ECBM projects in Texas low-rank coals. Additional studies are needed to characterize Wilcox regional methane coalbed gas systems and their boundaries, and to assess potential of other low-rank coal beds. Results from this study may be transferable to other low-rank coal formations and regions.
- Research Organization:
- Texas A & M Univ., College Station, TX (United States). Texas A & M Engineering Experiment Station
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-02NT41588
- OSTI ID:
- 945016
- Country of Publication:
- United States
- Language:
- English
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CO2 Sequestration Potential of Texas Low-Rank Coals
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