Open AccessCO2 Sequestration Potential of Texas Low-Rank Coals
Author(s) -
Duane A. McVay,
Jr Ayers,
Jerry L Jensen
Publication year - 2005
Language(s) - English
Resource type - Reports
DOI - 10.2172/861367
Subject(s) - coalbed methane , carbon sequestration , coal , environmental science , acre , flue gas , reservoir simulation , dewatering , carbon dioxide , petroleum engineering , environmental engineering , geology , coal mining , waste management , chemistry , engineering , geotechnical engineering , agroforestry , organic chemistry
The objectives of this project are to evaluate the feasibility of carbon dioxide (CO{sub 2}) sequestration in Texas low-rank coals and to determine the potential for enhanced coalbed methane (ECBM) recovery as an added benefit of sequestration. The main objectives for this reporting period were to perform reservoir simulation and economic sensitivity studies to (1) determine the effects of injection gas composition, (2) determine the effects of injection rate, and (3) determine the effects of coal dewatering prior to CO{sub 2} injection on CO{sub 2} sequestration in the Lower Calvert Bluff Formation (LCB) of the Wilcox Group coals in east-central Texas. To predict CO{sub 2} sequestration and ECBM in LCB coal beds for these three sensitivity studies, we constructed a 5-spot pattern reservoir simulation model and selected reservoir parameters representative of a typical depth, approximately 6,200-ft, of potential LCB coalbed reservoirs in the focus area of East-Central Texas. Simulation results of flue gas injection (13% CO{sub 2} - 87% N{sub 2}) in an 80-acre 5-spot pattern (40-ac well spacing) indicate that LCB coals with average net thickness of 20 ft can store a median value of 0.46 Bcf of CO{sub 2} at depths of 6,200 ft, with a median ECBM recovery of 0.94 Bcf and median CO{sub 2} breakthrough time of 4,270 days (11.7 years). Simulation of 100% CO{sub 2} injection in an 80-acre 5-spot pattern indicated that these same coals with average net thickness of 20 ft can store a median value of 1.75 Bcf of CO{sub 2} at depths of 6,200 ft with a median ECBM recovery of 0.67 Bcf and median CO{sub 2} breakthrough time of 1,650 days (4.5 years). Breakthrough was defined as the point when CO{sub 2} comprised 5% of the production stream for all cases. The injection rate sensitivity study for pure CO{sub 2} injection in an 80-acre 5-spot pattern at 6,200-ft depth shows that total volumes of CO{sub 2} sequestered and methane produced do not have significant sensitivity to injection rate. The main difference is in timing, with longer breakthrough times resulting as injection rate decreases. Breakthrough times for 80-acre patterns (40-acre well spacing) ranged from 670 days (1.8 years) to 7,240 days (19.8 years) for the reservoir parameters and well operating conditions investigated. The dewatering sensitivity study for pure CO{sub 2} injection in an 80-acre 5-spot pattern at 6,200-ft depth shows that total volumes of CO{sub 2} sequestered and methane produced do not have significant sensitivity to dewatering prior to CO{sub 2} injection. As time to start CO{sub 2} injection increases, the time to reach breakthrough also increases. Breakthrough times for 80-acre patterns (40-acre well spacing) ranged from 850 days (2.3 years) to 5,380 days (14.7 years) for the reservoir parameters and well injection/production schedules investigated. Preliminary economic modeling results using a gas price of $7-$8 per Mscf and CO{sub 2} credits of $1.33 per ton CO{sub 2} indicate that injection of flue gas (87% N{sub 2}-13% CO{sub 2}) and 50% N{sub 2}-50% CO{sub 2} are more economically viable than injecting 100% CO{sub 2}. Results also indicate that injection rate and duration and timing of dewatering prior to CO{sub 2} injection have no significant effect on the economic viability of the project(s)