Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Potential for Enhanced Methane Production from Coal, with Concomitant CO2 Sequestration – Examples from a High-Rank Coal (Pottsville Formation, Black Warrior Basin) and a Low-Rank Coal (Wilcox Group, Texas Gulf Coast Basin)
(1) Petroleum Engineering, Texas A&M University, College Station, TX.
(2) Saudi Aramco Oil Company, Dhahran, Saudi Arabia.
(3) Schlumberger Wireline Services, Duncan, OK.
(4) Pioneer Natural Resources, Irving, TX.
Point sources emissions from industrial and power plants are primary sources of CO2, a major greenhouse gas. Capture of and injection this CO2 in unminable coals may be a viable method of reducing CO2 emissions, while simultaneously enhancing methane recovery from coal. To assess feasibility of CO2 sequestration and enhanced coalbed methane (ECBM) recovery, we evaluated Pottsville bituminous coal (technical feasibility, only) and Wilcox subbituminous coal (both technical and economic viability).
For the Pottsville, we simulated ECBM recovery and CO2 storage, using a 3-layer reservoir model of Pottsville coal zones in Blue Creek field. Factors investigated included: volumes of methane recovered and CO2 sequestered; CO2 injection rates; injection pressures; well spacing; advance coal dewatering; soak benefits; injected gas composition; and single vs. multiple zone injection.
Injection of pure CO2 resulted in methane recovery two times greater than injection of flue gas (90% N2-10% CO2). Dewatering prior to CO2 injection delayed breakthrough time and allowed higher injection rates but did not significantly affect the CO2 volume stored. Soak time did not significantly impact CO2 storage. If 100% CO2 is injected in an 80-ac, 5-spot well pattern, completed in only the major coal zone, 0.20 Bcf of ECBM would be produced and 0.57 Bcf of CO2 would be stored.
For the Wilcox, we used a reservoir simulator to assess well spacing, injectant fluid composition, injection rate, and dewatering on ECBM recovery and CO2 sequestration. Probabilistic simulation of 100% CO2 injection in an 80-ac, 5-spot pattern indicates that Wilcox coals can produce 0.48-0.85 Bcf ECBM and store 1.27-2.25 Bcf CO2. Results of flue-gas (87% N2-13% CO2) injection indicate that Wilcox coals can store 0.34-0.59 Bcf CO2 with ECBM recovery of 0.68-1.20 Bcf. Economic modeling of CO2 storage and ECBM recovery for 100% CO2 injection indicates negative economic results for the conditions investigated, using natural gas prices of $2 to $12/Mscf and CO2 credits of $0.05 to $1.58/Mscf CO2 ($1.00 to $30.00/ton CO2). Injection of flue gas results in better economic performance than injection of 100% CO2.
These study results suggest that CO2 storage with concomitant ECBM production may be technically feasible in both high- and low-rank coals. Economic modeling of the Texas low-rank coals indicates that moderate increases in either gas price or carbon credits could generate attractive economic conditions.