First-of-a-Kind Field Test for Enhanced Coalbed Methane Recovery with Simultaneous CO2 Sequestration
Injection of CO2 began in a first-of-a-kind US Department of Energy–sponsored field trial of enhanced coalbed methane recovery with simultaneous CO2 sequestration in an unmineable coal seam.
CONSOL Energy Inc., West Virginia University, and the National Energy Technology Laboratory (NETL) are collaborating in the $13 million field trial, located in Marshall County, W.Va. The site was chosen because of its accessibility, availability, and typical northern Appalachian topography and geology. The project is funded by DOE’s Office of Fossil Energy and managed by NETL.
In advance of CO2 injection, horizontal coalbed methane wells were drilled in a modified five-spot pattern over a 200-acre area into the unmineable Upper Freeport coal seam, 1,200 to 1,800 feet below ground, and separately into the overlying mineable Pittsburgh coal seam. These wells have been producing coalbed methane and water since 2004. The center wells in the Upper Freeport seam have now been converted to CO2 injection wells, and a Class II underground injection control permit was obtained from the West Virginia Department of Environmental Protection Office of Oil and Gas.
Researchers plan to inject CO2 at a pressure of up to 700 psi (4.8 MPa) and a rate of about 27 short tons per day over the next 2 years into the center wells in the Upper Freeport coal seam. The impacts of CO2 injection on the production and composition of the coalbed methane produced in the peripheral and overlying wells will be carefully monitored. Injection will stop when either 20,000 short tons have been injected or the coalbed methane from the peripheral or overlying wells becomes contaminated with CO2.
The field test is incorporating numerous site characterization and monitoring activities to ensure the safety and efficacy of CO2 injection. These activities, which will continue for 2 years after CO2 injection ceases, include:
- Monitoring gas and water produced from active coalbed methane wells and abandoned deep gas wells in the area.
- Monitoring the quality of groundwater and stream water.
- Perfluorocarbon tracer testing.
- Use of surface tilt meters to measure reservoir deflection and track movement of the CO2 plume.
NETL researchers are playing a large role in computational modeling and monitoring for the project. Pre-test injection simulations they conducted in collaboration with West Virginia University and the Zero Emission Research and Technology (ZERT) team, headquartered at Montana State University, will help determine reservoir properties, CO2-injection and methane-production rates, and structural responses of the reservoir. This work will provide data to formulate effective CO2 injection procedures, evaluate the CO2 adsorption capacity of an Appalachian coal seam, and assess the economic feasibility of this potential greenhouse gas mitigation approach.
In July 2007, two observation wells were drilled at the Marshall County site, and core samples were collected for laboratory analysis. Information from the core samples, such as pressure, production data, and composition of the produced gases, helped identify the Upper Freeport seam’s capacity for CO2 storage. The core samples also provided information about the coal seam that NETL researchers are now using in simulations of CO2 injection and coalbed methane production.
Monitoring-and-simulation is an iterative process. NETL researchers will collect monitored data—such as the amount, rate, and pressure of the injected CO2—and feed it back into their simulations to help update predictions. This cycle, which could last up to a year, will improve understanding in a short period of time of what is required for the injection process.
Many factors are expected to affect this field test; one of the most important may be coal swelling. When CO2 is stored in a coal seam, the coal can swell. This reduces permeability (ability of CO2 to flow through the coal), which in turn reduces injectivity (ability to receive the CO2). It is believed that horizontal wells will help minimize the negative effects of coal swelling. NETL researchers have also developed a coal-swelling model for use in simulations to help predict this behavior.