CONSOL Energy Inc. (CONSOL) is demonstrating a horizontal drilling and production process that reduces potential methane emissions from coal mining, produces usable methane (natural gas), and creates a geologic storage option for carbon dioxide (CO2) in unmineable coal seams. The CONSOL project has employed horizontal drilling to drain coalbed methane (CBM) from a mineable coal seam and an underlying unmineable coal seam. After drainage of 50-60 percent of the CBM, two of the wells are being used for CO2 injection (Figure 1) to stimulate additional methane production and store the CO2 in the unmineable seam. The technique starts with drilling a vertical well from the surface followed by a guided borehole that extends up to 3,000 feet horizontally in the coal seam, allowing for production over a large area from relatively few surface locations.
The project involves development of two stacked coal seams in a 200-acre area (Figure 2). The lower, unmineable seam was initially degassed and is now being injected with CO2 to increase both storage and methane production in nearby production wells. The upper, mineable seam was degassed to produce coalbed methane, thus avoiding methane emissions when the seam is mined. The upper, mineable seam is isolated from the lower, unmineable seam to prevent CO2 migration from the unmineable seam into the mineable seam.
The overall goal of the Department of Energy’s (DOE) Carbon Storage Program is to develop and advance technologies that will significantly improve the effectiveness of geologic carbon storage, reduce the cost of implementation, and prepare for widespread commercial deployment between 2020 and 2030. Research conducted to develop these technologies will ensure safe and permanent storage of carbon dioxide (CO2) to reduce greenhouse gas (GHG) emissions without adversely affecting energy use or hindering economic growth.
Geologic carbon storage involves the injection of CO2 into underground formations that have the ability to securely contain the CO2 permanently. Technologies being developed for geologic carbon storage are focused on five storage types: oil and gas reservoirs, saline formations, unmineable coal seams, basalts, and organic-rich shales. Technologies being developed will work towards meeting carbon storage programmatic goals of (1) estimating CO2 storage capacity +/- 30 percent in geologic formations; (2)ensuring 99 percent storage permanence; (3) improving efficiency of storage operations;and (4) developing Best Practices Manuals. These technologies will lead to future CO2 management for coal-based electric power generating facilities and other industrial CO2 emitters by enabling the storage and utilization of CO2 in all storage types.
The DOE Carbon Storage Program encompasses five Technology Areas: (1) Geologic Storage and Simulation and Risk Assessment (GSRA), (2) Monitoring, Verification, Accounting (MVA) and Assessment, (3) CO2 Use and Re-Use, (4) Regional Carbon Sequestration Partnerships (RCSP), and (5) Focus Area for Sequestration Science. The first three Technology Areas comprise the Core Research and Development (R&D) that includes studies ranging from applied laboratory to pilot-scale research focused on developing new technologies and systems for GHG mitigation through carbon storage. This project is part of the Core R&D GSRA Technology Area and works to develop technologies and simulation tools to ensure secure geologic storage of CO2. It is critical that these technologies are available to aid in characterizing geologic formations before CO2-injection takes place in order to predict the CO2 storage resource and develop CO2 injection techniques that achieve optimal use of the pore space in the reservoir and avoid fracturing the confining zone (caprock). The program’s R&D strategy includes adapting and applying existing technologies that can be utilized in the next five years, while concurrently developing innovative and advanced technologies that will be deployed in the decade beyond. This project demonstrates a novel drilling and production process that will help control and produce coal methane while creating potential geologic storage for CO2.
This project will provide a documented case study of the effectiveness and economics of geologic storage of carbon dioxide in an unmineable coal seam. It will demonstrate that methane can be degassed from, and CO2 can be successfully stored in, coal seams with the added benefit of increased CBM production. This helps NETL’s Carbon Storage program meet the goal of estimating storage potential in coals seam formations within +/- 30 percent, developing and validating technologies that demonstrate 99 percent storage permanence, and providing insight on improving reservoir storage efficiency while ensuring containment effectiveness. This project is the first effort to investigate the effects of injecting CO2 into coal seams and recovering CBM and has greatly increased the understanding of the potential for using coal seams for CO2 storage, and has also provided insight on how CO2 interacts with coal and CBM production. Additionally, the results can be used by mining and power generation companies that wish to store CO2 in unmineable coal seams, and also by regulatory agencies and the public to aid in policy and permitting decisions.
The project goals include performing the first-ever geologic storage of CO2 and simultaneous enhanced CBM (ECBM) production using horizontal drilling technology in an unmineable coal seam in the Northern Appalachian Basin and evaluating the effectiveness and conceptual economics of a commercial-scale project. Specific objectives include:
- Demonstrate the use of horizontal drilling technology for CBM production from two relatively thin, undulating coal seams.
Demonstrate, after using the horizontal wells to partially degasify the coal seam, that CO2 can be injected into the unmineable seam for storage and for simultaneous enhanced CBM production.
Demonstrate that CO2 remains in the coal seam in which it was injected by monitoring the behavior of the injected CO2.
Demonstrate the application of coal seam methane production technology using horizontal drilling to degasify an unmineable coal seam.
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