Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Enhancing Appalachian Coalbed Methane Extraction by Microwave-Induced Fractures
The goal of this research is to determine whether the permeability of coal seams under in situ stress conditions can be enhanced by induced fractures generated by short-time exposure to microwaves. To achieve this, it must be shown that microwaves can cause new cleats (fractures) to form in coal with exposure times on the order of seconds. Once produced, the aperture, petrographic location, length, and surface roughness of the fractures will be quantified and the permeability to methane gas measured. The potential for enhancing the permeability of coalbed methane reservoirs through microwave stimulation will then be assessed.
Pennsylvania State University, State College, PA 16802
Nottingham University, Nottingham, England
Methane can be extracted from coalbeds for use as a fuel, but because it is adsorbed to the coal matrix, release of the gas can be very slow. Residual gas levels may be as great as 32% for high-volatile bituminous coals. To improve the economics of coalbed methane production, the gas release rate must be increased by increasing the permeability of the coal, particularly near the wellbore.
Microwaves are known to induce fractures in coal in the absence of confining stress. This research is an attempt to provide “proof of concept” that fractures can in fact be induced by microwaves in coalbeds under in situ stress conditions, thereby providing a potential mechanism for augmenting permeability in the subsurface. The mechanism under which this occurs is presumed to be through the flashing of the coal’s natural moisture to steam, resulting in high localized stresses. These stresses result in the creation of new cleats and/or the expansion of existing cleats.
A core obtained from an Appalachian bituminous coal seam will be split into two lithographically equivalent half-core slabs and exposed to water vapor in a humidity-controlled atmosphere. The cores will then be scanned using high resolution X-ray computed tomography (CT). Cleat identification and cleat aperture calibration will be carried out by means of optical microscopy and the coal’s permeability to methane will be quantified. One core will be exposed to microwaves and then rescanned and re-evaluated to measure its post-microwave permeability. The other core will undergo the same tests while placed in a microwave-transparent pressure vessel where in situ confining stress representative of the depth of the coal core sample site will be simulated. Comparisons will be made between the original scans and the rescanned cores. Permeability to methane will be contrasted between the exposed and unexposed cores. Additionally, selected cleats from exposed cores will be evaluated for surface roughness on opposing cleat surfaces and compared to the surface roughness of cleats in unexposed cores.
Project deliverables are to include monthly status reports, a final report, a technical presentation and paper at the International Coalbed Methane conference, a technical presentation at the North American Coalbed Methane Forum, and a paper submitted for publication in a peer-reviewed journal.
While it is known that microwaves can induce fractures in coal, it is unknown whether microwaves can induce fractures under in situ stress states in coalbeds. It is also unknown whether these fractures or cleats, once created, can remain open. If this research demonstrates that short bursts of microwaves can indeed enhance permeability in coal under its natural stress state, it will increase the likelihood that microwave technology could be developed to enhance production of methane gas from coalbed methane wells. It could also result in technologies to enhance the degassing of coal seams to improve coal mine safety. If coalbeds are drained of methane prior to mining, the chance for an explosion would be reduced, and the energy needed for mine ventilation would likewise decrease. Coalbed methane emissions from coal mines would also be lessened, reducing their impact on climate change. The research, if successful, could lead to the development of microwave-stimulation technologies that would be applicable to both coalbed methane extraction and the sequestration of carbon dioxide in unminable coal seams.
Work on this project began on November 21st 2008 and as of yet there have not been any major accomplishments to report with this initial summary.
Five tasks are slated to be accomplished in conjunction with the research. The key tasks are summarized below. Work is currently under way on the first two of these tasks.
Complete project management plan. A work breakdown structure and supporting narrative will be developed with the objectives and approach stated for each task and subtask. Schedules, expenditures, milestones, and decision points per task will be included.
Perform technology status assessment. A summary report will be prepared that details the state-of-the-art of the proposed technology as well as the positive and negative aspects of any existing alternatives to the proposed technology.
Prepare and Scan Core. A coal core obtained from the Pittsburgh Coal seam, will be cut into two lithographically equivalent sections and exposed to water vapor in a humidity-controlled atmosphere for two months or until there is no significant change in mass. The core will then be scanned and the permeability to methane gas quantified. Once scanned, the core will be sent to Nottingham University where it will be exposed to short bursts of microwave energy. Part of the core will be removed and polished at Nottingham and then will undergo image analysis. The plane polished section will be examined at Nottingham through optical techniques for the determination of aperture and length of cleats and fractures. The remaining core will be re-scanned in the X-ray CT facility at PSU. A rescanned image of the exposed core will then be compared to the original scan. Permeability to methane in the exposed cores will also be compared to permeability in the unexposed cores. The induced cleats will be mapped in 3D, and for selected cleats, the surface roughness of opposing cleat surfaces will be identified with the optical profiler.
Expose coal to microwaves at in situ stresses. The remaining core that was split from the initial core from CONSOL Energy will undergo the same treatment in the humidity-controlled atmosphere as in the previous task and will be scanned and tested for permeability to methane. At Nottingham University, this core will be exposed to short bursts of microwaves within a constructed microwave-transparent pressure vessel. The core will then be re-scanned in the X-ray facility at PSU and then compared with the original scan. Permeability to methane will be re-evaluated and then compared to the permeability of the unexposed core. The induced cleats will be mapped in 3D, and part of the core will be sent to Nottingham where it will be polished and undergo image analysis and correlation of the induced fracture and lithotype occurrence.
Execute technology transfer. Technology transfer activities will take place throughout the project’s duration and will include at a minimum the presentations and papers listed as deliverables.
Project Start: November 21, 2008
Project End: November 20, 2009
DOE Contribution: $79,409
Performer Contribution: $36,556
RPSEA – Kent Perry (email@example.com or 847-768-0961)
NETL – Virginia Weyland (Virginia.Weyland@netl.doe.gov or 281-494-2517)
Performer Company –Pennsylvania State University- Dr. Jonathan P. Mathews (firstname.lastname@example.org or 814-863-6213)