2002 ROCKIES COALBED METHANE SYMPOSIUM

Based on a symposium co-sponsored by The Rocky Mountain Association of Geologists (RMAG), PTTC Rocky Mountain Region and the Gas Technology Institute (GTI) held June 19, 2002, Denver, Colorado

BOTTOM LINE

Coal-bearing basins in the United States are in competition for frontier coalbed methane (CBM) resources. Acreage position and knowledge of the best geological and engineering methods for evaluation and developing CBM resources are needed for successful exploitation.

PROBLEM ADDRESSED

CBM plays in the San Juan, Powder River, Raton and Uinta basins are maturing, and lessons learned in these basins are not necessarily applicable for new plays and other basins. The goal of the 2002 CBM Symposium was to explore all the existing and emerging technologies and focus on how to apply them to new CBM plays, such as in British Columbia and eastern Kansas. The number of participating companies, sponsors and exhibitors at the symposium indicate the high interest in CBM exploration and development.

KEY WORDS:

Cleat System, Coalbed Methane (CBM), Diagnostic Fracture Injection Test, Environmental Risks, Sorption/ Desorption, Stimulation

SPEAKERS

Paleofluid Flow Induced Cleat Mineralization in Coal Measure Sequences on the Bowen Basin, Queensland, Australia: Implications for Coalbed Methane Exploration Strategies in Foreland Basins
Basim Faraj, Faraj Consultants Pty LTD, Wynnum, Brisbane, Australia

Isotopic Characterization of Fruitland Formation Waters, San Juan Basin, CO and NM: Implications for Fluid Flow and Hydrocarbon Systems
W. C. Riese, BP America Production Co., G. T. Snyder, University of Rochester, et al

Gas-in-place in the Powder River Basin: Coal Cores - Why do them? Some Field Results, Comparisons, and Suggestions
R. Marc Bustin, The University of British Columbia, Vancouver and Robert A. Downey, Energy Ingenuity Company 

Diagnostic Fracture Injection Test in Coals to Determine Pore Pressure and Permeability
Muthukummarappan Ramurthy, Halliburton; Douglas M. Marjerisson, BP Canada; Scott B. Davis, Markwest Hydrocarbon, Inc. 

Environmental Risk Assessment Methods Useful for Coalbed Methane Development: Cost-Effective Ways to Manage Risk
Anthony W. Gorody, Universal Geoscience Consulting, Inc.; James H. Viellenave, and Frank V. Fontana

Completion Approach for Frontier Coalbed Gas Plays
David G. Hill and Steve Lambert, TICORA Geosciences, Inc.

Coal Depositional Environments
John C. Horne, Orion International Limited

Geotechnical Uncertainty (Risk) in Coalbed Gas Exploration and Development
William B. Hanson, Don J. Duhrkopf, and William L. Pelzmann, BP America Production Company, Houston, TX
Tongue River Coal Multi-seam Completion Approaches, Powder River Basin, Wyoming and Montana
W. Travis Brown, Jr., Geological Consultant, Denver, CO

Williams Raton Basin Project - Completions, Stimulations and Production Overview
Tim Clawson, Williams Company

Overview of the CBM Potential of Some Cretaceous and Tertiary Coal Basins in British Columbia
Barry Ryan, New Ventures Branch, British Columbia Ministry of Energy and Mines, Victoria, British Columbia

Eastern Kansas - Some Considerations for Coalbed Methane
Lawrence L. Brady, Kansas Geological Survey, Lawrence, KS

Tools to Solve Coalbed Methane's Permeability Puzzle
Trent W. Green, Pinnacle Technologies, Denver, CO

TECHNOLOGY OVERVIEW

Paleofluid Flow Induced Cleat Mineralization in Coal Measure Sequences on the Bowen Basin, Queensland, Australia: Implications for Coalbed Methane Exploration Strategies in Foreland Basins
Cleat mineralization is defined as analogs to cement formation in conventional reservoirs. It is critical in control of paleofluid flow during coal development. The Bowen Basin in Queensland, Australia has extensive Late Permian coal deposits, which have been affected by two episodes of mineralization. The 1st episode involved clay cementation along mineral faces and fracture systems, and is responsible for a thick barrier to water circulation between major coal beds. The 2nd episode occurred in the Early Jurassic, creating additional barriers. Regional uplift and erosion in the Cretaceous has created a pattern of mineralization in some coalbeds and lack of mineralization in others. Understanding of the cleat mineralization is important in exploration strategies and has significance to similar basins worldwide.

Isotopic Characterization of Fruitland Formation Waters, San Juan Basin, CO and NM: Implications for Fluid Flow and Hydrocarbon Systems
Isotope studies of the water in the Fruitland Formation have proved significant in interpreting the history and distribution of CBM reserves. Mass spectrometry of iodine isotopes has been used to study the hydrogeologic sequence in the San Juan basin. The center of the San Juan basin has anomalous high and low iodine concentrations. Concentrations can be mapped in NW-SE trends, which correlate with variations in coal isopach maps. Additional studies relate the isotopes to fractures and permeability zones, which can be detected by magnetic and gravity linears. The spatial distribution of isotopic signatures in the Fruitland formation indicates negligible infiltration and recharge of meteoric waters in the north central San Juan basin. Iodine isotopes have proven to be a valuable tool for mapping the migration of water and fractures in the Fruitland.

Gas-in-place in the Powder River Basin: Coal Cores—Why Do Them? Some Field Results, Comparisons, and Suggestions
The thick Wyodak coals of the Fort Union formation have been the primary target for over 12,000 CBM wells in the Powder River basin of Wyoming. Development is now spreading to deeper beds, which do not have free gas and the coals are undersaturated. The sorption capacity of coals is very sensitive to moisture content, and it is important to avoid drying coals since they are difficult to resaturate. Undersaturated coals tend to produce water for greater periods prior to the beginning of coalgas production. Sorption data can be used to predict water saturations, and it correlates with pressure conditions in the coal seams. Because gas content is highly variable in the Fort Union formation, many operators fail to properly characterize the resources, thus losing valuable production. Capital costs can be reduced by coring and analyzing gas content prior to drilling and coalbed development. Knowledge of gas content cannot account for lost gas volumes, but it can prevent completion of coal seams with insignificant amounts of adsorbed gas. Wireline retrievable cores are recommended to minimize lost gas volume errors in collection and analysis. 

Diagnostic Fracture Injection Test in Coals to Determine Pore Pressure and Permeability
Measuring permeability from coal cores is difficult, because it is stress dependent and does not always reflect true reservoir conditions. A diagnostic fracture injection test (DFIT) is a cost-effective, easy test that has been used successfully in the Piceance basin in Utah. The test is of short duration and has three stages: 1) a G-function derivative analysis to identify leakoff mechanism and closure, 2) a calibrated analysis using modified Mayerhofer method to determine permeability before closure, and an 3) after-closure analysis to determine pore pressure and permeability. The technique is an outgrowth of pressure-transient testing and interference testing used in coals. It applies specifically to sorption data. The method depends on the identification of closure in induced hydraulic fractures. Examples were provided from coalbed methane deposits in Canada and the San Juan Basin of Colorado and New Mexico. In some low-permeability coals, maintaining fracture pressure during pressure injection falloff tests is difficult. DFITs do not suffer from this limitation. 

Environmental Risk Assessment Methods Useful for Coalbed Methane Development: Cost-Effective Ways to Manage Risk
CBM development in U.S. basins has generated an environmental controversy, which threatens every CBM operating company with increased demands for high-cost regulatory compliance. Management of environmental risk assessment from the planning stages though development is necessary to avoid costly litigation. A risk assessment code (RAC) has been developed for use in the San Juan, Black Warrior, Powder River and Raton basins. The 1st stage is to identify the potential risks: What can go wrong, and what are the consequences for each potential action or result? Detailed lists of planning, drilling and development stages of CBM production suggest risk areas in each step. Analysis of each risk is the next stage; including when, where, and how likely each risk is, as well as the consequences. Data are compiled in coded charts and ranked as low risk, medium risk and high risk. Loss of domestic water quality due to CBM activities is a major risk in all U. S. basins and is the most significant cause of controversy from landowners, concerned citizens and environmental groups. Depth and distance from aquifers plays an important part in determining risk to water quality. More than 50% of domestic water wells in CBM producing areas are likely to experience water quality problems. Problems may include increased bacteria growth, increased amounts of fluoride and salt, and, in some cases, dissolved methane in the water. Another risk is methane seeps, which can kill vegetation and damage soils in areas along side of or above coal seams. Establishing natural seepage prior to CBM development is important, and has been a particular problem in the San Juan basin. A reasonable estimate of the cost of environmental compliance per CBM well in the U.S. is $2000 per year. Proper risk assessment can lower this cost significantly.

Completion Approach for Frontier Coalbed Gas Plays
CBM plays being developed today are more heterogeneous, often in deeper or shallower reservoirs and generally more complex than the mature plays in the San Juan and Black Warrior basins. The focus on developing frontier plays has been to understand the local resource and the flow capacity of the coal gas. When analyzing the completion process, it is important to study both the flow capacity of the reservoir and the potential for damage to the flow capacity by drilling and production practices, including hydraulic fracturing stimulation. The best approach to completion focuses on resource evaluation and knowledge of the mechanisms of production. Geologic assessment should identify the zones with the most producible natural gas. Selection of the stimulation fluids (water, foam, water-based gels) becomes more difficult as the complexity of the reservoir increases with more coal seams, contrasts in stresses, and increased vertical separation of coal seams. Understanding the individual reservoir is the key to production success.

Coal Depositional Environments
Characterization of coalbeds is enhanced by knowledge of the depositional environment of the coal. Three-dimensional modeling focuses on thickness and lateral extent of coal beds. The sedimentary environment preceding the formation of the coal swamp affects the topography of the swamp and the thickness of the coals that develop. Post-depositional processes modify coal deposits through channeling, scouring, and washouts. Regional-scale models can be used to predict variations in coal deposits. The post-depositional environments strongly affect coal preservation and quality, specifically sulfur and trace element content. The structural integrity of the roof of coal beds depends upon the sediments deposited over the original peats, including grain size, cementation, bed thickness and burrowing. Tectonic forces are superimposed over depositional and post-depositional influences. 

Geotechnical Uncertainty (Risk) in Coalbed Gas Exploration and Development
Geotechnical risks in coalbed gas development can be characterized as; coal thickness, prospective area, gas content, gas saturation, permeability, permeability continuity, seal and hydrogeology, gas composition and percent recovery. Coalbeds are complex fractured natural gas reservoirs, and water and gas content strongly affect reservoir performance. Most subsurface coals contain some recoverable gas. Saturated coalbeds are the most producible. Definitions for coalbed gas, coalbed methane and conventional gas are used to separate these resources and to better understand all the risk factors. Coalbed gas does not require structural closure to trap and retain gas in the coalbed. Methods for measuring gas content of a reservoir, productive area and thickness are discussed. Effective permeability is an expression of fracture spacing and interconnection. Coal is highly elastic compared to most lithologies and therefore is susceptible to closure of fractures during burial, with permeability ranging up to several hundreds of md. Structural control of permeability is found in examples from the Black Warrior and San Juan basins, and may be negative in highly folded belts causing dewatering of the coals. Analyses of desorption and isotherm data for a basin is necessary to determine if the saturation of the coals is sufficient for production. 

Tongue River Coal Multi-Seam Completion Approaches, Powder River Basin, Wyoming and Montana
Multiple coal seam completions from a single wellbore reduce costs and simplify CBM operations. The multi-seam completion approach also allows thinner coal seams to be developed that would not be economic from single wellbores. The Tongue River coals in the Powder River basin were discussed as examples of multi-seam completion technology. Coal seam depth, individual and aggregate thickness, and completion methodology are the most important considerations in any producing area. 

Williams Raton Basin Project—Completions, Stimulations and Production Overview
Williams's recent acquisition of properties in the Raton Basin prompted them to assess the most effective completion, stimulation and production technologies for the 196 producing wells. Coal seam targets, the Raton and Vermejo formations, are at depths from 500 to 2,500 ft. The coals are discontinuous and relatively thin with partial barriers composed of sand channels. The technique employed is to drill twin wells from the same 160-acre drilling pad to each of the two target coals. Equal spacing and consistent completion techniques have allowed uniform dewatering of the coals. Stimulation with borate-crosslinked gels has increased the pump rate, and the net result is higher and more consistent production from both formations. 

Overview of the CBM Potential of Some Cretaceous and Tertiary Coal Basins in British Columbia
Three distinct types of coals are targeted for CBM development in British Columbia: Jurassic-Cretaceous coals of the northern Rocky Mountains, Cretaceous rocks on Vancouver Island, and coals in fault-bounded Tertiary basins. The CBM potential for the Peace River field in the Rocky Mountain trend is over 60 tcf. Knowledge of the regional fold belt and the local geology is necessary to predict where the coal seams are steeply folded and where there are flat-lying beds. Studies of the adsorption isotherms in the Rocky Mountain coalfields are used to distinguish between low-volatile and medium-volatile bituminous coals. Coalfields on Vancouver Island are characterized by open folds and a gentle regional dip. The coal seams are separated by dipping normal or reverse faults. Although the potential amount of recoverable CBM is less on Vancouver Island, the resource is still economic. The Tertiary coalfields in south-central British Columbia were originally exploited as a source of coal for electrical generation. No data on the CBM potential of these fields is available yet, but coal resources are estimated at over 10 billion tons. Each of these areas will require different CBM production strategies.

Eastern Kansas—Some Considerations for Coalbed Methane
Bituminous coal resources in Pennsylvanian-age formations are widespread in eastern Kansas, and 32 deep coal resources have CBM potential. The Cherokee Group contains the most deep bituminous coal resources, however six stratigraphically higher coal beds also have economic potential for CBM development. For the deep coal resources, it has been determined that a coal bed must be a minimum of 14 inches thick to be economic for CBM production. Significant resources have been identified in the Cherokee (37 billion tons) and Forest City (16 billions tons) basins. Radioactive black shales in Kansas may also have potential for CBM production. Most CBM wells in Kansas produce large volumes of water, which is currently re-injected into Cambrian-Ordovician age Arbuckle Group formations. Based on data from over 600 geophysical wells, the coal resource base for Kansas is estimated at over 50 billion tons, which suggests significant CBM potential. 

Tools to Solve Coalbed Methane’s Permeability Puzzle
Because of high natural gas consumption in North America, unconventional resources, including coalbed methane gas production, will play an increasingly important role in fulfilling demand. Pinnacle Technologies has taken the lead in supplying low-pressure matrix injection testing technology for reliable in-situ reservoir permeability tests. The tests are designed to work in any water-saturated reservoir to help assess CBM as a source of natural gas supply. 

CONNECTIONS:

Abstract Proceedings available through Rocky Mountain Association of Geologists, phone 303-573-8621 or Email RMAGdenver@aol.com for $20.

Lawrence L. Brady
Kansas Geological Survey, Lawrence, KS
Email: lbrady@kgs.ukans.edu

W. Travis Brown, Jr.
Geological Consultant, Denver, CO
Email: travisteg@earthlink.net

R. Marc Bustin
The University of British Columbia, Vancouver, British Columbia, Canada
Email: bustin@unixg.ubc.ca

Tim Clawson
Williams Company
Email: tim.clawson@williams.com

Basim Faraj
Faraj Consultants Pty LTD, Wynnum, Brisbane, Australia
Email: basim_faraj@gticalgary.ca

Anthony W. Gorody
Universal Geoscience Consulting, Inc.
Email: agorody@compuserve.com

William B. Hanson
BP America Production Company, Houston, TX
Email: Hansonwb@bp.com

David G. Hill
TICORA Geosciences, Inc.
Email: dave-hill@qwest.net

John C. Horne
Orion International Limited
Email: johnhorne@orionlimited.com

Muthukummarappan Ramurthy
Halliburton
Email: Kumar.Rathmuthy@halliburton.com

W. C. Riese
BP America Production Co.
Email: rriese1@bp.com

Barry Ryan
British Columbia Ministry of Energy and Mines, Victoria, British Columbia, Canada
Email: Barry.Ryan@gems4.gov.bc.ca

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