POWDER RIVER BASIN COAL BED METHANE

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POWDER RIVER BASINCOAL BED METHANE

• COAL VOLUME AND
• GAS IN PLACE ESTIMATES
• ANDREW K FINLEY, JIMMY E GOOLSBY
• GOOLSBY ASSOCIATES, LLC
• January 12, 2001

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POWDER RIVER BASINCOAL BED METHANE

• INTRODUCTION
• METHODOLOGY USED FOR DETERMINING COAL VOLUME
• GAS IN PLACE ESTIMATES
• SUMMARY
• ACKNOWLEDGMENTS

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INTRODUCTION

• Background
• Project was sponsored by the Wyoming State
  Geological Survey and by the Wyoming Oil and Gas
  Conservation Commission
• Previously published estimates predicted
  approximately 12 TCF recoverable gas from the PRB
  CBM play
• This study predicts approximately 25 TCF
  recoverable gas from the PRB CBM play using
  currently accepted limits

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METHODOLOGY USED FOR DETERMINING COAL VOLUME
ESTIMATES

• Study area covers 4 million acres in Campbell,
  Johnson and Sheridan Counties, Wyoming

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METHODOLOGY

• Mapped thickness of coal from seams greater than
  20 feet thick and greater than 200 feet deep
• Mapped thickness by depth using intervals from
  200-500, 500-1,000, 1,000-1,500 and deeper
  than 1,500
• Gridded and contoured data with Geographix using
  a minimum curvature algorithm and a grid spacing
  of 1,500 feet yielding the ability to map
  features as small as 13 acres
• Calculated coal volume from these gridded isopach
  maps using Geographix

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METHODOLOGY

• Data from 8,500 conventional oil and gas wells,
  coal bed methane wells and USGS strat tests
• Removed suspect or non-useable data leaving 6,500
  data points with coal information
• 1,900 data points from the entire coal section

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METHODOLOGY
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METHODOLOGYDATA BIAS

• Calculating coal thickness from data over the
  entire coal section (1,900 data points) results
  in a conservative coal volume estimate because
  this data set misses large area of thick coals

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METHODOLOGYDATA BIAS

• Calculating coal thickness from data over
  portions of the coal section (6,500 data points)
  also results in a conservative coal volume
  estimate because this data set is incomplete

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METHODOLOGY

• Conclusion
• Although both data sets result in conservative
  estimates, the 6,500 point data set results in a
  more accurate coal volume by depth
• Coal volume by depth is necessary in order to
  apply more accurate gas contents because gas
  content generally increases with depth

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METHODOLOGY

• Calculated coal volume by depth (in order to
  apply meaningful gas contents)
• Calculated total coal volume from seams thicker
  than 20 feet and deeper than 200 feet
• Calculated total coal volume without thickness or
  depth constraints

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COAL VOLUME AND TONNAGE
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CONCLUSIONS

• Both data sets used to calculate coal volume
  result in conservative estimates
• Coal volume by depth is necessary to apply
  reasonable gas contents
• Data bias appears to be more severe when
  calculating coal volume by depth
• Although conservative, Total coal gt 20 thick
  yields the most reasonable coal volume estimate

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GAS CONTENT METHODOLOGY

• Obtained all non-proprietary Powder River Basin
  coal gas content data from the BLM in Casper
• Results of this data are suspect and appear to
  underestimate gas content in areas currently
  producing coal bed methane
• Published isotherm data from adsorption studies
  appear to overestimate gas content in areas
  currently producing coal bed methane

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GAS CONTENT METHODOLOGY

• Estimated gas content versus depth using current
  production to constrain gas content values
• Verified gas content by depth estimates with
  various operators who have proprietary gas
  content data from a wide depth range
• Gas content estimates used in our study appear to
  be reasonable but slightly conservative

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GAS IN PLACE ESTIMATE
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CONCLUSIONS

• Approximately 37.5 TCFGIP from coals thicker than
  20 feet and deeper than 200 feet
• Currently accepted recovery factors range from
  50 to 90
• Assuming a recovery factor of 67, the Powder
  River Basin Coal Bed Methane play holds on the
  order of 25 TCF recoverable gas
• We believe these estimates are reasonable
  although they may be somewhat conservative

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ACKNOWLEDGMENTS

• Lance Cook, Wyoming State Geological Survey
• Don Likwartz, Wyoming Oil and Gas Conservation
  Commission
• Devon Energy Production Company, LP
• Wally Reaves
• Gary Winter, Associated Energy Consultants