SPE Reservoir Evaluation & Engineering
Volume 14, Number 1, February 2011, pp. 60-75

SPE-131791-PA

Coalbed Methane: Current Field-Based Evaluation Methods

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DOI  More information 10.2118/131791-PA http://dx.doi.org/10.2118/131791-PA

Citation

  • Clarkson, C.R. and Bustin, R.M. 2011. Coalbed Methane: Current Field-Based Evaluation Methods. SPE Res Eval & Eng 14 (1): 60-75. SPE-131791-PA. doi: 10.2118/131791-PA.

Discipline Categories

  • 6.6.2 Core Analysis
  • 6.6.3 Pressure Transient Testing
  • 6.9.1 Coalbed Methane (CBM)
  • 6.10.2 Naturally-Fractured Reservoirs
  • 6.11.1 CO2 Sequestration

Keywords

  • Coalbed methane, Gas content, Relative permeability, Absolute permeability

Summary

Coalbed methane (CBM) produced from subsurface coal deposits has been produced commercially for more than 30 years in North America, and relatively recently in Australia, China, and India. Historical challenges to predicting CBM-well performance and long-term production have included accurate estimation of gas in place (including quantification of in-situ sorbed gas storage); estimation of initial fluid saturations (in saturated reservoirs) and mobile water in place; estimation of the degree of undersaturation (undersaturated coals produce mainly water above desorption pressure); estimation of initial absolute permeability (system); selection of appropriate relative permeability curves; estimation of absolute-permeability changes as a function of depletion; prediction of produced-gas composition changes as a function of depletion; accounting for multilayer behavior; and accurate prediction of cavity or hydraulic-fracture properties. These challenges have primarily been a result of the unique reservoir properties of CBM. Much progress has been made in the past decade to evaluate fundamental properties of coal reservoirs, but obtaining accurate estimates of some basic reservoir and geomechanical properties remains challenging.

The purpose of the current work is to review the state of the art in field-based techniques for CBM reservoir-property and stimulation-efficiency evaluation. Advances in production and pressure-transient analysis, gas-content determination, and material-balance methods made in the past 2 decades will be summarized. The impact of these new methods on the evaluation of key reservoir properties, such as absolute/relative permeability and gas content/gas in place, as well as completion/stimulation properties will be discussed. Recommendations on key surveillance data to assist with field-based evaluation of CBM, along with insight into practical usage of these data, will be provided.

© 2011. Society of Petroleum Engineers

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History

  • Original manuscript received: 16 February 2010
  • Meeting paper published: 23 February 2010
  • Revised manuscript received: 4 October 2010
  • Manuscript approved: 11 October 2010
  • Published online: 7 February 2011
  • Version of record: 21 February 2011