SPE Production & Operations
Volume 27, Number 2, May 2012, pp. 185-194

SPE-135683-PA

Analysis of Nitrogen Stimulation Technique in Shallow Coalbed-Methane Formations

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DOI  More information 10.2118/135683-PA http://dx.doi.org/10.2118/135683-PA

Citation

  • Settari, A., Bachman, R.C., and Bothwell, P. 2012. Analysis of Nitrogen Stimulation Technique in Shallow Coalbed-Methane Formations. SPE Prod & Oper 27 (2): 185-194. SPE-135683-PA. http://dx.doi.org/10.2118/135683-PA.

Discipline Categories

  • 4.11 Fundamental Research in Projects, Facilities and Construction

Keywords

  • Facilities and Construction Project Management

Summary

Nitrogen (N2) stimulation has become the preferred technique for stimulation of coal seams in the Horseshoe Canyon play in Alberta. It consists of stimulating each seam by pumping at very high rates for short time (2-4 minutes). Because the coal is producible at shallow depths, the Energy Resource Conservation Board (ERCB) has been developing and updating regulatory guidelines that aim to protect the freshwater supply.

This study was undertaken to improve the understanding of the process and provide recommendations on the regulatory guidelines for shallow depth (less than 200 m). The study was provided with extensive data from the industry (more than 20,000 fractures in more than 2,000 wells) and has carried out several types of analyses to estimate fracture orientation and dimensions and their dependence on N2-injection rate and duration and on reservoir parameters. This included statistical analysis of large amounts of surface pressure data, pressure-transient analysis (PTA) of downhole pressure data, analysis of fracture-mapping data, and conceptual simulations of the injection process using coupled reservoir and geomechanical models. Coupled geomechanical modeling provided a realistic physical model of the process (in comparison with conventional models). Stress dependence of coal permeability and permeability anisotropy were shown to be the controlling mechanisms. This model was then used to investigate height-growth mechanisms.

After considering the results of the analysis, its limitations, uncertainties in geological description of the coal and shale sequences, available case histories, and other factors, recommendations were made for modifications, resulting in the revised ERCB Directive 27, Shallow Fracturing Operations--Restricted Operations, released 14 August 2009.

© 2012. Society of Petroleum Engineers

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History

  • Original manuscript received: 16 September 2010
  • Meeting paper published: 20 September 2010
  • Revised manuscript received: 25 April 2011
  • Manuscript approved: 22 June 2011
  • Published online: 6 February 2012
  • Version of record: 1 May 2012