Analysis of Nitrogen Stimulation Technique in Shallow Coalbed-Methane Formations
- Antonin Settari (Taurus Reservoir Solutions) | Robert C. Bachman (Taurus Reservoir Solutions) | Paul Bothwell (Energy Resources Conservation Board of Alberta)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- May 2012
- Document Type
- Journal Paper
- 185 - 194
- 2012. Society of Petroleum Engineers
- 5.8.3 Coal Seam Gas, 4.8 Facilities and Construction Project Management, 5.3.4 Integration of geomechanics in models, 5.6.3 Pressure Transient Testing
- Facilities and Construction Project Management
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- 1,101 since 2007
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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.
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