How is natural gas from coal produced?

Drilling and testing an NGC (coalbed methane) well is not significantly different than drilling and testing a conventional natural gas well. The drilling rig, testing and safety equipment, and surface facilities are identical, as are the regulations. Economically producible NGC reservoirs tend to be relatively shallow, so drilling, completing and testing an NGC well generally takes less time than deeper conventional wells. Once completed, a typical well pad measures four metres by four metres for "dry" coals, but can be bigger for wells that require pumping equipment. Because of their unusual storage mechanism and producing pressures that are lower than conventional reservoirs, higher compression may be required to maximize gas desorption and recovery.

As with conventional wells, optimal well density for NGC wells is determined based upon the resource in place and the reservoir flow capacity. In Canada thus far, optimal well densities are expected to range from two to eight wells per section. In comparison, conventional oil and gas fields have well densities from one well per section to as high as 16 per section or more.

Stages of NGC development

1. Screening - Screening, the process of identifying a trend or play, involves studying existing data, land opportunities, infrastructure, commercial environment and market access.

2. Exploration and pilot projects - Because the location of the coal is usually known, NGC exploration mainly involves tests for coal thickness, gas in place and permeability. Coring, testing, and special analyses are also commonly undertaken to evaluate the important NGC properties.

   If the results are favorable, a pilot project, including extensive production tests, is conducted to validate the exploration well results. Pilot projects typically consist of five to nine closely spaced wells drilled to allow for constructive interference and local depressurizing of the coal seams to initiate gas production.

3. Appraisal - Appraisal further delineates the play to determine its lateral extent and the consistency of coals and reservoir properties. This step may include drilling more exploration or pilot wells to provide additional data for determining the best way to develop the play.

4. Completion and production - During this stage, wells are usually drilled through the coal seams and cased with a steel pipe secured by a cement sheath from the bottom of the hole to the surface. This prevents mingling of fresh and saline water and gas migration into aquifers. Target coal seams are accessed by perforating the casing. They are then "stimulated", usually with a hydraulic fracture treatment, to increase permeability and therefore the well's ability to flow gas. If necessary, the coal is depressurized by removing naturally occurring water to allow the NGC to desorb and flow freely to the surface of the well. NGC is collected and compressed at the surface, then shipped via pipeline to markets.

5. Development - In the development stage, two to eight wells are drilled per section, depending on local coal properties and project economics. Careful pre-drill planning and public consultation is required to optimize the location of wells (current and future), pipelines, and surface facilities. Operating pressures are usually lower than those associated with conventional natural gas reservoirs to maximize gas desorption and recovery, resulting in the need for extra compression to attain pipeline standards. Separate water lines and water