Wireline formation evaluation tools have been used for over 50 years in conventional formations to acquire formation pressures, permeability, fluid samples and many other reservoir characteristics. These same wireline tools have now been used successfully to characterize coal bed methane (CBM) formations in Alberta, Canada.
Field case studies indicated that conventional pressure transient analysis can be used to interpret CBM wireline formation pressure draw down and build up transients. Downhole optical tools were used during pump out to predict formation fluids in place and determine in situ critical desorption pressures.
This method of formation characterization offers a potentially superior and more complete method of acquiring CBM formation properties than more traditional injection fall off tests. Ambiguities caused by fall off testing can be caused by inflation of coal cleats and fractures, multi-phase permeability and well bore storage.
Formation pressures, permeabilities, in situ critical desorption pressure and formation fluid type are important reservoir properties in CBM plays as in any hydrocarbon bearing formation. Traditional methods of injection fall off data acquisition may be cost effective but difficulties in data quality and interpretation may not justify the initial cost savings.