DECIPHERING COALBED METHANE EXPLORATION DATA IN REAL TIME

Collecting coalbed methane (CBM) exploration data in green field areas is always a balance between cost, information and the timeliness of that information. Arguably, the two main functions of an exploration program are to (1) define gas in-place to a sufficient certainty for future resource and reserve certification over a maximised area, and (2) gain enough information on the reservoir to give maximum potential for success in a pilot program. To accomplish these goals, gas volume, quality, and type as well as maximum gas holding capacity and permeability are all usually measured. The more data of this type will help to decrease the uncertainty in achieving the stated goals.

There are, however, additional data types (proximate analysis, vitrinite reflectance, maceral analysis) that can be collected during CBM exploration. The cost of these data analyses are low, quick to obtain and because the amount of data points can be numerous, give useful insight into trends of gas properties. For example, in basin “A” in SE Asia, down hole moisture values from coal seams in eight drill wells indicated there were two rank trends separated geographically. Only the higher rank area desorbed gas, though it was still significantly under-saturated. Combining moisture and vitrinite reflectance data allowed prediction of the depth at which commercially viable levels of gas saturation might occur. The prediction was shown to be valid upon drilling a subsequent well. Similarly, in basin “B”, also in SE Asia, reversals of holding capacity and gas saturation in relation to depth was explained using ash yield results. Samples with very low ash yield had more potential to hold gas than higher rank, deeper samples containing more inorganic material. Finally, in basin “C”, in north Asia, holding capacity varied greatly between samples from stratigraphically equivalent coal beds of the same rank. Maceral analysis indicated that seams with low gas holding potential had high (up to 72%) inertinite whilst seams with low to moderate (16%) inertinite had much higher holding capacities.

There are more examples where relatively inexpensive analyses aid in understanding the CBM system of a basin. Taking the time to analyse and interpret these results will allow more considered exploration and development decisions to be made with little monetary risk.