Wellsite Canister Gas Desorption
Gas content is the actual volume of gas contained in a rock at the time it is sampled. It is empirically measured and one of the key elements in determining gas-in-place in unconventional reservoirs.
Unconventional gas reservoirs typically have three gas storage mechanisms: compression of gas within rock pores, absorption of gas by mobile hydrocarbons or brine, and adsorption of gas within micropores. These complex gas storage mechanisms are compounded by the fact actual gas content is a function of geological factors which affect the retention of gas within the reservoir. Thus, accurate gas content data often cannot be calculated solely from knowledge of physical rock properties. Instead, it must be directly measured from freshly cut rock samples.
Understanding gas content is critical when attempting to assess gas-in-place volumes for an unconventional coal or shale gas play.
The method for determining the gas content involves collecting the core, placing it in a sealed canister, placing the canister in a water bath at reservoir temperature, and measuring the volume of gas that is released from the canister. Critical early time data allows for the calculation of the volume of gas lost as the sample is brought to the surface. The core sample is then crushed to liberate any remaining gas volume as a part of the crushed gas analysis. Total gas content is determined by the summation of lost gas, measured gas, and residual gas volumes divided by the core sample weight. Gas samples are also collected throughout the degassing process, which are used to identify compositional and isotopic fractionation of gas over the life of the core sample.
Weatherford Laboratories is recognized as the world leader in this technology.
Weatherford Laboratories' experience includes over 1,000 well studies in 30+ basins with 200+ clients over the past 20+ years. We have published more than 100 technical papers about coal bed methane analysis, authored the Gas Research Institute books on gas content and reservoir engineering, and presented hundreds of times to the industry to underscore our "frontier and emerging gas resource expertise".
Gas content is one of the many key elements required to accurately estimate gas-in-place.
Geophysical logs can be calibrated to provide accurate gas-in-place volumes, with substantial quality control and quality assurance, utilizing the following: empirical gas content measurements from freshly cut core, the adsorbed gas storage capacity from adsorption isotherm analysis, the free gas storage capacity from modified Dean Stark analysis, and comprehensive petrography.