Pseudovitrinite: Possible Implications for Gas Saturation in Coals and Surrounding Rocks
Coal Petrography is for many a black science using terms that are for some not only incomprehensible but also in flux. For utilization purposes, the organic component of coal is generally broken down into reactive and non-reactive macerals, often with little further differentiation of the macerals. The main incentive to differentiate further is the recognition that the degree of reactivity in vitrinite macerals and the degree of non-reactivity in inert macerals, both vary.
Coalbed gas desorption in canisters: Consumption of trapped atmospheric oxygen and implications for measured gas quality
Abstract Desorption canisters are routinely employed to quantify coalbed gas contents in coals. If purging with inert gas or water flooding is not used, entrapment of air with ~ 78.08 vol.% nitrogen (N2) in canisters during the loading of coal results in contamination by air and subsequent overestimates of N2 in desorbed coalbed gas. Pure coalbed gas does not contain any elemental oxygen (O2), whereas air contamination originally includes ~ 20.95 vol.% O2 and has a N2/O2 volume ratio of ~ 3.73. A correction for atmospheric N2 is often attempted by quantifying O2 in headspace gas and then proportionally subtracting atmospheric N2. However, this study shows that O2 is not a conservative proxy for air contamination in desorption canisters. Time-series of gas chromatographic (GC) compositional data from several desorption experiments using high volatile bituminous coals from the Illinois Basin and a New Zealand subbituminous coal document that atmospheric O2 was rapidly consumed, especially during the first 24 h. After about 2 weeks of desorption, the concentration of O2 declined to near or below GC detection limits. Irreversible loss of O2 in desorption canisters is caused by biological, chemical, and physical mechanisms. The use of O2 as a proxy for air contamination is justified only immediately after loading of desorption canisters, but such rapid measurements preclude meaningful assessment of coalbed gas concentrations. With increasing time and progressive loss of O2, the use of O2 content as a proxy for atmospheric N2 results in overestimates of N2 in desorbed coalbed gas. The indicated errors for nitrogen often range in hundreds of %. Such large analytical errors have a profound influence on market choices for CBM gas. An erroneously calculated N2 content in CBM would not meet specifications for most pipeline-quality gas.
Numerical Simulation for Natural State of Two-Phase Liquid Dominated Geothermal Reservoir with Steam Cap Underlying Brine Reservoir
Hydrothermal reservoir which liquid-dominated hydrothermal reservoir is a type of geothermal reservoir that most widely used for power plant. The exploitation of mass and heat from the geothermal fluid will decrease the pressure in the reservoir over time. Therefore the pressure drop in the reservoir will have an impact on the formation of boiling zones or boiling will increase. The impacts are an increase in the fraction of steam, dryness, in the reservoir and with good vertical permeability will form a steam cap underlying the brine reservoir. The two- phase liquid dominated reservoir is sensitive to the porosity and difficult to assign average properties of the entire reservoir when there is boiling zone in some area of the reservoir. These paper showed successful development of two-phase liquid dominated geothermal reservoir and discussed the formation of steam cap above brine reservoir through numerical simulation for state natural conditions. The natural state modeling in steam cap shows a match with the conceptual model of the vapor-dominated developed. These paper also proofed the presence of transition zone, boiling zone, between steam cap and brine reservoir.