Economic sensitivity study of UCG based on field performance, theory, and operational experience

This paper provides the results of an economic analysis in which uncertainty has been minimized through the use of the following three types of information: (1) theoretical and experimental correlations of underground coal gasification (UCG) operating parameters; (2) detailed process design based on operational experience; and (3) sensitivity variables. Independent variables cannot be fixed with certainty - for example, gas heating values are known for short-term field tests but remain uncertain for a long-term commercial operation. Such variables are designated sensitivity variables and are over their entire probable range. Other sensitivity variables are percent gas loss, well spacing, and the volumetric combustion sweep efficiency (VCSE). Depth and thickness of the coal seam are also designated sensitivity variables because they are strictly site-specific. A total of 1,296 cases have been considered in order to cover a full range of all sensitivity variables. Only-dirty gas selling prices are calculated in order to avoid assumptions concerning unproven methods of gas cleanup. Results show that the seam depth/thickness ratio is the most important variable affecting the economics of UCG. Low BTU gas from a thick coal seam of moderate depth (30 ft. seam at 600 ft.) can compete with current natural gas prices on a BTU basis even under poor operating conditions such as high leakage and low heating value. Well spacing and gas heating value also have notable impacts on the economics of UCG. The gas leakage rate and VCSE affect the economic results to a lesser extent for the range of values considered. Further research is needed in optimum well spacing, methods for control of the gas heating value, gas cleanup and utilization, environmental impact, and subsidence

Bench-scale simulation of quenching and stabilization of MIS retorts

This research was conducted to evaluate in situ retort stabilization methods. The objective of the bench-scale simulations was to evaluate possible post-retorting operating procedures for the optimum cleaning of spent retorts. After simulating conditions of modified in situ (MIS) retorts at the time retorting had ended, procedures to accelerate retort cleanup without using large volumes of water were investigated. Samples from various levels of the retort were used to determine the amount of water-soluble constituents in the spent shale and the rehydration characteristics of the spent shale