Costs of Drilling, Completing and Linking Process Wells for Underground Coal Gasification as a Function of Linking Method, Coal Bed Thickness and Depth

摘要

Costs in underground coal gasification for drilling, completing and linking process wells are considered. Both row spacing (sweep width) and column spacing for rectangular arrays of process wells were examined: coal bed thickness and depth were varied; linking methods were estimated which included reverse combustion, directional drilling using the Dyna-drill and a hypothetical tool capable of drilling horizontal channels from a process well (right-angle drill), and shaped-charge assisted reverse combustion. The cost penalty for a linking method which causes override of the coal seam in UCG was estimated to be 0.75 $/10 exp 6 Btu using the Hoe Creek No. 2 gas composition. For reasonable coal thickness and depths, such as 30' thickness and 500' depth, 0.75 $/10 exp 6 Btu is much larger than the differences in linking cost, and reliable but more expensive linking methods may be more cost-effective. However, considering the drilling and linking costs only, reverse combustion appears to be the lower cost linking option at depths less than 500', while at greater depths, the directional drilling methods, in particular the hypothetical right-angle drilling method may offer potential cost advantages. (ERA citation 04:044218)