"Hanna IV, the fourth in a series of underground coal gasification experiments fielded and conducted by the Laramie Energy Technology Center, was originally designed as a three-well linear module. A major process objective was to confirm the ability to relay the reverse combustion linking and forward gasification techniques from one pair of process wells to another. Operational difficulties between the first pair of process wells forced an extended interruption of the experiment and precluded the relaying of the process as originally conceived. The initial phase of Hanna IV is referred to as Hanna Iva; the continuation of the experiment is referred to as Hanna IVb. Gasification of Hanna Iva was terminated in June 1978. An evaluation was made of the well completions and of the coal seam conditions on Hanna IVb. After the decision was made to continue the experiment, two new process wells and six new instrument wells were drilled into Hanna IVb. Open-hole logging in the instrument wells indicated three major permeable zones exist within the coal seam; one low, and two high in the seam. The major flow pathway across the original Hanna IV well pattern was determined to be through the overlying aquifer, a permeable zone approximately 80 feet (24 m) above the coal seam. This situation was caused by poor well completions. After well 3 was recompleted by a perforation and cement squeeze above the coal seam and a double casing in the coal seam, the surface piping system was reinstalled and Hanna IVb was started."