Instrumentation Results from an In-Situ Coal Gasification Experiment
Authors: Bartel L.C. , Beckham L.W. , Reed R.P. 
Published: December 2007

Abstract
Electrical resistivity and passive acoustic techniques have been used to remotely monitor the location of the reaction zone in an in situ coal gasification experiment conducted near Hanna, Wyoming. Thermal measurements were made to provide diagnostic information, to aid in provide diagnostic information, to aid in understanding the process, and to evaluate the effectiveness of the remote techniques. From a comparison of field resistivity data and model calculations the path of the reaction zone was determined. Source locations in the overburden for acoustical events during gasified area. The feasibility of these remote techniques to monitor in situ coal gasification has been demonstrated.

Introduction
The Laramie Energy Research Center (LERC) conducted an underground coal gasification (UCG) experiment at a site near Hanna, Wyoming from March 1973 to March 1974. This experiment, Hanna I, demonstrated that western coals were suited to underground gasification and that it was possible with only air injection to produce 125 Btu/scf gas for an extended period of time. Sandia Laboratories participated during this experiment and demonstrated that resistivity, acoustic, and temperature measurements could detect effects associated with the process. Phase 1 of a Hanna II experiment was conducted Phase 1 of a Hanna II experiment was conducted May through August, 1975. This phase was designed to determine in situ permeability, to examine pneumatic and combustion linking of wells and to conduct a brief gasification test. Phases 2 and 3, the linkage and gasification Phases 2 and 3, the linkage and gasification between a pair of wells and evaluation of a linedrive concept for areal recovery were conducted from April through July, 1976.
These experiments have been based on the linked vertical well concept. In this concept communication between the injection and production (recovery) wells through the coal seam production (recovery) wells through the coal seam is accomplished by thermal linking. In this method the coal is ignited at the production well, while air is supplied at the injection well. The combusion front follows natural fissures toward the source of oxygen and develops a localized permeable path of hot, carbonized coal. When the permeable path of hot, carbonized coal. When the combusion front reaches the injection well there is an abrupt drop in injection pressure to less 50 psi with a significant increase in the flow rate. psi with a significant increase in the flow rate. Once linkage is established combusion mode in which the combusion front moves in the direction of air flow along the permeable link.
LERC is now conducting a second UCG experiment which has been designated as Hanna II. Sandia Laboratories' participation in the Hanna II series of experiments is to develop and evaluate instrumentation techniques that will provide subsurface diagnostic information as an aid toward understanding the retorting process and to study commercially practical techniques to observe the subsurface burn with remote monitoring.