Imaging the Underground Coal Gasification Zone with Microgravity Surveys

Andrzej Kotyrba,Krzysztof Stańczyk,Łukasz Kortas

doi:10.1515/acgeo-2015-0002

Abstract

The paper describes results of microgravity measurements made on the surface over an underground geo reactor where experimental coal gasification was performed in a shallow seam of coal. The aim of the research was to determine whether, and to what extent, the microgravity method can be used to detect and image a coal gasification zone, especially caverns where the coal was burnt out. In theory, the effects of coal gasification process create caverns and cracks, e.g., zones of altered bulk density. Before the measurements, theoretical density models of completely and partially gasified coal were analysed. Results of the calculations of gravity field response showed that in both cases on the surface over the gasification zone there should be local gravimetric anomalies. Over the geo reactor, two series of gravimetric measurements prior to and after gasification were conducted. Comparison of the results of two measurement series revealed the presence of gravimetric anomalies that could be related to the cavern formation process. Data from these measurements were used to verify theoretical models. After the experiment, a small cavern was detected at the depth of the coal seam by the test borehole drilled in one of the anomalous areas.

Highlights

Underground coal gasification (UCG) is a process of converting a solid body into an energy fuel in gas form, which occurs in a seam (Gregg and Edgar 1978, Burton et al 2005, Shafirovich and Varma 2009)
Results of the conducted tests confirm the initial assumptions that the microgravity method can be used for imaging and controlling the development of coal gasification process in a shallow seam
In the case described in the paper, the gasification experiment lasted too short to cover a bigger volume of coal

Summary

Introduction

Underground coal gasification (UCG) is a process of converting a solid body into an energy fuel in gas form, which occurs in a seam (Gregg and Edgar 1978, Burton et al 2005, Shafirovich and Varma 2009). The transformation may be complete and a cavern formation is observed in the area where the coal had been gasified. It may be a partial process, and a zone of structurally and chemically transformed coal together with solid products such as char and ash remains in the coal seam. Among 123 references to this paper only one provides brief information concerning practical application of ground penetrating radar for imaging and monitoring the UCG process (StaĔczyk et al 2010)

Objectives

Results

Conclusion