Imaging the Underground Coal Gasification Zone with Microgravity Surveys

Abstract

A b s t r a c tThe 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.

Sensing underground coal gasification by ground penetrating radar

“…Interpretation of the anomaly seen on Figs. 10c and 11 was positively verified by gravity survey (Kotyrba et al 2015) and a test borehole B1 drilled within the anomaly area.…”

Some Influences of Underground Coal Gasification on the Environment

“…The thermal-physical parameters of the coal layers were replaced by thermo-physical parameters of ash after gasification of each coal element without taking into account the influence of the oxidizer. The structure of overburden and the thickness of each layer in the model was selected based on the borehole information [60] for the Barbara mine. The thermal-physical parameters (density, heat conductivity and specific heat capacity) were sought in variety of literature sources [71][72][73][74][75].…”

Monitoring the gasification area and its behavior in underground coal gasification by acoustic emission technique instead of temperature measurement

“…Instead of temperature measurement, some techniques have been introduced to monitor the gasification area of UCG. Application of geophysical monitoring techniques has been discussed such as electrical resistance tomography 9 , electrical resistivity method 10 , microgravity survey 11 , and ground penetrating radar 12 , 13 . The estimation of the cavity growth and the velocity of gasification flame by means of a mathematical model has been also described 14 – 17 .…”