MODERN EXPLORATION METHODS AS KEY TO FIGHTING OF UNCONTROLLED COAL FIRES IN CHINA

Uncontrolled coal fires are occurring at about 750 localities in the People’s Republic of China. Approximately 20 million Mt of coal reserves are directly burned annually, moreover, more than 100 Mt pa are lost as mineable reserves due to mechanical and thermal destruction. Emissions from the smoldering fires are polluting the soil, groundwater and the atmosphere. Protection of the environment and of natural resources are the reasons for the Chinese Government to aim for the control over these fires.

In order to extinguish fires an accurate knowledge of the locations of the hot spots is required. In test areas in Xinjiang and Inner Mongolia, conventional and modern exploration methods were successfully combined. During a first phase, the terrain and the thermal anomalies at the surface are surveyed by GPS and thermal mapping by means of an IR-camera is performed. Thereafter, a detailed, small-scale geological mapping and sampling campaign provides the basis for the elaboration of a structural model of the deposit. Based on these surveys, a first clue of the hot spots can be obtained in order to allow the planning of the second phase. This phase concentrates on geophysical surveys of selected areas. The thermal de-magnetization of rocks can be surveyed by a geo-magnetic investigation. Geo-electrical surveys are based on the observation that the resistivity increases in burned rocks. Seismo-acoustic surveys are aiming to “listen” to the fires. The coal seams on fire are expected to break apart as well as the surrounding rock. This cracking can be regarded as micro tremors. Hence, a set of geophones allows the detection of the source of a tremor. Moreover, airflow measurements and gas analyses are completing the exploration campaign. The correlation of all results and the integration into a combined model allows to determine the location and depth of the fire zone. Even the direction and rate of the prograding fire can be interpreted. In order to validate the exploration results it is recommended to drill a few directed holes and to survey the temperature gradients down-hole.