19 - Advanced measurements and monitoring techniques

Abstract

Measurement and monitoring techniques for both underground coal gasification (UCG) and underground coal fires have several commonalities. In this chapter, we will present several of these techniques that were initially developed for UCG but have subsequently found applications also in the detection of underground combustion pertaining to coal fires. While there is strong commonality between both phenomena, their fundamental nature is different: UCG is a controlled reaction with targeted outcomes while an underground (or subsurface) coal fire is usually an uncontrolled reaction where we would like to contain or put-out the reaction as much as possible. The presence of an underground coal fire is usually felt through changes in the ambient air quality (foul smells), smoke, or heat emanating from the ground. Typically, these symptoms only manifest themselves long after the fire has persisted and spread over a wide area. In extreme cases, the detection becomes a relatively moot point as smoke emanating from the ground or subsidence of the soil makes it evident that there is an underground coal fire. UCG reaction fronts and their behavior are harder to detect as they are typically deep underground and are not likely to have such visual indicators. Therefore, it is rather challenging to detect them and requires tools and diagnostics beyond the human sensory perception.