Fluid Pressure Monitoring in Deep Cement Grouted Boreholes

The installation of pressure transducers in deep boreholes is a key feature of determining the effectiveness of gas drainage and the effect of mining on the groundwater regime. This paper covers the work undertaken to ensure reliability of data obtained from deep formation monitoring boreholes for both coal seam gas and groundwater. Cementing technology has enabled strings of transducers to be installed at greater depths with reliable zonal isolation between close sensing points. However the behaviour of grout at depth can be problematic with the effect of filtration, consolidation, skin and dehydration of the grout rendering the installation only partially effective. A review of cementing grouts and additives was undertaken and mix designs developed, to suit the requirements of deep borehole monitoring. Techniques were developed to mitigate the vicissitudes of grout and ensure both zonal isolation and connectivity of the transducer to the formation. The paper also reviews the automated data acquisition systems used for monitoring installations.