Underground » Geology
Inseam directional drilling plays an important role in Australian underground coal mining for coal seam degasification purposes. The path of an inseam borehole is also of interest from an exploration perspective but too often the geological data from inseam boreholes remains ambiguous and of uncertain value. Providing a quantitative means of measuring formation properties through inseam logging is clearly a desirable outcome and will have important implications for improving the confidence of the mine planning process.
This project tested the most suitable available downhole logging systems in a highwall and Medium Radius Surface to Inseam borehole. Sites were provided at Anglo Coal’s German Creek Mine (from a highwall) and at BHPB Illawarra (Surface to Inseam). Significant engineering modifications were necessary to prepare the sensors for logging deployment in Australian conditions. This was particularly so for the Medium Radius Surface to Inseam application.
The benefits of geophysical logging an inseam borehole are self evident and detailed herein. The logging systems demonstrated have identified geological structures (particularly dykes) and provided unequivocal data that confirms the position of the drill hole in relation to seam roof and floor. The unsuitability of current systems for deployment in the range of inseam drilling applications is demonstrated and a conceptual design for the next generation of logging tools is presented. The project has established what can be achieved from geophysical logging of inseam boreholes and identified the inadequacies of current practice. An incremental program of development is required to bring Australian inseam drilling up to oilfield standards at a fraction of the cost of using systems available from the petroleum sector.
This project has also resulted in the development of drill rig performance monitoring systems, in particular the ‘P Logger’ (a means to measure downhole annular pressure) and the Torque / Thrust Sensor (located at the borehole collar). Both these systems have provided excellent results, and at time of writing are being used in active directional drilling projects in Australia. Both tools are in a near-commercial state.
The main objective of this program of work was “to develop prototype instrumentation to collect, analyse and display real-time and post-drilling measurements of important drill and geophysical parameters”. This objective was only partially met. Prototype instrumentation was developed for drill rig performance monitoring and a conceptual design developed for a geophysical logging tool capable of deployment in a range of inseam drilling conditions.
After review of the initial results from field trials, it was clear that funds were insufficient to build a prototype geophysical logging tool with the kind of features desired, and as a result the manufacturing focus shifted to the development of rig performance monitoring systems, supported partially by additional funds obtained from a drilling company. In addition it became clear that further work was required to determine exactly what kind of geophysical logging tool needed to be built to satisfy the requirements of the Australian coal mining industry. It was decided to concentrate on a comprehensive field program for geophysical logging (inseam and surface to inseam), the conceptual design of a new “Super Tool”, and the development of the aforementioned rig performance prototype systems.
A direct result from this project is a conceptual design for a logging tool that is suitable for deployment in the range of Australian inseam drilling conditions encountered. The manufacture of this geophysical logging tool is part of a new and current ACARP Project (C16018, Advanced Logging Systems).