High Speed In-seam Drilling System for Effective Gas Drainage

A continuous feed, high speed drilling system for underground gas drainage promises to transform productivity of underground coal gas drainage drilling. CRCMining has been developing continuous waterjet drilling technology for over two decades. Recent commercialization of the surface to inseam variant, TRD, has demonstrated the commercial reliability and performance of the tools for the surface to inseam application. This project aimed to address the remaining technical risks associated with Underground In-seam deployment for cross panel drainage. The UIS application is referred to as High Speed Cross Panel Drilling.

Since the last High Speed Cross Panel drilling project (completed 2005), wherein the drilling results were poor due to immature drill head technology, water jet drill head design breakthroughs have resulted in a boost to drilling performance and drilling tool reliability, with up to 300m+ long laterals drilled during the surface-based Tight Radius Drilling (TRD) trials at Broadmeadow Mine in 2010. In 2013, TRD was applied at BMC's South Walker Creek mine in a 5 well stimulation commercial pilot, proving that water jet drilling can be applied economically. Continuous drilling rates of between 2 and 4m/min were regularly demonstrated during this operation. With a peak productivity of 535m total laterals drilled in just 6 hours, the vision for a 1000m per shift drilling technology has been set as a reasonable target. The recent outstanding success of the TRD application has led to greater confidence in the waterjet drilling technology. This confidence boost has resulted in the waterjet technology being identified for possible use in a wider range of applications, for both the open cut and underground sectors.

The proposed works were divided into two phases. A first Risk Mitigation Phase comprises a laboratory based investigation of the four key outstanding technical risks. This was followed by a field deployment phase. As proposed the first Phase risk mitigation tasks were:

1. Long lateral drilling

· Assess options for improving drilling range. These relate primarily to net system thrust, friction effects and dynamic pressure effects in the borehole.

· Investigate the use of hose injectors, agitation & vibration effects on hose friction.

2. Steering control improvement

· Assess feasibility to optimize steering orientation through hose twisting.

· Add a collapsible centralizer to the TRD tool body to maintain better trajectory.

· Investigate the steering bias consistency

3. Survey accuracy assessment

· Develop tool calibration process, equipment and procedures for field assessment & optimization of survey accuracy.

· Investigate cutting edge technologies which may be best applied to continuous survey whilst drilling in a relatively high vibration environment.

4. Borehole quality optimization for operation in all coal types

· Investigate the feasibility of consistent borehole quality (straightness, diameter etc) in variable borehole conditions.

The second phase included preparation for and deployment to a field trial in a portal entry mine, Peabody Wambo Mine.  

This report details the outcomes of these investigations. Upon the instructions of the industry monitors, the field trial was cancelled after it became apparent the host mine selected site was unsuitable due to a range of operational and geological constraints.