4.6 Hydraulic Fracturing TreatmentsSCT recognised early on that hydraulic fracturing is useful in placing large fractures into rock masses to change the caving characteristics of the rock strata. In 1999, SCT began developing methods of using hydraulic fracturing at Moonee Colliery that allowed the mine to control the timing and size of caving events that were previously producing significant wind blasts. Fracturing has since been used by four other longwall coal operations in NSW and Queensland.

Hydraulic fractures can be extended to 50 m radius or more from a single borehole, allowing fracturing of a large volume of rock from a few boreholes. The in situ stress exerts a strong effect on hydraulic fracture growth and stress change monitoring and 3D overcore stress measurement play an important part in designing and monitoring hydraulic fractures. Monitoring the growth of hydraulic fracture by measuring temperature change in offset monitoring boreholes has also proven to be very useful in measuring fracture interaction away from the injection borehole.

SCT has often partnered with CSIRO in projects that used hydraulic fracturing for either cave inducement or preconditioning. CSIRO have equipment and specialised models that can be applied to undertaking trial investigations at sites with full scale hydraulic fracturing also supported. However, in some cases the mines wish to purchase equipment and undertake the fracturing work directly. SCT can assist by providing design advice followed by ongoing monitoring and quality assurance advice.

For more information on cave preconditioning and inducement using hydraulic fracturing, please contact Dr Ken Mills or Rob Jeffrey.

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