EGU22-3353, updated on 27 Mar 2022
https://doi.org/10.5194/egusphere-egu22-3353
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

A novel method to predict hydraulic fracturing breakdown pressure.

Ben Powlay1, Murat Karakus1, Khalid Amrouch2, and Chris Chester3
Ben Powlay et al.
  • 1University of Adelaide, Civil, Environmental, and Mining Engineering, Adelaide, Australia (benjamin.powlay@adelaide.edu.au)
  • 2University of Adelaide, Australian School of Petroleum and Energy Resources, Adelaide, Australia
  • 3OZ Minerals, Adelaide, Australia

Hydraulic fracturing is increasingly becoming utilized within Underground hard rock mines such as block caves and Sub Level Caves as a way to promote controlled cave propagation, increase resource recovery, and seismic hazard through the manipulation of rock mass properties through fracture surface creation and limiting of stress concentration.
While hydraulic fracturing is not a new application, it is still in its infancy in mining projects such as cave mining. It is used on entirely different scales, under different stress regimes and with varying motives. Therefore, more research needs to be carried out in understanding the fundamentals of fracture growths that can help improve hydraulic fracturing applied in mining projects.  

Predicting breakdown pressure is an important part of the designing of hydraulic fracturing with accurate prediction being the baseline of designing and implementing a successful preconditioning campaign in all industries, but especially so in block cave mining.
The most commonly used breakdown pressure theoretical model is the conventional breakdown model and is based on tensile strength and confining stresses acting upon the borehole. This might be imprecise within hard rock mining environments and increasingly so at depth of higher stresses. 

This work compares indirect tensile strength results and their fracture toughness, from both conventional Brazilian Disc Testing and the recently developed Adelaide University Snapback Indirect Tensile Testing (AUSBIT).
By using lateral strain control to stabilise the brittle material responses, AUSBIT allows for the capture of true post-peak behaviour, i.e. controlled fracture propagation can be achieved.

The captured post-peak behaviour allows practitioners to measure a more reflective tensile strength and fracture toughness from just one testing method, Alongside this are laboratory hydraulic fracture experiements on the same rock unit, which in turn is used to propose a new Hard Rock Breakdown Pressure prediction based on the conventional method which incorporates fracture toughness when checked against the results of the lab fracture experiments, and other lab studies. 

The results of this work factors in a progressive toughness of a rock at depths, and creates a more accurate predictor of breakdown pressure in underground hard rock mines under varying stress conditions.  

How to cite: Powlay, B., Karakus, M., Amrouch, K., and Chester, C.: A novel method to predict hydraulic fracturing breakdown pressure., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3353, https://doi.org/10.5194/egusphere-egu22-3353, 2022.

Comments on the display material

to access the discussion