Energy Analysis of Hydraulic Fracturing

A. Golshani
CESRC, Faculty of Engineering and Surveying, University of Southern Queensland, Toowoomba, QLD, Australia
T. Tran-Cong
CESRC, Faculty of Engineering and Surveying, University of Southern Queensland, Toowoomba, QLD, Australia
Keywords: Hydraulic Fracturing, Micromechanics, Numerical Modeling
ABSTRACT: In this paper, numerical simulations of circular boreholes under internal hydraulic pressure are
carried out to investigate the energy transferred to the surrounding rock and the breakdown pressure. The
simulations are conducted by using a micromechanical continuum damage model proposed by Golshani et al.
(2006). The simulation results suggest that the borehole breakdown pressure and the energy transferred to the
surrounding rock are dependent on the mechanical properties of the rock and borehole size. Although the energy
transferred to the surrounding rock increases with increasing borehole size, the borehole breakdown pressure
decreases.
1 Introduction
Stresses are applied inside the boreholes either to produce deformations in order to determine the modulus of the
rock or to induce fractures (Jaeger and Cook, 1969). Hydraulic fracturing is one of the techniques used to
stimulate the production of oil or gas in reservoirs. This technique involves pumping a fluid under pressure into a
borehole. This pressurized fluid introduced into the borehole produces stress concentration in the surrounding
rock causing the development of fractures. Other applications of hydraulic fracturing have been recently found in
geotechnical engineering for ground reinforcement and in environmental engineering for solid waste disposal. In
fact, attention is focused on the prediction of the borehole pressure and is usually the only parameter available to
evaluate the operation (Papanastasiou, 1997). However, the energy transferred to the rock during pressurization
of the borehole can be considered as another parameter for the evaluation of the operation.
Energy can be stored in or released from the rock medium in the vicinity of a borehole subjected to internal
pressure. If the internal energy exceeds the limit that the material can withstand, the energy release will occur to
re-establish the internal energy level within a tolerable limit. Griffith (1920) suggested that a potential relief
mechanism is the micro-cracking. According to his theory the excess of energy is dissipated with the growth of
microcracks during rock failure.
The energy transferred to the surrounding rock associated with the phenomena occurring in the borehole under
breakdown pressure (the energy requirements for rock fracturing) is given by

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