Download files
Abstract
Growing global energy demand has prompted the exploitation of non-conventional resources such as Coal Bed Methane (CBM) and
conventional resources such as gas-condensate reservoirs. Exploitation of these resources primarily depends on stimulation by hydraulic
fracturing. Traditional hydraulic fracturing practices, however, are in many ways inadequate in addressing difficulties associated with these
non-conventional and conventional resources. For example, complex in-situ stress distribution, large material property contrasts and unique
production mechanism complicate the implementation of hydraulic fracture treatments in CBM and gas-condensate reservoirs respectively.
An integrated approach to optimise hydraulic fracture treatments in reservoirs under complex conditions is developed in this thesis. The
optimisation methodology integrates a fracture geometry model which predicts fracture geometry for a given set of treatment parameters, a
production model which estimates reservoir productivity after stimulation and an economic model which calculates net present value. A
stochastic optimisation algorithm combining features of evolutionary computations is used to search for the optimum design. Numerical
techniques such as finite element analysis, iterative semi-analytical methods and evolutionary computation are also used.
The following are the major contributions of this thesis:
1. A three-dimensional hydraulic fracture geometry model which accounts for poroelastic effects, in-situ stress and rock material properties,
has been developed to provide a more realistic description of the hydraulic fracture geometry. This served as a tool to visualise hydraulic
fracture propagation for a given in-situ stress distribution, rock material properties and treatment parameters. Furthermore, by accounting
for poroelastic effects, it is possible to identify the causes of exceptionally high treatment pressures.
2. An innovative production model was formulated in this thesis to quantify the well deliverability due to hydraulic fracturing. The
production model has been used for a range of production scenarios for CBM and gas-condensate reservoirs such as: multiple wells at
arbitrary locations and various well types (stimulated and unstimulated wells).
3. The optimisation methodology presented in this work provides a platform for operators to assess risks and gains associated with different
field development scenarios. The added feature of sub-optimal NPV contouring provided flexibility to calibrate the treatment design in
real-time. The strength of the optimisation methodology lies in the flexibility to: (1) impose design constraints, (2) optimise multiple
variables and (3) simulate multiple objectives.