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Time-dependent mechanical behaviour of shale: implications for self-sealing of fractures and boreholes

Dr Chrysothemis Paraskevopoulou (SEE), Prof Quentin Fisher, Dr Martin Dutko (Rockfield)

Project partner(s): Rockfield Software Limited (CASE)

Contact email: c.paraskevopoulou@leeds.ac.uk

Overview

This project will be of interest to someone looking for a multidisciplinary project involving fieldwork, laboratory analysis and numerical modelling in the broad areas of engineering and engineering geology, petroleum engineering and geomechanical modelling. The research will place the successful candidate in an ideal position to gain future employment in industry or academia.

Scientific background

Shale is the most abundant sedimentary rock and has extremely low permeability (

Aims and objectives

The main aim of the project will be to assess the time-dependent mechanical properties of shale (i.e. creep) as this will ultimately control the ability of shale to re-seal. The objectives include:-

  • Gaining understanding of how shale has affected fluid flow on a range of time-scales (i.e. from production to geological time-scales).
  • Improving understanding of the mechanical properties of a range of shale samples as a function of the stress conditions, pore fluid chemistry and time.
  • Developing constitutive relationships to describe the mechanical and fluid flow behaviour of shale.
  • Assessing the implications of these results for issues such as closure of hydraulic fractures, borehole stability and well bore abandonment.

These objectives will be met with the help of state-of-the art laboratory facilities and numerical modelling software.

Methods

The project will begin by collecting observational evidence from the geological record (e.g. data for the distribution of petroleum and overpressure below deformed shale regarding the controls sealing capacity and data for the distribution of cemented fractures in shale); the latter may involve conducting outcrop studies. The student will be trained how to critically appraise this evidence so that conclusions can be generated regarding how shale controls fluid flow at a range of time-scales. Laboratory experiments will then be conducted on the time-dependent mechanical behaviour of shale. These experiments will be undertaken in the Rock Mechanics/Engineering Geology and Geotechnical (RMEGG):

http://www.see.leeds.ac.uk/business-and-consultation/facilities/engineering-geology-laboratory/

and the Wolfson Multiphase Flow Laboratory at the University of Leeds:

http://www.see.leeds.ac.uk/business-and-consultation/facilities/wolfson-multiphase-flow-laboratory/

Experiments such as nano-indentation may be conducted in the Faculty of Engineering. Samples tested will be characterized using techniques such as scanning electron microscopy. The results from the experiments will then be used to develop a time-dependent constitutive model for shale. This model will then be incorporated into geomechanical modelling software (Elfen) to address key issues such as whether or not fractures in shale will self-seal or whether ductile deformation of shale can be used to improve the efficiency and reduce the costs of well bore abandonment.

PhD Schedule, Outputs and Training

This PhD will commence 1st October 2018 and run for 3.5 years. During this period the student will be eligible for all the postgraduate training typically provided to students attending the University as part of the SPHERES Doctoral Training Programme. The student will receive a thorough training in the critical appraisal of subsurface data, experimental rock mechanics and finite-element based numerical modelling. The latter will be gained via extended visits to our case partner, Rockfield Software Limited, who are the developers of ELFEN, a state-of-the-art finite-element modelling package that already has advanced modelling capabilities for anisotropic elasto-plastic materials such as shale. This multi-disciplinary training will pace the successful student in an ideal position to work in a range of industries or take up an academic appointment.

Figure 1. The project provides the opportunity for the student to integrate results from fieldwork, laboratory analysis and numerical modelling.

Related undergraduate subjects:

  • Civil engineering
  • Engineering
  • Geological science
  • Geology
  • Geoscience