Rock Fractures and Fluid Flow
Main research fields
Knowing the mechanical properties of potential reservoir rocks is vital in understanding how fracture networks may develop in reservoirs containing hydrocarbon, magmatic or geothermal fluids. Through our collaboration with University College London (UCL) we have been able to measure many of these properties and apply the findings to areas ranging from understanding how cooling can influence cracking in thermally stressed volcanic rocks, to understanding how anisotropy may affect fracture propagation in unconventional hydrocarbon reservoirs.
Properties that are commonly measured by the group members at the rock-physics laboratories include:
- Dynamic and Static Young’s modulus
- Poisson’s ratio
- Unconfined Compressive Strength (UCS)
- Tensile strength
- Fracture toughness
It is well known that in layered media fracture propagation paths, such as deflection and arrest, are strongly affected by the contrast in mechanical properties between layers, and in particular the contrast in Young’s modulus. Being able to measure these properties in the lab and then use them in our numerical models improves our confidence in the results and interpretations gathered from the models. The group is also working in collaboration with the rock-physics group at the University of Portsmouth in order to understand how the fracture toughness of rocks alters at depth.
UCS test using uniaxial press. Here the axial and circumferential strain is measured in order to calculate the static Young’s modulus and Poisson’s ratio of the material, in this case limestone.
First arrival of a P-wave passed through a sample of material, in this case shale. The first arrival time is used to calculate the P-wave velocity of the material, which is useful in calculating the anisotropy, and the dynamic Young’s modulus.
Limestone and shale alternations at Nash Point, South Wales (A4 card for scale). The two materials are known to have contrasting mechanical and elastic properties, including Young’s modulus. The more competent limestone has a higher fracture density than the more compliant shale. In addition the fractures in the shale often deflect within a bed or even become arrested, whereas the fractures in the limestone are usually more continuous and straight.