Coupled fluid-fracture mechanics in the applied geosciences: mechnical, temperature, and viscosity effects

This project tackles two inter-related themes:

1. The safe operation of unconventional oil reservoirs requires not only extensive knowledge of the tensile fracture mechanics of the mudrock, but also how permeable new fracture networks are to different types of fluid. In addition, elevated pore fluid pressure may have a detrimental effect on the rock mass stability via increased pore fluid pressure. To better understand these issues, this project will apply well-constrained laboratory rock physics tools to link measured permeability of freshly generated fracture networks to the fracture density and geometry across a range of fluids, and with reference to the microseismic response during initial fracture, which itself may be used as a proxy for damage and fracture zone properties.

2. Elevated pore fluid temperatures and viscosities may have a detrimental effect on the rock mass stability via the lowered wetting effect and pore fluid activity. To better understand these issues, this project will apply well-constrained laboratory rock physics tools to link measured permeability of freshly generated fracture networks to the fracture density and geometry across a range of fluids, and with reference to the microseismic response during initial fracture, which itself may be used as a proxy for damage and fracture zone properties. The measured fracture data (density and aperture) will be correlated across a range of fluid viscosities and temperatures: impossible in the typical field scenario. This project will seek to evaluate the induced fractures as a function of the viscosity of the fluid using water and water/glycerine mixtures, and using low viscosity “slick water” often used in the initial stages of hydraulic fracture, but is poorly understood mechanically.

Includes two studentships@55.5k each = £111k income

A unique laboratory setup will mimic the field geometry. Samples of 40mm diameter and 100mm length are encapsulated in a rubber jacket fitted with an 3D array for micro-acoustic sensors and instrumented for axial and radial strain. A central axial borehole will be pressurised within an outer shell of rock to simulate a range of depths to 4km by using high pressure hydraulics. Fracture area and size will be derived from the spatio-temporal data, validated by post-test X-ray Computed Tomography.