New Experimental Equipment Recreating Geo-Reservoir Conditions in Large, Fractured, Porous Samples to Investigate Coupled Thermal, Hydraulic and Polyaxial Stress Processes

Abstract Use of the subsurface for energy resources (enhanced geothermal systems, conventional and unconventional hydrocarbons), or for storage of waste (CO2, radioactive), requires the prediction of how fluids and the fractured porous rock mass interact. The GREAT cell (Geo-Reservoir Experimental Analogue Technology) is designed to recreate subsurface conditions in the laboratory to a depth of 3.5 km on 200 mm diameter rock samples containing fracture networks, thereby enabling these predictions to be validated. The cell represents an important new development in experimental technology, uniquely creating a truly polyaxial rotatable stress field, facilitating fluid flow through samples, and employing state of the art fibre optic strain sensing, capable of thousands of detailed measurements per hour. The cell’s mechanical and hydraulic operation is demonstrated by applying multiple continuous orientations of principal stress to a homogeneous benchmark sample, and to a fractured sample with a dipole borehole fluid fracture flow experiment, with backpressure. Sample strain for multiple stress orientations is compared to numerical simulations validating the operation of the cell. Fracture permeability as a function of the direction and magnitude of the stress field is presented. Such experiments were not possible to date using current state of the art geotechnical equipment

An Investigation of Leak-off Test Data for Estimating In-situ Stress Magnitudes: Application to a Basinwide Study in the North Sea

The leak-off test (LOT) procedure has been examined within the theoretical framework pertaining to hydraulic fracturing stress measurements (HFSMs). LOT records have then been compared with the results of HFSMs where both measurements have been made in the same boreholes. From this comparison, we make recommendations on the use of LOT data, and suggest a new method of estimating the minimum horizontal stress magnitude (σh) from LOT pressure/volume plots. In-situ stress magnitudes have been investigated by applying these methods to data from over 1000 LOTs in North Sea boreholes. The results of this investigation imply that tectonic stress increases significantly with depth in some parts of the North Sea. which is consistent with the mapped distribution of borehole breakouts