This datasets contains 323 observations of borehole breakouts across and drilling induced tensile fractures from borehole imaging used to re-characterise the UK stress field orientation in 2016. This was published in the Journal of Marine and Petroleum Geology and is openly available using doi:10.1016/j.marpetgeo.2016.02.012 The observations relate to 39 wells from Central and Northern England and are provided with links to screen grabs of the images for clarity. The basic well meta data is supplied along with a description of the dataset. The Images were generated in the IMAGE DISPLAY module of the Landmark RECALL software. and are supplied on an “as shown” basis. Descriptions of the tools and the techniques used are listed in the accompanying paper: KINGDON, A., FELLGETT, M. W. & WILLIAMS, J. D. O. 2016. Use of borehole imaging to improve understanding of the in-situ stress orientation of Central and Northern England and its implications for unconventional hydrocarbon resources. Marine and Petroleum Geology, 73, 1-20.

This dataset contains the borehole image interpretation of the United Downs 1 borehole, Cornwall (BGSID: 21246966) The acoustic borehole images have been interpreted for faults, breakouts and conductive and resistive fractures. For faults and fractures each line in the file defines a plane passing through the borehole. This includes: • Depth at which the plane intersects the borehole wall, this is defined as the midpoint of the feature as each plane has a top and bottom intersection. • Azimuth, this is the azimuth of the dip direction of the plane, it is at 90 degrees to the strike of the feature. • Dip, this is the dip angle of the plane. • Type, this is a classification of the feature. For breakouts each line represents an individual feature which covers and area of the borehole wall. This includes: • Depth the midpoint depth of the breakout. • Azimuth, this is the orientation of the breakout. • Type, this is a classification of the feature. • Breakout Height, the length of the breakout in meters. • Breakout Width, the width of the breakout in degrees. • Type, this is a classification of the feature. The work was undertaken by BGS as part of the GWatt Project award reference number NE/S004262/1. It was funded by the UKRI Natural Environment Research Council.

A number of processes, both natural and anthropogenic, involve the fracture of rocks subjected to tensile stress, including vein growth and mineralization, and the extraction of hydrocarbons through hydraulic fracturing. In each case, the fundamental material property of mode-I fracture toughness must be overcome in order for a tensile fracture to nucleate and propagate. Whilst measuring this parameter is straightforward at ambient pressure, estimating the fracture toughness of rocks at depth, where they experience a confining pressure, is technically challenging. Here, we report a new analysis combining results from standard thick-walled cylinder burst tests with quantitative acoustic emission to estimate the mode-I fracture toughness (KIc) of Nash Point Shale at elevated confining pressure, simulating in-situ conditions to approximately 1km. In the most favorable orientation, the pressure required to fracture the rock shell (injection pressure, Pinj) increases from 6.1 MPa at 2.2 MPa confining pressure (PC), to 34 MPa at 20 MPa confining pressure. When fractures cross the shale bedding, the required injection pressures are 30.3 MPa (at Pc = 4.5 MPa) and 58 MPa (at Pc = 20 MPa), respectively. Applying the model of Abou-Sayed (1978) to estimate initial flaw size, we calculate that this pressure increase equates to an increase in KIc from 0.6 MPa.m1/2 at 3.2 MPa differential pressure (Pinj - PC) to 4.1 MPa.m1/2 at 22 MPa differential pressure. We conclude that the increasing pressure due to depth in the Earth will have a significant influence on fracture toughness, which is also a function of the inherent anisotropy.

This datasets contains 323 observations of borehole breakouts across and drilling induced tensile fractures from borehole imaging used to re-characterise the UK stress field orientation in 2016. This was published in the Journal of Marine and Petroleum Geology and is openly available using doi:10.1016/j.marpetgeo.2016.02.012 The observations relate to 39 wells from Central England, Northern England and Northern Scotland and are provided with links to screen grabs of the images for clarity. The basic well metadata is supplied along with a description of the dataset. The Images were generated in the IMAGE DISPLAY module of the Landmark RECALL software and are supplied on an “as shown” basis. Descriptions of the tools and the techniques used are listed in the accompanying paper: KINGDON, A., FELLGETT, M. W. & WILLIAMS, J. D. O. 2016. Use of borehole imaging to improve understanding of the in-situ stress orientation of Central and Northern England and its implications for unconventional hydrocarbon resources. Marine and Petroleum Geology, 73, 1-20.

The dataset contains the raw timeseries of broadband magnetotelluric data collected at 10 sites around St Austell, Cornwall and one remote site in Bodmin Moor, Cornwall. Data were collected by BGS staff in March 2023 using Phoenix Geophysics Ultra-wideband MTU-5C systems.