Abstract
Abstract Stress magnitude data across the UK is limited spatially and stratigraphically with information available for only 21 sites in the latest release of the World Stress Map. This information is largely derived from geothermal resource exploration and radioactive waste storage site assessment. Active exploration of unconventional resources in the UK has highlighted a lack of information to adequately characterise the stress field, in particular in regions underlain by potentially prospective shale formations. Understanding the in-situ stress conditions is critical to the planning of sub surface operations and the potential extraction of unconventional resources. Legacy stress magnitude data from 75 sites is combined with new analysis of wireline data to re-characterise the stress field across two regions which are underlain by the Bowland Shale Formation which has resource potential for unconventional hydrocarbons. These regions are: East Yorkshire and North Nottinghamshire, and Cheshire and Lancashire. Vertical stress gradients vary between 23 and 26 MPakm−1 for the regions studied. Pore pressure is similar for both regions and is hydrostatic with a gradient of 10.19 MPakm−1. Lower bounds for the minimum horizontal stress have been estimated from the available data and show that the magnitude of the minimum horizontal stress is 2.6 MPakm−1 higher to the east of the Pennines. The compiled legacy data show that the Maximum Horizontal Stress is consistently greater than the vertical stress, which in turn is greater than the minimum horizontal stress, indicating that at depth within the two regions, the faulting regime is predominantly strike-slip.
Highlights
Knowledge of the in-situ stress field is a key constraint in the exploitation of the subsurface and development of any subsurface resources including, storage of carbon dioxide, radioactive waste disposal, mining, unconventional hydrocarbon exploration, civil engineering and fault stability (Nirex, 1997; Zoback et al, 2003; Tingay et al, 2005; Williams et al, 2016)
The knowledgebase is extended with calculation of the stress magnitude from newly derived data sources to give a more complete understanding of the stress field in those regions which are potentially prospective for shale gas
Due to lack of data in the two regions, SHMax magnitude data have been compiled from across the UK in order to evaluate the stress state. This information has been sourced from: peer-review publications, data referenced in the World Stress Map (WSM) database (Fig. 1), and records identified in the UK National Geoscience Data Centre (NGDC) hosted by the British Geological Survey (BGS)
Summary
Knowledge of the in-situ stress field is a key constraint in the exploitation of the subsurface and development of any subsurface resources including, storage of carbon dioxide, radioactive waste disposal, mining, unconventional hydrocarbon exploration, civil engineering and fault stability (Nirex, 1997; Zoback et al, 2003; Tingay et al, 2005; Williams et al, 2016). The stress field is critical to understanding fracture mechanics. This is highly important as the UK investigates the possibility of developing unconventional hydrocarbon resources which require stimulation of the rock mass through hydraulic fracturing. The knowledgebase is extended with calculation of the stress magnitude from newly derived data sources to give a more complete understanding of the stress field in those regions which are potentially prospective for shale gas
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