OR/15/013 Model datasets

Woods, M A, Newell, A J, Haslam, R, Farrant, A R and Smith, H. 2015. A physical property model of the Chalk of southern England. British Geological Survey Internal Report, OR/15/013.

Datasets that have been included or created for the model comprise the following:

• Digital Terrain Model: OS Terrain 50 was used to provide elevation attribution to DigMap GB-50 geological linework. This DTM was also used during the SKUA Structure and Stratigraphy modelling process when it was variously resampled depending on the chosen grid resolution.
• Geological linework: BGS DigMapGB-50 (V7) for Chalk Group formations
• Geophysical log interpretations: These comprise interpretations of borehole geophysical logs from the BGS digital archive in RECALL as well as from the BGS Regional Geophysics paper archive in National Geological Records Centre (NGRC). A list of interpreted boreholes is given in Appendix 2. All log data were loaded into WellCad, either as depth attributed scanned images (paper records) or as .las files (digital log data). Geophysical logs (mainly combinations of gamma, sonic, resistivity) were used to interpret lithofacies, stratigraphy and marker-beds (see below).
• Interpretations of borehole digital images and core logs: Depth-attributed digital (.jpeg) files were loaded into Well Cad and used to interpret lithofacies, stratigraphy and marker-beds (see below).
• Outcrop section interpretations: Selected published sections in research papers and BGS Technical Reports were scanned, scale-attributed and loaded into WellCad. Sections were selected for their completeness, geological detail and accurate location data. Facies logs of these sections were generated in WellCad, and location, stratigraphy and marker-bed details recorded in a separate Excel pro-forma, together with source reference.
• Facies Log Data: These logs were generated by interpretation of geophysical logs, digital borehole images, core logs and published and unpublished logs of outcrop successions (see above). A simple, widely reproducible suite of facies types were created for representation on the facies logs. These comprise: Chalk, Marl, Marly Chalk, Hardground, Hard Chalk, Faulted/Fractured/Channelised Interval, Sandy/Silty Chalk, Nodular Chalk, Significant Geophysical Log Feature, Clay-filled Solution Pipe, Stylolitic Marl. Some of these facies types, relying on visual information (e.g. Nodular Chalk, Stylolitic Marl), are not applicable to borehole geophysical logs from which the bulk of facies data are derived. Whilst desirable to collect a wide range of recorded facies data, there has been some rationalisation of these terms to more widespread equivalents (e.g. nodular chalk = hard chalk; stylolitic marl = marl) for the purpose of facies modelling. Following creation of the WellCad facies files, these were exported as text files and imported into Excel, using IF factors to translate facies text data into a numerical code. In this format, the facies data can be loaded into GOCAD SKUA for modelling.
• SOBI Borehole Well Path Data: Well path data, comprising Easting, Northing and OD of log reference datum, were compiled into an Excel spreadsheet for all SOBI boreholes used in the model.
• Formational Stratigraphy Interpretations (SOBI Boreholes): The depths of the tops of formations recognised in SOBI boreholes from geophysical logs, core logs and digital core images were compiled into an Excel pro-forma for uploading into GOCAD SKUA modelling software. All borehole stratigraphy interpretations were also loaded into the BGS Borehole Geology (BoGe) database.
• Marker-Bed Stratigraphy Interpretations (SOBI Boreholes and outcrop sections): The depth references of key Chalk marker beds (e.g. named flints, marls, hardgrounds) in SOBI boreholes and outcrop sections used for modelling were compiled into an Excel pro-forma. All marker beds are assigned a unique letter code (Lex Rock codes have been used where these already exist), and equivalent names for the same horizon are shown in the pro-forma (Appendix 2). Some marker-beds define formational boundaries, and the presence of these marker beds provides the formational subdivision data for the outcrop sections.