OR/19/049 Geophysical (wireline) logs
|Kearsey, T, Gillespie, M, Entwisle, D, Damaschke, M, Wylde, S, Fellgett, M, Kingdon, A, Burkin, J, Starcher, V, Shorter, K, Barron, H, Elsome, J, Barnett, M, and Monaghan, A. 2019. UK Geoenergy Observatories Glasgow: GGC01 cored, seismic monitoring borehole — intermediate data release. British Geological Survey Internal Report, OR/19/049.|
Geophysical logging is the process of measuring the properties of a formation using sensors attached to a winch cable (wireline) suspended in the borehole. Measurements are made continuously down the borehole by raising or lowering the sensor tools. The property measurements are then converted to a standard series of geophysical logs including: Density, P-Wave Transit Time, Neutron Porosity etc.
Description of geophysical logging technology is beyond the scope of this report, there are a number of textbooks which cover the acquisition and interpretation of wireline logs including: Serra (1983); Hearst et al. (2000) and Ellis and Singer (2007). Wireline logs have also been used extensively as part of the Integrated Ocean Drilling Program with a number of resources available online[note 1].
LAS format for conventional log data
File name: GGC01_Composite_Certified.las and 6 similar named files
Conventional geophysical logs are provided in LAS format[note 2], version 2.0. This is a column separated ASCII format. Almost all specialist logging software is capable of loading and interpreting geophysical log data in LAS format. In addition to this LAS files can also be viewed in any software capable of manipulating an ASCII text file, including Notepad (Windows), VI (Unix) or spreadsheets (e.g. Microsoft Excel).
Data provision of borehole imaging data in dlis fomat
File name: GGC01_Acoustic_2.dlis
Acoustic borehole image logging was acquired for borehole GGC01. When processed using specialist software this file provides an unwrapped interior borehole wall image. The image facilitates visualisation of the physical condition of the borehole’s wall, such as presence of breakouts, open fractures etc. and also some details of geological features visible on the borehole wall, such as intersections of some beds with the borehole and some types of discontinuity which are not open.
Borehole imaging data is provided in the form of Digital Log Interchange Standard (DLIS) files. This binary format cannot be read with anything other than specialist borehole imaging software, which is required to interpret the data files. The file was acquired and processed by Robertson Geo Ltd using the WellCAD software and the associated DLIS file integrity has been checked by BGS scientists using Schlumberger Techlog borehole imaging software.
Note: The Robertson Geoscience AWS imaging tool DLIS format is not supported by all specialist borehole imaging software and so additional processing stages may be needed to load the data. DLIS files contain array-formatted data, which prevented their conversion into the LAS (Log ASCII Standard) format used to report the other logging parameters. The borehole image logging data can however be viewed in the field prints, ‘GGC01_acoustic updated.pdf’.
Log acquisition metadata
Three LAS files are supplied with a standard metadata package defining the well metadata and acquisition (Table 7).
|STRT||M||0||First reference value|
|STOP||M||198.856||Last reference value|
BJ 3754BGS ID_20650619
|EGL||M||9.66||Ground Level Elevation|
|FL||Glasgow||Geographical area name|
|OPER||BGS||British Geological Survey|
|UNKNOWN||GGC01||Full well title|
|WELL-NAME||NS66SW/3754||Single Onshore Borehole|
|TOP_LOGGED_INTERVAL||0.0 m||Top Logged Depth|
|BTM_LOGGED_INTERVAL||198.86 m||Bottom Logged Depth|
This file contains the main geophysical logs that define the geological succession that would typically be included in an industry composite plot.
This file contains the flowmeter outputs that show the fluid ingress into the well bore.
This is the full wave form sonic including the interval transit time between the multiple source receiver pairs that allow the detailed sonic profile to be constructed.
|SVEL||µs/ft||5 Interval Transit Time|
|TA||µs||1 Transit Time TX1-RX1|
|TB||µs||2 Transit Time TX1-RX2|
|TC||µs||3 Transit Time TX2-RX1|
|TD||µs||4 Transit Time TX2-RX2|
Summary composite log image files
File names: GGC01_Comp_Plot_1_200.pdf and GGC01_Comp_Plot_1_500.pdf
Two composite log image files are included in the data pack at scales of 1:200 and 1:500.
- SERRA, O E. 1983. Fundamentals of well-log interpretation. Elsevier.
- HEARST, J R, NELSON, P H, PAILLET, F L. 1999. Well logging for physical properties: a handbook for geophysicists, geologists and engineers. 2nd Edition. Wiley.
- ELLIS, D V, and SINGER, J M. 2007. Well Logging for Earth Scientists. 2nd Edition. Springer. https://doi.org/10.1007/978-1-4020-4602-5