PRESERVATION, DIGITAL CONVERSION AND ACCESSIBILITY OF THE MINNESOTA GEOLOGICAL SURVEY DOWNHOLE GEOPHYSICAL DATABASE

The Minnesota Geological Survey houses approximately 7650 downhole geophysical logs collected from nearly 6300 boreholes over the past 35 years. Geophysical logs are imperative for mapping the subsurface where outcrops are scarce, and are commonly used to interpret water-bearing properties in our aquifer systems. The majority of logs contain gamma-ray data, and a small percentage also include measurements of electrical resistivity, spontaneous potential, water flow, temperature, and conductivity within open-hole intervals. Work is underway to create and update the digital infrastructure of these logs, focused currently on gamma-ray data, for preservation and accessibility, using funds awarded from the National Geological and Geophysical Data Preservation Program (NGGDPP). Data from about 5050 logs are being converted from proprietary Century Geophysical Corporation format into Log ASCII Standard (LAS) format, as well as converted to PDF documents for efficient dissemination. Nearly 2600 logs previously existed only on paper and have now been scanned to PDF images before these logs become further damaged or lost. A select number of these scanned logs deemed most important based on areas of low data density, deep drill holes and active mapping projects will be digitized using the automated digitizing software available in NeuraLog (www.neuralog.com). This process extracts x, y, and z data from static log images, allowing conversion to digital data in the LAS file format. An inventory database with metadata, at present not readily available to the public, exists for the entire collection and will continually be updated and checked for accuracy throughout the remainder of the project. Future work will involve setting up access for the public to query and obtain the metadata, PDFs, and LAS files online, and to eventually integrate the digital log database with the more widely used County Well Index (CWI) water-wells database housed at the Minnesota Department of Health to further streamline our mapping procedures. Our end goal is to increase the ease and use of our downhole geophysical database both for our staff and for the public, and to encourage collaborative work within the geoscience community by sharing our wealth of georeferenced geophysical data.