The PESGB thank Task Geoscience for sponsoring this Aberdeen Evening Lecture

Borehole images: a basic introduction to recent advances

Giancarlo Rizzi, Task Geoscience Limited

Tuesday 16 March 2010, 6pm for 6.30pm presentation
Copthorne Hotel, 122 Huntly Street, Aberdeen AB10 1SU

Who should attend:       Geologists, with little, if any knowledge of borehole images.   Geophysicists and Petrophysicists are also encouraged to attend, as are the under-graduate and post-graduate community. 

Learning outcomes:        How spatial data, such a fracture orientations are generated from borehole images; how these date can be used as inputs for seismic-compatible three-dimensional geo-visualization software.   

Improvements in computing power in recent years have facilitated the development of increasingly sophisticated methods of image log interpretation.  Manual dip picking, bulk structure analysis and image lithofacies analysis; are now complemented by three-dimensional views of along-the-borehole dip data, the re-construction of sand-body geometries from manually picked dip data, and the generation of robust, extrapolated surfaces.   Accordingly, image-based interpretations can now be extended away from the borehole, into areas where seismic images are not available, such as the ‘sub-salt’ scenario.

This short lecture will begin with a review of borehole imaging technology; from wireline logging through to logging while drilling (LWD).  This will be followed by a summary of borehole image geometry.  Here, emphasis will be placed on the intersection of typically planar features, such as fractures, with borehole ‘cylinders’.   

Quality control of both raw and processed borehole image data will concentrate on tool orientation checks and polarity checks against open hole log data. This will conclude with a brief summary of borehole image artefacts and how these can be distinguished from real geological features exposed along the borehole wall. 

The generation of spatial data will begin with an explanation of manual dip picking.  Emphasis will be placed on geological classification of features, quality rating procedures and the advantages of manual dip picking over computer generated autodips.  

Of interest to Geophysicists will be the sections on bulk structural dip determination and how this can be used to verify seismic-scale surface orientations.  The special problem of structural dip determination within shale-free intervals, such as those found within aeolian dune sandstones, will also be considered in this section.   Fractures analysis will review classification systems and how fracture counts can be corrected for bore-hole bias, so as to ensure they have not been under-determined.  

Characterization of reservoir heterogeneities will focus image lithofacies analysis for net-to-gross calculations, and sediment dispersal analysis.  The integration of this data with other down-hole data such as wireline logs, core and cuttings descriptions will also be addressed.  

The lecture will conclude with a summary of borehole image data as inputs for three-dimensional geo-visualisation software and how these data can be extrapolated between adjacent wells.   The lecture will be illustrated throughout by a variety of released examples of borehole images.