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Unformatted text preview: 1 GY 305: Geophysics GY 305: Geophysics Lecture 6: Lecture 6: Electric (Wire Line) Logs 2: Electric (Wire Line) Logs 2: Gamma Ray Logs Gamma Ray Logs UNIVERSITY OF SOUTH ALABAMA Last Time Last Time Electric Logs 1 Introduction (first electric logs) Resistivity Logs SP Logs (Spontaneous Potential) Electric Logs Formation Resistivity Pelchelbronn, France September 5, 1927 Consisted of a line dropped down the bore hole Doveton, J.H., 1994. Geological Log Interpretation. SEPM Short Course Notes 29 ., 169p. Electric Logs There are numerous types of logs that provide a wide variety of information. Well look at the most important 1) Resistivity 2) SP 3) Gamma Ray 4) Neutron 5) Sonic/Density Resistivity Logs Can be used to resolve lithology, but they are most useful for assessing fluid composition. Shallow versus deep induction Resistivity Logs Ultimately resistivity of a rock (R t ) is controlled by: Salinity of formation pore water Volume of pore space Geometry of pore space (Lab 2) Temperature of the logged zone Morphology and types of clays Phases of pore fluids 2 ht p:/ www.spwla.org/library_info/glos ary/reference/glos s/images/glsp85f1.gif Spontaneous potential is... most useful as a basic tool to distinguish lithology (sandstone versus shale) SP Logs ht p:/ www.kgs.ku.edu/Dakota/vol1/petro/gifs/fig08.gif SP Logs Sand line versus Shale Line Beware of signal drift SP Logs htp:/www.gomr.mms.gov/images_opt/graphics/re/sp.gif SP logs can also allow you to resolve broad stratigraphic and...
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- Fall '10