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A629 COMBINATION TOOL – Gamma / SP / PR / 16” / 64” RESISTIVITY This tool accomplishes the following logs. Natural Gamma, Short Normal, Long Normal, SP and PR. The Gamma, Short Normal and Long Normal logs are recorded on one run. The SP and PR logs are acquired on a separate run. Gamma The tool detects natural gamma radiation emanating from the sub-surface rocks. Gamma rays are very high frequency electromagnetic radiation and are derived from the radioactive decay of various elements. In borehole applications the most common radioactive elements are radioisotopes of potassium, thorium and uranium. Resistivity Resistivity logs may be usefully applied in a number of areas. In Ground-water studies, electrical resistivity logs have been regarded as vital for many years. Apart from general geological / stratigraphic information, resistivity values provide excellent information on two important hydro-geological aspects: aquifer location water quality In sedimentary sequences (consolidated or otherwise) aquifers are usually much more resistive than aquicludes such as clay layers and shale. In igneous and carbonate sequences, secondary aquifers formed by fracturing or dissolution are often less resistive than the adjacent massive rocks. In Coal studies, electrical resistivity logs indicate that the seam has been coked by an igneous intrusion, or has been affected by oxidation. PR (point resistance) measurements are used to ascertain depths and thicknesses of strata. These measurements will often clearly define the strata boundaries. The SP log measures small, naturally occurring spontaneous potential generated by electrochemical differences between differing rock types, water and drilling fluids. Occasionally there is another component called streaming potential created by fluids entering of leaving the borehole. Recognition of this is important in some engineering applications. Specifications
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