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Geology _ Geophysics in Oil Exploration

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Unformatted text preview: etectors detect γ ray which emitted from excited atoms which related to the formation. Notes: • The borehole must be perfectly vertical (no washout) because in this case, the tool will measure air response & causing errors in data. • Drilling muds with high density will absorb gamma rays efficiently, such as barite filled muds, will effect the detector readings. However, the effect of these muds is compensated for automatically by the spine and ribs correction. ФD= (ρb‐ρma) / (ρf‐ρma) Where: ρb = the bulk density of the formation ρma = the density of the rock matrix ρf = the density of the fluids occupying the porosity ФD = the porosity of the rock. Calibration: The primary calibrations are made by inserting the tool into a block of pure limestone saturated with fresh water of accurately known density. Secondary (check) calibrations are made in the wireline tool workshop by inserting the tool into large blocks of aluminum, sulphur and magnesium of known density. Tool operation: The tool is physically very similar to the formation density tool. It has enhanced detectors, and the distance between the long spacing and the short spacing detectors has been decreased. This decrease has increased the vertical resolution of the tool and improved its overall counting accuracy. The accuracy of the density measurement of the litho-density tool is approximately 0.01 to 0.02 g/cm3, whereas that of the formation density tool is approximately 0.02 to 0.03 g/cm3. The density measurement has a vertical bed resolution of 50 to 60 cm, which is slightly better than the formation density tool. The enhanced resolution results from the shorter distance between the short and the long spacing detectors. The log is commonly referred to as the photo-electric factor log (PEF). 58 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Neutron Tools: (CNL & SNP) (SNP): Sidewall Neutron Porosity Tool. (CNL): Compensated Neutron Log Tool. The neutron log is sensitive mainly to the amount of hydrogen atoms in a formation. Its main use i...
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