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Spectral Gamma Ray Tools Spectral gamma ray tools provide insight into the mineral composition of formations. The total gamma ray spectra measured is resolved into the three most common components of naturally occurring radiation in sands and shales—potassium, thorium, and uranium (K, Th, and U, respectively). These data are used to distinguish important features of the clay or sand around the wellbore. The clay type can be determined, and sand can be identified as radioactive. The deposition of radioactive salts behind the casing by the movement of water can also be identified. Applications ■ ■ ■ ■ ■ ■ ■ ■ NGS Natural Gamma Ray Spectrometry tool The NGS* Natural Gamma Ray Spectrometry tool uses five-window spectroscopy to resolve the total gamma ray spectra into K, Th, and U curves. The standard gamma ray and the gamma ray minus the uranium component are also presented. The computed gamma ray or Th curve can be used to evaluate the clay content where radioactive minerals are present. Hostile Environment Natural Gamma Ray Sonde HNGS The increased sensitivity of the Hostile Environment Natural Gamma Ray Sonde (HNGS) set of detectors improves the tool’s statistical response to the formation gamma rays to produce a better spectral analysis than that of previous tools. The improvement in measurement also results from the use of two detectors instead of one. The HNGS can log at a faster speed than other tools that measure the formation natural gamma ray emissions. Its 500°C [260°C] temperature rating makes it suitable for operations in hot borehole environments. Cation exchange capacity studies Reservoir delineation Detailed well-to-well correlation Definition of facies and depositional environment Igneous rock recognition Recognition of other radioactive materials Estimated uranium and potassium potentials Lithologic analysis log input Measurement Specifications NGS Tool Output Logging speed Range of measurement Vertical resolution Accuracy Depth of investigation Mud type or weight limitations Combinability HNGS Gamma ray; corrected gamma ray for uranium; potassium, thorium, and uranium curves 1,800 ft/hr [549 m/h] 1,800 ft/hr [549 m/h] 0 to 2,000 gAPI 0 to 2,000 gAPI 8 to 12 in. [20.32 to 30.48 cm] 8 to 12 in. [20.32 to 30.48 cm] K: ±0.4% (accuracy), 0.25% (repeatability) K: ±0.5% (accuracy), 0.14% (repeatability) Th: ±3.2 ppm (accuracy), 1.5 ppm (repeatability) Th: ±2% (accuracy), 0.9 ppm (repeatability) U: ±2.3 ppm (accuracy), 0.9 ppm (repeatability) U: ±2% (accuracy), 0.4 ppm (repeatability) 9.5 in. [24.13 cm] 9.5 in. [24.13 cm] In KCl muds, KCl content must be known In KCl muds, KCl content must be known Combinable with most tools Combinable with most tools Mechanical Specifications Temperature rating Pressure rating Borehole size—min. Borehole size—max. Outer diameter Length Weight Tension Compression NGS Tool HNGS 302°F [150°C] 20,000 psi [138 MPa] 41⁄2 in. [11.43 cm] No limit NGT-C: 3.625 in. [9.21 cm] NGT-D: 3.875 in. [9.84 cm] 8.6 ft [2.62 m] NGT-C: 165 lbm [75 kg] NGT-D: 189 lbm [86 kg] 50,000 lbf [222,410 N] 20,000 lbf [88,960 N] 500°F [260°C] 25,000 psi [172 MPa] 43⁄4 in. [12.07 cm] No limit 3.75 in. [9.53 cm] www.slb.com/oilfield FE_04_039_0 ©Schlumberger August 2004 *Mark of Schlumberger Produced by Marketing Communications, Houston. 11.7 ft [3.57 m] 276 lbm [125 kg] 50,000 lbf [222,410 N] 23,000 lbf [102,310 N]