Download Spectral Gamma Ray Tools

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
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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]