Dual-Burst Thermal Decay Time logging principles
The Dual-Burst TDT (TDT-P) tool is a 1 11/16-in. diameter pulsed neutron, dual detector tool system that uses a new method of analyzing the decay of a burst of fast neutrons in the downhole environment. The method provides an accurate measurement of the neutron capture cross section of the formation by employing a physically realistic model of the decay rather than displaying the decay as a sum of exponentials from the formation and borehole. Intrinsic sigma is computed directly from the decay curve instead of by using correction charts. The model is evaluated using over 2,000 data obtained in well characterized laboratory test formations. The benefit of the method is that the formation cross section is independent of the fluid in the borehole. The TDT-P tool is a kit upgrade to the TDT-M tool, and its hardware has been especially configured to make high precision measurements of the decay curve. A unique dualburst technique uses a short burst of neutrons (approximately 20 ..mu..s) after which counting gates are positioned very close to the burst. This allows measurement of the faster decay without saturating the detector at high counting rates. A long burst (approximately 150 ..mu..s) follows the first set of counting gates, and it is used to provide good counting statistics at long times to measure the slower formation decay component. The statistical behavior of nonlinear least squares fitting algorithms used to extract the sigmas from the decay curve is examined, and a measure of the ability of an algorithm to extract two components from decay curves is presented. This quantity measures the contrast between the components.
- OSTI ID:
- 7013633
- Report Number(s):
- CONF-861080-
- Resource Relation:
- Conference: Society of Petroleum Engineers annual technical conference and exhibition, New Orleans, LA, USA, 5 Oct 1986
- Country of Publication:
- United States
- Language:
- English
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03 NATURAL GAS
RESERVOIR ROCK
NEUTRON-GAMMA LOGGING
ACCURACY
ALGORITHMS
CAPTURE
DECAY
FAST NEUTRONS
LEAST SQUARE FIT
MATHEMATICAL MODELS
NATURAL GAS DEPOSITS
NEUTRON DETECTORS
NEUTRON REACTIONS
NEUTRON SOURCES
PETROLEUM DEPOSITS
PULSED NEUTRON TECHNIQUES
TIME DEPENDENCE
WELL LOGGING EQUIPMENT
BARYON REACTIONS
BARYONS
ELEMENTARY PARTICLES
EQUIPMENT
FERMIONS
GEOLOGIC DEPOSITS
HADRON REACTIONS
HADRONS
MATHEMATICAL LOGIC
MAXIMUM-LIKELIHOOD FIT
MEASURING INSTRUMENTS
MINERAL RESOURCES
NEUTRON LOGGING
NEUTRONS
NUCLEAR REACTIONS
NUCLEON REACTIONS
NUCLEONS
NUMERICAL SOLUTION
PARTICLE SOURCES
RADIATION DETECTORS
RADIATION SOURCES
RADIOACTIVITY LOGGING
RESOURCES
WELL LOGGING
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