Sourceless Neutron-Gamma Density (SNGD): Principles, Field-Test Results and Log Quality Control of a Radioisotope-Free Bulk-Density Measurement
- Nicole Reichel (Schlumberger Ribound Formation Evaluation Center) | Mike Evans (Schlumberger Houston Formation Evaluation Center) | Françoise Allioli (Schlumberger Ribound Formation Evaluation Center) | Marie-Laure Mauborgne (Schlumberger Ribound Formation Evaluation Center) | Luisa Nicoletti (Schlumberger Ribound Formation Evaluation Center) | Fabien Haranger (Schlumberger-PTC) | Nicolas Laporte (Schlumberger Ribound Formation Evaluation Center) | Christian Stoller (Schlumberger-PTC) | Valentin Cretoiu (Valentin Cretoiu) | Emad El Hehiawy (Enap Sipetrol) | Ramy Rabei (PetroShahd)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2013
- Document Type
- Journal Paper
- 91 - 103
- 2013. Society of Petrophysicists & Well Log Analysts
- 4 in the last 30 days
- 189 since 2007
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Bulk density is among the most critical formation parameters for geoscientists. Traditional acquisition technology employs a radioisotope (137Cs) as a source of gamma rays. With a half-life of 30.17 yr, this radioisotopic source continually emits 662-keV gamma rays, posing health, security, and environmental risks that need to be minimized through rigorous and expensive transportation, storage, handling, and deployment procedures. The well logging industry has been seeking an alternative to the radioisotope-based technology for years; some of these alternatives have focused on finding a way to "make do" without a density measurement. However, the industry standard technique of comparing neutron and density measurements favors the development of a cleaner and safer way to acquire a true formation bulk density.
Pulsed-neutron generators (PNG) have been successfully used by the well-logging industry to acquire a variety of measurements. Electronically controlled pulses of high-energy neutrons can be emitted in precisely timed bursts. The inelastic collision of high-energy neutrons with the nuclei of formation atoms can put them into excited states, which decay through the emission of gamma rays. The characterization of the transport of these gamma rays in the formation can be used to determine the bulk density, in a manner similar to the traditional gamma gamma- density (GGD) measurement. While the principles behind this method are well understood (Evans et al., 2000; Gilchrist et al., 2011), the practical development of an industry-grade measurement has taken years of careful development and testing.
This paper reviews the principles behind the sourceless neutron-gamma density (SNGD) measurement and explains its measurement specifications, applications, and quality-control indicators. The term sourceless indicates that this measurement does not use any radioisotopic sources of gamma rays. The new measurement was tested and benchmarked using data from a multifunction logging-while-drilling tool that incorporates the PNG and detectors required for the SNGD measurement and a GGD density section. Comparing the results from both density measurements allows rigorous benchmarking and performance evaluation of the SNGD measurement versus the GGD in a diverse range of environments. This is illustrated through field test results detailing the accuracy and precision of the new measurement.
|File Size||13 MB||Number of Pages||13|