W. D. Flanagan, R. L. Bramblett, J. E. Galford, R. C. Hertzog, R. E. Plasek and J. R.. Olesen
Schlumberger, Houston, Texas
Abstract
A new generation openhole nuclear combination tool has been developed to provide formation measurements with significantly reduced environmental effects and enhanced log quality control, This modular tool consists of an accelerator based epithermal neutron porosity sonde, a gamma lithology density sonde, and a natural gamma ray spectroscopy sonde utilizing one common electronic cartridge. New measurements in conjunction with new processing methods provide significant performance improvements when compared to existing openhole nuclear services.
The neutron porosity sonde features a pulsed neutron generator that provides new measurement capabilities. The high neutron yield of this generator allows the use of an epithermal detection system which reduces the environmental effects due to thermal absorbers, fluid salinity and temperature. New measurements and processing techniques provide a more accurate porosity determination with improved vertical resolution and less tool standoff effect.
The new system uses a full spectral analysis for both the lithology density and natural gamma ray measurements, the benefits of which include reduced environmental effects, faster logging speeds, and improved log quality control. The new natural gamma ray sonde also incorporates a technique that enables a direct measurement of potassium in the borehole and compensation for heavy mud effects.