Abstract
Bulk density is one of the most important formation parameters for formation evaluation. The radioisotope chemical sources are widely used in conventional nuclear logging tools. Considering security and environmental risks, the pulsed neutron generators have successfully replaced the Am-Be source in neutron porosity logging tools. However, the Cs-137 is still mainly used for bulk density measurement. However, the physical process of the neutron-gamma density (NGD) measurement is more complicated than that of the GGD measurement. The neutron-induced secondary gamma-ray source cannot be considered as a “point” source. The distribution of the inelastic gamma source is a function of the neutron transport. Due to the high gamma energy values, the attenuation of inelastic gamma-ray is affected by Compton scattering and pair production. Therefore, the bulk density can be measured when the effects of neutron transport and pair production are considered. A new open hole wireline logging tool has been developed to provide measurement of formation bulk density. The paper reviews the NGD measurement physics and discusses the various facets of bulk density algorithm. Data from laboratory testing examples are presented to demonstrate tool performance.
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