Experimental Determination of Environmental Corrections For A Dual-Spaced Neutron Porosity Log

All environmental corrections which affect the determination of formation porosity have been experimentally and/or theoretically determined for a dual - detector thermal neutron porosity tool. Corrections which are a function of tool design have been derived from experimental data in over 100 laboratory test formation environments. These corrections are presented both in analytical form and as charts with the defining data points included. The theoretical bases for other corrections are discussed, and the resulting correction curyes are presented. Field logs run in a variety of borehole and formation conditions are compared with core data to verify the accuracy of the corrections. The effects of trace elements with large thermal neutron capture cross sections have also been quantified.