An Accelerator-Based Epithermal Neutron Porosity Tool

A new porosity tool has been developed. This tool has several advantages over conventional neutron porosity tools. Because the measurement is made with epithermal neutron detectors, the porosity estimate is unperturbed by the presence of strong thermal neutron absorbers. Trace amounts of strong absorbers are frequently present in shales and can increase by several units the apparent porosity estimate made with conventional compensated neutron porosity tools. The statistical precision of the porosity estimate made with this new tool is comparable to conventional compensated tools at medium porosities and better at low porosities. Unlike the chemical sources used in conventional tools, the accelerator source is inactive until power is applied, making the new tool a safer one to operate. Finally, the new design is implemented as a mandrel device and therefore provides an alternative to the mechanically complex sidewall epithermal neutron tool. The response characteristics of the new tool are presented in this paper, as are the results of several field tests.