Low-cost neutron-gamma borehole detectors for hydrogen content prediction

In an oil well, high hydrogen content within the surrounding rocks is one indicator of the presence of hydrocarbons. Nuclear well-logging entails the deployment of a detector tool and neutron source downhole to characterise the strata properties as a function of depth. After neutron bombardment, the resulting distribution of radiation is sensitive to the hydrogen content. Current detectors favour use of radioisotopes, such as Am-Be or Cf-252 sources. Potential improvements in both safety and data collection capabilities are possible using Deuterium-Tritium Pulsed Neutron Generators (D-T PNGs) as an alternative neutron source when coupled with fast timing and position sensitive detectors. We propose a low-cost, modular detector system, that can measure the flux of thermal neutrons and gammas at various distances from a pulsed fast neutron source. The detector modules consist of in-house manufactured plastic scintillator coupled to BN:ZnS(Ag) thermal neutron converter foils. These mixed-field detectors show good figure of merit for neutron-gamma discrimination at low-cost, allowing us to construct positional and temporal distributions of detected neutrons and gammas. Based upon early simulations, these distributions are sensitive to the hydrogen content.