Design and Simulation of a New Generation Radiation Detector for Oil and Gas Exploration

Radiation detection is extensively used in borehole logging — a technique widely employed in oil and gas, and mineral exploration. The workhorse of this detection application for many years has been traditional 3He tubes in neutron porosity tool and NaI:Tl scintillators coupled with photomultiplier tube (PMT) in γ ray density tool. Although PMTs are a well proven technology which can operate in the high temperature conditions (typically of order 100°C) and pressures (10 MPa) encountered during logging activities, they are however fragile and have a large form factor and require a high-voltage power supply thereby occupying significant space within the borehole probe. However, to survey for oil and gas, γ ray density and neutron porosity tools must be used conjointly. Additionally, the demand for neutron detection technology is increasing while the supply of 3He gas is extremely scarce. These issues have led to the characterisation of an alternative dual radiation detection technology based on 6Li (GS20), which could replace 3He tube and NaI:Tl crystal respectively. We have shown that GS20 is capable of measuring both electron density and hydrogen content, eliminating the need for two separate tools. Furthermore, we have evaluated CsI:Tl scintillators coupled to standard 6×6 mm2 SiPMs from Hamamatsu and SensL as a function of temperature as an alternative to NaI:Tl scintillator coupled to PMT. In addition, we have shown that these prototypes operate effectively up to a temperature of 80°C which could satisfy the requirements of some applications of borehole logging where the maximum temperature encountered is 75°C.