Putting delicate scintillation detector crystals into a shock resistant hermetic casing, or shielding a photomultiplier tube (PMT) from background radiation all while drilling is one thing, ensuring that the tool can continue to operate in temperatures well above 165C is quite another matter.
When Flashpoint first began to distribute its NaI(Tl) crystals and PMT tubes in 1995 the maximum temperature a tool was expected to operate was 165C. By 2003 that temperature was pushed to 175C and by 2011 it had been pushed to 200C.
Aside from the work that FlashPoint was doing to ensure suitability at these temperatures, a team at Halliberton Sperry-Sun was also working to achieve this "holy grail" of harsh environmental operations:
The objective of this project was to build a high temperature, cost effective,
logging while drilling (HT-LWD) system with the ability to operate at 175°C with more than 100 hours mean time between failures (MTBF). Such a commercial real-time formation evaluation (FE) system would help operators to drill and produce hydrocarbon resources from moderately deep, hot reservoirs which otherwise might be uneconomic to drill.
Here is the formal paper: