Radiation Sources in Drilling Tools: Comprehensive Risk Analysis in the Design, Development and Operation of LWD Tools

Abstract

Abstract Nuclear logging while drilling (LWD) methods containing chemical sources of ionizing radiation have become commonplace in the past 15 years. However, introducing radioactive sources into a drillstring's bottomhole assembly (BHA) involves a level of risk greater than similar tools deployed on wireline. Such tools must meet acceptable standards not only in terms of performance, but environmental and personnel safety. In addition, stringent regulatory requirements are imposed on the transport, storage, handling, abandonment and eventual disposal of chemical radioactive sources. Comprehensive risk analysis has driven the development of two generations of nuclear LWD tools at one oilfield service company. We discuss these tools, their Health, Safety and Environmental (HSE) performance and the process of continuous improvement, both incrementally and in fundamental design changes, as risks were better quantified. Substituting a pulsed neutron generator (PNG) in place of chemical sources can eliminate many of the risks, while increasing the measurements available for petrophysical analysis. PNGs have been used successfully in wireline-deployed tools but, until recently, have not been sufficiently robust for LWD application. Prototype LWD tools are successfully proving the viability of a new generation of PNG. These PNG-based LWD tools open the door to an enhanced suite of LWD measurements without the HSE risks of chemical source-based tools.