A Sourceless Alternative to Conventional LWD Nuclear Logging

Abstract

Abstract An experimental pulsed-neutron logging-while-drilling (LWD) tool is currently under field test. The tool provides a suite of nuclear measurements that include neutron porosity, thermal neutron capture cross section (i.e. sigma), pulsed-neutron density and the relative abundance of certain elements (e.g., calcium, silicon, iron, sulfur, etc.) that are used to calculate mineralogy. The tool provides azimuthal measurements in real time that are useful for geosteering applications. Use of a pulsed-neutron source eliminates the need for radioactive-chemical sources that are used in conventional nuclear LWD tools. This results in increased wellsite safety and efficiency. Procedures and equipment required for radioactive-source handling, storage and retrieval are also eliminated. The experimental LWD tool is the result of a joint collaboration that began in 1995 between the Japan National Oil Corporation and Schlumberger. The primary goal of the tool is to demonstrate feasibility of pulsed-neutron measurements in the hostile LWD environment. Introduction An experimental pulsed-neutron LWD tool has been developed that has successfully logged several test wells. The prototype tool represents a merging of pulsed-neutron wireline measurements with LWD measurement technology. The applications of pulsed-neutron measurements for formation evaluation are well established. Pulsed-neutron wireline tools are used to determine water saturation, neutron porosity and formation mineralogy in both open and cased holes. In addition to the rich variety of measurements, pulsed-neutron technology eliminates the radioactive-chemical sources used in conventional nuclear tools. Source-storage pits, transport shields, loading shields, collar shields and handling tools are therefore not required. Transportation logistics, wellsite safety and wellsite efficiency are all improved.