New Development in Pulsed Neutron Technologies to Enhance Faster Data Recovery and Reduce Operation Logging Time for Three-Phase Saturation Analysis

Abstract

A new wireline pulsed neutron technology has recently been introduced in the offshore area of the Niger Delta to improve service and data quality with a faster speed and a simultaneous acquisition of multiple measurement modes, resulting in substantial reduction of rig and operational time. The scope of this application was to qualify this new technology and to demonstrate the capability to log up to three times faster than previous-generation tools with the same precision and accuracy, while providing simultaneous pulsed neutron capture (PNC) measurements for gas saturation, and inelastic carbon oxygen (C/O) ratio-based modes for oil saturation from the same logging pass. Two wells were logged with both existing and new technologies for comparison purposes in mature fields that have been in active production since the 1960’s and which are still under development. A third well was logged with only the new tool after the benefits of the new technology were proven, but this paper will focus on the results from the wells in which both legacy and new tools were directly compared. The key features of the new instrument include: 1) three Lanthanum Bromide (LaBr3) detectors with high density, high count-rate and high-resolution characteristics, 2) an enhanced pulsed neutron source with higher output, 3) and digital electronics capable of processing the increased gamma ray count rate. The new instrument allows faster logging speed and time savings with the same precision as previous generation tools with either a single pass at legacy slower speeds, or logging in multiple passes at up to three times faster speeds. In addition, a new logging mode has been introduced that allows simultaneous acquisition of C/O and PNC (e.g. Sigma Σ and gas indicators) ratio based gas saturation measurements from three detectors for simultaneous 3-phase saturation determination. Nuclear modeling is used to predict various measurement responses over a wide range of borehole, casing, formation, and fluid conditions. The combination of these models with actual field measurements determines the fluid saturation profile with high accuracy. Results confirmed the same or higher saturation evaluation quality with 65 percent savings in logging time and 40-55 percent savings in total operation time. This paper presents field examples, and reports on results and data quality from this technical development.