Introduction of a New Through-Tubing Multifunction Pulsed Neutron Instrument

Abstract

We are introducing a new 1-11/16-inch multi-function pulsed neutron instrument. The Reservoir Performance Monitor (RPM) has operating modes allowing pulsed neutron decay, pulsed neutron spectrometry, pulsed neutron holdup, neutron activation water flow, and radioisotope measurements. The tool is combinable with fluid density, spinner flowmeter, or more advanced production logging instruments. The new instrument includes three gamma-ray detectors arrayed above a new neutron generator that can be pulsed at different frequencies and modes for different types of measurements. The system employs short tool sections for ease in shipping and handling. In the pulsed neutron capture mode, the tool pulses at 1 kHz, and records a complete time spectrum for each detector. An energy spectrum is also recorded for maintaining energy discrimination levels. Time spectra from short-spaced and long-spaced detectors can be processed individually to provide traditional thermal neutron capture cross section information, or the two spectra can be used together to automatically correct for borehole and diffusion effects and produce results that are very close to intrinsic formation values. In the pulsed neutron spectrometry mode, the instrument pulses at 10 kHz, and records full inelastic and capture gamma ray energy spectra from each detector. These data are processed to determine critical elemental ratios including carbon/oxygen and calcium/silicon from the inelastic spectra and silicon/calcium from the capture spectra. The pulsed neutron holdup imager mode yields both energy spectra and time decay spectra from each detector simultaneously. Measurements can be used to determine holdups of gas, oil, and water, and when combined with other production logs can provide a comprehensive production profile picture, even in deviated or horizontal wells. The neutron activation mode provides water-flow measurements using one of several data acquisition methods. Stationary measurements are made in either of two modes, and measurements at different logging speeds can be used to segregate different flow rates in either an annulus or in an adjacent tubing string. With the neutron generator turned off, the RPM can also be used to detect the distribution of materials, tagged with radioactive tracers, that are injected into the well during well treatments. In this manner, the effectiveness of operations such as hydraulic fracturing or gravel pack placement can be evaluated.

Optimizing Memory Multidetector Pulsed Neutron Logging in Slim Horizontal Coil Tubing Drilled Wells Using a Carrier Assembly

“…The physics and different modes of operation of this tool are discussed by Gilchrist et al (5) . The tool records induced gamma rays emitted as a result of inelastic, capture, and activation events as the neutrons interact with borehole and formation.…”

Mathematical modeling problems connected with pulsed neutron-gamma logging

“…We cannot and do not attempt to present here an overview of the inversion methods, but at the same time we refer the reader to works on the determination of the elemental composition [9][10][11][12][13]42] as certain necessary guidelines. In contrast to the approximate approaches, this section deals with the exact method.…”

“…Of course, these parameters are intermediate on the way to the true (geological) petrophysical parameters, i.e., to the content of elements, minerals, fluids, and oxides (see, for example, [2,7,38]); the definition of the latter is the second stage of the measurement data's interpretation. Sometimes inversion is performed using a synthetic approach, which combines some approximations to the transfer process and parameter dependences of the readings obtained either experimentally or by the Monte Carlo methods [see, e.g., [9][10][11]]. An approximate approach of a quite different type, which is directly related to PNGL, was developed in [12,13].…”

Multi-Sensor through-Casing Density and Saturation Measurement Concepts with a Pulsed Neutron Source: A Modeling Assessment

“…Thus, the width of the response quadrilateral is an indicator of how well a design will be able to resolve the formation oil saturation from the presence of oil (or oil hold-up) in the borehole. 3 In order to judge the ability of our conceptual model to mimic the response of current tools, we compared the response quadrilaterals obtained from the configurations in Figure 2 with those from two commercial dualdetector designs, one with centralized detectors and the other with focused detectors. We note the following.…”

“…[1][2][3] Since the tools are slim, they can pass through most tubing and with advanced detectors and interpretation algorithms, one single tool run in multiple modes can estimate multiple parameters.…”