地层元素测井中中子-伽马能谱解析理论和方法

对在模型中进行地层元素中子-伽马能谱测井实验中所得中子-伽马谱解析方法进行了研究,即对非弹伽马谱与俘获伽马谱解析方法进行了研究。理论上推导出分别用非弹谱和俘获谱求出地层元素质量分数的公式,得到了标准非弹伽马谱和标准俘获伽马谱,并在理论推导的基础上编制了相应的解谱程序。     

地层元素测井中子-伽马谱解析方法的实际应用

本文利用地层元素测井中子伽马谱的解析理论和解析方法，对两个油田的四口井连续获取的中子伽马谱，用自行设计与研制的软件系统，进行连续处理，获得H、C、O、Si、Ca、Fe、Mg、Al的质量分数随井深的变化曲线。同时，获得新C/O和新Ca/Si比值随井深的变化曲线，即测井曲线。随之利用新C/O比值求得有关井段地层的含油饱和度及划分水淹等级，而且利用元素质量分数求得有关地层的矿物含量，接着求得地层密度、宏观俘获截面和渗透率等。     

利用脉冲中子伽马能谱判断岩性及影响因素的蒙特卡罗模拟

RPM(储层特性监测仪)能够在不同的时间内获取非弹性散射伽马能谱和热中子俘获伽马能谱,对谱数据进行处理获取C/O和地层的宏观吸收截面的同时,也可以利用得到的Si/O和Ca/O以及Si/Fe和Ca/Fe的交会图来判断岩性.通过蒙特卡罗方法模拟在套管井各种地层条件下的非弹和俘获能谱,研究利用交会图判断岩性,并给出饱和度、孔隙度、矿化度、井眼套管、持率、泥质含量等影响因素下的交会图,为利用RPM测井资料获取地层岩性信息及其影响因素提供了理论指导.     

地层元素测井技术最新进展及其应用

地层元素测井是一种通过测量中子与地层元素原子核作用放出的伽马射线,得到元素含量进而确定矿物含量的中子伽马能谱测井技术,在复杂储层岩性识别、非常规储层评价等方面得到了广泛应用。本文简要介绍了元素能谱测井的核物理和地质基础,并对元素俘获能谱测井（ECS）、地球化学测井（GEM）和地层岩性能谱测井（FLS）等几种仪器技术指标进行分析;系统讨论了确定元素含量的谱分析技术及矿物含量的氧化物闭合模型和统计分析方法;总结了元素能谱测井在地层评价中的应用。最后提出采用可控中子源和多探测器系统、多参数测量是地层元素测井的发展趋势。     

直接确定地层有机碳含量测井方法的数值模拟

非常规资源逐渐成为我国油气勘探的重要领域,其"源储一体"的特性使得对源岩特别是有机碳含量的连续定量评价成为关键。传统测井评价方法均是基于测井资料的间接评价,受多种因素影响,计算结果有一定的不确定性。本文利用快中子与地层元素原子核发生反应产生的非弹性散射伽马能谱和俘获伽马能谱,通过谱分析技术获取地层元素含量,根据与无机碳相关的钙、镁等元素含量确定无机碳含量,从总碳含量中扣除无机碳含量可直接提供高精度的有机碳含量信息。借助于蒙特卡罗数值模拟方法,建立了6种四川盆地龙马溪组和筇竹寺组页岩地层模型,模拟不同地层条件下的混合伽马能谱,并利用模拟元素的标准伽马能谱对模拟能谱进行谱解析。模拟结果表明,本文的方法可直接提供高精度的有机碳含量,有机碳含量大于2%时,其计算值相对误差小于6%。     

可控中子及X射线源测井技术发展现状及趋势

随着核仪器技术的进步以及安全健康的工业发展需求,具有人工可控性的中子源及X射线源逐步在测井领域得到推广应用,为油气等矿产资源的勘探开发提供了关键技术手段。可控中子及X射线源测井技术是以中子发生器或X射线管产生的中子或X射线与地层物质作用,通过探测中子、伽马或X射线从而进行地层孔隙度、密度、油气饱和度和元素含量的测井技术。本文概述了可控中子及X射线源测井技术,回顾了其发展历程;介绍了可控中子及X射线测井技术在数值模拟、仪器研制及数据处理方法方面的研究现状及应用,并展望了可控中子及X射线源测井技术的发展前景,认为未来可控中子及X射线源测井技术可从以下三个方面开展研究：分析不同射线在能量、时间及空间的分布规律,开展探测理论基础研究;联合不同学科优势,开展多类型多模式的新型仪器研制;增强谱数据校正及解析方法研究,开展谱信息综合分析及应用。     

可控中子及X射线源测井技术发展现状及趋势

随着核仪器技术的进步以及安全健康的工业发展需求,具有人工可控性的中子源及X射线源逐步在测井领域得到推广应用,为油气等矿产资源的勘探开发提供了关键技术手段。可控中子及X射线源测井技术是以中子发生器或X射线管产生的中子或X射线与地层物质作用,通过探测中子、伽马或X射线从而进行地层孔隙度、密度、油气饱和度和元素含量的测井技术。本文概述了可控中子及X射线源测井技术,回顾了其发展历程;介绍了可控中子及X射线测井技术在数值模拟、仪器研制及数据处理方法方面的研究现状及应用,并展望了可控中子及X射线源测井技术的发展前景,认为未来可控中子及X射线源测井技术可从以下三个方面开展研究:分析不同射线在能量、时间及空间的分布规律,开展探测理论基础研究;联合不同学科优势,开展多类型多模式的新型仪器研制;增强谱数据校正及解析方法研究,开展谱信息综合分析及应用。     

基于核脊回归方法预测的中子俘获率在s-过程模拟中的应用

慢中子俘获过程(s-过程)产生了自然界中约一半比Fe重的元素，中子俘获率是s-过程研究的关键核物理输入量。近年来，机器学习方法在核物理研究中的应用取得了很大的成功，其中包括了机器学习核脊回归方法对中子俘获率的研究。为了探究机器学习方法对中子俘获率的修正对s-过程研究的影响，本文分别利用修正前后的中子俘获率数据，基于核反应网络进行了s-过程模拟，并对所得s-过程丰度进行了对比分析。结果表明，机器学习对中子俘获率的修正对s-过程模拟所得的丰度分布整体影响较小，但对处于s-过程路径上的个别重要核素的丰度影响可达30%左右。     

PNN测井热中子时间谱的多尺度滤波研究

PNN(脉冲中子-中子)测井是利用He-3管记录热中子时间谱,进而求取地层宏观俘获截面的一种测井方法。热中子时间谱滤波处理是获取有效地层宏观俘获截面值的研究基础。针对热中子时间谱的特点,以X井为研究对象,在探讨小波基及阈值的量化处理基础上,采用了基于阈值收缩的多尺度滤波方法,分别在纵向和横向对热中子时间谱进行了多尺度滤波处理。滤波结果显示热中子计数随时间呈指数规律衰减,满足时间谱后处理的需要。这些探索为PNN测井时间谱的滤波处理提供了一种新方法。     

一种利用中子瞬发伽马能谱确定含油饱和度方法及数值模拟

剩余油饱和度的定量解释对于提高油气产能及指导油田后期开发具有重要意义。脉冲中子饱和度测井通过记录地层中C、O原子核与高能中子作用产生的特征伽马射线来确定剩余油饱和度。骨架矿物组成和粘土矿物类型等因素的变化会使剩余油饱和度解释结果存在误差。为确定岩性对非弹能谱中碳窗和氧窗伽马计数比（C/O）、俘获能谱中硅窗和钙窗伽马计数比（Si/Ca）的影响,采用蒙特卡罗方法（MCNP）模拟不同岩性、孔隙度和饱和度地层条件下的伽马能谱。模拟结果显示：传统碳氧比解释模型进行碳氧比差值计算时未考虑岩性影响,是造成剩余油饱和度解释存在误差的主要原因。通过在碳氧比差值计算时引入岩性校正因子,提出一种改进的碳氧比解释模型,提高饱和度解释精度。模拟算例和实测结果表明,该改进碳氧比解释模型满足砂岩地层饱和度解释精度要求的同时,在混合岩性地层计算饱和度误差小于10%。     

地层元素测井中探测器响应数值模拟研究

地层元素测井中常利用LaBr₃、BGO等晶体探测器测量γ能谱确定元素和矿物含量,晶体探测器计数效率与能量分辨率等参数是决定能谱质量和元素含量计算精度的关键因素。本文通过对比研究LaBr₃和BGO两种晶体探测器的能谱响应特性,利用蒙特卡罗方法建立了不同元素含量与种类的地层模型,模拟研究了两种晶体探测器的γ响应能谱,并利用最小二乘法计算了元素含量。结果表明：当地层矿物模型中元素种类较少时,两种晶体探测器测得的元素含量差异较小;当元素种类较多时,由于能谱中不同元素γ射线重叠及互相干扰,LaBr₃晶体探测器测得的元素含量计算精度优于BGO晶体探测器,体现了在复杂地层岩性元素含量测量中,高能量分辨率晶体探测器的探测优势。     

Simulation of energy spectra of slow He ions scattered from a copper surface

Scattering of low energy (2 keV) He⁺ ions from a polycrystalline copper surface is studied. Experimental Time-Of-Flight (TOF) spectra are presented for different values of the angle of incidence α and a fixed scattering angle θ = 129°. Using Monte Carlo simulation, based on the TRIM (TRansport of Ions in Matter [6]) code, energy spectra are calculated and compared to experimental data. The influence of different combinations of interaction potential and inelastic energy loss on the spectrum shape and on the angular distribution of the scattering yield is considered in the simulation. Simulations show very good agreement with the experiment for all investigated geometries. An analysis of the experimental yield of scattered particles in different parts of the spectrum is performed to gain information on the relative contributions of surface single scattering and multiple scattering.     

A digital spectrometer approach to obtaining multiple time-resolved gamma-ray spectra for pulsed spectroscopy

Neutron-induced gamma-ray emission and its detection using a pulsed neutron generator system is an established analytical technique for quantitative multi-element analysis. Traditional gamma-ray spectrometers used for this type of analysis are normally operated either in coincidence mode - for counting prompt gamma-rays following inelastic neutron scattering (INS) events when the neutron generator is ON, or in anti-coincidence mode - for counting prompt gamma-rays from thermal neutron capture (TNC) processes when the neutron generator is OFF. We have developed a digital gamma-ray spectrometer for concurrently measuring both the INS and TNC gamma-rays using a 14 MeV pulsed neutron generator. The spectrometer separates the gamma-ray counts into two independent spectra together with two separate sets of counting statistics based on the external gate level. Because the TNC gamma-ray yields are time dependent, additional accuracy in analyzing the data can be obtained by acquiring multiple time-resolved gamma-ray spectra at finer time intervals than simply ON or OFF. For that purpose we are developing a multi-gating system that will allow gamma-ray spectra to be acquired concurrently in real time with up to 16 time slots. The conceptual system design is presented, especially focusing on considerations for tracking counting statistics in multiple time slots and on the placement of pulse heights into multiple spectra in real time.     

Experimental and computed spectra of neutrons and photons emitted from spherical iron models with a <Superscript>252</Superscript>Cf source at the center

Series of experiments and calculations in which the spectra of neutrons and photons emitted from 20, 40, 50, 60, 70, and 100 cm in diameter spherical models with a ²⁵²Cf source at the center are studied are described. The neutron spectra are measured with spectrometers based on stilbene and a hydrogen counter and the photon spectra are measured with spectrometers based on stilbene and a Si(Li) detector. The calculations are performed using the ROZ-6 computer program and the BNAB-78 28-group neutron constants library. The experimental fluxes of >0.8 MeV neutrons are, for the most part, greater than the computed values, and the fluxes of >0.35 MeV photons are also greater than the computed values. The differences reach a factor of 2–3. The data obtained show that the the cross sections for elastic and inelastic neutron scattering and radiative capture of neutrons need to be changed, leaving the total cross sections for the interaction of neutrons with iron in the constants library tested unchanged.__________Translated from Atomnaya Énergiya, Vol. 98, No. 1, pp. 54–61, January, 2005.     

Transient dynamic and inelastic analysis of shells of revolution — a survey of programs

Advances in the limits of structural use in the areospace and nuclear power industries over the past years have increased the requirements upon the applicable analytical computer programs to include accurate capabilities for inelastic and transient dynamic analyses. In many minds, however, this advanced capability is unequivocally linked with the large scale, general purpose, finite element programs. This idea is also combined with the view that such analyses are therefore prohibitively expensive and should be relegated to the “last resort” classification. While this, in the general sense, may indeed be the case, if the user needs only to analyze structures falling into limited categories, however, he may find that a variety of smaller special purpose programs are available which do not put an undue strain upon his resources. One such structural category is shells of revolution.This survey of programs will concentrate upon the analytical tools which have been developed predominantly for shells of revolution. The survey will be subdivided into three parts: (a) consideration of programs for transient dynamic analysis; (b) consideration of programs for inelastic analysis and finally; (c) consideration of programs capable of dynamic plasticity analysis. In each part, programs based upon finite difference, finite element, and numerical integration methods will be considered. The programs will be compared on the basis of analytical capabilities, and ease of idealization and use. In each part of the survey sample problems will be utilized to exemplify the state-of-the-art.     

An ab initio Monte Carlo study of low energy positron and electron implantation in elemental metals and multilayers

A Monte Carlo code developed at Brookhaven to study positron and electron implantation in solids will be discussed. This code models the trajectories of a large number of positrons or electrons as they move through the material and uses this information to calculate stopping profiles, backscattered fractions and transmitted fractions. The particle-atom interactions are incorporated via elastic and inelastic scattering cross-sections. The incident particle energies vary from 1 to 10 keV and the simulation stops when the particle energy goes down to 25 eV or if the particle is backscattered. Main results of our Monte Carlo simulations of the mean implantation depth and implantation profiles for both semi-infinite metallic elements and multilayers will be discussed.     

On the neutron scattering transformation matrices

The computations of some neutron elastic transformation matrices with the two recently developed methods, the BRC method (Bersillon et al., 1983) and the BGU method (Ofek et al., 1984), have shown that the present ENDF/B transformation matrices, evaluated with the Amster method, suffer from inaccuracies and have to be used with precautions. On one hand, the BRC method, by which each element of the transformation matrix is expanded into a Taylor series of the inverse mass of the scattering nucleus, is indeed a single precision stable, but it is limited to scattering nuclei with A > 1. On the other hand the BGU method, with which the representation of a matrix element by an integral with Legendre polynomials is converted to a sum of integrals with rational functions, solves the evaluation of the matrix elements in a closed form and it is valid for A < 1 as well, but it suffers from roundoff instability in computing high order matrix elements. Herein, we extend the BGU method and generalize some of the expressions, which reduce the roundoff instability. Hence, better precision is obtained. In particular, a computation of the hydrogen transformation matrix with the BGU method indicates that the high order elements of the ENDF/B-V hydrogen matrix are erroneous. Moreover, since the discrete level inelastic transformation matrices are equivalent to the elastic ones, the BGU method also enables the computation of inelastic transformation matrices for neutron energies close to the threshold of the reaction. In addition, we present here new explicit expressions for some matrix elements, which may facilitate the computation of the transformation matrices.