多孔介质中泡沫生成及稳定性机理的CT实验研究

近年来,泡沫流体在三次采油中越来越受到学者重视,在提高三次采油采收率机理研究方面,计算机层析(CT)有着自身技术上的优势。本文利用ACTIS微焦点X-rayCT技术对三次采油中泡沫驱油岩心进行研究与分析,直观地描述岩心中泡沫的特征与分布规律。采用可视化新方法研究得出泡沫驱油中的流体饱和度分布,揭示泡沫驱油特征机理。研究结果对于指导矿场试验具有重要意义。     

浅议储层地质研究中的CT技术

CT技术具有无损、三维并可与计算机应用模拟相结合等特点,使其在储层地质研究中作用独特。本文从CT技术特点入手,总结分析其在储层地质研究中的应用发展历程:储层岩石组构识别、储层表征、微观流体输运过程的在线监测及剩余油分布研究等。随着高分辨率工业CT及数字岩心技术的发展,CT扫描三维数据体与数字岩心相结合,不仅可以提取岩石物理属性参数,如储层岩石的孔渗、地层因子、弹性模量、横纵波分析等,建立三维孔喉网络模型,还可以直接对复杂的孔喉系统进行定量化的结构表征和微渗流数值模拟。最后,本文作出展望,随着计算机技术的提高和油气勘探需求的增长,其应用会越来精细,越来越广泛。      

用核磁共振测井资料评价碳酸盐岩等复杂岩性储集层

对于碳酸盐岩等复杂岩性油气藏,由于其储集空间复杂、非均质性强等因素,用常规测井技术难以进行准确描述.核磁共振测井测量的对象是储层空间中的流体,因而可以直接用来划分储集层,而且能提供几乎不受岩性影响的孔隙度和渗透率等参数;同时,由于其T2分布表征了岩石的孔隙结构,所以可以根据T2分布形态判断有效裂缝和溶蚀孔洞.通过多口井的岩心对比和成像测井对比,研究出了一套用MRIL和CMR 的T2分布形态评价储集空间的方法;此外,在特定条件下,根据核磁计算的有效孔隙度和可动流体体积给出了一个计算含油饱和度的公式.利用这些核磁测井技术及其分析方法对车古20古潜山碳酸盐岩储集层裂缝及溶蚀孔洞发育特征进行准确描述,还计算了埕北潜山复杂复杂岩性油气藏的饱和度,对于储量计算具有重要意义.     

三维数字岩心技术岩石物理应用研究进展

三维数字岩心可在孔隙尺度上对岩石的微观结构进行精细表征,以数字岩心为载体的岩石微观结构分析与岩石物理属性模拟研究已成为岩石物理分析的重要发展方向之一.本文从数字岩心建模、数字岩心图像分析及岩石物理属性模拟三个方面对数字岩心技术进行了介绍.将数字岩心技术在岩石物理领域的应用分为两大类:基于三维数字图像的直接分析和基于三维数字岩心的岩石物理属性数值模拟.通过三维图像分析可获得孔隙结构、矿物成分、粒度分布等信息;通过岩石物理属性模拟可以研究储层岩石电性、弹性、渗流和核磁共振特征.多种手段相结合建立多尺度、多组分数字岩心,突破分辨率与样品尺度的矛盾限制是数字岩心技术未来的发展趋势.数字岩心技术已发展成为岩石物理实验的重要组成部分,如何将孔隙尺度得到的岩石物理参数升尺度到数字井筒、数字油藏中是数字岩心技术发展亟需解决的难题.     

基于数字岩心动态应力应变模拟的非均匀孔隙介质波致流固相对运动刻画

地震波传播激发的不同尺度的流固相对运动(宏观、中观和微观)是许多沉积岩地层中地震波频散和衰减的主要原因,然而野外观测和试验测量都难以对非均匀多孔介质孔隙压力弛豫物理过程进行精细刻画.通过数字岩石物理技术,本文建立了三个典型的数字岩心分别用于表征孔隙结构、岩石骨架和斑状饱和流体引起的非均质性,利用动态应力应变模拟技术计算数字岩心的位移和孔隙流体增量图像.通过分析和比较三个数字岩心的位移和孔隙压力增量图像,细致刻画了发生于非均匀含流体多孔介质内的宏观、中观和微观尺度的流固相对运动:1)宏观尺度的波致孔隙流体流动导致波长尺度上数字岩心不同区域的孔隙压力和位移差异;2)中观尺度的流体流动发生在软层与硬层之间、气层与液层之间;3)微观尺度的流体流动发生在孔隙内部或相邻孔隙之间.数值模拟试验也证明基于数字岩心的动态应力应变模拟技术可以从微观尺度上更好的理解波致孔隙流体流动发生的物理机理,从而为建立岩石骨架、孔隙流体、孔隙结构非均质性和弹性波频散-衰减特征的映射关系奠定基础.     

岩石物理驱动下地震流体识别研究

地震流体识别指利用地震资料对储层含流体特征进行识别与描述.含流体储层地震岩石物理是地震流体识别的基础,是搭建储层弹性参数与物性参数的桥梁,是实现含油气储层流体定量表征的重要发展方向.岩石物理驱动下地震流体识别研究有助于认识地下油气储层含流体特征及分布规律.文章概述地震流体识别及相关基础研究中的关键科学问题,着重评述国内外岩石物理驱动下地震流体识别研究的主要进展,探究地震流体识别研究面临的机遇,挑战及未来的研究方向.理论研究和实际应用表明,地震流体识别要以岩石物理及数值模拟为理论基础,发展有效的流体敏感参数构建及评价方法;以地震资料为数据支撑,形成有效的地震资料品质评价方法;以地震反演为技术保障,发展可靠的地震反演策略.     

低渗特低渗砂岩储层流体识别技术研究综述和展望

低渗、特低渗储层是国内外油田地质研究的重点,而其流体识别问题更是一个焦点问题.本文根据以往的研究成果,再认识了低渗、特低渗储层流体识别的难点,进而梳理和归纳了流体识别的常规技术和新技术.研究表明,利用单一的测井解释方法容易引起多解性,技术风险高;基于地区地质、岩心、录井等资料,结合多种测井曲线,开展流体的综合识别评价是一个重要的技术思路;将现代地质数学方法和信号分析技术引入流体识别中将会产生积极地意义,本文对此进行了展望.     

岩石物理弹性参数规律研究

根据辽东湾凹陷某区在地层条件和不同流体相态(气饱和、水饱和等)下岩石纵波速度、横波速度及密度等岩心测试数据,以及岩石矿物成分、孔隙度等常规岩心分析数据,统计分析了岩石弹性参数变化规律.采用有效流体模型、斑块饱和模型进行了纵、横波速度理论计算,并和实验测量结果比较,认为高孔、高渗岩石可以看作有效流体模型,低孔、低渗岩石更接近斑块饱和模型.这些规律和认识对于指导储层预测和油气检测及地震振幅综合解释有重要的意义.     

Petrophysical evaluation and its application to AVO based on conventional and CMR-MDT logs

常规测井为 AVO 分析提供了基础的资料, 成为联系岩石物理与地震资料的桥梁。然而如果储层存在有复杂的流体系统, 如地层被严重地层流体侵入、电阻率响应低及盐水矿化度复杂等的现象, 则常规测井无法提供高质量的测井资料, 导致得出错误的弹性计算结果, 使 AVO 结果与地震资料不吻合。中国渤海湾地区第三系裂缝性储层复杂, 我们利用常规测井和核磁共振测井与模块地层动态测试相结合的组合仪完成了地层评价和储层描述。研究结果表明岩石物理学家利用上述方法技术可以获得诸如空隙度、渗透率、含水饱和度、束缚流体以及空隙压力等重要的储层参数并进一步综合应用这些结果和以实验室测量数据为基础的岩性分析结果进行在地震域岩石物理研究和 AVO 分析。     

应用CT成像技术研究岩心孔隙度分布特征

清楚地识别岩心内部孔隙度分布特征,并对其进行定量描述,有助于深入研究岩心的渗流特性。应用CT成像技术,通过对干岩心和饱和地层水岩心扫描,重建了岩心不同扫描层面、沿某正交切面以及三维孔隙度分布图。应用孔隙度频率分布和累积频率分布曲线得到了岩心孔隙度分布的统计特征。将岩心孔隙度划分为“层面级”和“岩心级”两个级别,选用7种参数对岩心孔隙度分布的集中趋势、离散程度和分布形态进行表征。研究实例表明,同一岩心不同扫描层面孔隙度分布存在明显差异,其集中程度、离散程度和分布形态均有所不同。采用这7种表征参数可精细刻画岩心孔隙度分布特征。     

小型移动CT扫描仪的焦皮距问题研究

最小焦皮距是国标中限制CT扫描仪小型化的一个关键参数。本文介绍焦皮距的物理意义,分析X射线透视成像和X射线计算机断层成像的异同,以及滤过器在X射线计算机断层成像中对扫描孔内吸收剂量分布的重要影响。实验证明,由于滤过器的作用,大、小CT扫描仪扫描孔内的吸收剂量分布都是中心区域高、内壁区域低。源自X射线透视成像的最小焦皮距概念,在断层成像中不能发挥同样的作用,但是会限制CT扫描仪小型化的发展。      

基于数字岩心的岩石电性微观数值模拟(英文)

本文利用x射线CT获取反映岩心微观结构的三维数字岩心,利用数学形态学中的开运算模拟了岩石的油驱水排驱过程中,不同含水饱和度下油和地层水在孔隙空间中的分布。利用有限元方法计算了岩石电阻率,进而得到岩石地层因素和电阻率指数,并考查了岩石润湿性对岩石电阻率指数的影响。数值模拟结果表明：基于数字岩心的水湿岩石地层因素和电阻率指数数值模拟结果与实验结果一致,拓展了岩石电阻率实验的能力;岩石润湿性对岩石电性有重要影响,在相同含水饱和度下,油湿岩石电阻率高于水湿岩石电阻率,油湿岩石饱和度指数远大于水湿岩石饱和度指数。     

基于数字岩心的碳酸盐岩孔隙结构对弹性性质的影响研究(上篇):图像处理与弹性模拟

碳酸盐岩复杂的孔隙结构如何影响其弹性性质一直是地球物理研究的难点问题,在此基础上如何半定量甚至是定量地对碳酸盐岩储层预测,特别是如何有效地获取孔隙结构参数相关的地震属性体一直是油气工业界追求的目标.本研究从数字岩心角度入手,联合测井以及地震数据尝试探究这一问题的解决方案,包括如下几个方面:(1)代表性碳酸盐岩储层样品获取;(2)CT扫描数字岩心数据体获取;(3)数字岩心数据的图像处理;(4)数字岩心数据的静态弹性模拟;(5)数字岩心子数据体的孔隙结构因子提取;(6)孔隙结构因子表征与分类下的弹性性质与孔隙度的定量化量版建立;(7)数字岩心-井-地震联合的孔隙度属性提取;(8)孔隙结构因子的地震属性体获取.本研究分为两篇系列文章上篇与下篇,上篇主要阐述如上提出的(1)—(4)方面,重点在于针对碳酸盐岩二值化图像处理的流程建立与验证,以及数字岩心静态弹性模拟的理论方面,这两方面是基于数字岩心获得精确的碳酸盐岩弹性性质模拟结果的关键所在;下篇主要阐述利用数字岩心数据获得孔隙结构因子的思路、理论与流程,以及为碳酸盐岩储层预测为目标而获得孔隙结构因子的地震属性体的实际应用方面.由于两篇文章共享数字岩心数据,同时所涉及的研究思路与流程形成一个有机整体,因此写成两篇系列文章而非两篇独立文章.本文为两篇系列文章的第一篇:上篇.     

Digital core based transmitted ultrasonic wave simulation and velocity accuracy analysis

Transmitted ultrasonic wave simulation (TUWS) in a digital core is one of the important elements of digital rock physics and is used to study wave propagation in porous cores and calculate equivalent velocity. When simulating wave propagates in a 3D digital core, two additional layers are attached to its two surfaces vertical to the wave-direction and one planar wave source and two receiver-arrays are properly installed. After source excitation, the two receivers then record incident and transmitted waves of the digital rock. Wave propagating velocity, which is the velocity of the digital core, is computed by the picked peak-time difference between the two recorded waves. To evaluate the accuracy of TUWS, a digital core is fully saturated with gas, oil, and water to calculate the corresponding velocities. The velocities increase with decreasing wave frequencies in the simulation frequency band, and this is considered to be the result of scattering. When the pore fluids are varied from gas to oil and finally to water, the velocity-variation characteristics between the different frequencies are similar, thereby approximately following the variation law of velocities obtained from linear elastic statics simulation (LESS), although their absolute values are different. However, LESS has been widely used. The results of this paper show that the transmission ultrasonic simulation has high relative precision.     

利用混合法构建三维数字岩心(英文)

在弹性波有三维数字岩心描述了岩石的微观孔隙结构。X射线CT扫描是获取三维数字岩心最准确和直接的方法,但实验成本高。本文结合沉积过程模拟和模拟退火算法,提出了重建三维数字岩心的混合法,基于岩石二维图像重建三维数字岩心。利用岩石颗粒沉积算法构建初始数字岩心,作为模拟退火算法的初始状态。运用模拟退火算法调整岩石颗粒和孔隙的相对位置,使三维数字岩心与岩心二维图像具有相似的自相关函数,从而建立三维数字岩心。与传统模拟退火算法相比,该方法计算时间明显减小。运用局部孔隙度理论定量比较了重建数字岩心和岩心X射线微CT图像,两种数字岩心具有相似的均质性和孔隙连通性。利用有限元方法和格子玻尔兹曼方法分别模拟了重建三维数字岩心的地层因素和渗透率,数值模拟结果与实验结果相符。相比传统模拟退火算法,混合法重建数字岩心的传导特性更接近真实岩心的传导特性。     

龙马溪组页岩数字岩心动态法弹性等效数值建模

数字岩心是计算岩石弹性性质的一类常用方法.龙马溪组页岩具有多矿物构成、复杂微结构和强非均质等特征,常规岩石物理的弹性等效解析建模局限性较大,目前流行的静态数值等效建模方法的精度有限.本文基于高分辨率的页岩数字岩心数据,采用多阈值分割方法将数字岩心分解为黏土、石英、孔隙、TOC、长石类、黄铁矿类等六种矿物类型;利用矿物组分等效模量法计算各类矿物的弹性模量;采用二元函数分水岭方法表征不同压力下的岩石孔隙变形和颗粒接触关系变化;通过取向分布函数(ODF)定量分析矿物颗粒展布造成的各向异性特征.最后基于Biot孔弹方程,采用不分裂卷积完全匹配层(CPML)旋转交错网格有限差分法模拟不同压力下弹性波在数字岩心中的传播.以未加压的数字岩心为参考模型,计算不同压力下弹性波走时的平均时间差,进而估算各压力点的数字岩心等效速度.与该岩心样品的超声实验测量速度比较,动态法数值计算结果略偏高,据此校正数值计算过程中表征岩石微结构及颗粒接触关系随压力变化的二元函数,有效改善动态法弹性等效数值建模精度.     

Petrophysical study of faults in sandstone using petrographic image analysis and X-ray computerized tomography

Petrographic image analysis (PIA) and X-ray computerized tomography (CT) provide local determinations of porosity in sandstone. We have investigated small faults called deformation bands in porous sandstones using these techniques. Because the petrophysical properties of the fault rock vary at a small scale (mm scale), the ability of PIA and CT to determine porosity in small volumes of rock and to map porosity distribution in two and three dimensions is crucial. This information is used to recognize the processes involved in fault development and the different kinds of microstructures associated with dilatancy and compaction. The petrophysical study of fault rock in sandstone permits one to make predictions of the hydraulic properties of a fault and thereby evaluate the sealing or fluid transmitting characteristics of faulted reservoirs and aquifers. The results of this study indicate that faulting in sandstone alters the original porosity and permeability of the host rock: the porosity is reduced by an order of magnitude and the permeability is reduced by one to more than seven orders of magnitude for faults associated with compaction.     

Poroelastic finite-difference modeling for ultrasonic waves in digital porous cores

Scattering attenuation in short wavelengths has long been interesting to geophysicists. Ultrasonic coda waves, observed as the tail portion of ultrasonic wavetrains in laboratory ultrasonic measurements, are important for such studies where ultrasonic waves interact with small-scale random heterogeneities on a scale of micrometers, but often ignored as noises because of the contamination of boundary reflections from the side ends of a sample core. Numerical simulations with accurate absorbing boundary can provide insight into the effect of boundary reflections on coda waves in laboratory experiments. The simulation of wave propagation in digital and heterogeneous porous cores really challenges numerical techniques by digital image of poroelastic properties, numerical dispersion at high frequency and strong heterogeneity, and accurate absorbing boundary schemes at grazing incidence. To overcome these difficulties, we present a staggered-grid high-order finite-difference (FD) method of Biot’s poroelastic equations, with an arbitrary even-order (2L) accuracy to simulate ultrasonic wave propagation in digital porous cores with strong heterogeneity. An unsplit convolutional perfectly matched layer (CPML) absorbing boundary, which improves conventional PML methods at grazing incidence with less memory and better computational efficiency, is employed in the simulation to investigate the influence of boundary reflections on ultrasonic coda waves. Numerical experiments with saturated poroelastic media demonstrate that the 2L FD scheme with the CPML for ultrasonic wave propagation significantly improves stability conditions at strong heterogeneity and absorbing performance at grazing incidence. The boundary reflections from the artificial boundary surrounding the digital core decay fast with the increase of CPML thicknesses, almost disappearing at the CPML thickness of 15 grids. Comparisons of the resulting ultrasonic coda Q _sc values between the numerical and experimental ultrasonic S waveforms for a cylindrical rock sample demonstrate that the boundary reflection may contribute around one-third of the ultrasonic coda attenuation observed in laboratory experiments.     

致密砂岩储层CO2驱油特征的核磁共振实验研究

利用核磁共振技术对致密砂岩储层不同渗透率级别基质岩心和裂缝基质岩心不同驱替压力下CO2驱油特征进行了研究,简述核磁共振原理及实验方法。表明:致密砂岩储层特低、超低渗透基质岩心在初始CO2驱替压力下,岩心毛细孔隙和微毛细孔隙区间的油不同程度被采出,随着CO2驱替压力增大,特低、超低渗透基质岩心毛细孔隙区间油的采出程度不断增加且累积采出程度不同。裂缝致密砂岩储层岩心,裂缝和毛细孔隙区间的油在初始CO2驱替压力下,岩心裂缝中的油及毛细孔隙中的部分油被驱替出来,CO2驱替压力提高毛细孔隙、微毛细区间油的采出程度和累积采收程度较小。致密砂岩储层特低、超低渗透基质岩心和裂缝致密砂岩储层岩心,随着CO2驱替压力增大毛细孔隙区间的部分剩余油成正比增加进入到微毛细孔隙区间改变储层剩余油分布。核磁共振技术能够深入研究致密砂岩储层CO2不同驱替压力阶段,岩心裂缝、毛细孔隙区间、微毛细孔隙区间油的采出程度和剩余油分布情况,对于研究致密砂岩储层微观驱油机理具有较重要的价值。      

Micro-scale experimental investigation of the effect of flow rate on trapping in sandstone and carbonate rock samples

We present the results of a pore-scale experimental study of residual trapping in consolidated sandstone and carbonate rock samples under confining stress. We investigate how the changes in wetting phase flow rate impacts pore-scale distribution of fluids during imbibition in natural, water-wet porous media. We systematically study pore-scale trapping of the nonwetting phase as well as size and distribution of its disconnected globules. Seven sets of drainage-imbibition experiments were performed with brine and oil as the wetting and nonwetting phases, respectively. We utilized a two-phase miniature core-flooding apparatus integrated with an X-ray microtomography system to examine pore-scale fluid distributions in small Bentheimer sandstone (D = 4.9 mm and L = 13 mm) and Gambier limestone (D = 4.4 mm and L = 75 mm) core samples. The results show that with increase in capillary number, the residual oil saturation at the end of the imbibition reduces from 0.46 to 0.20 in Bemtheimer sandstone and from 0.46 to 0.28 in Gambier limestone. We use pore-scale displacement mechanisms, in-situ wettability characteristics, and pore size distribution information to explain the observed capillary desaturation trends. The reduction was believed to be caused by alteration of the order in which pore-scale displacements took place during imbibition. Furthermore, increase in capillary number produced significantly different pore-scale fluid distributions during imbibition. We explored the pore fluid occupancies and studied size and distribution of the trapped oil clusters during different imbibition experiments. The results clearly show that as the capillary number increases, imbibition produces smaller trapped oil globules. In other words, the volume of individual trapped oil globules decreased at higher brine flow rates. Finally, we observed that the pore space in the limestone sample was considerably altered through matrix dissolution at extremely high brine flow rates. This increased the sample porosity from 44% to 62% and permeability from 7.3 D to 80 D. Imbibition in the altered pore space produced lower residual oil saturation (from 0.28 to 0.22) and significantly different distribution of trapped oil globules.