CT扫描技术在低渗透砂岩岩心试验中的应用

CT扫描技术能够观测到岩心内部的结构变化情况,在碳酸盐岩岩心试验应用较多。以低渗透砂岩岩心为基础进行CT扫描分析,首先分析CT技术的基本原理,然后按照一定的方法和步骤对某区块气层岩心进行试验,最后按照CT扫描步骤进行扫描分析,并从3个方面对岩心进行分析:干岩心的CT数、岩心的孔隙度及分布特征、力学试验前后的CT扫描。由试验结果可以观察到,岩心越致密,其CT数值相对就越大;CT试验分析的岩心孔隙度值同测量值非常接近;岩心在受力条件下破裂,其裂纹呈现多样化特点。试验结果认为,CT扫描能够判断岩心的致密程度,并且能够确定岩心的孔隙度值,同时能够观察岩心破裂后的裂缝变化情况,便于低渗透岩心裂缝扩展的研究。     

岩心CT扫描图像分割计算缝洞孔隙度与测井资料处理结果对比研究

针对缝洞型储层岩心CT扫描图像特征,研究了一种图像分割方法计算岩心缝洞孔隙度,并与常规测井资料三孔隙度模型计算的缝洞孔隙度及成像测井图像分割提取的面孔隙度进行了对比。结果表明,基于CT扫描图像灰度特性的算法可以从CT扫描图像中分割出岩心上尺寸较大的缝洞孔隙。应用该方法从岩心CT扫描图像提取的缝洞孔隙度与三孔隙度模型计算的缝洞孔隙度及成像测井图像分割提取的面孔隙度存在一定的对应关系。     

应用CT技术研究岩石孔隙变化特征

应用CT扫描系统对13个岩心连续进行扫描,并应用三维重建技术得到岩心的三维孔隙变化,在"孔群级"尺度上清楚地观察到岩心内部的孔隙变化和非均质特征。应用统计学方法,对不同截面上测量的孔隙度进行定量分析与表征。S138号岩心存在着明显的层理现象,非均质性严重,岩心孔隙度的标准偏差和不均匀系数较高,孔隙分布不均匀,分选性差。71号岩心截面内低孔隙区较多,高孔隙区较少,岩心的平均孔隙度较低。S35号岩心的平均孔隙度高,岩心比较均质,岩心孔隙度的标准偏差与不均匀系数最小,孔隙分布均匀,分选性好。     

CT扫描技术在水敏伤害评价中的应用

常规储层敏感性评价方法无法准确反映发生伤害的具体区域,同时也缺少对敏感性伤害程度的定量评价。以2块采自同一层位的岩心为例,利用CT扫描技术开展储层水敏伤害评价实验研究,分别开展水驱和“设计”水驱实验,同时基于CT扫描原理建立相应的水敏伤害评价方法。水驱实验中注入压力和CT值的变化表明,实验用水与岩心接触时存在很强的水敏伤害。在“设计”水驱实验中,分析CT扫描孔隙度分布可确定水敏伤害主要发生在注入端附近,并可估算出平均孔隙度降低10%～15%;同时通过对比水敏伤害切片孔隙度图像前后变化,可准确反映出岩心中发生水敏伤害的具体区域。     

基于X-CT扫描的石油地质岩心储层渗透率估算

渗透率估算可以为石油地质岩心储层渗流能力分析提供数据支撑，为提高石油地质岩心储层的渗流能力，提出了基于X-CT扫描的石油地质岩心储层渗透率估算方法。根据油在两相共渗区的渗透率与水在两相共渗区的渗透率之比，引入Buckley-Leverett方程，计算岩心储层水驱油的分流率，利用X-CT扫描技术，扫描石油地质岩心的分布情况，计算出岩心储层含水饱和度。基于渗透区在井眼与地层之间出现的流体流动现象，计算出岩心储层中泥浆的体积模量和地层的剪切模量，利用斯通利波时差实测值与弹性斯通利波时差之间的差值，计算流体移动指数。根据等效孔隙度与流体移动指数之间的相关性和等效孔隙度与渗透率的相关性，估算出石油地质岩心储层的渗透率。实验结果表明该方法的估算精度可达到90%以上，对估算石油地质岩心储层渗透率具有重要意义。     

利用 CT技术研究裂缝性油藏改性淀粉凝胶调堵液流转向

针对常规方法研究裂缝性油藏封堵后液流转向过程不能观察油藏内部孔隙结构和流体运移特征的问题,运用改性淀粉凝胶封堵人工裂缝, 利用 CT扫描技术和岩心驱替实验, 研究了裂缝性油藏调堵液流转向机理, 通过 CT图像呈现岩心孔隙特征、 油水分布及裂缝封堵后注入水扩大波及体积过程。结果表明, 人工裂缝贯穿整条岩心, 孔隙分布均匀, 平均孔隙度 22.7%, 注入水沿着裂缝窜流, 不能建立起有效的驱替压差, 基质波及程度低, 一次水驱原油采收率仅为 10.6%。改性淀粉凝胶可有效封堵裂缝孔道, 迫使注入水液流转向, 启动岩心基质, 二次水驱波及体积大约扩大到岩心基质体积的 2/3, 最终采收率为 46.1%, 提高了 35.5%。CT扫描技术为研究封堵裂缝性油藏机理提供了可视手段。图 7参 18     

利用计算机层析（CT）确定岩心的基本物理参数

计算机层析 (CT)是对物体内部横断面进行成像的一种无损检测技术 ,在石油工业中已发展成为一门特殊的定量测试技术。利用CT确定岩心的基本物理参数 (体积密度、孔隙度、饱和度 )具有常规方法无法相比的优越性。用CT确定密度的方法有单能扫描法、双能扫描法、线性插值法 ;确定孔隙度的方法有单次扫描法、两次扫描法、测井解释法、图像分析法 ;确定饱和度的方法有单能两次扫描确定含水率、双能扫描确定含水率、单能扫描确定两相流体饱和度、单能扫描确定三相流体饱和度、双能扫描确定三相流体饱和度、图像分析法确定流体饱和度。利用ACTIS高分辨率工业CT对岩心进行了扫描 ,试验表明利用CT计算的结果与常规方法的测定值符合较好。CT法测得的平均密度与煤油法测定值相比 ,平均绝对误差不到 1 .2 %。饱和煤油法与氦孔隙计法测量孔隙度之间的平均误差为8.5% ,CT两次扫描法与饱和煤油法之间的误差为7.8% ,说明利用CT测量岩心的孔隙度是成功的。利用ACTIS工业CT对油水非稳态相对渗透率驱替试验进行扫描 ,计算驱替过程中饱和度的变化与重量法的计算值一致。图 5表 1参 7(李玉彬摘 )     

应用图象分析技术改进渗透率预测

了解流体在油气储集层中流动的关键是获得岩心，并测量岩心孔隙度和渗透率。因此，在不能取心的地区，可采用预先建立的局部渗透率－孔隙度关系根据电缆测井曲线计算的孔隙度预测渗透主率。本文研究了一个单一储层的弱相关（就预测而言）的渗透率－孔隙度关系，使用图象分析技术，对反向射散射电子显微镜扫描图象进行分析以认识和更好地约束这种孔渗关系，就预测而言，在渗透率－孔隙度关系图中如果使用图像孔隙度代替岩心孔隙度，可以得到更紧密的统计相关关系。通过考虑孔隙度大小分布，我们进行了进一步的研究，以确定引起这种关系增强的原因，结论是，图像孔隙率在测量时不包括微孔隙度，且微孔隙度对流体流动没有贡献。而在岩心分析中，岩心孔隙度测量包括了微孔隙度。     

基于CT扫描的蒸汽驱岩心孔隙结构特征及相渗分析

为明确蒸汽驱对疏松砂岩稠油油藏孔隙结构特征的影响，以LDB油田为例，应用CT技术扫描不同蒸汽驱阶段岩心，构建三维数字岩心模型，提取孔隙网络模型，获取不同蒸汽驱阶段的岩心孔隙度、绝对渗透率及孔隙结构相关特征等参数，并通过流动模拟得到相对渗透率曲线，开展定量统计及分析。结果表明：随着蒸汽驱的进行，岩心孔隙空间变大，平均孔隙半径、平均喉道半径、孔隙度及渗透率均增大，渗流能力变强，孔隙结构得到改善。研究成果可为稠油油藏蒸汽驱开发设计提供技术支持。     

微CT扫描重建低渗气藏微观孔隙结构——以新场气田上沙溪庙组储层为例

为了提高气藏采收率,从微观孔隙结构出发,建立孔隙网络模型,定量描述孔隙微观尺度上的渗流机理。以川西新场气田上沙溪庙组岩心为例,开展孔隙结构三维重构研究。首先采用微CT技术对岩心进行扫描获得投影数据,采用FDK算法重建岩心灰度图像,然后以宏观孔隙度为基础利用二值分割法分割灰度图像,最后使用光线跟踪算法得到三维孔隙结构图像,即数字岩心。对数字岩心的相关性质进行统计分析,得到的数字岩心孔隙度与岩心实验孔隙度基本一致,相对误差约为0.1。 这一数值与新场气田上沙溪庙组储层物性相吻合,说明微CT扫描法重构微观孔隙结构是可行的。该研究为建立孔隙网络模型及开展后续微观渗流模拟研究奠定了基础。     

POROSITY AND PERMEABILITY EVOLUTION ACCOMPANYING HOT FLUID INJECTION INTO DIATOMITE

An experimental study of silica dissolution was performed to probe the evolution of permeability and porosity in siliceous diatomite during hot fluid injection such as water or steam flooding. Two competing mechanisms were identified. Silica solubility in water at elevated temperature causes rock dissolution thereby increasing permeability; however, the rock is mechanically weak leading to compression of the solid matrix during injection. Permeability and porosity can decrease at the onset of fluid flow. A laboratory flow apparatus was designed and built to examine these processes in diatomite core samples. At the core level, we measured the pressure drop as a function of time for fixed injection rates to determine permeability variation and utilized an X-ray Computerized Tomography (CT) scanner to measure in-situ porosity. At the pore level, a scanning electron microscope (SEM) was used to observe changes in pore morphology. We found that porosity decreased initially due to compaction caused by the imposed pressure drop across the core. Later, porosity increased as silica dissolved. Dissolution of the rock matrix appeared to be relatively uniform; wormholes were not observed even after tens of pore volumes of fluid injection.     

POROSITY AND PERMEABILITY EVOLUTION ACCOMPANYING HOT FLUID INJECTION INTO DIATOMITE

An experimental study of silica dissolution was performed to probe the evolution of permeability and porosity in siliceous diatomite during hot fluid injection such as water or steam flooding. Two competing mechanisms were identified. Silica solubility in water at elevated temperature causes rock dissolution thereby increasing permeability; however, the rock is mechanically weak leading to compression of the solid matrix during injection. Permeability and porosity can decrease at the onset of fluid flow. A laboratory flow apparatus was designed and built to examine these processes in diatomite core samples. At the core level, we measured the pressure drop as a function of time for fixed injection rates to determine permeability variation and utilized an X-ray Computerized Tomography (CT) scanner to measure in-situ porosity. At the pore level, a scanning electron microscope (SEM) was used to observe changes in pore morphology. We found that porosity decreased initially due to compaction caused by the imposed pressure drop across the core. Later, porosity increased as silica dissolved. Dissolution of the rock matrix appeared to be relatively uniform; wormholes were not observed even after tens of pore volumes of fluid injection.     

CT在油气藏储量计算参数测定中的应用

本文研究了应用第三代医用CT扫描仪进行油气藏储量计算参数测定的可行性,并测定了八块岩心样品的孔隙度及油、水饱和度,证明其结果与常规方法的测定值符合较好.并研制了应用医用CT分析岩心孔隙度和油、水饱和度的配套软件.指出了医用CT在进行岩心分析上的局限性和克服的方法.最后明确了本实验的意义,并展示了裂缝型油气藏储层岩心CT分析的一些情况及其孔隙度测定的数据.     

Multiphase-flow properties of fractured porous media

Water–air imbibition and oil–water drainage displacements were conducted using a laboratory flow apparatus in fractured sandstone systems. During the experiments, porosity and saturation were measured along the core using a Computerized Tomography (CT) scanner. 3-D saturation images were reconstructed to observe matrix–fracture interactions. Differences in fluid saturations and relative permeabilities caused by changes of fracture width have also been analyzed. In the case of water–air imbibition, narrower fracture apertures showed more stable fronts and delayed water breakthrough compared to the wide fracture systems. However, the final water saturation was higher in wide fracture systems, thus showing that capillary pressure in the narrow fracture has more effect on fluid distribution in the matrix. During oil–water drainage, oil saturations were higher in the blocks near the thin fracture, again showing the effect of fracture capillary pressure. Oil fingering was observed in the wide fracture. Fine-grid simulations of the experiments using a commercial reservoir simulator were performed. Relative permeability and capillary pressure curves were obtained by history matching the experiments. The results showed that the assumption of fracture relative permeability equal to phase saturation is incorrect. It was found that both capillary and viscous forces affect the process. The matrix capillary pressure obtained by matching an experiment showed lower values than those reported in the literature.     

Spontaneous imbibition characteristics of diatomite

A systematic investigation of fluid flow characteristics within diatomite (a high porosity, low permeability, siliceous rock) is reported. Using an X-ray computerized tomography (CT) scanner, and a novel, CT-compatible imbibition cell, we study spontaneous cocurrent water imbibition into diatomite samples. Air–water and oil–water systems are used and the initial water saturation is variable. Mercury porosimetry and a scanning electron microscope (SEM) are employed to describe diatomite pore structure and the rock framework. Diatomite exhibits a fine pore structure and significant pore-level roughness relative to sandstone thereby aiding the flow of imbibing water. Despite a marked difference in permeability and porosity as compared to sandstone, we find similar trends in saturation profiles and dimensionless weight gain vs. time functions. Although diatomite is roughly 100 times less permeable than sandstone, capillary forces result in a strong imbibition potential for water such that imbibition rates rival and surpass those for sandstone     

油藏数值模拟中油水相对渗透率曲线处理方法

油水相对渗透率数据是油藏数值模拟输入的基础参数之一,是模拟预测中影响产油量和产水量的重要参数。针对没有岩心资料的区域如何选用油水相对渗透率曲线的问题,提出通过FZI(FlowZone Indicator,流动层指数)划分流动单元的方法,通过绘制RQI与z的双对数关系图,判断研究目标区与取心样品区是否具有相似的影响流体流动的岩石物理性质,从而决定油水相渗曲线的选用。该方法较全面地考虑了储层岩石内部孔隙结构、迂曲度、渗透率等参数对流体渗流能力的影响,具有较好的应用效果。     

碎屑岩储层物性非均质性的层次结构

储层物性非均质性与沉积体系内部的构成单位关系密切,可以分尺度进行研究:(1)在沉积体系级的大尺度范围内,不同的沉积体系具有不同的储集性能；在同一沉积体系中,不同的成因相孔渗值差别极大,主要取决于沉积作用过程中古水流能量和环境的变化。(2)在成因相级的中尺度范围内,各流体流动单元内部及不同的流体流动单元之间孔渗值存在明显的整体差别,这与构成流体流动单元的储层岩性相关系密切,如果叠加有不均匀的成岩作用的影响,那么流体流动单元的物性将会大大地降低。(3)在岩芯级的微尺度范围内,多孔介质具有各向异性特征。     

介电扫描测井技术在长庆油田的应用

低孔隙度低渗透率的储层中孔隙结构比较复杂,地层水矿化度未知,利用电阻率区分流体性质困难。介电扫描测井仪器采用铰接式极板,有4种不同的频率,具有不同的探测深度,最深可达到4in,能够测量地层介电常数。油气和水的介电常数差异很大,介电扫描测井通过反演得到的介电常数计算侵入带内的含水孔隙度,与常规测井或核磁共振测井得到的总孔隙度对比得到侵入带内的油气饱和度。介电扫描测井技术除可以得到地层的含水孔隙度外,同时能得到反映岩石结构的参数m、n或者阳离子交换能力。介绍介电扫描测井的基本方法、工作原理和应用。对长庆油田介电扫描测井实例进行了分析,测井解释结果与试油结论一致。