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.     

An investigation of the effect of wettability on NMR characteristics of sandstone rock and fluid systems

Predicting reservoir wettability and its effect on fluid distribution and hydrocarbon recovery remains one of the major challenges in reservoir evaluation and engineering. Current laboratory based techniques require the use of rock–fluid systems that are representative of in situ reservoir wettability and preferably under reservoir conditions of pressure and temperature. However, the estimation of reservoir wettability is difficult to obtain from most laboratory experiments. In theory, it should be possible to determine the wettability of reservoir rock–fluid systems by nuclear magnetic resonance (NMR) due to the surface-sensitive nature of NMR relaxation measurements. Thus, NMR logs should in principle be able to give an indication of reservoir wettability, however, as yet there is no proven model to relate reservoir wettability to NMR measurements. Laboratory NMR measurements in representative and well-characterised rock–fluid systems are crucial to interpret NMR log data.A series of systematic laboratory experiments were designed using a range of sandstone core plugs with the aim of investigating the feasibility of using NMR measurements as a means to determine wettability. NMR T₂ spectrum measurements were performed in reservoir core plugs at different saturations and wettability states. The samples were first cleaned by hot solvent extraction, then saturated with brine and a drainage/imbibition cycle performed. At the lowest brine saturation the same samples were aged in crude oil and a further drainage/imbibition cycle performed. NMR transverse relaxation time, T₂, was measured on fully saturated samples, at residual saturations and some intermediate saturation values. The wettability of the samples is evaluated using the Archie's saturation exponent and by Amott-Harvey wettability index.The wettability of the cores studied ranged from mixed-wet to oil-wet. The NMR T₂ results for cleaned and aged reservoir core plugs, containing oil and water, show that fluid distribution and wettability can be deduced from such measurements. The results on aged core plugs suggest that the oil occupies a wide range of pore sizes and is in contact with the pore walls. The results presented in the paper suggest that NMR T₂ relaxation has the potential to be an alternative technique to evaluate rock wettability in the laboratory and in the reservoir.     

油层岩石的孔隙结构与驱油效率的关系

根据岩石的毛管压力曲线资料．在矩法确定的岩石孔隙结构特征值基础上,提出了孔隙结构特征值函数的方法．室内驱油实验结果证明,孔隙结构特征值函数与水驱油效率有很好的正相关性,利用孔隙结构特征值函数可以预测油藏的水驱油效率．     

双河油田低阻油层成因研究

依据已证实低阻油层的地质、测井、测试和化验分析资料，分析了双河油田低阻油层的形成机理，认为岩性细、岩石颗粒表面粗糙；泥质含量大，泥质含量中绿泥石所占比例高；油层薄，油层内存在泥质夹层；含油高度小以及泥浆滤液的侵入等是形成低阻油层的主要原因。在此基础上，提出了解释低阻油层的基本思路。     

Gravity drainage in porous media: the effect of wetting

In order to relate the wetting properties at the pore scale to the macroscale hydrodynamics, a series of benchmark experiments on the effect of the wetting on flow in porous media were performed. Gravity drainage of hexane (oil) in a model porous medium consisting of water-wet sand was studied using γ-ray densitometry and weight measurements. The advantage of our system is that we know and control the wetting properties perfectly: we can tune the wetting properties by changing the salinity of the water. This allows us to perform porous medium flow experiments for the different wetting states without changing the transport properties (viscosity and density) of the oil. Drainage is found to be more efficient and, consequently, oil recovery more important for partial wetting.     

The effect of wettability heterogeneity on capillary pressure and relative permeability

The effect of wettability on fluid flow properties in porous media has been extensively studied, and is still a subject of highly active investigation. Most of the work has focused on cores of homogeneous wettability. Little attention has been paid to wettability heterogeneity effects at the core or pore scale. In a previous paper, we reported on a series of centrifuge experiments performed to study the effect of wettability heterogeneity on capillary pressure. An experimental technique, named cyclic aging, was developed to create regions of different wetting in the same core sample. In this paper, the work is extended to study the effect of wettability heterogeneity on both capillary pressure and relative permeability curves using centrifuge, continuous injection and steady state techniques.The experimental procedure consists of three steps: (1) the core plug is fully saturated with brine and subsequently a drainage experiment is performed targeting an initial oil saturation S_oi, (2) after aging, oil is displaced by water to residual oil saturation S_or, and (3) oil is injected targeting higher initial oil saturation. In the secondary drainage experiment (step 3), oil first displaces water from the pores exposed to crude oil in primary drainage (step 1) and then enters fresh pores not exposed to crude oil before.In our previous study, it was found that wettability heterogeneity caused a step change in capillary pressure which correlated very well with the saturation at which wettability contrast was expected. However, the height of the step could not be explained by wettability contrast and/or water trapping alone. An experimental artifact caused by the centrifuge technique made the step higher than expected. The experimental artifact was the result of the nonuniform saturation profile developed across the core at the end of the centrifuge experiment. In this study, new techniques were used which resulted in a uniform saturation profile along the core sample during the primary drainage experiment. It was found that in this case the step in the capillary pressure is determined by wettability contrast and water trapping. It was also found that the relative permeability curve changes its characteristics when oil accesses the pores not previously exposed to crude oil.The results of this study show that (1) only the part of the pore space exposed to crude oil undergoes wettability changes on both core scale and pore scale, and (2) ignoring wettability heterogeneity can lead to large errors in the estimated two phase flow functions with important consequences with respect to fluid flow in porous media.     

储层环境岩石电阻率变化规律研究

应用先进的模拟储层条件下岩石电阻率测试技术,利用保压密闭取心技术取得具有保持原始地层饱和状态的储层特征岩心,在储层环境下系统地研究了岩石电阻率与温度、压力、饱和度等参数之间的变化规律,同时对饱和原油及饱和水样品进行对比分析,从理论上探讨了不同流体饱体和介质在岩石电阻率测试中所产生的影响。研究储层环境下岩石电阻率的变化规律,不仅可以对测井曲线进行标定,而且可以通过饱和原油样品电阻率测定来确定储层含油饱和度。此项研究首次把保压密闭取心技术获得的岩心应用到电阻率测试技术上,开辟了电阻率研究的新领域。     

Physically-based network modeling of multiphase flow in intermediate-wet porous media

A capillary equilibrium-based network model is used to compute oil recovery and Amott wettability indices in intermediate-wet porous media. The pattern of wettability at the pore level is a generalization of the work of Kovscek et al. [Kovscek, A.R., Wong, H., Radke, C.J., 1993. A pore-level scenario for the development of mixed wettability in oil reservoirs, AICHE J., 39 (6) 1072–1085]. The model allows a single pore to contain both oil-wet and water-wet regions, with oil/water contact angles anywhere in the range 0–180°. We investigate models with varying contact angles, and where different fractions of the pore space are oil-wet. We show that oil recovery shows a complex, non-monotonic dependence with both contact angle and oil-wet fraction, and we explain the results in terms of competing displacement mechanisms at the pore scale. Strongly oil-wet media allow stable oil layers to form in the crevices of the pore space. These layers maintain the connectivity of the oil phase and allow low residual saturations to be achieved, but only by production well after breakthrough.     

高温高压下地应力对电阻率影响实验研究

塔里木盆地克深地区白垩系巴什基奇克组致密砂岩储层具有高温高压和高强地应力特征,地应力对地层电阻率影响显著,导致电阻率测井曲线识别储层流体性质常存在多解性。开展岩样在高温高压下,围压大于轴压和围压小于轴压2种加载方式下的电阻率及其各向异性系数随水平应力差变化的实验研究。在弹性形变内,岩石电阻率随水平应力差的增大呈e的指数形式增大;电阻率随压力的变化呈明显的方向性特征;沿加压方向电阻率变化幅度小,垂直加压方向电阻率变化幅度大;不同加载方式下的电阻率各向异性系数随水平应力差变化关系不一样。为山前盆地高陡地层处于强挤压状态下,用地应力校正电阻率测井曲线值提供了可靠的实验理论依据和途径。     

多孔介质中泡沫的直观特征研究

为了评价泡沫在多孔介质中的稳定性,借助可视化微观模型驱替装置,利用图像采集系统,通过对大量图片进行分析,研究了水湿和油湿介质中不同压力下单一泡沫体系、复合泡沫体系在多孔介质中的稳定性以及泡沫的形成与衰变机理。结果显示,单一泡沫体系和复合泡沫体系在水湿介质中形成的泡沫稳定性均较好,泡沫形成较为容易;同等条件下泡沫体系在油湿介质中泡沫的形成较水湿介质中困难,泡沫稳定性较水湿介质中差;压力相同时,水湿介质和油湿介质中添加了高聚物的复合泡沫体系比单一泡沫体系泡沫稳定性好。     

多孔介质孔隙网络模型的应用现状

孔隙网络模型广泛应用于多孔介质的微观模拟中,已经可以较好地实现对渗流参数的定量预测,并用来描述微观渗流过程.首先对孔隙网络模型建立方法和孔隙空间描述作了扼要介绍,总结了准静态和动态两类孔隙网络模型的特征及应用范围,然后着重论述了孔隙网络模型的应用情况及研究较活跃的几个方面,最后对其发展趋势进行了展望.     

多孔介质对凝析气露点压力影响研究

关于多孔介质对凝析气露点压力的影响,不同学者研究得出的结论各不相同,有的结论甚至相反.到目前为止还没有一种理论能较好地解释这种矛盾现象.在大量调研国内外多孔介质对相变影响的基础上开展实验研究,得出了多孔介质对凝析气露点压力有影响的结论;进行理论研究,建立了分别考虑毛细管压力和吸附现象的露点压力计算模型.针对中原油田白庙、桥口凝析气以及模拟凝析气流体分别进行了实例计算.结果证明毛细管压力和吸附现象对凝析气露点压力有影响.     

鄂尔多斯盆地高电阻率水层的成因分析

鄂尔多斯盆地属典型的特低渗透率油田,在存在大量因储层岩性发生变化而形成的低电阻率油层的同时,同样也存在因储层岩性发生变化而形成的高电阻率水层.以延长组的长3～长8储层为典型代表,其储层特点是在同一储层、水层和油层的电性十分接近,甚至好于油层,致使油层计算的含油饱和度明显偏高.经过对大量岩心的细致观察和对各种化验资料的分析认为,造成高电阻率水层的主要原因是由于储层岩石颗粒细,分选差,含有大量的粉末状物质,正是这些物质堵塞了储层的孔隙喉道,连通的孔隙变成了孤立的孔隙,使储层电阻率增加.这种情况表现为2种,即当储层胶结疏松时,表现为水层;当储层胶结致密时,表现为干层.由于这些高电阻率水层的广泛存在,严重影响了石油勘探和开发,使测井解释常常出现失误,并给测井解释带来了又一个难题.     

高阶煤的孔隙结构特征及其对煤层气解吸的影响

以沁水盆地高阶煤3^#煤层为研究对象,借助高压压汞实验对高阶煤的孔隙参数进行测试,研究了高阶煤的孔隙结构特征,采用解吸速率实验对高阶煤的解吸速率和解吸量进行分析,并探讨了孔隙结构对煤层气解吸产出的控制规律。结果表明:3^#煤层的孔隙半径较小,煤层孔隙结构复杂;煤层主要以气体吸附孔和气体扩散孔为主,气体渗流孔占比很少,煤层的吸附气体体积大、吸附性能强、气体的扩散、渗流条件差。3^#煤层孔隙结构分形特征曲线呈"两段型",孔径大于940.7 nm时,不具有分形特征;孔径小于940.7 nm时,分形维数介于2.67~2.76之间,具有很好的分形特征。高阶煤的煤层气解吸特征具有快速解吸和慢速解吸2个阶段,快速解吸时间短,解吸量占比低;慢速解吸时间长,解吸量占比高,煤层气解吸困难。煤层的孔隙结构对煤层气的解吸具有重要影响,高阶煤较差的孔隙结构控制着煤层气解吸速率慢、解吸量低、产出程度低,煤层气井生产实践中表现为开始阶段产气量增长快,产气高峰时间短,稳产气量低、生产时间长,煤层气开发难度大。研究结果为高阶煤的煤层气抽采效果评价提供参考依据。     

港东东营组低阻油层解释方法研究

本文将地质沉积背景与储层岩性结构有机结合,研究低阻油层的成历机理,提出地质条件的特殊性是形成低阻油层的根本原因,弱水动力沉积是低阻油层集中分布的主要地质条件。确定了以地质分析为基础、结合岩性、束缚水分析的综合解释方法,该方法在港东二区东营组应用效果良好。     

Visualization of imbibition in porous media by environmental scanning electron microscopy: application to reservoir rocks

The study of wettability and fluid distribution in porous media has been approached by means of environmental scanning electron microscope (ESEM). This method allows visualization of rock samples in the presence of fluids (both oil and brine). Fluids consisted of water and dodecane, which remain liquid under the observation conditions. Porous media consisted of homogeneous wettability sintered glass, and mixed wettability reservoir rock samples: a sandstone from the North Sea and a carbonate from the Middle East (preserved state). For sintered glass, (treated with octadecyltrichlorosilane to obtain an oil-wet surface), after the sample was saturated with water (nonwetting fluid), it was clearly possible to follow its appearance at the upper face of the core sample. For the sandstone samples, it was possible to observe the rise of oil through the water phase at the junction between quartz and kaolinite. For carbonate samples, tentative correlations were made between the appearance of oil at the upper face and the pore structure of the sample.     

姬塬-白豹地区低电阻率油层成因分析及解释方法

以认识鄂尔多斯盆地姬塬-白豹地区低电阻率油层的成因机理及精细解释为目的,利用该区岩性薄片分析资料、地层水分析资料及测井解释成果图,对该区延安组和延长组低电阻率油层的成因进行了较详细的剖析,认为地层水矿化度高、储层物性的变化、储层孔隙结构的变化、储层岩石颗粒的变细是延安组低电阻率油层的主要成因。储层物性的变化、储层孔隙结构的变化、储层岩石颗粒的变细、储层泥质含量的相对增高是延长组低电阻率油层的主要成因,进而总结出该区低电阻率油层3种解释方法,即交会法、可动水分析法和核磁共振测井差谱法。实践表明,这3种解释方法对该区低电阻率油层解释是完全适合的。     

川南地区龙马溪组页岩高压甲烷等温吸附特征

准确测定页岩吸附气含量对于页岩气储层的评价和开发都具有重要的意义,但目前国内外学者在页岩甲烷等温吸附实验中对模型选择、吸附模式及吸附特征参数的认识上存在着差异,并且对于高压等温甲烷吸附特性的研究较少。为此,在利用N_2/CO_2气体低压等温吸附实验对四川盆地南部地区下志留统龙马溪组页岩孔隙结构特征进行分析的基础上,采用重量法高压甲烷等温吸附实验,选取SDR、Langmuir、BET等3种不同的吸附模型对吸附态甲烷含量进行计算,并对样品甲烷吸附特征进行研究。研究结果表明:①页岩在0～50 nm孔径区间内比表面积分布具有双峰特征,孔体积分布具有三峰特征,较之于中孔,微孔比表面积发育较好,而其孔体积和非均质性均弱于中孔(D_1D_2);②3种模型中SDR和Langmuir模型的计算结果与实测值平均误差均小于6%,甲烷分子主要以单分子层与微孔充填吸附模式共存于页岩孔隙内;③在高压深埋藏情况下,温度是影响吸附态甲烷吸附量和密度值的主要因素,但热力学参数、孔隙结构、非均质性等也会对吸附态甲烷密度造成一定的影响;④低压阶段甲烷分子优先以单分子层形式吸附于吸附能较高、比表面积较大的孔径介于0.4～0.8 nm的微孔中,随后大部分甲烷分子以微孔充填与单分子层共存的形式吸附于孔径介于1.4～8.0 nm的微孔与中孔中,高压阶段极少部分甲烷以多分子层形式吸附于中孔及宏孔中。     

砂岩孔隙结构的分形特征及应用研究

研究了大庆、胜利等油田砂岩孔隙结构的分形特征及其对水驱油采收率的影响。建立了一套利用图像处理技术测定砂岩孔隙结构分形维数的方法，提出了砂岩孔隙结构的分形尺度下限，初步研究了孔隙结构的分形维数与油藏地质特征的关系，探讨了用孔隙结构的分形维数进行油藏分类评价的可能性。     

湘鄂西地区志留系龙马溪组页岩微观孔隙结构特征及定量表征

湘鄂西地区为南方海相页岩气勘探开发潜力区之一,志留系龙马溪组是其有利的页岩气层段.利用氩离子抛光-扫描电镜、低温低压氮气和二氧化碳吸附等实验对该区4口取心井的页岩样品孔隙结构进行了定性和定量的联合表征.实验结果表明:该区页岩发育有粒间孔、粒内孔、有机孔、有机质-黏土矿物复合孔以及解理缝,其中最为发育的是黏土矿物与自生矿...