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1.
We use a three-dimensional mixed-wet random network model representing Berea sandstone to extend our previous work on relative permeability hysteresis during water-alternating-gas (WAG) injection cycles [Suicmez, VS, Piri, M, Blunt, MJ, 2007, Pore-scale simulation of water alternate gas injection, Transport Porous Med 66(3), 259–86]. We compute the trapped hydrocarbon saturation for tertiary water-flooding, which is water injection into different initial gas saturations, Sgi, established by secondary gas injection after primary drainage. Tertiary water-flooding is continued until all the gas and oil is trapped. We study four different wettability conditions: water-wet, weakly water-wet, weakly oil-wet and oil-wet. We demonstrate that the amounts of oil and gas that are trapped show surprising trends with wettability that cannot be captured using previously developed empirical trapping models. We show that the amount of oil that is trapped by water in the presence of gas increases as the medium becomes more oil-wet, which is opposite from that seen for two-phase flow. It is only through a careful analysis of displacement statistics and fluid configurations that these results can be explained. This illustrates the need to have detailed models of the displacement processes that represent the three-phase displacement physics as carefully as possible. Further work is needed to explore the full range of behavior as a function of wettability and displacement path. 相似文献
2.
A quasi-static scheme based on pore space spatial statistics is presented to simulate pore-scale two-phase capillary-dominant displacement processes. The algorithm is coupled with computational fluid dynamics in order to evaluate saturation functions. Wettability heterogeneity in partial and fractional/mixed-wet media is implemented using a contact angle map. The simulation process is pixel-wised and performed directly on binary images. Bypassing and snap-off are tackled as non-wetting phase trapping mechanisms. Post-processing results include residual saturations, effective permeability and capillary pressure curves for drainage and imbibition scenarios. The primary advantages of the proposed workflow are eliminating pore space skeletisation/ discretization, superior time efficiency and minimal numerical drawbacks when compared to other direct or network-based simulation techniques. 相似文献
3.
利用基于Biot理论的孔隙弹性介质的高阶交错网格有限差分算法,模拟了具有随机分布特征的多种流体饱和岩石中声波在中心频率分别为25,50,75,100kHz时的声场特点. 对于一个由两种成分（气和水）饱和的岩石模型, 假设含不同流体的孔隙介质随机分布在不同的宏观区域,该区域尺度远小于计算的声波波长;组成模型的两种随机分布介质具有相同的固体骨架参数、渗透率和孔隙度,但分别被具有不同压缩性、密度和黏滞系数特性的水和气饱和. 计算和统计分析结果表明,在两种孔隙成分随机分布的部分饱和条件下纵波速度比较复杂,除骨架参数外,其变化主要依赖于中心频率、各种孔隙成分饱和度及饱和介质的速度. 比较该随机分布模型、Gassmann理论模型和White的“气包”模型,发现三种模型得到的纵波速度和衰减规律有较好的定性对应关系. 其次,按照这种随机计算模型的处理方法,本文还首次计算了一个三种流体成分充填饱和的例子,即岩石模型中的孔隙被水、油和气部分饱和,计算时保持模型含水饱和度不变而只改变含油和含气饱和度. 在这种计算条件下,纵波速度随中心频率呈增大的趋势但有起伏变化. 声场快照显示了各种转换波在多种孔隙成分充填（两种和三种孔隙成分）岩石中的声场特征,复杂的水-油-气界面的非均匀分布对声场有重要影响,纵波能量主要转换形成了较为复杂的多种慢纵波和横波. 相似文献
4.
In this study, carbon dioxide exsolution from carbonated water is directly observed under reservoir conditions (9 MPa and 45 °C). Fluorescence microscopy and image analysis are used to quantitatively characterize bubble formation, morphology, and mobility. Observations indicate the strong influence of interfacial tension and pore-geometry on bubble growth and evolution. Most of the gas exhibits little mobility during the course of depressurization and clogs water flow paths. However, a snap-off mechanism mobilizes a small portion of the trapped gas along the water flow paths. This feature contributes to the transport of the dispersed exsolved gas phase and the formation of intermittent gas flow. A new definition of critical gas saturation is proposed accordingly as the minimum saturation that snap-off starts to produce mobile bubbles. Low mobility of the water phase and CO2 phase in exsolution is explained by formation of dispersed CO2 bubbles which block water flow and lack the connectivity to create a mobile gas phase. 相似文献
5.
《Advances in water resources》2002,25(1):33-49
Experiments designed to elucidate the pore-scale mechanisms of the dissolution of a residual non-aqueous phase liquid (NAPL), trapped in the form of ganglia within a porous medium, are discussed. These experiments were conducted using transparent glass micromodels with controlled pore geometry, so that the evolution of the size and shape of individual NAPL ganglia and, hence, the pore-scale mass transfer rates and mass transfer coefficients could be determined by image analysis. The micromodel design permitted reasonably accurate control of the pore water velocity, so that the mass transfer coefficients could be correlated in terms of a local (pore-scale) Peclet number. A simple mathematical model, incorporating convection and diffusion in a slit geometry was developed and used successfully to predict the observed mass transfer rates. For the case of non-wetting NAPL ganglia, water flow through the corners in the pore walls was seen to control the rate of NAPL dissolution, as recently postulated by Dillard and Blunt [Water Resour. Res. 36 (2000) 439–454]. Break-up of doublet non-wetting phase ganglia into singlet ganglia by snap-off in pore throats was also observed, confirming the interplay between capillarity and mass transfer. Additionally, the effect of wettability on dissolution mass transfer was demonstrated. Under conditions of preferential NAPL wettability, mass transfer from NAPL films covering the solid surfaces was seen to control the dissolution process. Supply of NAPL from the trapped ganglia to these films by capillary flow along pore corners was observed to result in a sequence of pore drainage events that increase the interfacial area for mass transfer. These observations provide new experimental evidence for the role of capillarity, wettability and corner flow on NAPL ganglia dissolution. 相似文献
6.
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. 相似文献
7.
In the current paper, the effect of the geometrical characteristics of 2-D porous media on the relative permeability in immiscible two-phase flows is studied. The generation of the different artificial porous media is performed using a Boolean model based on a random distribution of overlapping circles/ellipses, the size and shape of which are chosen to satisfy the specific Minkowski functionals (i.e. volume fraction, solid line contour length, connectivity). The study aims to identify how each different Minkowski functional affects the relative permeability of each phase at various saturations of the non-wetting phase. A 2-D multi-relaxation time (MRT) lattice Boltzmann model (LBM) that can handle high density ratios is employed in the simulation. The relationship between the driving forces G and the relative permeabilities of the two phases for every artificial structure is quantified. It is found that for high non-wetting phase saturations (fully connected flow), a non-linear relationship exists between the non-wetting phase flow rate and the driving force, whilst this relationship becomes linear at higher magnitudes of the latter. The force magnitude required to approach the linear region is highly influenced by the pore size distribution and the connectivity of the solid phase. For lower non-wetting phase saturation values, its relative permeability in the linear regime decreases as the fraction of small pores in the structure increases and the non-wetting phase flow becomes disconnected. A strong influence of the solid phase connectivity is also observed. 相似文献
8.
We use an organic acid (cyclohexanepentanoic acid) to alter the wettability of three carbonates: Estaillades, Ketton and Portland limestones, and observe the relationship between the initial oil saturation and the residual saturation. We take cores containing oil and a specified initial water saturation and waterflood until 10 pore volumes have been injected. We record the remaining oil saturation as a function of the amount of water injected. In the water-wet case, with no wettability alteration, we observe, as expected, a monotonic increase in the remaining oil saturation with initial saturation. However, when the wettability is altered, we observe an increase, then a decrease, and finally an increase in the trapping curve for Estaillades limestone with a small, but continued, decrease in the remaining saturation as more water is injected. This behavior is indicative of mixed-wet or intermediate-wet conditions, as there is no spontaneous imbibition of oil and water. In contrast, Ketton did not show indications of a significant wettability alteration with a similar observed trapping profile to that observed in the water-wet case. Portland limestone also showed a monotonic increasing trend in remaining saturation with initial saturation but with a higher recovery, and less trapping, than the water-wet case. Again, this is intermediate-wet behavior with no spontaneous imbibition of either oil or water, and slow production of oil after water breakthrough. Finally, we repeat the same experiments but instead we age the three carbonates with a high asphaltenic content and high viscosity crude oil at 70 °C mimicking reservoir conditions. The results show a monotonic increase in residual saturation as a function of initial saturation but with higher recovery than the water-wet cases for Estaillades and Portland, with again no indication of wettability alteration for Ketton. We discuss the results in terms of pore-scale recovery process and contact angle hysteresis. In these experiments, water-saturated micro-porosity appears to protect the solid surfaces from a strong wettability alteration, particularly in Ketton. 相似文献
9.
含气饱和度预测是天然气储层地震解释工作的重要目标.本文将岩石物理分析与地震物理模拟技术相结合,构建了部分;饱和砂岩储层物理模型并进行含气饱和度预测分析.物理模型中设置了高孔渗常规砂岩和低孑孔渗致密砂岩两种模拟储层,每种储层都是由具有不同含水饱和度的气-水双相饱和砂体组成.岩石物理分析结果显示在低孔渗致密砂岩中气-水混合流体更加倾向于非均匀的斑块分布,而结合了Brie等效流体公式的Gassmann流体替换理论可以更准确地描述纵波速度随含水饱和度的变化趋势.对物理模型进行地震资料采集处理后,对比了AVO特征和叠前同步反演结果对两种砂岩储层含气饱和度预测能力的差异.AVO特征结果显示,对于混合流体均匀分布的高孔渗砂岩储层,AVO响应曲线和属性变化很难对含气饱和度进行估算;对于混合流体斑块分布的致密砂岩储层,AVO特征可以定性地分辨出储层是否为高、中、低含气情况.反演结果显示,密度及纵横波速度比分别对高孔渗及致密砂岩储层的含气饱和度有着较好的指示能力. 相似文献
10.
Low frequencies are necessary in seismic data for proper acoustic impedance imaging and for petrophysical interpretation. Without lower frequencies, images can be distorted leading to incorrect reservoir interpretation and petrophysical predictions. As part of the Foinaven Active Reservoir Management (FARM) project, a Towed Streamer survey and an Ocean Bottom Hydrophone (OBH) survey were shot in both 1995 and 1998. The OBH surveys contain lower frequencies than the streamer surveys, providing a unique opportunity to study the effects that low frequencies have on both the acoustic impedance image along with petrophysical time‐lapse predictions. Artefacts that could easily have been interpreted as high‐resolution features in the streamer data impedance volumes can be distinguished by comparison with the impedance volumes created from the OBH surveys containing lower frequencies. In order to obtain results from the impedance volumes, impedance must be related to saturation. The mixing of exsolved gas, oil and water phases involves using the Reuss (uniform) or Voigt (patchy approximation) mixing laws. The Voigt average is easily misused by assuming that the end‐points correspond to 0% and 100% gas saturation. This implies that the patches are either 0% gas saturation or 100% gas saturation, which is never the case. Here, the distribution of gas as it comes out of solution is assumed to be uniform until the gas saturation reaches a sufficiently high value (critical gas saturation) to allow gas to flow. Therefore, at low gas saturations the distribution is uniform, but at saturations above critical, it is patchy, with patches that range from critical gas saturation to the highest gas saturation possible (1 minus residual oil and irreducible water saturation). 相似文献
11.
为了研究孔隙流体对不同渗透率岩石地震波速度的影响,在实验室利用跨频带岩石弹性参数测试系统得到了应变幅值10-6的2~2000Hz频段下的地震波速度和1 MHz频率下的超声波速度,利用差分共振声谱法得到了频率600Hz岩石干燥和完全饱水情况下岩石声学参数.实验表明,在低饱和度下,致密砂岩在地震和超声频段下没有明显的频散;在高饱和度下纵波速度的频散变得明显.从干燥到完全水饱和条件,不同频率测量的致密砂岩的体积模量随岩石孔隙度增高而降低,且体积模量的变化量受岩石微观孔隙结构的影响较大.高孔、高渗砂岩无论在低含水度下还是在高含水饱和度下频散微弱,并且在地震频段下围压对于岩石纵横波速度的影响要大于频率的影响.高孔、高渗砂岩和致密砂岩不同含水饱和度下的频散差异可应用于储层预测,油气检测等方面,同时该研究可以更好地帮助理解岩石的黏弹性行为,促进岩石物理频散理论的发展,提高地震解释的精度. 相似文献
12.
指出了全直径岩心分析的Archie参数(m、n)对非均质储层含油(气)性评价的重要性.使用新疆测井公司开发的全直径岩心多参数分析实验装置及实验方法,以DQ油田XX区块的非均质火成岩气层评价为例,由7块全直径岩样该获得了储层的物性和Archie参数.当应用于该储层含气饱和度估算后,与密闭取心饱和度分析的含气饱和度结果比较,含气饱和度估算误差大致在5%以内,较按Archie参数的确省值(m=n=2)估算的含气饱和度的精度高 10%左右.考虑到非均质储层在岩性、物性、孔隙结构的特殊性,推荐“真正”使用全直径岩心分析方法应用于非均质储层的物性、含油(气)性的评价,并重视模拟油藏条件的全直径岩心分析装置的开发. 相似文献
13.
In the water flooding of mixed-wet porous media, oil may drain down to relatively low residual oil saturations (Sor). Various studies have indicated that such low saturations can only be reached when oil layers in pore corners are included in the pore-scale modelling. These processes within a macroscopic porous medium can be modelled at the pore-scale by incorporating the fundamental physics of capillary dominated displacement within idealised pore network models. Recently, the authors have developed thermodynamic criteria for oil layer existence in pores with non-uniform wettability which takes as input geometrically and topologically representative networks, to calculate realistic Sor values for mixed-wet and oil-wet sandstones [16, 21]. This previous work is developed in this paper to include (i) the visualisation of the 3D structure of this residual oil, and (ii) a statistical analysis of this “residual/remaining” oil. Both the visualisation and the statistical analysis are done under a wide range of wettability conditions, which is reported for the first time in this paper.The structure of residual oil for strongly water wet systems is well known (where residual = remaining oil) and our model agrees with this but this structure changes radically for mixed wet systems (where residual ≠ remaining) and this has not yet been visualised experimentally. We find that for more water-wet systems high final residual oil saturations are reached at relatively small amounts of water injected and this oil is present in the pores as bulk oil. On the other hand, for more oil-wet systems we find a slow decrease of the amount of remaining oil with increasing amounts of injected water. During the process, the remaining connectivity of the oil phase is increasingly provided by oil layers only, hence the slow drainage. The final residual oil saturation, only reached in the theoretical limit of an infinite amount of injected water, is almost entirely contained in large number of (relatively low volume) oil layers, which are present in pores of most radius sizes. 相似文献
14.
海洋环境中天然气水合物的形成除了合适的温压条件外,还必须有充分的甲烷供给.本文介绍了甲烷-水体系的甲烷饱和溶解度、水合物体系中甲烷水合物溶解度计算方法.在气-液二相平衡甲烷饱和溶解度计算中,关键在于状态方程的选择和合适的混合规则的运用,Duan的计算模型在温度、压力和盐度变化上都具有很大的适用性,且易于应用.在含水合物的相平衡体系中,在已知组分和假定可能存在相的前提下,可利用模拟退火算法优化总吉布斯自由能,确定是二相还是三相体系,并求解甲烷水合物溶解度.在海水环境下盐的存在使平衡发生移动,利用德拜—休克尔理论或Pitzer电解质溶液理论校正盐度对于海水活度的影响,求解海水环境中甲烷水合物溶解度.基于气-液二相平衡理论的K-K方程,在临近水合物生成条件下实验或计算确定亨利常数等参数后,可计算三相平衡甲烷水合物溶解度,且简单易用. 相似文献
15.
In this paper we extend to three-phase flow the nonequilibrium formalism proposed by Barenblatt and co-workers for two-phase porous media flow. The underlying idea is to include nonequilibrium effects by introducing a pair of effective water and gas saturations, which are linked to the actual saturations by a local evolution equation. We illustrate and analyze how nonequilibrium effects lead to qualitative and quantitative differences in the solution of the three-phase flow equations. 相似文献
16.
In situ denitrification relies on indigenous microorganisms to reduce nitrate to N(2) gas. However, when initial nitrate concentrations are large, produced gas volumes also can be very large, potentially resulting in reduced water saturation and hydraulic conductivity in the treatment zone. In this study, we investigated the fate of N(2) and other gases produced during denitrification in a laboratory flow cell containing packed sediment. Denitrifying activity was stimulated by additions of nitrate and ethanol. Microbial activity was monitored by measuring nitrate, nitrite, and ethanol concentrations; gas saturations were measured during the experiment using a gamma imaging system. Biomass was measured using phospholipid fatty acid analysis of sediment samples. Bioenergetic calculations calibrated to measured nitrate consumed and biomass produced predicted that 1.2 L N(2) gas/L water should have been produced following the addition of 100 mM nitrate. However, the maximum measured gas saturation was only 23%, indicating substantial gas loss from the sediment pack. Temporal gamma images and visual observations confirm that small gas bubbles formed in the sediment pack coalesced into larger bubbles and migrated upward through gas-filled channels to the sediment pack surface. Although gas saturations increased, there was no significant change in sediment pack hydraulic conductivity. These results suggest that in permeable reactive barriers used for in situ denitrification, gas production will not necessarily lead to unlimited gas accumulation in the pore space and that the effects of gas production on water saturation and hydraulic conductivity may be relatively minor. 相似文献
17.
根据鄂尔多斯盆地苏里格气田以往实测和新测的共17口井51块岩样超声波实验数据,得到304组不同孔隙度和不同含水饱和度下对应的纵横波速度、泊松比等弹性参数.重新优选计算体积模量和泊松比与含气饱和度的关系,表明苏里格气田上古生界二叠系石盒子组盒8致密砂岩储层的模型与Brie模型(e=2)相似度最高.由此建立的苏里格气田储层岩石物理模型,更好的表征了致密岩石储层物理参数随含气饱和度变化规律,为该区储层预测提供了理论依据.致密储层岩石物理模型研究成果应用于苏里格气田多波地震资料气水预测中,实际例子表明该模型适用于该区的储层和含气性预测,并取得了较好的效果. 相似文献
18.
讨论了不同水合物胶结类型的流体饱和多孔隙固体中地震波的衰减情况,分析了估算天然气水合物和游离气饱和度影响因素.结果表明, 地层孔隙度、纵波速度模型和弹性模量的计算方法是影响反演水合物和游离气饱和度的关键因素.含水合物地层的吸收与水合物胶结类型密切相关,当水合物远离固体颗粒,像流体一样充填在孔隙时,品质因子出现负异常,而当水合物胶结固体颗粒影响骨架的弹性性质,其品质因子出现正异常.根据布莱克海台地区164航次995井的测井资料,分别应用低频和高频速度模型估算了水合物和游离气饱和度.由低频速度模型得到的水合物饱和度(占孔隙空间的)10%～20%,游离气饱和度(占孔隙空间的)05%～1%;而由高频速度模型得到的水合物饱和度(占孔隙空间的)5%～10%,游离气饱和度(占孔隙空间的)1%～2%. 相似文献
19.
Rob Staples Paul Hague Toon Weisenborn Peter Ashton Barbara Michalek 《Geophysical Prospecting》2005,53(2):243-251
In the central North Sea ‘Gannet‐A’ field, a 50 ft oil rim is overlain by a gas cap of variable thickness. Oil is produced from horizontal wells which initially produced dry oil, but as the field became more mature, a significant water cut was seen in several wells. A dedicated 4D seismic monitor survey was acquired in order to assess the remaining distribution of oil reserves. By forward modelling the synthetic seismic response to parameters such as contact movement and residual saturations (using 2D and 3D wedge models), and comparing the results with real seismic data, we are able to decipher the contact movements across the field. It is shown that, in one part of the field, the increased water cut is caused primarily by the vertical displacement of the entire oil rim into the initial gas cap. This oil‐rim displacement produces a very different 4D seismic response from the case of a static gas–oil contact and rising oil–water contact (normal production). As a result of these observations, we are able to optimize field production by both re‐perforation of existing wells and by drilling sidetracks into the displaced rim: a brown‐field development opportunity that might otherwise be missed. 相似文献
20.
本文基于Biot理论,推导出Zoeppritz形式的双相介质分界面上弹性波的反射与透射公式,对单相Zoeppritz公式与双相反射系数公式进行了比较,对双相介质含油、水、气不同流体时的反射规律以及孔隙度、渗透率、饱和度等储层参数对纵波反射的影响进行了研究.数值模拟分析表明,双相与单相反射公式的主要差异在于双相介质反射公式中考虑了液相、固液耦合相弹性模量的影响;油砂、水砂、气砂岩的慢P波反射差异明显;快P波反射对孔隙度的变化敏感,饱和度次之,对渗透率和频率的变化不敏感. 相似文献