Experimental investigation of oil recovery during water imbibition

Capillary imbibition and gravity are the main forces acting in fractured reservoirs. The cores used in the laboratory are usually short while experimental investigation of the gravity forces requires long samples. Therefore an experimental study has been carried out on a long core with the length of 116 cm surrounded with a simulated fracture. Kerosene and a synthetic oil with a density very close to brine have been chosen in order to distinguish the capillary and gravity effects during the water oil displacement. After doing many carefully conducted tests at different rates, it is clear that the process is significantly influenced by gravity. The second part of the study involved experiments on the long core surrounded with a simulated fracture where the flow processes are dominated by either co-current or counter-current imbibition. We changed the recovery mechanism from co-current to counter-current by changing the boundary conditions from an advancing fracture water level to an immersion-type mechanism. Our co-current and counter-current experiments on a tall block showed that counter-current imbibition has lower recovery than co-current imbibition. A wettability study was done after cutting the core into many pieces and aging the pieces in crude oil. Different wettability states were obtained by applying different aging times. The cores with different wettability index were subjected to immersion-type experiment. The results showed that more water wet conditions gave higher oil recovery.     

Wettability alteration and spontaneous imbibition in oil-wet carbonate formations

Alkaline/surfactant flooding has been widely tested for its ability to improve oil recovery, but little effort has been made toward understanding the controlling mechanisms and variables. This paper investigates the effect of electrolyte concentration, surfactant concentration and water/oil ratio on wettability, phase behavior, and displacement from a narrow gap. Wettability of calcite can be altered to about intermediate-wet to preferentially water-wet with alkaline/surfactant systems. Anionic surfactant adsorption can be significantly reduced in the presence of sodium carbonate.     

Surfactant induced reservoir wettability alteration: Recent theoretical and experimental advances in enhanced oil recovery

Reservoir wettability plays an important role in various oil recovery processes.The origin and evolution of reservoir wettability were critically reviewed to better understand the complexity of wettability due to interactions in crude oil-brine-rock system,with introduction of different wetting states and their influence on fluid distribution in pore spaces.The effect of wettability on oil recovery of waterflooding was then summarized from past and recent research to emphasize the importance of wettability in oil displacement by brine.The mechanism of wettability alteration by different surfactants in both carbonate and sandstone reservoirs was analyzed,concerning their distinct surface chemistry,and different interaction patterns of surfactants with components on rock surface.Other concerns such as the combined effect of wettability alteration and interfacial tension (IFT) reduction on the imbibition process was also taken into account.Generally,surfactant induced wettability alteration for enhanced oil recovery is still in the stage of laboratory investigation.The successful application of this technique relies on a comprehensive survey of target reservoir conditions,and could be expected especially in low permeability fractured reservoirs and forced imbibition process.     

Wettability alterations due to aging in crude oil; wettability and Cryo-ESEM analyses

Several studies of fluid distribution and wettability on the pore scale have been reported, but to our knowledge, none of them have attempted to obtain quantitative measurements. In this paper, quantitative wettability results from Cryo Environmental Scanning Electron Microscopy (Cryo-ESEM) are reported and compared to wettability measurements with traditional methods. The wetting properties of sandstone cores, aged in crude oil, have been investigated using the combined Amott/USBM method. The results show that with increasing aging time, the wetting properties changed from water wet to mixed wetting. Pieces of the same cores have then been analyzed using an Electroscan 2020 ESEM with an attached Cryo unit. Combined with Energy Dispersive X-ray Spectroscopy (EDS), these analyses have given images of the surface, showing the liquid distribution and which phase is contacting the mineral surface.The combination of these methods has proved that using a Cryo-ESEM to investigate wetting properties can give very valuable information although the results are somewhat scattered. Compared to the traditional wetting analyses, this method also gives us an image of the liquid distribution, which is a very valuable input for pore network simulation. It is shown that there is a good agreement between the fraction of the pore walls that are contacted with brine and the Amott/USBM index. A new index based on ESEM data is proposed, with the same range as the Amott–Harvey index.Cryo-ESEM avoids two problems encountered in other SEM methods. First, there is no possibility of a coating layer showing up in the element analyses, since these samples are uncoated. Secondly, the same sample can easily be reexamined by simply refracturing.     

Recent advances in application of nanotechnology in chemical enhanced oil recovery: Effects of nanoparticles on wettability alteration,interfacial tension reduction,and flooding

Chemical methods of enhanced oil recovery (CEOR) are applied for improving oil recovery from different kinds of oil reservoirs due to their ability for modifying some crucial parameters in porous media, such as mobility ratio (M), wettability, spreading behavior of chemical solutions on rock surface and the interfacial tension (IFT) between water and oil. Few decades ago, the surfactant and polymer flooding were the most common CEOR methods have been applied for producing the remained hydrocarbon after primary and secondary recovery techniques. Recently, more attention has been focused on the potential applications of the nanotechnology in enhanced oil recovery (EOR). For this purpose, many studies reported that nanoparticles (NPs) have promising roles in CEOR processes due to their ability in changing oil recovery mechanisms and unlocking the trapped oil in the reservoir pore system. This paper presents a comprehensive and up-to-date review of the latest studies about various applications of nanoparticles (NPs) within the surfactant (S), polymer (P), surfactant-polymer (SP), alkaline-surfactant-polymer (ASP) and low salinity waterflooding processes, which exhibits the way for researchers who are interested in investigating this technology. The review covers the effects of nanoparticles on wettability alteration, interfacial tension reduction and oil recovery improvement, and discusses the factors affecting the rock/fluid interaction behavior in porous media through the nanofluid flooding.     

In situ wettability distribution and wetting stability in outcrop chalk aged in crude oil

This paper reports an investigation of in situ wettability distribution and wetting stability of moderately water-wet and nearly neutral-wet outcrop chalk cores, aged in crude oil at elevated temperature.In this paper, in situ wettability measurements by magnetic resonance imaging (MRI) tomography are shown to give Amott indices that agree well with the standard wettability indices based on average saturations. The in situ method provides information concerning Amott index distribution radially and along the length of the core plugs.Applying multidirectional crude oil flooding during aging, uniform wettability distributions, both radially and axially, were obtained.Tests of wetting stability confirmed that stable wettability alterations for repeated waterfloods and Amott tests were established. The results showed that the core plugs should not be dried or cleaned because this will render the core plugs strongly water-wet. Stable wettability conditions were measured for cores subjected to storage in brine at 90 °C.     

Drainage and imbibition relative permeabilities at near miscible conditions

The changes in gas and oil relative permeabilities as miscibility is approached are of particular importance in multi-contact miscible displacements. These changes are a function of the detailed phase behaviour of the fluids and their physical properties as well as the properties of the porous medium itself.In this work, we investigate the behaviour of two-phase drainage and imbibition relative permeability curves of four, different, equilibrated fluid pairs from a three component, two-phase system (cyclohexene, isopropyl alcohol and water) that exhibits a critical point at ambient conditions. The tie-lines of these fluid pairs are at varying distances from the system's critical point. Equilibrium phase compositions and interfacial tensions (IFT) were determined for each of the four fluid pairs. Dynamic displacements were then performed in a linear two dimensional, bead-pack. Unsteady state, drainage and imbibition relative permeabilities were determined for the various pre-equilibrated mixtures. The experimental results show a clear change in relative permeability as the fluid pairs approach the critical point. As the interfacial tension decreases the non-wetting phase relative permeability increases more rapidly than the wetting phase relative permeability and hysteresis becomes less important.Two correlations [Coats, K.H., 1980. An equation of state compositional model: SPE J, 20 (5): 363-376.; Whitson, C.H., and Fevang, Ø., 1997. Generalized pseudo pressure well treatment in reservoir simulation. In Proc., IBC Conference on Optimization of Gas Condensate Fields.], commonly used to model the changes in relative permeability with interfacial tension, and the development of miscibility, were compared with the experimental data. The Coats correlation, which uses a single adjustable parameter to model the changes in both relative permeabilities and residual oil saturation as a direct function of the IFT, yielded an unacceptable match to the experimentally determined fractional flow. However the Whitson–Fevang correlation, which relates the changes in relative permeability to the capillary number using two adjustable weighting functions, presents a satisfactory match.     

Experimental determination of the matrix-to-fracture transfer functions for oil recovery by water imbibition

Unique determination of the parameters of the triple-exponential matrix-to-fracture transfer functions is of profound importance to accurately simulate waterflooding and determine sweep efficiency in naturally fractured reservoirs. To accomplish this task, two novel approaches are investigated. Firstly, to our knowledge, the first attempt is made to facilitate not only the function values and their derivative, but also the integral to uniquely determine the transfer function parameters from a suite of in-house imbibition data. Secondly, a random number-based algorithm is applied to uniquely compute the parameters, and its results are compared to those generated through a conventional, nonlinear optimization method using spreadsheet software. The inclusion of the random component helps alleviate the inherent tendency of parametric optimization type algorithms to converge to that possible solution, predefined through the guessed values assigned to the parameters as starting values.Through precisely and more importantly uniquely determining the parameters of the matrix-to-fracture transfer function, experimental imbibition data can be correctly matched and better transposed to field applications. The presented approach of simultaneous correlation of the function and its derivative and integral provides an effective method to scale from laboratory experiments to field applications. Comparative studies presented in this paper delineate the outstanding advantages of the presented approach over the previous and frequently utilized function correlation approaches, which do not generally yield unique determination of transfer function parameters. With the help of a mathematically sound, uniquely defined model, a variety of issues pertaining to spontaneous imbibition can be addressed and resulting problems remedied. One such area of application is underbalanced drilling, where precise and advance knowledge of a formation's imbibition behavior would allow for optimized design and minimized formation damage. Another area is exploitation from naturally fractured reservoirs, in the presence of a strong water drive or a waterflood. Detailed understanding of the mechanisms governing matrix, fracture, and fluid interactions will result in optimized development and exploitation strategies.     

Spontaneous imbibition for mixed-wettability states in sandstones induced by adsorption from crude oil

Wettability control by methods that are of practical relevance to oil recovery is an ongoing problem in wettability research. The preparation of mixed-wettability cores by adsorption from an asphaltic crude oil at elevated temperature and pressure has been investigated. After aging, crude oil was displaced by flow of decalin, an intermediate solvent that was compatible with the crude oil with respect to asphaltene precipitation but not likely to cause undue desorption of polar components of crude oil from pore walls. The decalin was in turn removed by flow of refined oil.In tests of the stability of the induced wetting states obtained by this approach, imbibition measurements were repeated for up to six cycles of imbibition and drainage. In most cases, wettability changed slightly towards water wetness after the first cycle, but there was comparatively little or no change for further cycles of spontaneous imbibition and forced drainage. Factors in preparation of mixed-wet cores such as the volume of decalin used to flush crude oil from the core and the temperature of flushing were investigated during the course of development of the experimental procedures. Once established, the induced wetting states were stable with respect to further flushing with decalin and also to flushing with toluene, a stronger solvent for asphaltenes.In experiments on displacement of brine by high viscosity refined oils, the initial water saturation of mixed wet cores could be readily reduced to much lower values than the water saturation that was present at the time of aging. However, in contrast to the drastic reduction in imbibition rate for cores aged at low water saturation, low initial water saturation obtained by this means had very little effect on subsequent spontaneous imbibition. This observation is consistent with the concept of mixed wettability postulated by Salathiel (1973) [JPT (1973) 12616] that the distribution of water at the time of aging controls the distribution of adsorbed components of crude oil.     

气润湿反转提高采收率实验研究

注气开采是三次采油的一种重要开发方式,在气驱水的过程中,气润湿反转可以使毛细管压力由气驱阻力变为动力,从而提高气驱油效率.用N2和CO2做气驱水实验,研究气润湿反转对提高采收率的影响.实验所用岩心为长庆油田的低渗透率岩心,所用气润湿反转剂属阳离子型氟化物.对气润湿反转前后的岩心做气驱水实验,绘出气润湿反转前后水的采出程...     

Wettability and morphology of mica surfaces after exposure to crude oil

Reservoir wettability is determined by interactions between crude oil and mineral surfaces, mediated by an aqueous phase. Contact angles between immiscible fluids have long been used as probes to assess the effective wetting condition of surfaces after exposure to brine and oil, but there is a limit to the amount of information that can be deduced from contact angles in such nonideal conditions.In this study, atomic force microscopy (AFM) has been used to observe mica surfaces treated with a series of crude oils that produce a wide range of wetting conditions—water-advancing contact angles on these surfaces vary from water-wet to oil-wet. In the most water-wet case, the only adsorbed features appear to be small, water-wet particles that are probably inorganic. All of the other oils deposited organic coatings, with varying thickness, morphology, and durability. Weakly water-wet systems exhibited many surface features, but the waitings tended to be unstable and to detach from the surface, especially during AFM scanning in water. The most oil-wet systems exhibited thick, stable organic coatings that were not disturbed by AFM scanning.     

凝析油气藏气湿反转解水锁的实验研究

气湿反转是目前解决油气藏水锁损害的有效方法之一.通过溶胶-凝胶法和氟烷基甲基丙烯酸共聚物Zonyl 8740的修饰,使岩心表面的润湿性发生了气湿反转.通过做接触角测量实验,发现溶胶的陈化时间、溶胶-凝胶处理时间、热处理温度、氟化浓度和氟化时间对岩心的浸润性有明显的影响.毛细管上升实验结果表明,用溶胶和Zonyl 8740处理后,气/水体系和油/气体系中的润湿性由优先液湿转变为气湿.利用扫描电子显微镜对处理岩心表面的形貌和能谱进行分析显示,用溶胶和Zonyl 8740共同处理岩心后,岩心表面具备了微细的粗糙结构和低表面能物质.岩心驱替实验结果表明,通过Zonyl 8740处理后,岩心中水的渗透率比未处理时增大了4倍.     

Adsorption kinetics and enhanced oil recovery by silica nanoparticles in sandstone

This study addresses adsorption kinetics of silica nanoparticles on sandstone mineral surfaces and Enhanced oil recovery (EOR) by nanoparticles. It was shown that nanoparticle adsorption on quartz which is the major constituent of sandstone reservoirs was best described as second order process. Both rate and equilibrium adsorption increases with salinity. However, salinity reduces Intraparticle diffusion while enhancing film diffusion. Spontaneous imbibition with nanoparticles dispersed in low salinity water showed higher incremental recovery which may be due to increased structural disjoining pressure. This was supported by surface forces analysis based on particle size and zeta potential measurements of the nanofluids.     

Fluorescence evidence of polar hydrocarbon interaction on mineral surfaces and implications to alteration of reservoir wettability

Petrographic analysis of reservoir rocks in an apparently water-wet system under UV light indicates the ubiquitous presence of microscopic oil inclusions within quartz grains. The micro-sized inclusions are often trapped along healed micro-fractures or along quartz overgrowth boundaries. The apertures of the micro-fractures are usually a few microns in width, an order of magnitude smaller than the typical pore aperture (throat) of reservoir rocks.When these same reservoir rocks were analysed using a highly sensitive fluorescence spectrophotometer after series of cleaning steps using solvents and oxidizing agents, it was revealed that polar organic compounds are present on quartz grain surfaces. Examination of the quartz grain surface using scanning electron microscope (SEM) and an energy dispersive X-ray (EDAX) system confirmed the presence of fine residual hydrocarbon particles associated with clay minerals coated on the highly irregular quartz grain surface.The presence of polar organic compounds and/or asphaltenes on water-wet quartz surfaces results in wettability alteration under reservoir conditions, which may allow direct contact between hydrocarbon and the water-wet quartz grains, resulting in the formation of micro-size oil inclusions in quartz grains.     

Wettability/spreading of alkanes at the water–gas interface at elevated temperatures and pressures

The Hamaker–Lifshitz theory is used to calculate the spreading coefficient of alkanes on water or brine at elevated temperatures and pressures. The dielectric polarizability at elevated temperature and pressure is estimated as a function of density through the Clausius–Mosotti equation. When complete data is not available, the wetting transition can be estimated from the refractive index at elevated temperatures and pressures. The spreading of alkanes on brine can also be estimated from the refractive index of the brine as a function of electrolyte concentration. The approach used here for alkanes is also used to estimate the conditions for the spreading of H₂S between water and sulfur.     

Analysis of counter-current gas–water capillary imbibition transfer at different temperatures

Gas water counter-current matrix–fracture interaction due to capillary forces was studied. The focus was on the rate of capillary imbibition and the development of residual gas phase under low (20 °C) and high temperatures (90 °C). Berea sandstone and Indiana limestone samples with different shape factors were obtained by cutting the plugs 1, 2.5, and 5 cm in diameter and 2.5, 5, and 10 cm in length. All sides were coated with epoxy except one end. Static imbibition experiments were conducted on vertically and horizontally situated samples where the matrix–fracture interaction took place upward and lateral directions, respectively. The effects of the matrix shape factor, wettability, surface tension, and core position on the recovery rate and ultimate recovery were investigated.The experimental scheme followed was useful in identification of the development of residual gas saturation for fully counter-current matrix–fracture interaction. We investigated and clarified to what degrees the rock/fluid properties (wettability and matrix shape factor) and existing conditions (temperature, causing lowered IFT and brine viscosity, and gravity) become effective on the residual gas saturation. It was observed that the residual gas saturation is sensitive to the matrix shape factor. The effect of surface tension on the recovery rate and ultimate recovery was also critical. The vertical cases yielded different recovery rates and ultimate recoveries with increasing temperature. Lower residual gas saturation with increasing temperature was obtained only for large diameters. That was attributed to the reduction in surface tension.Finally, critical matrix and fluid properties were correlated to the residual gas saturation and different dimensionless groups were tested for scaling.     

平湖油气田三甘醇脱水系统扩容改造方案研究与实施

平湖油气田三甘醇脱水系统需进行扩容改造.通过对脱水系统分离器、脱水塔、三甘醇循环泵等设备的流量进行校核,提出了3种扩容改造方案,论证后选取了新型BX丝网波纹填料塔改造方案,实施后取得了良好的生产效果和较高的经济效益.平湖油气田三甘醇脱水系统的扩容改造,为我国海上其他平台(包括FPSO)的类似改造工程提供了极好的案例.     

注水调剖技术提高文明寨油田采收率

该文根据文明寨油田的油藏特点，阐述了影响其水驱采收率的层内、层间因素，并对调剖技术在改善该油田吸水剖面结构、提高驱油效率及提高复杂断块油田最终采收率等方面的应用效果作了扼要论述。