Oil-wet Media Research Articles

Determination of In Situ Wettability Using Wavelet Analysis and Nuclear Magnetic Resonance Log Data

Knowledge of reservoir rock wettability is crucial for the understanding of fluid displacement mechanisms and for adopting feasible solutions to enhance oil recovery. Highly sensitive to the strength of fluid–rock interactions, nuclear magnetic resonance (NMR) measurements are a well-suited candidate for in situ wettability determination. Changes in correlation coefficients between NMR porosity $$\left( {\phi_{\rm NMR} } \right)$$ and transverse relaxation time $$\left( {T_{2} } \right)$$ can be used as a diagnostic parameter to determine in situ wettability. This paper aimed to take advantage of this promising feature to specify the downhole wettability of an oil well running through two carbonate reservoirs. In this regard, the correlation coefficient between $$\phi_{\rm NMR}$$ and $$T_{2}$$ was first computed at each depth. As a superior technique in analyzing nonstationary signals, the wavelet transform was then applied to the correlation coefficient log to remove shale content. Finally, the wavelet transform was re-applied to the modified correlation coefficient log to derive the detail coefficients. Scrutiny of the detail coefficients revealed a strong correlation with experimental wettability results. The results obtained from this investigation indicated that positive detail coefficients are associated with water-wet, and negative ones with oil-wet media.

Effect of Surface Wettability on Immiscible Displacement in a Microfluidic Porous Media

Wettability has a dramatic impact on fluid displacement in porous media. The pore level physics of one liquid being displaced by another is a strong function of the wetting characteristics of the channel walls. However, the quantification of the effect is still not clear. Conflicting data have shown that in some oil displacement experiments in rocks, the volume of trapped oil falls as the porous media becomes less water-wet, while in some microfluidic experiments the volume of residual oil is higher in oil-wet media. The reasons for this discrepancy are not fully understood. In this study, we analyzed oil displacement by water injection in two microfluidic porous media with different wettability characteristics that had capillaries with constrictions. The resulting oil ganglia size distribution at the end of water injection was quantified by image processing. The results show that in the oil-wet porous media, the displacement front was more uniform and the final volume of remaining oil was smaller, with a much smaller number of large oil ganglia and a larger number of small oil ganglia, when compared to the water-wet media.

Prediction of three-phase saturation profiles from two-phase capillary pressure curves as a function of wettability

Gravity drainage of oil with gas is an efficient recovery method in strongly water-wet reservoirs and yields very low residual oil saturations. However, many of the oil-producing reservoirs are not strongly water-wet. Thus, predicting the profiles and ultimate recovery for mixed and oil-wet media is essential to design and optimisation of improved recovery methods based on three-phase gravity drainage. In this study, we perform two- and three-phase gravity drainage experiments in sand-packed columns with varying wettability. We propose a simple method for predicting the three-phase equilibrium saturation profiles as a function of wettability. In each case, the three-phase results were compared to the predictions from two-phase results of the same wettability. We find that the gas/oil and oil/water transition levels can be predicted from pressure continuity arguments and the two-phase data. The predictions of three-phase saturations work well for the water-wet media, but become progressively worse with increasing oil-wet fraction.

EXPERIMENTAL INVESTIGATION OF WETTABILITY EFFECT AND DRAINAGE RATE ON TERTIARY OIL RECOVERY FROM FRACTURED MEDIA

Vertical displacement of oil by gas is one of the most efficient methods for oil recovery from naturally fractured reservoirs. Unlike the homogeneous media, the ultimate oil recovery by gravity drainage in fractured media is more dependent on the production rate. Hence finding the optimum production rate for more oil recovery with respect to the properties of media seems to be essential. In this work, unconsolidated packed models of cylindrical geometry surrounded by fractures were utilized to perform a series of flow visualization experiments during which the contribution of different parameters such as the extent of matrix wettability and the withdrawal rate were studied. In addition, mutual effects of wettability and production rate on tertiary oil recovery efficiency through controlled and free fall gravity drainage processes were also investigated. Experimental results obtained from tertiary gravity drainage experiments demonstrated that just before gas breakthrough, lower withdrawal rates facilitate the tertiary oil recovery under the film flow mechanism, which leads to a higher ultimate recovery factor. However, after gas breakthrough, monitoring oil recovery by gravity drainage showed that higher production rates recovered more oil. Furthermore, under tertiary recovery processes in low-production cases, oil-wet systems achieved higher recovery factors, while at high withdrawal rates, more oil was recovered for 50% oil-wet media.

Experimental studying of pore morphology and wettability effects on microscopic and macroscopic displacement efficiency of polymer flooding

Pore morphology and wettability of a porous medium have dominating effects on microscopic displacement efficiency, and consequently on the ultimate oil recovery. To provide a better understanding of the effects of these parameters on microscopic displacement mechanisms and macroscopic performance of a polymer flood process, a comprehensive experimental study was conducted using five two-dimensional glass micromodels. A combination of three wettability conditions and five different pore structures was used in this study. The selected scenarios include four homogeneous synthetic pore networks at water-, mixed- and oil-wet conditions. A random network that represents the pore space in Berea sandstone was also used for further investigation. Image processing technique was applied to analyze and compare displacement mechanisms and displacement process efficiency in each experiment. Microscopic mechanisms, such as oil and polymer solution trapping, configuration of wetting and non-wetting phases, flow of continuous and discontinuous strings of polymer solution, polymer solution snap-off, distorted flow of polymer solution, emulsion formation, and microscopic pore-to-pore sweep of oil phase were observed and monitored in conducted experiments. Experimental results showed that water- and mixed-wet media generally have comparable and higher recoveries in contrast with oil-wet media. Moreover, the results confirmed a significant dependency on the pore structure and wettability of the media on both displacement mechanisms as well as oil recoveries. This experimental study illustrates the successful application of glass micromodel techniques for studying enhanced oil recovery (EOR) processes in a five-spot pattern, and also provides a useful reference for understanding the displacement mechanisms involved in a polymer flood process at different pore morphologies and wettabilities of porous media.

친수성에 의존하는 소수성 액체의 거동을 위한 분율 유동 접근 방식을 이용한 다상 유동 수치 모델링 개발

석유공학분야에서 보고된 분율 흐름 접근 방식을 이용하여 물리적 또는 화학적으로 불균질한 매질에서 완전한 삼상유체를 고려할 수 있는 다상 흐름 수치 모의 프로그램인 CHMPS가 개발되었다. 이 프로그램은 석희준과 G.T. Yeh (2008)에 의해 개발된 MPS을 확장하였는데, 친수성이 NAPL 거동에 미치는 영향을 모의하기 위하여 개발되었다. 대부분 존재하는 모델들은 물리적으로 불균질한 매질을 고려하고 이상흐름과 특정한 경계조건에 국한되어 있다. 게다가 대부분의 모델들은 주로 water-wet 매질에만 국한되어 있다. 그러나 실제 존재하는 시스템에서는 water-wet과 oil-wet 매질 사이의 친수성의 변화는 종종 일어난다 더군다나 기름에 의한 다공성 매질의 젖음은 균등하기 보다는 불균질 또는 부분적일 수 있다. 왜냐하면 친수성에 영향을 미치는 요소들과 지하 매질이 불균질하기 때문이다. 따라서, 이번 연구에서는 물리적으로 불균질한 매질 뿐만 아니라 친수성 변에서 화학적으로 불균질한 매질을 CHEMPS을 활용하여 수치모의 하였다. 그 외에도 개개의 상에 대해서 유량 경계조건 및 고정경계조건의 두 가지 형식의 결합으로 표현되는 일반경계조건이 고려되었다. The multiphase flow simulator, CHEMPS, was developed based on the fractional flow approach reported in the petroleum engineering literature considering fully three phase flow in physically and chemically heterogeneous media. It is a extension of MPS developed by Suk and Yeh (2008) to include the effect of wettability on the migration of NAPL. The fractional flow approach employs water, total liquid saturation and total pressure as the primary variables. Most existing models are limited to two-phase flow and specific boundary conditions when considering physically heterogeneous media. In addition, these models focused mainly on the water-wet media. However, in a real system, variations in wettability between water-wet and oil-wet media often occur. Furthermore, the wetting of porous media by oil can be heterogeneous, or fractional, rather than uniform due to the heterogeneous nature of the subsurface media and the factors that affect the wettability. Therefore, in this study, the chemically heterogeneous media considering fractional wettability as well as physically heterogeneous media were simulated using CHEMPS. In addition, the general boundary conditions were considered to be a combination of two types of boundaries of individual phases, flux-type and Dirichlet type boundaries.

Study of Microscopic and Macroscopic Displacement Behaviors of Polymer Solution in Water-Wet and Oil-Wet Media

Performance of a polymer flood process requires the knowledge of rheological behavior of the polymer solution and reservoir properties such as rock wettability. To provide a better understanding of effects of polymer chemistry and wettability on the performance of a polymer flood process, a comprehensive experimental study was conducted using a two-dimensional glass micromodel. A series of water and polymer flood processes were carried out at different polymer molecular weights, degrees of polymer hydrolysis, and polymer concentrations in both water-wet and oil-wet systems. Image processing technique was applied to analyze and compare microscopic and macroscopic displacement behaviors of polymer solution in each experiment. From micro-scale observations, the configuration of connate water film, polymer solution trapping, flow of continuous and discontinuous strings of polymer solution, piston-type displacement of oil, snap-off of polymer solution, distorted flow of polymer solution, emulsion formation, and microscopic pore-to-pore sweep of oil phase were observed and analyzed in the strongly oil-wet and water-wet media. Rheological experiments showed that a higher polymer molecular weight, degree of hydrolysis, and concentration result in a higher apparent viscosity for polymer solution and lower oil–polymer viscosity ratio. It is also shown that these parameters have different impacts on the oil recovery in different wettabilities. Moreover, a water-wet medium generally had higher recovery in contrast with an oil-wet medium. This experimental study illustrates the successful application of glass micromodel techniques for studying enhanced oil recovery (EOR) processes in five-spot pattern and provides a useful reference for understanding the displacement behaviors in a typical polymer flood process.

The influence of pore wettability on the microstructure of residual oil in surfactant-enhanced water flooding in heavy oil reservoirs: Implications for pore-scale flow characterization

Among many variables that affect the performance of surfactant-based chemical flooding processes, the reservoir pore wettability is considered as the foremost parameter after the reservoir geology. Although considerable attention has been paid to the obviously important subject of wettability effect in these processes, the effect of pore wettability on experimentally determined, quantitative information on blob microstructure and the statistics of blob populations are missing from the literature. The latter is important since changes in size distribution and shapes of blob provide insight into the mechanisms of trapping and mobilization of trapped, residual oil, and relative change in the magnitude of the viscous, capillary, and inertial forces at the pore level. In this study, the changes that occur with change in wettability, from water-wet to oil-wet, in the detailed microstructure of trapped, residual, high-viscosity oil in porous media have been evaluated. To obtain such invaluable information, satisfactory techniques for microscopically capturing statistically representative blob samples and measuring their size distribution have been devised. Once obtained, the experimentally determined oil blob size distribution and the detailed statistics of blob populations have been used to characterize the pore-scale flow behavior of surfactant-enhanced water flooding in the water-wet and oil-wet networks. This pore-scale flow behavior characterization includes the influence of wettability on construction of the relationships between the pore-scale mobilization capillary number and a quantity (which depends on pore geometric properties and the equilibrium radii of curvature of the meniscus of the blob) and the statistical distribution of the mean pore-scale Weber number. Furthermore, mean, median, and maximum pore-scale capillary number values have been determined in the water-wet and oil-wet media. This type of pore-scale flow characterization helps to gain proper knowledge of the change in the magnitude of the viscous, capillary, and inertial forces at the pore level using the statistics of oil blob length and diameter. Finally, the changes in size distribution and shapes of oil blob are linked to some of the pore-level events of oil trapping and mobilization, which are reviewed in this study. The gained knowledge helps modeling recovery of residual oil blobs under different wettability conditions.

Pore-scale network simulation of NMR response in two-phase flow

Wettability controls fluid saturation and distribution in reservoir rocks, that in turn affects two-phase properties such as Nuclear Magnetic Resonance (NMR) response. We simulated the NMR response of two-phase systems during drainage and waterflooding in pore-scale networks representing sand packs and sandstones using a random walk method. Different wettabilities were studied and the simulation results were compared with previously published experimental measurements. In oil-wet media, we predict a slow decay with a broad T 2 distribution because water in the center of the pores has a low bulk relaxivity; there is little surface relaxivity since the grain surfaces are covered by oil layers. This suggests a straightforward technique to indicate oil wettability in core samples.

Visualization and Quantification of Asphaltinic-Heavy Oil Displacement by Co-Solvents at Different Wettability Conditions

Despite numerous experimental studies, there is a lack of fundamental understanding on how the chemical composition of a co-solvent at different wettability conditions might affect the pore-scale events and oil recovery efficiency in 5-spot models. In this study visualization of solvent injection experiments performed on a one-quarter five spot glass micromodel, which was initially saturated with the crude oil. One hydrocarbon solvent was considered as base, and four other groups of commercial chemicals, as well as their mixtures, were used as co-solvents. Microscopic and macroscopic displacement efficiency of solvent mixtures in both strongly water-wet and oil-wet media has been studied. It has been observed that small aggregates of asphaltene can improve oil recovery to some extent during early stages of solvent injection. Different groups of chemicals showed various effects on oil recovery based on their nature. An optimum mixture with some percent of commercials containing alcohol group with greatest sweep efficiency was found. The observations confirmed that the presence of connate water in strongly water-wet medium could improve the final recovery, while the effect of wettability in absence of connate water was at minimum.

Pore-scale Simulation of Water Alternate Gas Injection

We use a three-dimensional mixed-wet random network model representing Berea sandstone to compute displacement paths and relative permeabilities for water alternating gas (WAG) flooding. First we reproduce cycles of water and gas injection observed in previously published experimental studies. We predict the measured oil, water and gas relative permeabilities accurately. We discuss the hysteresis trends in the water and gas relative permeabilities and compare the behavior of water-wet and oil-wet media. We interpret the results in terms of pore-scale displacements. In water-wet media the water relative permeability is lower during water injection in the presence of gas due to an increase in oil/water capillary pressure that causes a decrease in wetting layer conductance. The gas relative permeability is higher for displacement cycles after first gas injection at high gas saturation due to cooperative pore filling, but lower at low saturation due to trapping. In oil-wet media, the water relative permeability remains low until water-filled elements span the system at which point the relative permeability increases rapidly. The gas relative permeability is lower in the presence of water than oil because it is no longer the most non-wetting phase.

Fractional wettability effects on two-and three-fluid capillary pressure-saturation relations

Studies of the relation between capillary pressure ( P c) and fluid saturation ( S) for porous media containing oil-water or air-oil-water, often assume that the medium is strongly water-wet. Natural porous media, however, are composed of a variety of mineral constituents; such media are typically composed of water- and oil-wet fractions. This study reports on two- and three-fluid P c- S data for media of different fractions of water- and oil-west sands. The oil-water capillary pressure, defined as the oil minus the water pressure, was measured during drainage (primary and main curves) as well as inhibition (main curve only) of water. A decrease in oil-water pressure was observed as the oil-wet fraction increased in two-fluid media. The pressure became negative during imbibition of water for relatively oil-wet media. The P c- S data could be adequately described by modifying the van Genuchten model for water retention. The observed differences between primary and main drainage curves were partly attributed to the effect of initial saturation. In three-fluid systems with fractional wettability, the observed dependency of capillary pressures on fluid saturations suggested that there was no continuous intermediate phase — even for a relatively low oil-wet fraction (25%). The oil-water and air-water capillary pressures decreased, at a particular water saturation, as the fraction of oil-wet sand increased. The water pressure is greater when water acts as the intermediate fluid than when it is the wetting fluid. The oil pressure, and hence the air-oil capillary pressure, was relatively insensitive to whether oil acted as wetting or intermediate fluid. There is a need to model three-fluid P c- S curves that account for different wetting and intermediate fluids.

Effect of System Wettability on Oil Displacement By Micellar Flooding

This paper studies the recovery of waterflood residual oil by micellar floods using laboratory oil- and water-wet cores. Excellent agreement is found between experiment and theory. The study also shows greater chemical costs and decreases in injectivity for oil-wet systems. Introduction The recovery of waterflood residual oil in laboratory water-wet porous media by a micellar or microemulsion solution has been discussed extensively. Many studies have defined the requirements (mobility control and capillary number) for effective oil displacement, discussed the relationship of micellar fluid design and oil recovery performance, reported the laboratory data for design of field tests, discussed the mechanisms of oil displacement, and investigated surfactant loss. With few exceptions, similar studies in oil-wet media have not been reported, although at least three pilot micellar floods have been conducted or planned in intermediate or oil-wet reservoirs. Although one might expect the requirements for oil displacement to be similar in water- and oil-wet media, there are fundamental differences in the recovery of oil, as demonstrated by waterflood performance and in the physical structure and distribution of the waterflood residual oil. In particular, the reduction of interfacial tension required for displacement of the wetting phase has been investigated only theoretically and experimentally in synthetic systerms. Only one study containing laboratory micellar flood data in oil-wet cores has been presented. This study discussed the micellar fluid design for a planned pilot test and compared the fluid's oil recovery pilot test and compared the fluid's oil recovery performance in water-wet cores with oil-wet. The chosen performance in water-wet cores with oil-wet. The chosen surfactant system required almost twice the slug size for strongly oil-wet media to achieve the tertiary oil recovery obtained with water-wet cores. Such a comparison has not been determined yet because the requirements for oil displacement and the displacement mechanisms are not the same in oil- and water-wet systems. In other words, a fluid that is optimal for water-wet porous media may not be optimal for oil-wet porous media. This study was undertaken to determine whether there are significant differencesin the requirements for oil displacement by a micellar fluid in oil- and water-wet cores, andbetween the oil displacement mechanisms of micellar fluids in oil- and water-wet cores. The results of seven continuous-injection, micellar slug tests with three different micellar fluids are presented and discussed. Theories are proposed to explain differences in the oil recovery performance between oil- and water-wet cores. The results of a series of small-slug tests (7 to 35 percent PV micellar fluid injected) also are discussed. percent PV micellar fluid injected) also are discussed. Their performance is explained in terms of the proposed theories. The implications on micellar fluid design, both in oil- and water-wet media, are brought out. Evidence of a chromatographic separation of a micellar fluid is presented also. presented also. Requirements for Oil Displacement Effective oil displacement by micellar flooding requires an increase in mobility control and capillary, number (mu u/ gamma). Mobility control is a function of relative permeability. The water- and oil-wet relative-permeability permeability. The water- and oil-wet relative-permeability curves used in this study are depicted in Fig. 1. JPT P. 52

Linear Waterflood Behavior and End Effects in Water-Wet Porous Media

Introduction Theory indicates that linear waterfloods should exhibit scaling and stabilization properties in both oil-wet and water-wet porous media. Experimental verification of these properties in oil-wet media was obtained some time ago, and more recently, Perkins employing a high permeability unconsolidated sand and a low oil-to-water viscosity ratio, has obtained flooding data in a water-wet medium which follow the pattern of scaling and stabilization. Also, Root and Calhoun have found similar trends in the displacement of gas by liquids from unconsolidated sands. In general, however, the experimental evidence appears still somewhat conflicting since scaling and stabilization of water floods in water-wet media has not been observed in most of the studies to date. The purpose of this paper is to provide a more comprehensive picture of waterflood behavior in water wet media and to corroborate the validity of the scaling and stabilization concepts. The need for differentiating between the intrinsic nature of water-oil displacements inside a porous medium and perturbating secondary end effects is discussed, pertinent experimental procedures are outlined and the results of flooding tests conducted at low and at high oil-to-water viscosity ratios on consolidated, water-wet Alundum cores are analyzed.