Capillary number residual oil saturation

Bashiri, A. Heterogeneity of the hydrocarbon reservoirs can be defined in pore level or macroscopic scale. Pore level heterogeneity such as pore size and structure controls the quantity of hydrocarbon left residual saturation during production, whereas macroscopic heterogeneity determines zones that injected fluid sweeps Franklin, During simulation of a reservoir, macroscopic heterogeneity is represented by assigning different rock properties e.

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However, due to complex nature of pore entrapment mechanisms, it is only possible to represent pore scale heterogeneity with empirical correlations. Capillary Desaturation Curve CDC is a suitable correlation that links residual hydrocarbon saturation to physical properties of a given reservoir in pore scale.

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Therefore, accurate representation of CDC pattern can be critical for Improved Oil Recovery IOR processes evaluation as pore information is used as the basis for residual saturation prediction. Sign In or Register. Advanced Search. Sign In. Skip Nav Destination Proceeding Navigation. Close mobile search navigation.

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All Days. Previous Paper Next Paper. Article Navigation. Bashiri ; A. Iran University of Sci. This Site. Google Scholar. Kasiri N.You must log in to edit PetroWiki. Help with editing. Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment.

capillary number residual oil saturation

SPE disclaims any and all liability for your use of such content. More information. Relative permeability and capillary pressure defined capillary pressure as the difference in pressure across the interface between two phases.

Similarly, it has been defined as the pressure differential between two immiscible fluid phases occupying the same pores caused by interfacial tension between the two phases that must be overcome to initiate flow.

This page discusses capillary pressure forces.

Proper Use of Capillary Number in Chemical Flooding.

The relationship between capillary pressure and fluid saturation could be computed in principle, but this is rarely attempted except for very idealized models of porous media. Methods for measuring the relationship are discussed in Measurement of capillary pressure and relative permeability.

For this example, water is the wetting phase, and gas is the nonwetting phase. As shown in Figs. Wettability of a solid with respect to two phases is characterized by the contact angle. Popular terminology for saturation changes in porous media reflects wettability:.

Thus, the capillary pressure relationship in Fig. Water is the wetting phase. Gas does not penetrate the medium in Fig. As capillary pressure increases beyond this value, the saturation of the water continues to decrease.

Morrow and Melrose [2] argue that capillary pressure measurements have not reached equilibrium if the capillary pressure trend asymptotically approaches an irreducible water saturation. As the water saturation decreases during a measurement, the capacity for flow of water rapidly diminishes, so the time needed for equilibration often increases beyond practical limitations.

Hence, a difference develops between the measured relationship and the hypothetical equilibrium relationship, as shown in Fig. After completing measurements of capillary pressure for primary drainage, the direction of saturation change can be reversed, and another capillary pressure relationship can be measured—it is usually called an imbibition relationship.

Imbibition is often analogous to the waterflooding process. The primary drainage and imbibition relationships generally differ significantly, as shown in Fig.

This difference is called capillary pressure hysteresis—the magnitude of capillary pressure depends on the saturation and the direction of saturation change. For imbibition of a strongly wetting phase, the capillary pressure generally does not reach zero until the wetting-phase saturation is large, as shown in Fig. For a less strongly wetting phase, the capillary pressure reaches zero at a lower saturation, as shown in Fig. Capillary pressure behavior for secondary drainage is also shown in Figs.

Wettabilities of reservoir systems are categorized by a variety of names. Some systems are strongly water-wet, while others are oil-wet or neutrally wet. Spotty or "dalmation" wettability and mixed wettability describe systems with nonuniform wetting properties, in which portions of the solid surface are wet by one phase, and other portions are wet by the other phase.

Mixed wettability, as proposed by Salathiel, [3] describes a nonuniform wetting condition that developed through a process of contact of oil with the solid surface. Salathiel hypothesized that the initial trapping of oil in a reservoir is a primary drainage process, as water the wetting phase is displaced by nonwetting oil.Capillary number theory is very important for chemical flooding enhanced oil recovery.

The difference between microscopic capillary number and the microscopic one is easy to confuse.

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After decades of development, great progress has been made in capillary number theory and it has important but sometimes incorrect application in EOR. Experiments data from ASP flooding and SP flooding showed that remaining oil saturation was not always decreasing as capillary number kept on increasing. Relative permeability was proved function of capillary number; its rate dependence was affected by capillary end effects.

Proper Use of Capillary Number in Chemical Flooding

The mobility control should be given priority rather than lowering IFT. The displacement efficiency was not increased as displacement velocity increased as expected in heavy oil chemical flooding. Largest capillary number does not always make highest recovery in chemical flooding in heterogeneous reservoir. Misuse of CDC in EOR included the ignorance of mobility ratio, Darcy linear flow hypothesis, difference between microscopic capillary number and the microscopic one, and heterogeneity caused flow regime alteration.

Displacement of continuous oil or remobilization of discontinuous oil was quite different. Capillary number theory is regarded as the basic theory in polymer flooding, surfactant flooding, polymer-surfactant flooding SPand alkali-surfactant-polymer flooding ASPwhich are more appealing enhanced oil recovery EOR techniques in low oil price era.

The basic mechanism of chemical flooding in EOR can be summarized into mobility control based enlarging sweep efficiency and capillary number theory based improving displacement efficiency.

EOR mainly involves how to recover more remaining or residual oil and reducing oil saturation. Recently, there are some misunderstandings about capillary number theory and especially its application in chemical flooding.

In petroleum industry, it has been generally recognized that capillary desaturation curve CDC reflects the character and arrangements of the pores within the media and the distribution of fluids within the pores [ 1 ].

Capillary number was a dimensionless group describing the ratio of viscous to capillary forces [ 2 — 7 ].

Capillary Number - Christopher Sparages

Capillary number was crucial in determining the remaining oil saturation [ 8 ]. Some experiment results are summarized in Figure 1. In enhanced oil recovery like chemical flooding CDC has various applications in not only water flooding but also chemical flooding [ 12 — 16 ]; capillary number was frequently cited in explaining the mechanisms [ 10121718 ]. Typical classical CDC showed that larger capillary number leads to lower residual oil saturation and when capillary number increased to some certain critical value, the residual oil saturation could drop to a minimum value even zero.

However, recent literatures showed that CDC was often misunderstood by ignoring the difference between remaining oil saturation and residual oil saturation and the fundamental hypothesis in conducting capillary number definition. The sweep efficiency issue was not discussed in classic CDC and the importance of mobility control was not emphasized as it deserved.

The hypothesis underlying the deduction of capillary number including capillary bundle and Darcy flow should be checked when capillary number theory is used in low permeability and heavy oil reservoir.

In low permeability reservoir, flow behaves as some kind of non-Darcy feature, while in heavy oil chemical flooding the viscosity ratio is big enough to consider the mobility ratio and frontal stability.

Systematical review of capillary number in chemical flooding is helpful to understand the importance of mobility control and enlarging sweep volume in chemical enhanced oil recovery EOR. Capillary number was defined as ratio of viscous force to capillary force [ 711 ]. However, Manthey et al. The advantage is that its interpretation is more intuitive since for a large capillary number capillary forces dominate.

This definition sounds good but few ongoing studies are reported. Laboratory studies have shown that residual oil can be recovered if the displacing phase causes viscous forces acting on trapped residual oil blobs to exceed the capillary retaining forces. The derivation of capillary number can be seen in literature [ 20 ]. Recovery factor was found to be dependent on the capillary factor [ 7 ]. The capillary number provides satisfactory correlations of mobilization oil with widely different viscosities [ 5 ].

Capillary has many different mathematical definitions [ 45 ]. Differences were noted in CDC with different capillary number forms [ 6 ], while the most often applied definitions [ 10 ] are where was the IFT, is the superficial velocity, and is the viscosity of the displacing wetting phase.

In recent years, most research about capillary number is about its application in water and chemical flooding. Hilfer et al. They found that the capillary number is expressed as a function of saturationvelocity viand model lengthwhile in most previous studies the length was seldom given enough attention.

They also emphasized the difference between microscopic capillary number and the microscopic one, which is easy to confuse [ 2 ]. Many experiments showed that microscopic displacement efficiency increased as capillary number increased to a certain value and the effects of capillary number on residual oil recovery were also studied [ 35 — 7102122 ].Current Filters.

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SPE Disciplines. Geologic Time. Concept Tag. Oilfield Places. File Type. Petrowiki January, San Andres and Clearfork are two carbonate reservoir intervals that are present over a considerable area of the Permian Basin in west Texas. These reservoirs e. They are very-layered, heterogeneous carbonates and dolomites that have large variation in permeability from layer to layer.

Interestingly, because of the complex hydrocarbon-accumulation history of this basin, much of this area has an underlying interval that contains residual oil saturation. Most of these reservoirs were discovered in the late s and the s. Add feedback. More like this By text By views By concept tags. Abdul Manap, Azrif Azhan Petronas. OnePetro November, Field A is located offshore Malaysia, identified as the candidate for a pilot project to evaluate the effectiveness of alkali-surfactant AS slug to improve recovery factor through the reduction of residual oil saturation.

The pilot project utilized single well chemical tracer test technique SWCTT to measure residual oil saturation S or change near well bore. The pilot results could be used to evaluate the potential of this technology in a larger scope application later. The pilot project faced challenging technical and operational obstacles: offshore location, high reservoir temperature, sea water as injection water, water softening facilities requirement, unmanned satellite platform with limited space, no on-site laboratory - just to list a few.

In addition, stringent health, safety and environment HSE requirements needed to be complied to ensure the pilot operation was carried out in a safe and orderly manner. This paper will focus on the overall pilot design, planning and some results.

capillary number residual oil saturation

The test not only involves field operations and lab measurements, but also relies on curve fitting of the data acquired from these procedures. Here, we present a robust SWCTT simulator and use it to perform sensitivity analysis of different parameters over a wide range of reservoir and tracer properties. This sensitivity analysis and the "what-if" capability of our simulator provide in-depth understanding for the design and optimization of SWCTT. OnePetro October, Nanoparticles have great potential to mobilize trapped oil in reservoirs by reducing the oil-water interfacial tension, altering the rock wettability, stabilizing foams and emulsions, and heating the reservoir to decrease the oil viscosity.

However, the direct application of magnetic forces on paramagnetic nanoparticles in reservoir engineering applications has not be extensively investigated.

We demonstrate the enhanced oil recovery EOR potential of hydrophilic magnetic nanoparticles in oil production by direct observation using microfluidics.

We studied the mobilization of oil blobs by a ferrofluid a suspension of hydrophilic magnetic nanoparticles in water in a converging-diverging channel with varying depth so-called 2. The channel had a varying depth of microns and a varying width of microns, approximating a flow path in the rock. The nanoparticle suspension was injected at 0. The channel was made of glass and thus the water-based ferrofluid was the wetting fluid. Initial ferrofluid flooding experiments were performed under a static magnetic field.

Microscale Physics in Oil Displacement by Complex Liquids in Porous Media

This magnetic field caused oil droplet deformation, dynamic break-up into smaller droplets, and subsequent residual oil saturation reduction. Significant oil blob displacement was observed within 2 hours after the magnetic field was applied. During the flooding, the oil saturation within the observation area of the micromodel reduced from Fraction of pore volume occupied by oil at the end of oil displacement that used a specific fluid.

This reservoir engineering quantity signifies the ultimate recovery under a given displacement process and represents the endpoint of the relative permeability curves in reservoir simulation. The residual oil saturation quantity is the saturation achieved after an infinite number of pore volumes of the displacing fluid have flowed through a particular portion of reservoir rock. To define residual oil saturation, the displacement method and the type, volume, direction and velocity of the displacing fluid must be known.

Residual oil saturation is the ratio of the immobile residual oil volume divided by the effective porosity. Premium content requires special account permissions.

We need a little more information from you before we can grant you access. Explore the new Oilfield Glossary. Share This. Don't have an account? Click below to get started. Sorry, you do not have access to this content Premium content requires special account permissions.The capillary number Ca is a dimensionless number and it represents the relation between viscous forces and capillary forces, which occur between two immiscible liquids.

Over the years, the capillary number has been represented by a series of different forms across literature with one of the most common one being the formalism by Saffman and Taylor Figure 1, No. The capillary number is used to determine which forces dominate in a specific scenario. The capillary number theory was originally developed by basing the idea off of capillary tube bundles and Darcy's law.

The goal of the experiments driving this theoretical discovery was to determine the saturation movement of this residual oil after it is in contact with water forcing imbibition, which is the expansion of solid when it absorbs water.

capillary number residual oil saturation

The capillary number is used for example in chemical flooding situations where a decrease in capillary number corresponds to a decrease in remaining oil saturation. As mentioned above the capillary number is a representation of forces between two immiscible liquids gas or liquid. In the case of bubble suspension, the interaction is between a liquid and gas. A large reason for studies conducted with bubble suspension is to learn more about to develop models, characterize, and control the flow of the respective gas.

In order to achieve these goals, rheology tests are conducted while values for viscosity, velocity, and surface tension are taken see how capillary number effects the behavior of this bubbling. Comparing the bubble viscosity to the capillary number, results can be seen that with an increase in capillary number there is a sigmoidal response in the bubble viscosity Figure 3. The capillary number theory is also used as a basic theory for chemical flooding.

The capillary number is influential for chemical flooding because it is crucial in determining oil saturation. A common way to represent this data is by using a capillary desaturation curve CDC Figure 3. The CDC shows the pore arrangement within the media and fluid distribution within the pores.

However, to produce a corresponding CDC to a data set one must first test the wettability effect of the solids involved which has an effect on the overall saturation Figure 3. Wettability is one of the factors that contributes to relative permeability, which is effected by capillary number within a certain range. In terms of a microfluidic device, the use of rock and sand acts in a microfluidic way and can be developed into a controlled device. In the example provided here, uses a PDMS fabricated microfluidic device that was based on the geometry of sandstone.

capillary number residual oil saturation

Oil is flooded through the system and in order to increase its contrast with the PDMS has been dyed with Sudan Blue, which is oil-soluble. The percent of oil remaining in the channel is calculated based on the flow rate of fluids such as water being passed through the device to obtain shear rate. This can also be measured as a function of capillary number versus the percent of oil remaining, where the closer capillary number approaches one the closer the percent remaining of oil reaches zero.

Relative permeability takes into consideration wettability as mentioned above, capillary end effects, geometry of the pore, rock type, and imbibition or drainage.Injecting water into the reservoir is one available method.

During water flooding, the force responsible for displacing oil is a viscous force. Rather, the difference in viscosity between water and oil forms viscous fingers, which result in both early breakthrough and reduced sweep efficiency. Therefore, the use of a more viscous liquid than water is beneficial in improving the sweep efficiency in water flooding.

In a laboratory setting, Detling tested different types of materials for viscous water flooding. Barens used sugar and zinc chloride to improve water sweep in reservoirs partially invaded by aquiver water.

The results indicated that the use of viscous water can increase the ultimate oil recovery. However, the use of materials such as sugar and glycerin to increase water viscosity is not economically feasible. Water-soluble polymers work more efficiently as thickening agents. Sandiford added partially hydrolyzed polyacrylamide during water flooding to reduce water mobility and increase oil recovery. According to Pyecertain high molecular weight synthetic polymers in very dilute solutions can decrease the water mobility in porous media 5 to 20 times more than brine solution at the same viscosity.

The oil recovery efficiency overall displacement efficiency, E of any EOR technique is the amount of hydrocarbon displaced divided by the volume of hydrocarbon at the beginning of the EOR process; it also can be defined as the product of the microscopic efficiency E D and the macroscopic efficiency E Vas expressed in Equation below. Microscopic displacement efficiency, E D E D is reflected in the magnitude of the residual oil saturation, S orin the area that the displacing fluid contacts.

The microscopic efficiency also can be expressed in terms of saturation using Equation below. Factors affecting microscopic displacement behavior: The microscopic efficiency plays a significant role in the successful application of EOR techniques because it reflects the extent to which a certain displacement process can reduce the residual oil saturation.

The ratio of viscous to capillary forces is called the "capillary number," which can be defined as the ratio of the viscous pressure gradient viscous force to the interfacial tension. The capillary number has been reported in the range of 10 -6 to 10 -7 for water flooding processes Donaldson et al. The capillary number increases as the viscous force increases and the interfacial tension decreases.

Many researchers have conducted laboratory tests and field applications to improve the displacement efficiency by increasing the capillary number. The first step of any displacement process is to mobilize residual oil and form an oil bank that can be mobilized by increasing the capillary number above the critical capillary number Ncc. Figure p11 shows the effect of the capillary number on the residual oil according to different studies. Figure p Capillary number versus residual oil saturation Fulcher et al.

Microscopic displacement efficiency versus capillary number Donaldson et al. Recently, numerous studies have shown that viscoelastic polymer helps to improve the microscopic displacement efficiency more than water flooding Demin et al. Wenxiang et al. They found that when the capillary number was small, the recovery efficiency increased slowly, and the residual oil saturation decreased slowly as the capillary number increased; however, when the capillary number reached between 10 -3 and 10 -2the increase in the oil recovery efficiency and the reduction in the residual oil saturation was marked Wenxiang et al.


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