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Smart Surfactant-EOR Approach Optimizing Mature Waterfloods in AbuDhabi

Carbonate Reservoirs

Article  in  SPE Journal · October 2013

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SPE 165909

Electrokinetics Assisted Surfactant-EOR to Optimize Mature Waterfloods in AbuDhabi Carbonate Reservoirs

Arsalan Ansari, Muhammad Haroun, Nabeela Al Kindy, Basma Ali, Reena Amatya Shrestha, Hemanta Sarma, The Petroleum Institute, Abu Dhabi Copyright 2013, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Asia Pacific Oil & Gas Conference and Exhibition held in Jakarta, Indonesia, 22–24 October 2013. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract EOR technologies such as CO2 flooding and chemical floods have gained increased interest due to the decreasing number of new-field discoveries, increasing number of maturing fields and higher oil price. Therefore, promising results have been demonstrated in both lab scale and field pilots. Among the emerging EOR technologies, is the surfactant EOR integrated with the application of electrically enhanced oil recovery (EEOR), which is gaining increased popularity due to a number of reservoir-related advantages such as reduction in fluid viscosity, water-cut, increased reservoir permeability, reduced HSE concerns and increased targeting of the unswept oil. Core flood tests were performed using carbonate core-plugs from Abu Dhabi producing oilfields which were saturated with medium crude oil in a specially designed EK core-flood setup. Electrokinetics (DC voltage of 2V/cm) was applied on these oil saturated cores while waterflooding simultaneously until the ultimate recovery was reached. In the second stage, the recovery was further enhanced by injecting non-ionic surfactant (APG) along with sequential application of EK. This was compared with simultaneous application of EK-assisted surfactant flooding on oil-wet cores. A smart Surfactant-EOR process was done in this study that allowed shifting from sequential to simultaneous Surfactant-EOR alongside EEOR. The experimental results at ambient conditions show that the application of waterflooding on the carbonate cores yields recovery of approximately 42-64% along with an additional 6-14% incremental recovery that resulted upon the injection of non-ionic surfactant. However, there was a further 12-15% recovery enhanced by the application of EK-assisted surfactant flooding, which could be promising for water swept reservoirs. In addition, EK was shown to enhance the carbonate reservoir’s permeability by approximately 11-29%. Furthermore, this process can be engineered to be a greener approach as the water requirement can be reduced upto 20% in the presence of electrokinetics which is economically feasible.

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Introduction and Background A large fraction of original oil in place is left behind in the reservoir after primary recovery phase. Secondary (pressure maintenance) and tertiary (pressure maintenance along with playing with physiochemical properties of rock-fluid) phases are practiced to recover as much as possible from the remaining oil based on economic and environmental approaches [Dandona et al., 1972]. Since the last few decades, there has been a global increase in oil demand due to widespread power generation across the world. It is generally considered that approximately one-third of the hydrocarbon present in existing reservoirs is economically recoverable with commercialized technology (Hirasaki et al., 2011). The present primary recovery, secondary (pressure maintenance) and tertiary (pressure maintenance along with physiochemical properties of rock-fluid) recovery methods are practiced to recover the remaining oil based on economic and environmental approaches (Amba et al., 1964). The conventional primary recovery ranges from 3% with the help of the expansion of undersaturated oil upto about 15% with solution gas drive. The presence of active water drive or gas cap drive boosts the recovery significantly to about 50% or more by maintaining the reservoir pressure via gas and/or water injection (Dandone et al., 1972). Waterflooding still remains the most universally accepted method for enhancing oil recovery after initial natural pressure depletion due to easy availability, inexpensive relative to other fluids, ease of injection and the high efficiency in displacing oil in-situ (Guerithault et al., 2001) However, the low oil prices that prevailed from the mid-1980’s until recently provided little incentive for research on EOR, especially surfactant processes with substantial initial cost for chemicals. In the light of current higher prices and accompanying revival of interests, it seems appropriate to review understanding of, and prospects for surfactant EOR (Hirasaki et al., 2011) Abu Dhabi carbonate reservoirs contain vast amounts of residual hydrocarbons even though most of these reservoirs are in an advanced stage of depletion. However, several competitive EOR technologies are already been applied in various fields. In addition, the main objective is to target the unswept oil while having a minimum environmental impact with the use of ecofriendly and easily biodegradable while producing reduced formation water. The maturity of many fields will require the use of surfactant based recovery methods to recover residual oil in waterflooded reservoirs. Although surfactant flooding methods were developed mostly for sandstone reservoirs, it has been suggested that oil-wet fractured carbonate reservoirs have shown great potential for surfactant EOR applications (Manrique et al., 2004). Our proposed EK-Surfactant-EOR tertiary technique that was used on carbonate cores retrieved from an Abu Dhabi field, involved performing waterflooding followed by smart surfactant flooding, complimented by electrokinetics. After surfactant flooding stage, EK was applied both sequentially and simultaneously on these carbonate cores. The feasibility of conventional EEOR in carbonate reservoirs has been demonstrated by using Abu Dhabi carbonate rock samples in a previous study. (Haroun et al., 2009). There are over 190 pilot projects or field-wide chemical floods reported in the United States from 1960 until today, of which 178 were conducted on carbonate reservoirs (Manrique et al., 2007). These chemical floods were implemented at the early stages of waterflooding in order to increase the sweep efficiency of the reservoir which would then increase the final oil recovery. Manrique mentions a number of field pilots and their responses to chemical flooding. The Eliasville field was discovered in 1920 with the light crude oil (39o API). They initially started with waterflooding in 1980, however it produced poor results. Although after the chemical flooding was implemented, the oil production went from 375 BOPD to 1622 BOPD which was considered an all-time high enhancement in the oil production. The Byron Field was discovered in 1929, with a crude oil of 23o API. With this case they varied the concentration of the chemical they were injecting into the reservoir. They used 1000 ppm, 600

SPE 165909 3

ppm, and 330 ppm which showed a major increase in the oil production and water/oil ratio. However in this case, the polymer was retained by the reservoir which helped displace the oil out of the reservoir. Therefore, the reservoir must be flooded with water before the chemical flooding to reduce the amount of chemicals that is adsorbed by the reservoir. In a small-scale field pilot in Kuwait, the surfactant flooding economics was studied and surfactant flooding majorly consists of surfactant slug cost which is composed of the cost of crude, alcohol and sulfonates. Moreover, a typical project life for surfactant injection is 7 years with incremental recovery appearing in the 3rd year (Alkafeef et al., 2007). The optimum design was also calculated at a higher oil price of $25/rbbl and a higher operating cost of $0.40/bbl fluid (Wu et al., 1996). When surfactant flooding is implemented on these sandstone reservoirs, they found that it generated the highest recovery rate when compared to CO2 and Polymer flooding. Surfactant flooding can produce an extra 20-22% of the OOIP. It was also found that surfactant flooding would give the largest effect if it is implemented in the early life of the well after the waterflooding stage has been completed. These results are similar to those found in carbonate reservoirs; therefore, we can potentially implement this technology in any reservoir with similar results. In addition, many surfactants have shown adsorption properties in the field. Experiments conducted at the China University of Petroleum showed that the adsorption of surfactants increased as their concentration increased, making them directly proportional. However, these experiments also showed that in the case of oil sands, certain organic and polar substances could lead to the decrease in adsorption of the surfactant. As such, the conclusion was made that if surfactants were to be used in the field, sacrificial agents needed to be applied first so as to decrease the rate of adsorption. These same experiments also showed that similarly, as salinity increased, the rate of adsorption also increased; again making them appear directly proportional. The addition of the surfactants on washed sands created an electric double layer, which created repulsion between both, hence increasing adsorption. As such, it is vital that salinity is monitored and that a low salinity environment is achieved if possible so as to ensure maximum efficiency of the surfactants. (Haiyang et al., 2011) Tests have shown that as temperature increases to about 500oF, there is a decrease in concentration as well as pH levels, which is uneconomic and inefficient. These experiments demonstrate the need for thermal stability of the surfactants, which is observed in certain synthetic surfactants such as Chevron’s synthetic AAS, which exhibited no thermal decomposition. Therefore by modifying the surfactants, thermal stability can be achieved (Ziegler, 1988). Surfactant EOR Surfactants are surface active chemicals used to reduce interface tension and are amphiphilic compounds (containing hydrophilic and hydrophobic parts) that decrease the free energy through replacing the bulk molecules of higher energy at an interface. Cationic, anionic and nonionic surfactants can be used to enhance oil recovery (Mulligan et al., 2001). Surfactant flooding is based on the injection of chemicals into the reservoir and can enhance oil recovery by reducing the oil trapping in the pore throats and improving sweep efficiency (Hammond et al., 2010, Shupe et al., 1978). Chemical flooding is the process with the best potential for significantly reducing residual oil saturation. A typical chemical flood contains surfactant, co-surfactant and alkali (Taber et al., 1969, Jamaloei., 2009). A surfactant flood primarily creates a mixing zone between the aqueous and oleic phase known as the microemulsion. This is the zone of low IFT, which is responsible for reduced capillary pressure and increased capillary number. This is because the primary requirement for mobilizing the residual oil was a sufficiently low interfacial tension (IFT), which makes the capillary number large enough to overcome the capillary forces and make the oil flow. Therefore, enlarging displacement efficiency and enhancing oil recovery.

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In addition, given that the oil production from fractured reservoirs can occur by spontaneous water imbibitions, the use of surfactants can be attractive to improve oil recovery in oil-wet carbonate reservoirs by changing rock wettability to mixed / water wet also promoting the imbibition process (Xie et al., 2005, Seethipalli et al., 2004). The main objectives of surfactant flooding in carbonates are wettability alteration and reduction of the interfacial tension (IFT) along with reduced adsorption and concentration of surfactant. In order to achieve these goals, several studies have considered the use of different types of surfactants (anionic, cationic and non-ionic) (Manrique et al., 2004). Anionic surfactants such as alkyl aryl sulfonates and alkyl propoxylated sulfates have been identified as adequate surfactants to change the wettability of carbonate minerals and reduce IFT to very low values (<10-2 m N/m) with a West Texas crude oil. However, the adsorption was reduced significantly in the presence of an alkali (Seethipalli et al., 2004). Cationic surfactants that have been evaluated to modify the wettability of carbonate rocks by different research groups include Dodecyl Trimethyl Ammonium Bromide (DTAB), cocoalkyltrimethyl ammonium chloride (CAC) and anionic ethoxy sulfate (Seethipalli et al., 2004). Because of formation with negative electricity, the cationic surfactants can’t be used for flooding but can be used for sacrificial agents. However, Ethoxylated alcohols, poly-oxyethylene alcohol (POA) and Alkyl polyglycoside (APG) are three of the non-ionic surfactants that have been evaluated for the same purpose (Xie et al., 2005, Seethipalli et al., 2004) Smart EK- Surfactant Hypothesis

1. Conventional surfactant flooding

Fig 1 - Schematic view of conventional surfactant flooding

2. Sequential Surfactant and EK

Fig 2 - Schematic view of sequential surfactant flooding

∆1

0 X

Adsorption

∆1 = Penetration depth 0X = Core length/ flow direction

∆2

0 X

∆2 = Penetration depth 0X = Core length/ flow direction

SPE 165909 5

3. Simultaneous Surfactant and EK

Fig 3 - Schematic view of simultaneous surfactant flooding

Table 1 - Comparison of conventional versus EK-assisted Surfactant flooding

Conventional surfactant Flooding

Sequential surfactant flooding

Simultaneous surfactant flooding

Surfactant consumption

Very High High Low

Absorption capacity High Moderate Negligible

Penetration depth Low Medium High

Penetration depth trend

∆1 < ∆2 < ∆3

Materials and Methods The experiments were carried out at ambient conditions (room temperature and atmospheric pressure). The Abu Dhabi carbonate core plugs of 3” in length and 1.5'' in diameter were initially saturated with brine and brought to the oil saturation stage at irreducible water saturation using Abu Dhabi medium crude oil (29o API). There are four fundamental stages in the oil recovery experiments which are mentioned as follows:

Core Preparation: The cleaned carbonate cores were initially dried in an oven followed by the measurement of their rock properties such as porosity, pore volume and their saturation after placing them in a saturation cell for 24 hours (Byrne and Patey, 2004, Sharma, 2000). Brine and Oil Saturation: Initially the core plugs were brought to the initial reservoir conditions by flooding it with brine until the differential pressure was stabilized, followed by flooding it with medium crude (29o API) oil in order to produce the brine (4% NH4Cl) and thus determining the OOIP upon pressure stabilization (Sharma, 2000). Aging of core-plugs: A set of experiments were conducted on oil-wet core-plugs. These core-plugs were aged by placing them in an aging cell for about 2-3 weeks. Subsequently, the core-plugs were then flooded with oil in a series of experiments until the initial irreducible water saturation was obtained and verified to be significantly lower compared to that in water-wet core-plugs. Finally, EK-assisted surfactant flooding is conducted on the core-plugs as mentioned below.

∆3

0 X

∆3 = Penetration depth 0X = Core length/ flow direction

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• Waterflooding (Robertson et al., 2003): The core plugs were placed inside the rubber sleeve with the application of clamps in order to apply the confinement pressure. Brine solution was injected at a rate of 0.25ml/min which corresponds to an average reservoir flow rate of 1ft/D along with the collection of recovered oil in a burette separating oil and liquid. Moreover, the oil recovery and differential pressure across the cores were continuously monitored throughout the experiment until the pressure stabilized, indicating no further recovery of oil.

• Surfactant flooding: Non-ionic surfactant was injected at a concentration of 1% both in sequential and simultaneous stage. The concentration was selected because in the field, the adsorption of a surfactant increases with increasing concentration, therefore this low concentration in the field will be able to meet the objective of reducing strong rock adsorption and reducing HSE concerns of handling/transporting the surfactant if present in high concentration. The non-ionic surfactant was preferred over the cationic and anionic surfactants. The cationic surfactants will have a reduced residence time in the porous media in the presence of an electrical field, therefore, contacting less oil and reducing efficiency in low IFT. This will leave behind significant amounts of by-passed oil in the reservoir as the cationic surfactant will rapidly travel from the anode to the cathode because the surface charge of the core is positive. However, anionic surfactant would have the drawback of high adsorption capacity towards the core and will have an increased residence time enormously changing the wettability of the core. In addition, the APG (non-ionic surfactant) was found to exhibit thermal stability at high temperatures even in high salinity reservoirs (Obasi, 2012), making this as a model surfactant for this work.

• Application of DC (Electrokinetics): After the ultimate recovery from the waterflooding stage was achieved, a constant potential gradient of 2V/cm was applied with the injector as anode and producer as cathode until the pressure stabilization stage and the ultimate recovery was achieved. A summary of the experimental setup used in our study is illustrated in Fig.4

Smart EK-assisted surfactant flooding were done in different stages with different approaches both sequentially and simultaneously

• Sequential approach: In sequential EK-assisted surfactant flooding, the following stages were carried out in order to reach the ultimate recovery in both surfactant flooding:

o Waterflooding - Brine was injected through the core at a constant rate of 0.25 ml/min, which corresponds to an average reservoir flow rate of 1 ft/D, until ultimate waterflood recovery was reached, which was observed by achieving 100% water cut and stabilized differential pressure.

o Surfactant flooding - Then, sequential smart surfactant-EOR was applied using conventional surfactant flooding at (0.25 ml/min), by injecting 1% APG solution through the core to identify the enhancement in oil recovery up until ultimate conventional surfactant flooding oil recovery was reached.

o Application of DC (Electrokinetics) - The final stage of the sequential smart surfactant EOR was performed along with electrokinetics (DC voltage of about 2V/cm) on these oil saturated core plugs onto the existing hydrodynamic flow to identify the increase in oil recovery due to the application of EK assisted surfactant flooding.

• Simultaneous approach: In sequential EK-assisted Surfactant flooding, the following stages were carried out in order to reach the ultimate recovery in both Surfactant flooding:

o EK-assisted Waterflooding - Brine was injected through the core at a constant rate of 0.25 ml/min along with EK (DC voltage of about 2V/cm), until ultimate waterflood recovery was reached, which was observed by achieving 100% water cut and stabilized differential pressure.

SPE 165909 7

o EK-assisted Surfactant flooding - Then, EK was applied along with surfactant flooding to achieve the simultaneous surfactant-EOR by injecting APG at a 1% concentration through the core to identify the enhancement in oil recovery up until ultimate EK assisted surfactant stage.

Results There is a vast variation of the initial petrophysical properties of Abu Dhabi carbonate core plugs and the crude oil flown as summarized in Table 2. This is because the core plugs were taken from different depths having different lithologies. All cores were 3” in length and 1.5” in diameter. In addition, the porosity also varies from 3-27%. However, all the cores were tight in range of permeabilities which was extremely small within a range of 0.1-0.8 mD indicating that they are mostly carbonate mudstones and wackestones with a number of fractures. The voltage applied in the EK stage was calculated using the length by keeping a constant voltage gradient of 2V/cm. Moreover, oil recovery results of the 12 experiments are also summarized in Table 3 and 4. The number of injected pore volumes is within a range of 3 to 6 pore volumes in water-wet rocks and 7 to 11 pore volumes in oil-wet rocks depending upon the characteristics of the core and the type of experimental approach used. The small amount of injected pore volume in both water-wet and oil-wet rocks indicates that the project is economically and environmentally feasible. In water-wet cores, the maximum recovery factor achieved was 86% with simultaneous surfactant flooding which was already waterflooded to recover 63% of OOIP. However, while conducting the sequential surfactant flooding, the maximum recovery factor was about 82% in 50% sequential flooding and 79% in 100% sequential flooding, out of which 63% was recovered by waterflooding followed by 72% with surfactant flooding. Therefore, the maximum percentage increase in recovery factor achieved by surfactant is 15% along with a recovery of 12% due to EK. In oil-wet cores, the maximum recovery factor achieved was 18% with simultaneous surfactant flooding. However, while conducting the sequential surfactant flooding, the maximum recovery factor was about 12% in 50% sequential flooding and 16% in 100% sequential flooding. Therefore, the maximum percentage increase in recovery factor achieved by EK is 45%. Moreover, the maximum current density amongst all experiments is about 1.3 mA/cm2 in water-wet rocks and about 1.6 mA/cm2 which indicates that the power consumption from the application of EK would considerably be less. Finally, all our observations were compared with the obtained results graphically presented in Figs. 5 through 21, showing the comparison between the different rock types and different methods of surfactant flooding used. Moreover, the difference in oil recovery percentage between ordinary waterflooding, surfactant flooding and EK assisted surfactant flooding is also indicated. In addition, increase in oil recovery versus increase in irreducible water saturation is also demonstrated along with the variation in current density and power consumption.

Discussion Increase in Recovery factor due to Surfactant There is a significant increase in recovery after the waterflooding stage with conventional surfactant flooding and EK assisted surfactant flooding by about 15-36% depending upon the experimental approach used as seen in Table – 3. It was also observed from Fig. 5 that the higher recovery factors and significant increase in recovery with EK assisted surfactant were demonstrated with highly porous cores. This is because the increased recovery could be attributed to the increased pore volume present in the cores that might have some additional residual oil blobs which were moved by the surfactant particles causing wettability alteration and reduction in interfacial tension (IFT) with reduced surfactant adsorption.

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Decrease in Residual Oil saturation It was also observed from Fig. 6 that significant increase in Swirr (irreducible water saturation) and decrease in Sor (residual oil saturation) is observed after the application of EK by about 8-20% as compared to the decrease in Sor during surfactant flooding by about 3-10%. Therefore, the primary objective of the use of surfactant is achieved as the residual oil is mobilized with a sufficiently low interfacial tension (IFT) of the core that makes the capillary number large enough to overcome the capillary forces and makes the oil flow (Fig.– 7). Sequential application of EK-assisted Surfactant flooding It was seen in Fig. 10 that experiment No. 4 was carried out in four different stages in order to compare the effect of EK during waterflooding and surfactant flooding stages. The results indicate that a 7% enhancement in recovery was achieved with the EK application during waterflooding as compared to 10% during surfactant flooding. In addition, surfactant flooding resulted in an increase of 15% in the ultimate recovery. This indicates that the EK has better impact on the oil recovery during surfactant flooding because the injected surfactant resulted in a reduction of the IFT between crude oil and formation water which leads to a wettability alteration changing the core to mixed wet from an oil wet core. In addition, the application of EK during the surfactant flooding also causes an enhancement in displacement efficiency due to the reduction in capillary forces. However, during conventional waterflooding, the wettability of the core is unaltered so the recovery factor is enhanced exclusively by the application of EK. In addition, the recovery is also enhanced due to the production of micro-emulsions (Figs. 8-9) that causes decreased adsorption at the rock surface leading to an increased sweep of residual oil towards the cathode (Ansari et al., 2012). The number of injected pore volumes of about 4-6 pore volumes as in Table – 3 were significantly high for the sequential process as it is divided into several stages with continuous flooding of brine or surfactant. Therefore, this process will not be economically and environmentally feasible due to the high capital expenditures (CAPEX) and operational costs (OPEX). Moreover, it was also seen that for sequential flooding, applying EK at 50% water-cut increases the recovery factor by 5% while reducing the water consumption by 36%. This is due to the fact that EK acts simultaneously after applying 50% sequential flooding leading to all the drive mechanisms working in conjunction simultaneously in an integrated manner reducing water consumption and increasing the recovery factor. Simultaneous application of EK-assisted Surfactant flooding However, during simultaneous surfactant flooding, there was an additional 6-22% increase in oil recovery due to the application of EK-assisted surfactant flooding applied after the waterflooding ultimate recovery of 53-65% was reached (Table– 3). It was also demonstrated that a maximum recovery factor of 86% was achieved in experiment – 5. The waterflooding oil recovery recorded was 63% followed by an additional 24% recovery due to the application of EK-assisted surfactant flooding (Fig. 11). The simultaneous surfactant flooding results in reduced amount of surfactant injection comparatively of about 3-4 pore volumes (Fig. 12) because the EK is applied as soon as the surfactant flooding starts. Moreover, the higher recovery factor was achieved during simultaneous flooding which is due to the fact that surfactant and EK affect simultaneously on the carbonate core to enhance the oil recovery. Therefore, the EK assisted surfactant flooding uses different drive mechanisms in an organized way to significantly enhance the recovery as the flow takes place across small conduits especially in oil-wet reservoirs where most of the oil is by-passed. So this by-passed oil is recovered by surfactant as it alters the rock wettability. The electroosmotic flow is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane, micro channel, or any other fluid conduit.

SPE 165909 9

Oil wet EK-assisted surfactant EOR Simultaneous surfactant flooding produced 2.7% higher recovery than sequential surfactant flooding, while reducing the surfactant/water consumption by 55% (Fig. 13-14). However, sequential surfactant flooding produces almost the same RF with 25% reduced water consumption when EK is applied at 50% water cut rather than 100%. Moreover, sequential surfactant flooding produces a lower current density and power consumption when compared to simultaneous surfactant flooding (Figs. 15-18). For surfactant flooding, it can be seen in Figure 14 that the incremental recovery factor due to EK reaches a maximum of about 45% of the original RF, in 50% sequential oil-wet core-plugs followed by 35% of the original RF in 100% sequential oil-wet core-plugs. However, it was the least amongst water-wet core-plugs experiments of about 12% (Fig 13). This indicates the economic and environmental potential of EK assisted surfactant flooding in oil-wet cores. Comparison between sequential and simultaneous surfactant flooding It can be seen from Fig. 15 that comparatively simultaneous surfactant flooding has a higher recovery of 4-10% as compared to sequential surfactant flooding. This is because there is a precise targeted transport of surfactant through the micro pores towards the cathode in the presence of EK leading to increased oil sweep efficiency. In addition, the application of EK in simultaneous surfactant flooding has consistently resulted in increasing the net recovery factor by taking the advantage of all the drive mechanisms (Electrosomostic force, hydrodynamic force, microemulsions force) working in conjunction simultaneously in an integrated manner on one big volume of by-passed oil to produce one cumulative net driving force. Moreover, application of EK at 50% water-cut instead of 100% water-cut results in providing a higher recovery by 5% due to an increased residence time between the rock and surfactant leading to a decrease in adsorption which also causes a reduction in interfacial tension. This also reduces the micro-emulsions leading to a lower sweep efficiency of by-passed oil in the rock (Figs. 8-9). Therefore, simultaneous surfactant flooding results in targeting more of the present by-passed oil as it has a precise targeted transport of surfactant and micro-emulsions through the core. Moreover, it can also be seen in Table – 3 and Fig. – 15 that simultaneous surfactant flooding has a lower number of injected pore volumes (3-4) as compared to the sequential surfactant flooding (5-7) by about 200%. Therefore, it reaches the plateau faster leading to 50% lower surfactant and water consumption and production indicating lower costs spent on CAPEX and OPEX. In terms of reservoir scale this difference could lead to saving in the range of millions of barrels of water or surfactant savings and significant reduction of operating costs due to the corrosion and many other flow assurance problems caused in long terms. However, an increased amount of power consumption will be required which can be reduced by optimizing certain parameters during our up-scaling future experiments currently being conducted at the PI-EKRC. Power consumption and Current density It was observed from Table – 3 and Fig. – 16 and 17 that the current density was almost constant and higher for sequential surfactant flooding as compared to simultaneous surfactant flooding. This indicates that there are reduced micro-emulsions produced in simultaneous flooding according to Ohm’s law which states that the higher the resistance, the lower the current density. Therefore, there is a reduced amount of resistance in the movement of ions resulting in huge transport of ions across the fluid indicating a higher current density in simultaneous flooding. Therefore, as the recovery increases, the current density decreases both in oil and water-wet cores which is majorly due to the increased resistance created by the production of micro-emulsions that helps in increased movement of residual by-passed oil towards the cathode. Power consumption is higher for simultaneous flooding by about 12% as compared to sequential which

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is due to the continuous use of EK in simultaneous flooding from the beginning (Fig. 18-19). Oil wet cores have lower current density and power consumption as compared to water-wet cores which is mainly due to large resistance due to the presence of large amount of oil in oil-wet cores. However, in water-wet cores, the flow of brine leads to easy flow of current and a large amount of power consumption is also obtained which can be environmentally feasible due to a large recovery factor in water-wet cores. Conclusion Based on the lab results and taking all the experimental conditions and limitations into considerations, the following conclusions can be drawn:

1. Simultaneous surfactant flooding results in increase in oil recovery by about 15% as compared to sequential surfactant flooding which is because of flooding mechanisms. Simultaneous flooding works in an integrated way on a single larger unit of oil as opposed to sequential flooding which works on an unstructured manner on scattered volumes of by-passed oil.

2. Simultaneous surfactant flooding generates 2.7% (20% of original RF) higher recovery than sequential surfactant flooding, while reducing the surfactant/water consumption by 55%.

3. Simultaneous surfactant flooding results in lower costs because of reduced water, surfactant consumption and this, in turn, reduces adverse environmental impact.

4. Similar recovery factors are achieved with 25% reduced water consumption when EK is applied at 50% water cut rather than 100% in oil-wet core-plugs.

5. Oil-wet experiments have approximately 10 times the water consumption when compared to that of water-wet core-plugs.

6. Higher EK yield potential observed in oil-wet reservoirs as EK-assisted sequential surfactant EOR produced 45% of the original recovery factor in oil-wet, while producing 14% of original recovery factor in water-wet core-plugs. (Fig.13).

7. Current density generated by sequential surfactant flooding is higher than that of simultaneous surfactant flooding due to reduced amount of micro-emulsions formation.

8. The power consumption in simultaneous surfactant flooding is higher than that in sequential surfactant flooding because of continuous use of electricity from the beginning.

9. The effectiveness of this proposed smart surfactant process is as follows: RFWF < RF SF < RF EKSFSQ < RF EKSFSM

10. Sequential surfactant flooding reduced the power consumption by 12%. However, the simultaneous surfactant flooding was more beneficial as the recovery factor was enhanced by 4% and the water and surfactant consumption was reduced by 50%.

11. The following sequential trend as observed for the recovery factor under the four EOR strategies (WF, SF, EKSQ and EKSM) we studied. We infer the recovery factors were affected by the depth penetration capacity that was predicted in our hypothesis. (Fig. 21) RFWF < RF SF < RF EKSQ < RF EKSM

12. EK-assisted simultaneous flooding enhances recovery factor by 6%, with an increased power consumption of 18%, and reduced water/surfactant consumption by 76%.

Current research phase undergoing at the PI- EKRC is targeted towards using cationic surfactant. We will also be able to take into account the above factors and subsequently adjust each parameter; such as surfactant concentration, type of surfactant and injection mechanism and rate. This strategy will be used to further improve the surfactant penetration depth as evident in our smart EK-surfactant method. Acknowledgement The authors are thankful to the Petroleum Engineering Department, The Petroleum Institute, Abu Dhabi and ADNOC, for providing the Electrokinetic research center (PI-EKRC) and support needed to conduct this research.

SPE 165909 11

Nomenclature ADNOC Abu Dhabi National Oil Company APG Alkyl polyglycoside API American Petroleum Institute BOPD Barrels of Oil per day DC Direct Current EOR Enhanced Oil Recovery EEOR Electrically Enhanced Oil Recovery EK Electrokinetics EKSFSM EK assisted Simultaneous Surfactant flooding EKSFSQ EK assisted Sequential Surfactant flooding IFT Interfacial Tension OOIP Original Oil in Place PI-EKRC Petroleum Institute Electro-kinetic Research Center R&D Research and Development Rbbl Reservoir Barrel

References

Alkafeef, S.F. and Alforgi, M.Z. Review of and Outlook for Enhanced Oil Recovery Techniques in Kuwait Oil Reservoirs, IPTC 11234, December 2007. Al Shalabi, E., Ghosh, B. and Haroun, M. R. Application of Direct Current Potential to Enhancing Waterflood Recovery Efficiency, Journal of Petroleum Science and Technology, published by Taylor & Francis, DOI: 10.1080/10916466.2010.547902, Vol30, issue 20, pp. 2160-2168, 2012 Al Shalabi, E., Haroun, M. R., Ghosh, B., and Pamucku, S. Effect of DC Electrical Potential on Enhancing Sandstone Reservoir Permeability and Oil Recovery, Journal of Petroleum Science and Technology, published by Taylor & Francis, DOI: 10.1080/10916466.2010.551233 Vol30, issue 20, pp. 2148-2159, 2012 Al Shalabi, E., Haroun, M. R., Ghosh, B., and Pamucku, S. Stimulation of Sandstone Reservoirs using DC Potential, Journal of Petroleum Science and Technology, published by Taylor & Francis, DOI:10.1080/10916466.2010.551811, Vol30, issue 20, pp. 2137-2147, 2012 Amba S.A., Chilingar G.V., and Beeson C.M., Use of Direct Electrical Current for Increasing the Flow Rate of Reservoir Fluids During Petroleum Recovery: J.Canadian Petroleum Technology, vol. 3, No. 1., pp. 8 - 14, 1964. Amba, S.A., Chilingar, G.V. and Beeson, C.M. Use of Direct Electrical Current for Increasing the Flow Rate of Oil and Water in a Porous Medium: J.Canadian Petroleum Technology, vol. 4, No. 1. pp. 81 - 88, 1965. Amba, S.A. Use of Direct Electrical Current for Increasing the Flow Rate of Reservoir Fluids During Petroleum Recovery, PhD dissertation, U. of Southern California, Los Angeles, 255 pp, 1963. Dandona, A.K. and Morse, R.A. The Influence of Gas Saturation on Water Flood Performance –Variations Caused by Changes in Flooding Rate, Society of Petroleum Engineers, SPE 3881, 1972.

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Ansari, A., Haroun, M. R., Sayed, N. A.,Kindy, N., Ali, B., Shrestha, R. A., Sarma, H., 2012, A New Approach Optimizing Mature Waterfloods with Electrokinetics- Assisted Surfactant Flooding in Abu Dhabi Carbonate Reservoirs, SPE 163379.

Byrne, M. and Patey, I., Core Sample Preparation – An Insight in to New Procedures, SCA2004-50 Chilingar, G.V., El-Nassir, A. and Steven, R.G. Effect of Direct Electrical Current on Permeability of Sandstone Core, Journal of Petroleum Technology, 2332-PA, 1968.

Das, O.P., Aslam, M., Bahnuguna, R., Khalaf, A., Al Shatti, M., and Yousef, A.T. Water Injection Monitoring Techniques For Minagish Oolite Reservoir In West Kuwait, Society of Petroleum Engineers, IPTC 13361, December 2009.

Guerithault, R. and Ehlig-Economides, C.A. Single-Well Waterflood Strategy for Accelerating Oil Recovery, Society of Petroleum Engineers, SPE 71608, 30 September 2001. Haiyang, Y., Yefei, W., Yani, Z., Peng, Z., Wuhual, C. Effects of Displacement Efficiency of Surfactant Flooding in High Salinity Reservoir: Interfacial Tension, Emulsification, Adsorption. Advances in Petroleum Exploration and Development, vol. 1 no. 1, pp. 4-5, 2011. Hammond, P. & Pearson, J.. Pore-scale flow in surfactant flooding. Transport in Porous Media, 83(1): 127-149, 2010. Haroun, M., Wittle, J.K., Chilingar, G.V. Method for Enhanced Oil Recovery from Carbonate Reservoirs, Patent Publication No. WO/2012/074510, Geneva, June 2012

Haroun, M.R., Ansari, A., Al Kindy, N., Abou Sayed, N., Ali, B. and Sarma, H. Smart Nano-EOR Process for Abu Dhabi Carbonate Reservoirs, presented at ADIPEC, 2012.

Haroun, M., Chilingar, G.V., Pamukcu, S., Wittle, J.K., Belhaj, H., Al Bloushi, M.N. Optimizing Electroosmitic Flow Potential for Electrically Enhanced Oil Recovery (EEORTM) in Carbonate Rock Formations of Abu Dhabi Based on Rock Properties and Composition, Society of Petroleum Engineers, IPTC 13812, December 2009.

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Mulligan, C., Yong, R. & Gibbs, B. Surfactant-enhanced remediation of contaminated soil: a review. Engineering Geology, 60(1-4): 371-380, 2001 Obasi, D. C., Applicability of alkyl polyglucosides for surfactant flood in high temperature – high salinity carbonate reservoir through low tension displacement and wettability alteration, Thesis of Master Science in Petroleum Engineering, The Petroleum Institute, UAE, 2012.

Reed, R.L. and Healy, R.N. Some Physiochemical Aspects of Microemulsion Flooding: A Review, Academic Press, pp. 383-347, 1977

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Seethepalli, A., Adibhatla, B., and Mohanty, k.: Wettability Alteration during Surfactant Flood in Carbonate Reservoirs, Paper presented in SPE/DOE Symposium on Improved Oil Recovery (Apr 17 – 21, 2004) Tulsa USA

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Shupe, R. & Maddox J., Surfactant oil recovery process usable in high temperature, high salinity formations. US Patent 4077471, 1978

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Electrically Enhanced Oil Recovery- EEORSM is the Service Mark of Electro-Petroleum, Inc.,

996 Old Eagle School Rd., Wayne, PA 19087 USA

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Appendix

Table 1 – Initial Petrophysical properties of the water-wet and oil-wet 1.5-in core-plugs with 1%

Table 2 - Sequential and Simultaneous APG Surfactant flooding in Oil and Water-wet cores

Core no.

Length, cm

Diameter, cm

Porosity (%)

Pore volume (Vp) (cc)

Voltage (V)

Permeability (mD)

Medium Crude Oil 28.4 oAPI, Viscosity 47.9 cP at 20 oC, Flow rate = 0.25 ml/min 1 4.834 3.801 20.387 11.183 9.67 0.068 2 7.515 3.811 8.508 7.293 15.03 0.076 3 8.220 3.810 3.600 3.373 16.44 0.828 4 5.560 3.847 16.543 13.820 11.12 0.145 5 5.586 3.847 23.482 18.016 11.17 0.146 6 6.745 3.847 16.073 13.522 13.49 0.114

Exp. No Wettability

Pore volume injected (cc)

Number of injected pore volumes

Recovery with WF (%)

Recovery with WF + surfactant (%)

Recovery with WF + surfactant + EK (%)

% increasedue toSurfactant

% increase due to EK

Current density (mA/cm^2)

Sequential surfactant flooding, Medium Crude Oil 28.4 oAPI, Viscosity 47.9 cP at 20 oC, Flow rate = 0.25 ml/min 1 Oil-wet 87.13 7.79 - 12.32 16.54 - 34.20 2.64 E-04 4 Water-wet 13.82 6.30 62.79 72.09 79.54 14.82 11.85 1.29 E-03

Simultaneous surfactant flooding Medium Crude Oil 28.4 oAPI, Viscosity 47.9 cP at 20 oC, Flow rate = 0.25 ml/min 2 Oil-wet 77.324 10.602 - - 18.234 - - 5.26 E-045 Water-wet 18.02 2.90 62.60 - 86.54 9.063 - 0.224 E-03

50% Sequential surfactant flooding, Medium Crude Oil 28.4 oAPI, Viscosity 47.9 cP at 20 oC, Flow rate = 0.25 ml/min3 Oil-wet 37.250 11.044 - 8.557 12.435 - 45.318 1.59 E-03 6 Water-wet 13.52 4.60 60.74 - 82.96 36.59 - 0.172 E-03

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Fig 4 - EEOR Lab apparatus in PI-EKRC for core flooding at ambient conditions

Fig 5 - Recovery Factor against Porosity for WF and EK-assisted Surfactant flooding Stage

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Fig 6 - Increase in Recovery Factor against increase in Swirr for Surfactant, EK-assisted Waterflooding and EK-assisted Surfactant flooding Stages

Fig 7 - Approximate Configuration of Trapped oil (Ganglion), showing Exclusion of Water (left) and Electroscan Micrograph (right) (After Reed and Healy, 1972)

 

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Fig 8 - Micro Emulsions after Different Injected Pore Volumes (Hirasaki et al., 2011)

Fig 10 - Different Stages in Sequential Application of EK-assisted Surfactant Flooding

Fig 9 - Micro Emulsion for One Experiment (Hirasaki et al., 2011)

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Fig 11 - Different Stages in Simultaneous Application of EK-assisted Surfactant Flooding

Fig 12 - Recovery Factor comparison with EK assisted Surfactant flooding in Water-Wet Cores at Room Temperature

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Fig 13 - Recovery Factor comparison with EK assisted Surfactant flooding in Oil-Wet Core-plugs at Room Temperature 

Fig 14 - Recovery Factor in Oil and Water-Wet Core-plugs for surfactant flooding at Room Temperature as a function of injected pore volumes 

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Fig 15 – Comparison of Recovery Factors for Sequential and Simultaneous Application of EK-assisted Surfactant Flooding

Fig 16 – Recovery Factor for Oil-Wet Core-plugs for surfactant flooding at Room Temperature as a function of current density

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Fig 17 - Recovery Factor for Oil-Wet Core-plugs for surfactant flooding at Room Temperature as a function of

current density

Fig 18 - Recovery Factor for Oil-Wet Core-plugs for surfactant flooding at Room Temperature as a function of power consumption

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Fig 19 - Recovery Factor for oil-Wet Core-plugs for surfactant flooding at Room Temperature as a function of power consumption

Fig 20 - Comparison of feasibility of using Smart-surfactant EOR at room temperatures

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Fig 21 - Comparison of EK Simultaneous surfactant flooding versus EK Sequential surfactant flooding

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