An experimental investigation on enhancing water flooding performance using oil-in-water emulsions in an Iranian oil reservoir
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Emulsions are extensively prevalent in the oil industry in both advantageous and disadvantageous ways. In the literature, conventional water flooding in high permeability oil reservoirs has confronted with water channeling and poor sweep efficiency. In this paper, the remedial application of O/W emulsions as an EOR method in improving water performance is discussed. To this purpose, a series of flooding experiments were carried out in one of the Iranian oil reservoirs in reservoir condition of 75 C and 2000 psi. Then, visual stability measurements were conducted to inspect the stability characterization of the emulsion. Sodium dodecyl sulfate was applied helping simple dispersion of the gasoil into the water phase, and emulsions with water percentage of 90, 80, 70 and 60 were developed to introduce into the porous media. It was found out from flooding experiments that emulsion injection after conventional water flooding can lead to additional oil recovery (up to 20%). Besides, the emulsion with 80% water cut was determined as the optimum emulsion for injection in this reservoir considering financial aspects. Moreover, results of the stability test revealed that the aqueous phase with one wt% surfactant or higher had formed emulsions which have been stable during a long period of 6 months.
KeywordsEmulsion flooding Enhanced oil recovery Sweep efficiency O/W emulsion Sandpack
Initial oil in place
Sodium dodecyl sulfate
American Petroleum Institute
Critical micelle concentration
High pressure–high temperature
High-performance liquid chromatography
Technically speaking, primary production from oil reservoirs cannot recover more than 30% of IOIP. Moreover, with recent growing demand for more energy resources, the role of implementation of secondary and tertiary oil recovery methods has been highlighted. To fulfill this, many researches have been conducted to propose sufficient ways to extract more crude oil from the underground (Policy 2012). In the secondary oil production, water flooding is considered as the primary method, bringing in several advantages including lower operation cost which was performed for the first time in an oilfield of northeast America in the late eighteenth century (Craig 1993; Sheng 2014).
In the last decades, injection of water with varieties of dissolved compositions into the oil reservoirs by the mean of improving oil recovery has been the subject matter of many scientific works (Craig 1993; Willhite 1986). To be more precise, low-salinity water flooding is one of the most promising methods of oil recovery improvement that has gotten several attentions lately (Sheng 2014). Although this method has led to few increases in oil recovery by raising capillary number subsequently after reduction in oil–water interfacial, its poor sweep efficiency and unfavorable mobility ratio as a result of early breakthrough and water channeling still are regarded as some of its principal drawbacks which may get severe in reservoirs with vertical heterogeneity (Liu et al. 2006, 2010; Sheng 2014; Sydansk and Romero-Zeron 2011). On the other hand, from a financial standpoint, water treatment procedures possess cost in the range from 5 to more than 50 cents per water barrel to oil companies which turn out to be $40 billion to deal with unwanted water in aggregate (Crabtree and Romano 2000). Unfortunately, some portions of this produced water are related to the inefficiency of water flooding which bypasses from injection to production well leaving a massive amount of reservoir oil intact (Dong et al. 2007; Liu et al. 2010). Therefore, the utilization of useful water control technology can bring out a significant reduction in expenditures and improve oil recovery (Crabtree and Romano 2000). One of these water control technologies is the application of emulsions for the injection in the reservoirs (Bai et al. 2000; Taylor et al. 2015). Emulsions are usually defined as a combination of two different immiscible liquids that are dispersed in each other consisting of two distinct phases, the dispersed or internal phase, and the continuous or external phase (Bande et al. 2008; Gewers 1968; Maaref et al. 2017; Pietrangeli et al. 2014). Generally, two types of emulsions are used in this technique, which are O/W and W/O emulsions (Winsor 1948). Between these two, O/W emulsions have shown a better performance and higher oil recovery in the literature (Gogarty 1967). These emulsions can improve water injection profile through the selective plugging process. This means that they can prevent water from passing through areas with lower moveable oil saturation and reduce water cut, while the oil recovery factor is increasing (Arastoo and Zohoorparvaz 2015; Bai et al. 2000; Breston 1957; Moradi et al. 2014; Yu et al. 2018). In the 1970s, McAuliffe was the first who investigated in O/W emulsions flooding as an EOR method. He introduced emulsion into two parallel cores and stated that emulsions drops have been trapped in high-perm layers and formed a barrier against water flow. He attributed this fact to the larger diameter of emulsion oil drops compared to the pore throat diameter.
Emulsions aside, there are a plethora of studies worked on various selective plugging agents such as gels, cement and polymers to control water cut in production wells (Bai and Zhang 2011; Breston 1957; Liu et al. 2017; Stavland et al. 2006; Wang et al. 2003). Among these, although emulsion is not capable as much as the others in permeability reduction of formations, it has its unique distinctions (Seright and Liang 1995). In Bai et al. investigation, it is shown that more recovery factor has been obtained from emulsion injection over gel injection due to the formation damage it induced on target areas and lack of the incident of selective plugging process during the gel injection. They created an emulsion with a high percentage of water content and introduced it in one of the oil reservoirs in the North Sea to diminish water cut up to 30% in their oilfield study (Bai et al. 2000). Furthermore, the other advantages of O/W of emulsion flooding are its accessibility and lower cost of transportation as well as its more in-depth coverage into the formation and so its undemanding injectivity (Hasan et al. 2010; Kumar and Mahto 2016; Mcauliffe 1973a, b; Romero et al. 1996; Yu et al. 2018). Romero et al. studied on the effect of fracture plugging of in situ O/W emulsions by injection of an optimum amount of water/oil ratio in sandpacks and observed a massive reduction of 90% in water relative permeability as well as injectivity. This matter even was more evident in the initial part of their model (Romero et al. 1996). According to Starvland et al. (2006), the amount of this permeability reduction varies from zone to zones, with regard to the fluids saturations. Demikhova et al. (2018) attributed this matter to retention of dispersed oleic droplets of O/W emulsions in the pore throat as a consequence of two mechanisms: (1) size exclusion and (2) droplets/pore walls interactions in porous media. Yu et al. (2018) declared that permeability reduction of their sandpack models was a function of the volume of emulsion slug, oil and water fraction in emulsions, injection flow rate and the absolute permeability of the models. Zohoorparvaz and Arastoo in their experimental work evaluated the ability of inverse water in oil emulsions in water cut control after water flooding in both homogeneous and heterogonous reservoirs and concluded that the reductions of effective permeability of water in high-perm layers have led to almost 30% improvement in oil recovery (Arastoo and Zohoorparvaz 2015; Taylor et al. 2015). Mandal et al. used O/W emulsions with different oil contents of 5, 10, 20 and 30%, made by gear oil and injected them into sandpack models. The result of their flooding experiments illustrated that in the emulsion with the oil content of 10 percent, a significant amount of oil recovery has been obtained and after that with the increase in oil percentage, only slight growth in oil production is observed (Mandal et al. 2010). Later on, Pei et al. enforced O/W emulsions by using few quantities of HPAM and noticed more stable emulsions with higher shear viscosity. They experienced improved sweep efficiencies and more than 30% enhancement in oil recovery when they injected them in sandpack models (Pei et al. 2017).
Typically, using one or several surface active agents play a significant role in the formation of stable emulsions. In Romero et al. (1996), experiments emulsions had been formed as a result of alkaline injection. Torrealba and Hoteit observed the in situ generation of thermodynamically stable microemulsions in their reservoir model based on the injection of cyclical surfactant slugs after mixing with existed oil in the reservoir using a chemical flooding simulator (UTCHEM 2000). They found the successful treatment of conformance problems as a result of the formation of the high viscosity microemulsions in the high-perm zones inducing a crossflow into the low permeability zones. In their research, the viscosity of the injected fluids was typically low which preserved injectivity and ensured the invasion of the conformance agent toward the thief zones leading to plugging of thief layers (Torrealba et al. 2018). Bai et al. (2000) synthesized a new emulsifier and created stable emulsions even with 80% of water content. Long Yu et al. characterized the properties of the O/W emulsions which have been formed from heavy crude oil information brine. According to their observations, heavy crude oil could be emulsified in formation brine using surfactants (Span 60 and Tween 80) and NaOH. In their work emulsions with oil/water IFTs, less than 1 mN/m exhibited high stability and a highly effective plugging performance in sandpack (Yu et al. 2018).
In this study, we attempt to evaluate the efficiency of O/W emulsion in an Iranian onshore oil reservoir conditions that suffer from high produced water cut after water flooding. To cut down the operation costs, the emulsions were formed from gasoil and SDS as an emulsifier in the distilled water. Through this study, the optimum amount of the surfactant is gained, and the best water/oil ratio is nominated to perform in the oilfield aiming to reduce water cut production in the future.
The composition of formation brine and synthesized sea water (ppm)
Synthesized sea water
Sandpack flooding experiments
Summary of sandpack flooding experiments and their properties
Pore volume (cc)
Absolute permeability (mD)
SW 0.5 PV 90/10 emulsion SW
SW 0.5 PV 80/20 emulsion SW
SW 0.5 PV 70/30 emulsion SW
SW 0.5 PV 60/40 emulsion SW
Results and discussions
Sandpack flooding experiments
Determination of emulsion stability in surfactant concentrations
It was determined by electrical conductivity measurement that critical micelle concentration of sodium dodecyl sulfate occurs in 2510 ppm or 8.7 × 10−3 mol/L in double-distilled water at room temperature.
It was inferred from the flooding tests that utilization of O/W could significantly enhance the water flooding performance by improving sweep efficiency, recovery enhancement (up to 22%) and water cut reduction. Besides, the water/oil ratio of 80/20 was determined as the sufficient emulsion to inject into the studied reservoir.
Visual characterization of the emulsion stability showed that having a surfactant concentration beyond the CMC improves the stability of the emulsion significantly.
It was also obtained that for a long period (over 6 months) 1 wt% was regarded as an optimum concentration of SDS when the ultrasonic homogenizer along with the magnetic stirrer was used for making emulsions.
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