Oil displacement process

Miscible fluid displacement (miscible displacement) is an oil displacement process in which an alcohol, a refined hydrocarbon, a condensed petroleum gas, carbon dioxide, liquefied natural gas, or even exhaust gas is injected into an oil reservoir, at pressure levels such that the injected gas or fluid and reservoir oil are miscible the process may include the concurrent, alternating, or subsequent injection of water. 

In these displacement studies it was necessary to limit the presssure drop in the test core to a value comparable to that encountered in reservoir, about 1 psi/ft. Excessive pressure gradients can artiflcially cause oil to flow as a consequence of providing sufficient force to overcome the lowered interfacial tension produced by the surfactants. The swelling of the oil accompanied by a significant decrease in viscosity makes it possible to follow carbon dioxide with water injection to effectively recover additional oil in the immiscible oil displacement process. Tests were performed in this manner to evaluate the effect of mobility control agents on this process. 

Figure 3. Schematic illustration of the role of surface charge in the oil displacement process.

In oil recovery processes, the formation of an oil bank is very important for an efficient oil displacement process in porous media. This was established from studies on the injection of an artificial oil bank followed by the surfactant formulation which can produce ultralow interfacial tension with the injected oil. We observed that the oil recovery increased considerably and the residual oil saturation decreased with the injection of an oil bank as compared to the same studies carried out in the absence of an injected oil bank (54). Figure 17 schematically represents the oil bank formation and its propagation in porous media, which is analogous to the snowball effect. If an early oil bank is formed then it moves through the porous medium accumulating additional oil ganglia resulting in an excellent oil recovery, whereas a late oil bank formation will result in a poor oil recovery. 

The flow velocity is in the order of 10 m/s. The radius of an oil thread is about 10 m. The relaxation time of polymer solution used in the oil displacement process is about 10 to 10 s. Under these conditions, the range of Deborah number, Noe, is between 0.1 and 10. Figure 6.26 shows the normal stress of the viscoelastic fluid with different Deborah numbers. The stress acts on the undulated oil/water interface. When the representation in Figure 6.26 was constructed, the fluid velocity of 3.47 x 10 m/s and the relaxation time of 0.247 s were used. In the figure, negative stress represents that the stress direction is opposite to the external normal line of the acting surface. We can... 

Figure 4 Schematic diagram of the role of surface charge in the oil displacement process. High surface charge density results in high oil recovery, while low surface charge density results in low oil yields.

It is well established that ultralow interfacial tension plays an important role in oil displacement processes [16,18]. The magnitude of interfacial tension can be affected by the surface concentration of surfactant, surface charge density, and solubilization of oil or brine. Experimentally, Shah et al. [23] demonstrated a direct correlation between interfacial tension and interfacial charge in various oil-water systems. Interfacial charge density is an important factor in lowering the interfacial tension. Figure 6 shows the interfacial tension and partition coefficient of surfactant as functions of salinity. The minimum interfacial tension occurs at the same salinity where the partition coefficient is near unity. The same correlation between interfacial tension and partition coefficient was observed by Baviere [24] for the paraffin oil-sodium alkylbenzene sulfonate-isopropyl alcohol-brine system. 

Fig. 10. The effect of surface charge density of oil/brine interface on the oil displacement process (Ref. 8).

Both sandpacks and Berea cores gave similar results. The results of this study demonstrate the importance of transient phenomena at oil/dilute micellar solution interface for oil displacement process with emphasis on the effect of alcohol and salinity. 

A comparison of Cases B and D in Table 2 suggests that predominantly water-soluble species of the equilibrated aqueous phase of the surfactant solution worsen the oil displacement process as compared to brine flooding presumably due to the formation of stable emulsions or a decrease in coalescence rate in porous media. It is hypothesized that a rigid surfactant film... 

It should be emphasized that the entire study reported in this paper relates to the low surfactant concentration (< 0.5%) and does not involve the formation of middle phase microemulsions (23), etc. in this oil displacement process. At all times, the oil/brine/surfactant systems were composed of only two phases, oil and brine, with surfactant distributed in both phases. Also, this study is carried out at low salinity (< 2% NaCl) although we have reported elsewhere on high salinity formulations (24-26) which can produce ultralow IFT in millidynes/cm range at salt concentrations as high as 32%. 

The Importance of the Salinity of Polymer Solution in Oil Displacement Process... 

The proceedings cover six major areas of research related to chemical flooding processes for enhanced oil recovery, namely, 1) Fundamental aspects of the oil displacement process, 2) Microstructure of surfactant systems, 3) Emulsion rheology and oil displacement mechanisms, 4) Wettability and oil displacement mechanisms, 5) Adsorption, clays and chemical loss mechanisms, and 6) Polymer rheology and surfactant-polymer interactions. This book also includes two invited review papers, namely, "Research on Enhanced Oil Recovery Past, Present and Future," and "Formation and Properties of Micelles and Microemulsions" by Professor J. J. Taber and Professor H. F. Eicke respectively. 

Abstract. This article describes a hydrodynamic model of collaborative flnids (oil, water) flow in porons media for enhanced oil recovery, which takes into account the influence of temperature, polymer and surfactant concentration changes on water and oil viscosity. For the mathematical description of oil displacement process by polymer and surfactant injection in a porous medium, we used the balance equations for the oil and water phase, the transport equation of the polymer/surfactant/salt and heat transfer equation. Also, consider the change of permeabihty for an aqueous phase, depending on the polymer adsorption and residual resistance factor. Results of the numerical investigation on three-dimensional domain are presented in this article and distributions of pressure, saturation, concentrations of poly mer/surfactant/salt and temperature are determined. The results of polymer/surfactant flooding are verified by comparing with the results obtained from ECLIPSE 100 (Black Oil). The aim of this work is to study the mathematical model of non-isothermal oil displacement by polymer/surfactant flooding, and to show the efficiency of the combined method for oil-recovery. 

Table 1 gives a information about influence of polymer and surfactant concentrations on the main parameters of mathematical model of oil displacement process by polymer and surfactant solutions. The table shows that both polymer and surfactant effect viscosities of the both phases and do not effect the relative permeabilities. Capillary pressure takes into account the influence of surfactant concentration and the absolute permeability of rock decreases during injection of the polymer. 

Earlier parts of this book have discussed the various aspects of polymer structure, stability, solution behaviour, in-situ rheology and transport in porous media that are relevant to their ultimate task of improving oil recovery. In this chapter, an attempt is made to pull these strands together by describing the main mechanisms of polymer oil displacement processes in reservoir systems. For this purpose, the main multiphase flow equations that may be used in the design and simulation of polymer floods are developed, along with some simpler solutions for certain limiting cases. 

The results from the more complex eight layer cross-section, and the previous Brent Sands model, have confirmed that the same recovery mechanisms operate as were discussed in detail for the simple two layer model above. In particular, the importance of the polymer in changing the viscous forces in the oil displacement process is emphasised and results in viscous cross-flow of fluids between layers in heterogeneous formations of this type. The cross-sectional examples also show the importance of carrying out some simple scoping calculations in order to establish the mechanism... 

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