Polymer oil displacement

Another issue that has only been addressed in a few studies is the effect that polymer adsorption has on the relative permeability of the aqueous and oleic phases that subsequently flood a core. In conventional polymer flooding, this is not a very important consideration since the process usually occurs in one particular saturation direction for example, if the formation is strongly water-wet then the oil displacement by water or polymer solution is an imbibition process. In such a case, the oil would not normally flow at a high saturation in a polymer-flooded zone, although such behaviour is conceivable (but unlikely) in certain polymer oil displacements in layered systems (see... 

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. 

There are basically three types of laboratory experiment that may be carried out on candidate polymer solution(s), injection brine and field core combinations. These involve polymer compatibility and screening, the generation of polymer core flood data and polymer/oil displacement experiments. Each type of experiment serves a different function as follows. 

Intermixing of the polymer mobility control fluid with the surfactant slug can result in surfactant - polymer interactions which have a significant effect on oil recovery (476). Of course, oil - surfactant interactions have a major effect on interfacial behavior and oil displacement efficiency. The effect of petroleum composition on oil solubilization by surfactants has been the subject of extensive study (477). 

OSR may be used in structure of oil-sweeping liquids. Injection of polymers water solutions into heterogeneity layers provides oil recovery at the expense of increase of coefficients of layer coverage as a result of decrease of ratio of water mobility and displaced oil. At present for oil displacement from layers carboxymethylcellulose (CMC) are the most widely used. However, wide application of CMC in oil-production industry is limited by limited volumes of its production and high cost [15], OSR as it was already mentioned was significantly cheaper than CMC and might be obtained from agricultural waste that makes it even more advisable. 

Case viscOS is the same as Case visc02, except that the polymer concentration is adjusted so that the polymer mobility is the same as the oil mobility only (not total mobility). Note that in Case viscOS, as well as in Cases viscOl and visc02, the initial oil saturation is 0.5. In this situation, the cross-section area available for polymer to displace the oil phase is half the whole cross-section area. The other half cross-section area is used for polymer to displace the water phase ahead. In other words, the polymer mobility to displace the oil is reduced by half. Mathematically, we should determine the polymer viscosity required using the following equation ... 

Relative permeability curves were also determined for the displacement of oil by water following the polymer/oil tests. Figure 5.53 compares the relative permeability data for the oil and water phases before (with the subscript 1) and after (with subscript p) polymer contact. RRF in the figure denotes in the text. In the water-wet rocks, there was little difference between the residual oil saturation obtained before and after polymer contact, as would be expected. Oil... 

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... 

For oil displacement purposes, alkali can be co-injected with any displacing agents except an acid or carbon dioxide. For example, aUcaline-polymer (AP), alkaline-surfactant (AS), aUcaline-gas, alkaline-steam, aUcaline-hot water, and more can be used. This chapter discusses alkaline-surfactant flooding. 

Pusch, G., Lotsch, T, Muller, T, 1987. Investigation of the oil displacing efficiency of suitable polymer products in porous media, aspects of recovery mechanisms during polymer flooding. DGMK—Report, German Society Petrol. Sci. Coal Chem., 295-296, Hamburg. 

Wang, D.-M., Xia, H.-E, Liu, Z.-C., Yang, Q.-Y, 2001b. Study of the mechanism of polymer solution with viscoelastic behavior increasing microscopic oil displacement efficiency and the forming of steady Oil Thread flow channels. Paper SPE 68723 prepared at the SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 17-19 April. 

Pithapurwala, A.K., Sharma, R.C. and Shah, D.O. (1986) Effect of salinity and alcohol partitioning on phase-behavior and oil displacement efficiency in surfactant-polymer flooding. /. Am. Oil Chem. Soc., 63(6), 804-813. 

Sandiford, B.B. "Flow of Polymers Through Porous Media in Relation to Oil Displacement, Improved Oil Recovery bv Surfactant and Polymer Flooding, edited by Shah, D.O., and Schecter, R.S., Academic Press, Inc., San Francisco, California, 1977, pp 491-495. 

In all applications, it is as well to remember that there are other considerations. In the case of the supertanker, for example, one of the major oil companies made a careful calculation of the possible economic advantage to ejecting polymers in the boundary layer to reduce the drag, assuming that the polymer was manufactured by the company in question, taking account of the value of the crude oil displaced by the polymer which must be carried, the changes in time at sea versus time in port, and the relative costs of each, and other factors. They concluded that they would just break even, and decided not to pursue the matter. 

The effectiveness of a polymer for oil displacement in enhanced oil recovery is determined by the mobility ratio (M) of the polymer slug and the oil. The mobility ratio (M) is defined as the ratio kj np/kp nw. where n - viscosity and k - permeability. Values of M 1 stabilize the displacement process. 

A third sequence of experiments was done on one core following the flow experiments at residual oil saturation. The core was heated to 60C and polymer flooded at maximum rate using the 1500 ppm solution to reduce the oil saturation and increase brine permeability. Oil displaced by this polymer flood caused the brine permeability to increase from 10 md to about 90 md. Thus, it was possible to conduct polymer flow experiments on a core with the same internal pore configuration but with a different permeability. 

Considerable effort has been expended to develop a surfactant-based oil recovery system that would be less complex, and potentially less costly than the various micellar-polymer systems proposed by many major oil companies, examples of which are given in an excellent review by Gogarty (25). One system which shows considerable promise, based on initial laboratory oil displacement studies, is a combination of dilute petroleum sulfonate and sodium... 

Laboratory studies on oil displacement efficiency by surfactant-polymer flooding process have been reported by a number of investigators (1-10). In general, the process is such that after being conditioned by field brine or preflush, a sandstone core or a sandpack is oil-saturated to the irreducible water content. It is then waterflooded to the residual oil level. Finally, a slug of surfactant solution followed by a mobility buffer is injected. 

Because of the cost and the time factors involved, oil displacement studies are always preceded by certain test tube screening procedures. Specifically, the interfacial tension (IFT) of less than 0.01 dyne/cm is recognized to be the necessary but not the sufficient criterion for selection of a surfactant system. Many investigators (10-15) have shown that ultralow IFT of less than 0.001 dyne/cm can be achieved with less than 0.1 wt. % surfactant solution. Since this low surfactant concentration system is several hundred times more dilute than the ones used in a typical surfactant-polymer flooding process, the economics dictates that the oil displacement by such low surfactant concentration solution should be explored. Moreover, it should be established that the... 

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

Oil displacement experiments were performed under different salinity conditions (1) constant salinity of pol3nner solution at 1.5% NaCl (i.e. optimal salinity of the soluble oil formulation), and variable connate water salinity (2) constant salinity of connate water at 1.5% NaCl and variable salinity of pol3mier solution and (3) the salinity of polymer solution equals the salinity of connate water, both varied simultaneously. Sand packs were chosen as the model porous media in order to avoid the effects of porous media heterogeneity, clays and surfactant adsorption loss. The compositions of aqueous formulation and soluble oils are specified in Figures 1 and 2. The difference between their compositions reflects the density difference between water and dodecane whereas the surfactant and alcohol concentrations (w/v) are the same in both types of formulations. The polymer solution used was 1000 ppm PUSHER-700 in brine. For polymer solution in distilled water, the polymer concentration was reduced to 250 ppm to avoid excessive viscosity. Several experiments were repeated and the reproducibility was established to be within 2% in tertiary oil recovery. 

Maximal oil recovery still occurred at 1.5% NaCl polymer solution. The interfacial tension between effluent oil and brine (or microemulsion) remains approximately the same (for both sand packs at a given salinity) as shown in Figure 3. The pressure drop history during tertiary flooding also shows nearly identical behavior for long and short sand packs. These observations indicate that the transport process in porous media is nearly the same for the 1.1 and 4 ft long sand packs and the conclusions drawn in section 1 should also be valid for oil displacement in 4 ft long sand packs. 

The Effect of Salinity of Polymer Solution on Oil Displacement in Berea Cores... 

Table 3. Salinity Shock Design of Polymer Solutions for Oil Displacement in Berea Cores > ...

Fig. 4. The effect of salinity change of polymer solution on oil displacement efficiency and surfactant recovery for connate water of 2.1% NaCI.

For oil displacement in Berea cores especially in the presence of 1% CaCl2 in connate water, surfactant loss was quite significant and the oil recovery was greatly reduced. Maximal oil recovery was obtained when the salinity of polymer solution was at or slightly below the optimal salinity of surfactant formulation,... 

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