Polymer Waterflooding

The polymer in a polymer waterflooding process acts primarily as a thickener. It decreases the permeability of the reservoir and thus improves the vertical and lateral sweep efficiency. 

Associative copolymers of acrylamide with N-alkylacrylamides, terpoly-mers of acrylamide, N-decylacrylamide, and sodium-2-acrylamido-2-methyl-propane sulfonate (NaAMPS), sodium acrylate (NaA), or sodium-3-acrylamido-3-methylbutanoate (NaAMB) have been shown to possess the required rheologic behavior to be suitable for enhanced oil-recovery processes [1184]. 

Other copolymers of acrylamide with the zwitterionic 3-(2-acrylamido-2-methylpropyldimethyl ammonio)- -propane sulfonate (AMPDAPS) monomer also have been examined. 

The low-tension polymer flood technique consists of combining low levels of polymer-compatible surfactants and a polymer with a waterflood. This affects mobility control and reduces front-end and total costs. [929]. 

The synergism of surfactant-polymer complex formation has been studied by gel permeation chromatography [114], 

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Before inverse emulsion was injected, the field went through primary depletion, waterflooding, polymer flooding, and post-polymer waterflooding. By July 2004, the water cut in the test area was 90.64%, with a recovery factor of 50.1 %. With 1 injector, Well 21-4, and 5 producers, the injection of inverse emulsion was started in December 2004 at one injection well pattern. The injection program was 10 m polymer solution of 8000 mg/L concentration, 15 m inversion emulsion with 6000 mg/L polymer, and 1167 mg/L phase inversion agent, followed by chase water drive. Four producers out of 5 wells responded to the injection in this test. The injection pressure increased from 7.5 to 9.5 MPa, the water cut reduced from 92.5 to 91.4%, the oil rate increased from 31.9 to 44 fid, and the liquid rate increased from 423.1 to 513.2 fid for the well pattern (Lei et al., 2006). 

Manji, K. H. and B. W. Stasiuk, Design Consideration for Dome s David Alkaline/Polymer Waterflood During Uncertain World Prices, JCPT 27 (3), 49-54 (1988). 

Rowalt, R. J. (1973) A case history of polymer waterflooding—Brelum Field Unit. SPE 4617, Proceedings of the SPE 48th Annual Fall Conference, Las Vegas, NV, 30 September-3 October 1973. 

The first consequence of the polymer waterflooding which increased formation pressure was a rapid three-fold increase in production. Oil cuts remained constant in each of the producing wells during this period. The second major effect was the arrival of tertiary oil... 

Rowalt, R.J. 1973. A Case History of Polymer Waterflooding Brelum Field Unit. Paper SPE 4671 presented at the SPE Annual Meeting, Las Vegas, 30 September-3 October. DPI 10.2118/4671-MS. 

One problem facing engineers in this situation, where the process is applied from waterflood initiation, is how to quantify the incremental recovery resulting from the polymer additive. 

Polymer Flooding. Even in the absence of fractures and thief 2ones, the volumetric sweep efficiency of injected fluids can be quite low. The poor volumetric sweep efficiency exhibited in waterfloods is related to the mobiUty ratio, Af, the mobiUty of the injected water in the highly flooded (low oil saturation) rock, divided by the mobiUty of the oil in oil-bearing portions of the reservoir, (72,73). The mobiUty ratio is related to the rock permeabihty to oil, and injected water, and to the viscosity of these fluids by the following equation ... 

An alternative to this process is low (<10 N/m (10 dynes /cm)) tension polymer flooding where lower concentrations of surfactant are used compared to micellar polymer flooding. Chemical adsorption is reduced compared to micellar polymer flooding. Increases in oil production compared to waterflooding have been observed in laboratory tests. The physical chemistry of this process has been reviewed (247). Among the surfactants used in this process are alcohol propoxyethoxy sulfonates, the stmcture of which can be adjusted to the salinity of the injection water (248). 

For modestly viscous oils—those having viscosities of approximately 20-100 centipoise (cP)-water-soluble polymers such as polyacrylamides or xanthan gum have been used to increase the viscosity of toe water injected to displace oil from toe formation. For example, polyacrylamide was added to water used to waterflood a 24 cP oil in toe Sleepy Hollow Field in Nebraska. Polyacrylamide was also used to viscosify water used to flood a 40 cP oil in the Chateaurenard Field, France. With this process, toe polymer is dissolved in toe water, increasing its viscosity. 

While water-soluble polymers can be used to achieve a favorable mobility waterflood for low to modestly viscous oils, usually toe process cannot economically be apphed to achieving a favorable mobility displacement of more viscous oils—those having viscosities of from approximately 100 cP or higher. These oils are so viscous that the amount of polymer needed to achieve a favorable mobility ratio would usually... 

Injecting a polymer solution as a protecting slug and then continuing with waterflooding [1823]... 

A chemical-enhanced oil-recovery technology can be used to remove oily contaminants from soil. Laboratory studies demonstrated that a variety of alkaline-surfactant combinations can be used with a polymer to reduce the residual oil saturation in waterflooding [1435]. 

Organic and inorganic polymers have been used to improve the results obtained in waterflooding. Crosslinked polymers (see below) have been used to reduce the permeability of fractures and high permeability streaks so that injected water flows through a larger fraction of the reservoir volume. The polymer is injected with a crosslinker or the crosslinker may be injected after the... 

Careful sizing of the treatment and choice of injection rates is required to prevent inadvertent overtreatment i.e., excessive treatment of oil-containing rock. The post-treatment fluid injection rate is usually significantly less than that prior to treatment. While successful applications of this technology in waterfloods and in surfactant polymer floods have been reported, temperature and pH stability limitations of the polymer and the crosslinking chemistry result in few if any applications in steam and CO2 injection wells. 

Several agents are currently used for plugging high permeability strata. These include small fibers that are carried in the waterflood and deposited in the high permeability zgnes and chemical reactions forming insoluble precipitations. Some of the current methods available, for example polymers or foams, are subject to deterioration and are costly. This gives them limited application as they are not able to penetrate deep into the strata. 

Improved Oil Recovery (ior), where a range of more exotic fluids such as steam (hot water), caustic solutions, carbon dioxide, foams, polymers, surfactants, and so on are injected to improve recovery beyond what might be obtained by waterflooding alone. 

Polymer augmented waterflooding waterflooding in which organic polymers are injected with the water to improve areal and vertical sweep efficiency. 

FIGURE 1,2 Schematic of macroscopic displacement efficiency improvement by polymer flooding (b) over waterflooding (a). Source Courtesy of Surtek, a chemical EOR service company in Golden, Colorado. 

Salinity is essential for all chemical processes. It directly affects polymer viscosity, and it determines the type of microemulsion a surfactant can form. Salinity effects in waterflooding, in both sandstone and carbonate reservoirs, have recently drawn research interest. This chapter briefly discusses sahnity and ion exchange. At the end of this chapter, the sahnity effects on waterflooding in sandstone and carbonate reservoirs are summarized. 

Preformed particle gels have been applied in about 2000 wells in China to reduce fluid channels in waterfloods and polymer floods (Liu et al 2006c). PPG treatment has been widely accepted and is seeing more and more use by operators because of its unique advantages over traditional in situ gel including... 

One obvious mechanism in polymer flooding is the reduced mobility ratio of displacing fluid to the displaced fluid so that viscous Angering is reduced. When viscous Angering is reduced, the sweep efficiency is improved, as shown in Figure 1.2. This mechanism is discussed extensively in the waterflooding literature it is also discussed in Chapter 4. When polymer is injected in vertical heterogeneous layers, crossflow between layers improves polymer allocation in the vertical layers so that vertical sweep efficiency is improved. This mechanism is detailed in Sorbie (1991). 

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