Waterflooding

The surfactants described or characterized for waterflooding are summarized in Table 16-2. Conunercial alkene sulfonates are a mixture of alkene sulfonate, hydroxy alkane sulfonate, and olefin disulfonate [211]. 

To develop improved alkali-surfactant flooding methods, several different injection strategies were tested for recovering heavy oils. Oil recovery was compared for four different injection strategies [641]  

The effect of alkaline preflush was also studied under two different conditions. All of the oil-recovery experiments were conducted under optimal conditions with a viscous, nonacidic oil and with Berea sandstone cores. 

Ethoxylated methylcarboxylates Propoxyethoxy glyceryl sulfonate Alkylpropoxyethoxy sulfate as surfactant, xanthan, and a copolymer of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate Carboxymethylated ethoxylated surfactants (CME) Polyethylene oxide (PEG) as a sacrificial adsorbate Polyethylene glycols, propoxylated/ethoxylated alkyl sulfates Mixtures of sulfonates and nonionic alcohols Combination of lignosulfonates and fatty amines Alkyl xylene sulfonates, polyethoxylated alkyl phenols, octaethylene glycol mono n-decyl ether, and tetradecyl trimethyl ammonium chloride Anionic sodium dodecyl sulfate (SDS), cationic tetradecyl trimethyl ammonium chloride (TTAC), nonionic pentadecylethoxylated nonylphenol (NP-15), and nonionic octaethylene glycol N-dodecyl ether Dimethylalkylamine oxides as cosurfactants and viscosifiers (N-Dodecyl)trimethylammonium bromide Petrochemical sulfonate and propane sulfonate of an ethoxylated alcohol or phenol Petrochemical sulfonate and a-olefin sulfonate 

Polymers can be used for mobility control. The interaction between polymers and surfactants is shown to be affected by pH, ionic strength, crude oil type, and the properties of the polymers and surfactants [642]. 

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Steam is injected into a reservoir to reduce oil viscosity and make it flow more easily. This technique is used in reservoirs containing high viscosity crudes where conventional methods only yield very low recoveries. Steam can be injected in a cyclic process in which the same well is used for injection and production, and the steam is allowed to soak prior to back production (sometimes known as Huff and Puff). Alternatively steam is injected to create a steam flood, sweeping oil from injectors to producers much as in a conventional waterflood. In such cases it is still found beneficial to increase the residence (or relaxation) time of the steam to heat treat a greater volume of reservoir. 

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. 

Most CO2 miscible EOR projects are located in the west Texas Permian Basin where as much as two-thirds of the oil remains after waterflooding. An incremental (10%) recovery is typical for Permian Basin CO2 floods, which could correspond to as much as 0.5 x 10 (3-4 x 10 bbl) (23). 

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). 

Microbial-enhanced oil recovery involves injection of carefully chosen microbes. Subsequent injection of a nutrient is sometimes employed to promote bacterial growth. Molasses is the nutrient of choice owing to its low (ca 100/t) cost. The main nutrient source for the microbes is often the cmde oil in the reservoir. A rapidly growing microbe population can reduce the permeabiHty of thief zones improving volumetric sweep efficiency. Microbes, particularly species of Clostridium and Bacillus, have also been used to produce surfactants, alcohols, solvents, and gases in situ (270). These chemicals improve waterflood oil displacement efficiency (see also Bioremediation (Supplement)). 

In the petroleum industry, the term system and process are often considered synonymous. This is basically because engineering designers in the industry create systems that will carry out needed operational processes (e.g., waterflood project). 

During caustic waterflooding the alkali can be consumed by the dissolution of clays and is lost in this way. The amount lost depends on the kinetics of the particular reaction. Several studies have been performed with kaolinite, using quartz as a yardstick, because the kinetic data are documented in the literature. The initial reaction rate has been found pH independent in the pH range of 11 to 13 [517]. The kinetics of silica dissolution could be quantitatively described in terms of pH, salinity, ion-exchange properties, temperature, and contact time [1549]. 

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... 

Waste water-soluble alcohols are useful for miscible waterflooding [886]. 

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. 

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]. 

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

B. licheniformis JF-2 and Clostridium acetogutylicum were investigated under simulated reservoir conditions. Sandstone cores were equilibrated to the desired simulated reservoir conditions, saturated with oil and brine, and flooded to residual oil saturation. The waterflood brine was displaced with a nutrient solution. The MEOR efficiency was directly related to the dissolved gas/oil ratio. The principal MEOR mechanism observed in this work was solution gas drive [505]. 

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

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