Aqueous brines injections

Acrylamide polymers are used as multipurpose additives in the oil-producing industry. Introduction of polymers into drilling fluids-drilling muds improves the rheological properties of the fluids in question, positively affects the size of suspended particles, and adds to filterability of well preparation to operation. Another important function is soil structure formation, which imparts additional strength to the well walls. A positive effect is also observed in secondary oil production, where acrylamide polymers additives improve the mobility of aqueous brines injections, which contribute to... 

It should be noted that the well skin and hydrostatic pressure of the aqueous and nitrogen phases combine to form a constant of integration in Eq. 2. Once this constant is evaluated from brine injection, it remains unaltered by polymer injection, as long as the skin remains constant. The polymer mobility predictions from this model are therefore not dependent on well depth and fluid densities. These terms are not lumped together as a constant for completeness. 

A typical sequence followed in this test series consists in injecting (1) a micellar slug of one pore volume of aqueous solution of 4% of the preceding pseudobinary system (2% sulfonate/2% Genapol) (2) a slug of desorbent solution corresponding to a fixed amount of additive (e.g. equal to 1 PV at a concentration of 0.5 %) (3) at least 1.5 PV of brine with no additive. 

Initially the free C02 is distributed in radially decreasing concentrations in zones around the injection site (Fig. 2a van der Meer 1996). Nearest the injection site lies a zone of near completely saturated pores, containing isolated beads of trapped brine, some of which evaporate into the C02 (Pruess etal. 2003). The middle zone contains mixed brine and C02 (Saripalli McGrail 2002 Pruess et al. 2003). In the outer zone C02 is present only as aqueous species. Following injection, C02 saturations around the injection site are predicted to decrease over tens of years as the free C02 rises buoyantly, spreads laterally, and dissolves into the brine (Weir et al. 1995). Over time-scales of hundreds of years, dispersion, diffusion, and dissolution can reduce the concentration of both free and aqueous C02 to near zero (McPherson Cole 2000). 

In the Salton Sea area, California, silica in the hyper-saline brine (Table 3) has been removed from solution in special brine clarification tanks. A sludge containing precipitates of silica and various sulphides is injected into hot brine in the tanks. The precipitates in the sludge act as nuclei for precipitation of additional silica and the rate of precipitation is sufficiently high for removal of aqueous silica to < 100 ppm. This method most likely only applies to very saline waters. 

A solution of 15 ml. of glacial acetic acid and 30 ml. of water is deoxygenated as described above and then slowly injected with a syringe into the reaction. Refluxing is continued for 6 hours, the flask is cooled, and its contents are poured into a 1-1. separatory funnel along with 200 ml. of water. The solution is extracted four times with 100-ml. portions of ether, and the combined ether extracts are washed successively with 100 ml. of 6N aqueous hydrochloric acid, 100 ml. of water, and 100 ml. of brine. The organic extracts are dried over anhydrous magnesium sulfate, filtered, concentrated with a rotary evaporator, and distilled to yield 13.2-13.8 g. (65-67%) of l-methyl-4,... 

A particularly interesting part of the pilot involved the treating of produced emulsions. Over the life of the pilot, 93% of the injected surfactant was produced at the production wells, and this situation led to serious emulsion problems. Heating the emulsion to a specific, but unreported, temperature caused the surfactant to partition completely into the aqueous phase and leave the crude oil with very low levels of surfactant and brine. The resulting oil was suitable for pipeline transportation. The critical separation temperature had to be controlled to within 1 0. At higher temperatures, surfactant partitioned into the oil, and at lower temperatures, significant quantities of oil remained solubilized in the brine. Recovered surfactant was equivalent to the injected surfactant in terms of phase behavior, and had the potential for reuse. 

The product stream from the production well is a mixture of oil and water/brine, and the oil can easily be separated by gravity. Note that oil has a specific gravity of about 0.9, while water/brine at or slightly above 1.0. Thus, even if one allows the mixture to stand in a holding tank, the oil will naturally accumulate as a top layer of fluid. The bottom aqueous layer can be reused typically by pumping it back through the injection wells, for a closed-loop operation with some additional make-up water to replace the oil removed from the reservoir. 

It is also suggested that seawater be used as brine or aqueous phase in microemulsion formulations, because high salinity levels are observed in marine reservoirs. The enhanced recovery methods employ different injection fluids, such as microemulsions, to act in areas where the conventional process cannot provide good recovery rates. With this in mind, it is important to determine all parameters that affect microemulsion formation and stability, like surfactant and cosurfactant types, as ratio, and salinity. 

Figure 5.21. Selective reduction in the aqueous-phase permeability by treatment with HPAM. Test sequence (1) relative perm to brine at residual oil-kei (2) relative perm to oil at residual brine-koi (3) flush with brine-kei (4) polymer injected (5) relative perm to brine at residual oil-kap (6) relative perm to oil at residual brine-kop (from White et aL, 1973).

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