Preflush

Eig. 3. This polymer flooding method requites a preflush to condition the reservoir, the injection of a polymer solution for mobihty control to niinimi2e... 

Amoco developed polybutene olefin sulfonate for EOR (174). Exxon utilized a synthetic alcohol alkoxysulfate surfactant in a 104,000 ppm high brine Loudon, Illinois micellar polymer small field pilot test which was technically quite successful (175). This surfactant was selected because oil reservoirs have brine salinities varying from 0 to 200,000 ppm at temperatures between 10 and 100°C. Petroleum sulfonate apphcabdity is limited to about 70,000 ppm salinity reservoirs, even with the use of more soluble cosurfactants, unless an effective low salinity preflush is feasible. 

Additives and mixtures to reduce or prevent lost circulation Density-increasing or weighting agents Free water control and solid suspending agents Spacers and chemical washes or preflushes Specialty cement blends... 

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. 

Micellar flooding is a promising tertiary oil-recovery method, perhaps the only method that has been shown to be successful in the field for depleted light oil reservoirs. As a tertiary recovery method, the micellar flooding process has desirable features of several chemical methods (e.g., miscible-type displacement) and is less susceptible to some of the drawbacks of chemical methods, such as adsorption. It has been shown that a suitable preflush can considerably curtail the surfactant loss to the rock matrix. In addition, the use of multiple micellar solutions, selected on the basis of phase behavior, can increase oil recovery with respect to the amount of surfactant, in comparison with a single solution. Laboratory tests showed that oil recovery-to-slug volume ratios as high as 15 can be achieved [439]. 

Key mechanisms important for improved oil mobilization by microbial formulations have been identified, including wettability alteration, emulsification, oil solubilization, alteration in interfacial forces, lowering of mobility ratio, and permeability modification. Aggregation of the bacteria at the oil-water-rock interface may produce localized high concentrations of metabolic chemical products that result in oil mobilization. A decrease in relative permeability to water and an increase in relative permeability to oil was usually observed in microbial-flooded cores, causing an apparent curve shift toward a more water-wet condition. Cores preflushed with sodium bicarbonate showed increased oil-recovery efficiency [355]. 

Broaddus, G.C. "Preflush Concepts in Fracture Acidizing," 1975 Proc. Annu. Southwest Pet. Short Course, 91 97. 

Inert material of the sampling device (bags, tubes, valves), no losses by diffusion Preflushing Prediction equipment Volume of the sample Sampling time.pump speed Storage time(<24h) Inert tube material (PTFE. stainless steel, glass) Preflushing Predilution equipment Heated probe jf Dust filters required... 

Preflushing during half an hour is recommended, especially in the case of long tubes. Predilution should be provided in order to prevent condensation. 

Glass syringes (preflushed with nitrogen) are used for all transfers. Trichloro-silanet is freshly distilled and degassed by freeze-pump-thaw techniques before use. Teeda is distilled from CaH2 after stirring at room temperature... 

Our procedure employed the Metrohm pH-Stat system in which the reaction proceeds at constant temperature and pH in an unbuffered, balanced-ion medium calculated to afford optimal conditions for enzyme activity. The closed reaction vessel is preflushed with nitrogen. In this inert atmosphere there is no interference from atmospheric C02, and because there is no spontaneous hydrolysis of the substrates during the short reaction period, blank runs are unnecessary. Only enough substrate is added to allow a linear reaction for a maximum of 10 minutes at the highest activities encountered, so that substrate inhibition is minimal. A description of our final version of this method, which is now being standardized on human subjects, will be published elsewhere. 

The produced water had some polymer. The produced water may be injected before or after the main polymer slug as preflush or postflush slugs. A calculation showed that 2.5% incremental oil recovery could be obtained if the produced water was injected as preflush and 0.9% as postflush. A laboratory test showed that if the produced water had 400 mg/L polymer (with solution viscosity of 2.5 mPa s), the incremental oil recovery factor was about 3% (Zhang, 1998). 

After the preflush slug (waterflood), a water/polymer slug as a salinity gnard with the optimum salinity is preferred, bnt not necessary. 

For the optimum salinity, in the cases krl to kr5, the optimum phase type is type II(+) in Case kr2, not type III in Case krl, and the optimum salinity is 0.415 meq/mL, not the conventional optimum salinity of 0.365 meq/mL at the middle of Csd and Cse . In Case OSP7, we keep the optimum salinity of 0.415 meq/mL in the 0.4 PV polymer slug after the surfactant slug and in the preflush water, but change the salinity in the chase water from 0.415 to 0.335 meq/mL. Thus, the salinity profile follows the proposed optimum salinity prohle. The RF from this case is higher than the RF from Case kr2, and actually higher than any RF from Cases krl to kr5. In other words, the RF from the OSP case is the highest. 

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