Surfactant flooding negative

A comparison of the residual NAPL saturations after surfactant flooding based on both partitioning tracers and mass balance measurements is presented in Table 6. The apparent final residual DNAPL saturation estimates range from —0.0038 to 0.0046 from the mass balance and from 0.0001 to 0.005 from the partitioning tracers. The negative values from the mass balance are obviously experimental error and indicate that the mass balance error is on the order of 0.004 saturation units. This corresponds to only about 0.2 mL of DNAPL. 

Nelson and Pope concluded that chemical flood design should be such as to maintain as much surfactant as possible in the type III phase environment. This condition can be accomplished by designing the micellar fluid such that the initial phase environment of the immiscible displacement is type II(+). A negative salinity gradient is imposed, and it moves the phase environment to type III and, eventually, to II(-). 

For all these cases, the total amount of each chemical was the same. The core flood results are shown in Figure 13.21. We can see that the incremental oil recovery factors over waterflooding in Schemes 2 and 4 were obviously higher than that in Scheme 1. The alkali and surfactant concentration gradients from high to low can overcome the negative effects at the displacement front caused by dilution, alkali consumption, and surfactant adsorption. 

Three-Phase Displacement. Provided that the alcohol free surfactant system shows a classic phase behavior, II( —) -> III II( -f) by increasing the salinity without forming gels or stable macroemulsions during the phase transitions, the chemical flood can be performed as a three-phase flood using a negative salt gradient. 

It also reduces adsorption of the (mostly anionic) surfactant on the reservoir rock, essentially by enhancing the negative surface charge. In some cases (alkaline-polymer floods), where there are high levels of saponifiable crude oil acids present in the crude oil (high acid number) added surfactant is not even required. The polymer is present to assist in mobility control and to ensure that the injected chemical slug remains intact and promotes the formation of an oil bank ahead of it. 

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