Chase water slug

Cases OSP5 and OSP6 are really interesting. These cases are based on Case kr4. In Case OSP5, the salinity of 1.0 PV chase water is 0.340, just below Csei, which is equal to 0.345. The RF is 92.94%. In this case, the chase water mis-cibly drive the type ll(-) microemulsion. In Case OSP6, the salinity of chase water is 0.350, just above Csei = 0.345, and the RF is 84.8%. These two cases show that the salinity in the chase water slug should be less than Csei. 

The driver or chase water slug is a solution injected after the polymer slug whose viscosity progressively decreases, ending up as brine [109, 115, 119, 133, 141]. This slug is used, instead of a large polymer slug, to cut down the operation and the chemical costs. 

In Case OSPl, the salinity in the chase water after the guard slug (polymer slog) is 0.335 meq/mL. Because the slug before the surfactant slug is not... 

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. 

In other words, the polymer molecules in the blend solution slug would adsorb and coat the water-wet portions of the pore walls, so that the alkaline agent would have only limited sites for the rock dissolution and ion exchange reactions. Hence, the saved useful alkalinity could be used for the reactions with the organic acids in the crude oil in order to mobilize the residual oil. Moreover, as in the first version of PAAF, chasing fresh polymer slug would provide the mobility control and the efficient volumetric sweep. 

Surfactant slugs are frequently used in EOR processes to mobilize residual oil by changing rock wettability or by reducing oil/water interfacial tension. To increase the efficiency of such processes, polymers can be either co-injected with the surfactant slug or as a chase. In both cases, surfactant and polymer mixing is to be expected. The effects of Triton X-100 (a nonionic surfactant) and Neodol 25-3S (an anionic surfactant) on the viscosity of HPAM solutions were examined by Nasr-El-Din et al. [41]. 

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