Packed mobile flooded

Tertiary oil was increased up to 41% over conventional CO2 recovery by means of mobility control where a carefully selected surfactant structure was used to form an in situ foam. Linear flow oil displacement tests were performed for both miscible and immiscible floods. Mobility control was achieved without detracting from the C02-oil interaction that enhances recovery. Surfactant selection is critical in maximizing performance. Several tests were combined for surfactant screening, included were foam tests, dynamic flow tests through a porous bed pack and oil displacement tests. Ethoxylated aliphatic alcohols, their sulfate derivatives and ethylene oxide - propylene oxide copolymers were the best performers in oil reservoir brines. One sulfonate surfactant also proved to be effective especially in low salinity injection fluid. 

Instead of relying completely on theory for the determination of mobility, most researchers also performed experimental measurements of the quantities of interest. Many of the first experiments on foam were performed with water and gas with the outlet at ambient pressure, and many were simply gas floods of packs or cores saturated with surfactant solution. Although for many such transient experiments, the published data were insufficient for the estimation of the steady-state mobilities required for the estimation of mobility-control effectiveness, this was not true for some of them. Calculated values of mobility and relative mobility were derived by Heller et al. (22), from the data published in six different papers (23—28). The values they found, given in terms of relative mobilities, ranged from 0.001 to 0.6 cP-1, or in terms of effective viscosities from 1000 down to 1.6 cP (1 to 0.0016 Pa-s). Not enough information was available to trace all of the relevant parameters that may have caused these differences. 

Recently, Wellington and Richardson [J5] presented an interesting paper discussing the mechanism of low surfactant concentration enhanced water flood. The surfactant system consisted of alkyl-PO-EO glyceryl sulfonate with small amounts of an ethoxylated cationic surfactant to control phase behavior, interfacial activity, and surfactant loss. The surfactant systems had the ability to reduce their cloud point and interfacial tension when diluted, which was regarded as very useful for an effective flood performance. A surfactant concentration of about 0.4% removed essentially all the residual oil from sand packs in just over f PV with a surfactant loss of less than O.f PV. Mobility control by polymer was strongly required for good displacement and sweep efficiency and to reduce surfactant loss. 

Figure 16 shows a schematic view of a petroleum reservoir as well as the process of water or chemical flooding by an inverted five-spot pattern [33]. Several thousand feet below the ground, oil is foimd in tightly packed sand or sandstones in the presence of water as well as natural gas. During the primary and secondary recovery processes (water injection method), about 35% of the available oil is recovered. Hence, approximately 65% is left in the petroleum reservoir. This oil remains trapped because of the high interfacial tension (20-25 mN/m) between the crude oil and reservoir brine. It is known that if the interfacial tension between crude oil and brine can be reduced to around 10 mN/m, one can mobilize a substantial fraction of... 

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