Surfactant-polymer flooding optimization

Figure 18. A summary of various phenomena occurring at the optimal salinity in relation to enhanced oil recovery by surfactant-polymer flooding.

Mohanunadi, H., 2008. Mechanistic Modehng, Design and Optimization of Alkaline/Surfactant/ Polymer Flood. Ph.D. dissertation. University of Texas at Austin. 

Zerpa, L.E., Queipoa, N.V., Pintosa, T.S., Salagerb, J.L., 2005. An optimization methodology of alkaUne-surfactant-polymer flooding processes using field scale numerical simulation and multiple surrogates. J. Pet. Sci. Eng. 47, 197-208. 

OPTIMAL SALINITY OF POLYMER SOLUTION IN SURFACTANT-POLYMER FLOODING PROCESS... 

One parameter that has been discovered to be crucially important in the successful implementation of the surfactant-polymer flooding process is the salinity of the aqueous phase. As discussed previously, addition of salt to the microemulsion system induces the change from lower- to middle- to upper-phase microemulsion (Fig. 15) [33]. It was found that at a particular salt concentration, deemed the optimal salinity, a number of important parameters were optimized for the oil recovery process. The optimal salinity was found to occur when equal amounts of oil and brine were solubilized by the middle-phase microemulsion [50]. 

Figure 17 summarizes the various parameters that are important in the surfactant-polymer flooding process as a function of salt concentration [33,51-54]. It is evident that all of these parameters exhibit a maximum or a minimum at the optimal salinity. Thus, it appears that all of these processes are interrelated for the oil displacement in porous media by the surfactant-polymer flooding process. It also appears that the optimal salinity value is a crucial parameter for consideration of a system to be used in this process. 

It was observed that the formulations consisting of ethoxylated sulfonates and petroleum sulfonates are relatively insensitive to divalent cations. The results show that a minimum in coalescence rate, interfacial tension, surfactant loss, apparent viscosity and a maximum in oil recovery are observed at the optimal salinity of the system. The flattening rate of an oil drop in a surfactant formulation increases strikingly in the presence of alcohol. It appears that the addition of alcohol promotes the mass transfer of surfactant from the aqueous phase to the interface. The addition of alcohol also promotes the coalescence of oil drops, presumably due to a decrease in the interfacial viscosity. Some novel concepts such as surfactant-polymer incompatibility, injection of an oil bank and demulsification to promote oil recovery have been discussed for surfactant flooding processes. 

Theories of surfactant flooding and polymer flooding are discussed in Chapters 5 to 7. This chapter focuses on surfactant-polymer (SP) interactions and compatibility. Optimization of surfactant-polymer injection schemes is also discussed. The methodology and even some conclusions in the presented optimization may be applied to other processes as well. Finally, this chapter presents a field example. 

In this section, simulation results are compared with the information from the literature for different polymer and surfactant-polymer injection schemes. We expect that UTCHEM simulation of a core-scale chemical process is the best simulation approach to study mechanisms. In this study, we use a ID core flood model with 100 blocks to represent a 1-foot-long core. The permeability is 2000 md, and the water and oil viscosities are 1 and 2 mPa s, respectively. To optimize injection schemes, we compare the incremental oil recovery factors over waterflooding and chemical costs. Chemical costs are evaluated using the amounts of chemicals injected per barrel of incremental oil (Ib/bbl oil). 

In this paper, a new technique for plugging fractures is also presented. Also, surfactant-enhanced alkall/polymer flood is alternated with water injection in order to optimize oil production. This technique uses a shorter sequence of chemical injection and therefore increases the possibility of plugging the fractures. 

The salinity of poljmier solution can influence four major parameters of surfactant-pol)mi r flooding process, namely, interfacial tension, mobility control, surfactant loss and phase behavior. When polymer solution of various salinities are equilibrated with surfactant solution in oil, the formation of lower, middle and upper phase microemulsion has been observed (1) similar to the effect of increasing connate water salinity (2,3). In general, there is an optimal salinity (2) which produces minimum interfacial tension and maximal oil recovery (1,4). On the basis of interfacial tension alone, the salinity of polymer solution should then be designed at or near the optimal salinity of the preceding surfactant formulation. 

Reservoir simulators in eombination with an economics model are useful to optimize the design of a ehemieal flood using surfactant and polymer. Projeet profitability is found to vary significantly at different surfactant concentrations. Reeently, Wu et al. [6i] found that the best results were obtained for the ease where low concentrations of both surfactant and polymer were simultaneously injected, i.e. under a LTPF condition. Sensitivity analysis on the optimum design showed that the most important economic variables were oil price, discount rate, operating cost and chemical prices. 

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