A considerable amount of oil resides in many reservoirs around the world such as the Snorre reservoir, a sandstone reservoir in the North Sea. The effect of lowsal waterflooding was explored in this field and the laboratory via Single Well Chemical Tracer (SWCT) and coreflood tests. Since the results showed that the amount of oil recovery after lowsal waterflooding was insignificant, the effect of alkaline/surfactant/polymer (ASP) flooding is investigated.
Mechanistic modeling of ASP injection is performed based on the geochemichal reactions such as aqueous, ion exchange, and precipitation/dissoloution using the reservoir properties. Due to lack of ASP flood of the laboratory corefloods for the Snorre reservoir, first, ASP coreflood is modeled based on the performed laboratory coreflood to validate the procedure of the mechanistic modeling of ASP. Second, the feasibility of ASP method for the Snorre oil field is investigated by a series of 1D coreflood simulations. Different strategies are designed to identify key parameters and an optimum design is determined based on the simulation results.
Since the propagation of alkali, in-situ surfactant (soap), and surfactant plays a vital role to succeed ASP method, mechanistic modeling of ASP flooding in the core is an effective tool to ensure the proper propagation to support low IFT and favorable salinity gradient. The results of different strategies demonstrate that alkali, surfactant, and polymer propagate simultaneously and in consequence, ASP flood can be feasible in the Snorre reservoir. The effect of the combination of low-salinity with ASP in order to provide optimum salinity for the soap/surfactant phase behavior is studied. The results also verify that the amount of oil recovery increases by injecting more slug size of chemicals; however, almost the same amount of oil is recoverable by injecting half or less of chemicals by designing the salinity gradient in the injected fluids. The effect of cation exchange reaction (CEC) is also investigated. The results show that the higher CEC leads to higher alkali consumption and it results in slower propagation of the alkali and pH front.
Mechanistic modeling of ASP is a highly sophisticated process due to the complicated ASP phase behavior and the geochemical reactions that happen in the reservoir. In this paper, all of the key parameters such as the chemical reactions, alkali consumption, soap generation, and the effect of the phase behavior are considered using the UTCHEM simulator. Geochemist’s Workbench® release 6.0 database is used to find the thermodynamic reaction equilibrium data for solution and solid species. The initial equilibrium concentrations of aqueous, solid, and adsorbed species are calculated using the EQBATCH program.