Mechanistic Modelling of Alkaline/Surfactant/ Polymer Flooding Process at Under-Optimum Salinity Condition for Enhanced Oil Recovery

Abstract

Alkaline-Surfactant-Polymer (ASP) flooding is potentially the most efficient chemical EOR methods. It yields extremely high incremental recovery factors in excess of 95% of residual oil for water flooding. The current opinion is that such extremely high recoveries can only be achieved at optimum salinity conditions, i.e. for the Winsor type III micro-emulsion phase characterized by an ultra-low interfacial tension (IFT). This represents a serious limitation since several factors including alkali-rock interaction, initial state of reservoir water and salinity of injected water may shift the ASP flood design to either under or over optimum conditions. A recent experimental study of ASP floods, based on a single internal olefin sulfonate (IOS), in natural sandstone cores varying salinity from under-optimum to optimum conditions indicated that indeed high recovery factors can be obtained also at under-optimum salinity conditions (see parent paper in this conference by Battistutta et al (2015). In this paper a mechanistic model is developed to explore the causes behind the observed phenomena. The numerical simulations were done using the UTCHEM research simulator (University of Texas at Austin) together with the geochemical module EQBATCH. UTCHEM combines multiphase multicomponent simulator with a robust phase behaviour modelling. An excellent match of the numerical simulations with the experiments was obtained for oil cut, cumulative oil recovery, pH profile, surfactant, and carbonate concentration at effluents. The simulations gave additional insight into the propagation of alkali consumption, salinity, surfactant and polymer profiles within the core. The study showed that the initial condition of the core is important in designing an ASP flood. Due to the uncertainties in the various chemical reactions taking place in the formation, an accurate geochemical model is essential for operating the ASP flood at a particular salinity region. Moreover, simulation results demonstrate for the crude oil with considerably low acid number, the ultralow IFT and low surfactant adsorption can be achieved over a wide range of salinities less than optimal salinity. The results provide a basis to perform better modelling of the under-optimum series of experiments and optimizing the design of ASP floods methods for the fields scale with more complicated geochemical condition.

Review and Perspective on the Mechanisms and Application ofIn SituEmulsification for Enhanced Oil Recovery

“…It is suggested that, for reservoirs with weak heterogeneity, EOR should focus on enhancing oil displacement efficiency; for reservoirs with strong heterogeneity, EOR should be based on improving sweep efficiency. Hosseini-Nasab et al 116 used numerical simulation, which proved that the surfactant prepared with low-salinity water has less adsorption retention than the surfactant prepared with the optimal salinity, and produced 66% of the surfactant. However, only 15% of the surfactant can be produced above the optimum salinity.…”

“…Hosseini-Nasab et al used numerical simulation, which proved that the surfactant prepared with low-salinity water has less adsorption retention than the surfactant prepared with the optimal salinity, and produced 66% of the surfactant. However, only 15% of the surfactant can be produced above the optimum salinity.…”

Relationship of Various Interfacial Tensions of Surfactants/Brine/Oil Formulations to Oil Recovery Efficiency

“…After Winsor’s pioneering work, ,, oil/water phase behavior tests, and their evaluations, have been the major focus of surfactant formulation development and selection before core flood tests. − The IFT values between oil and aqueous phases are usually estimated based on the phase behavior results, including water and oil solubilization, and surfactant structure, or are not reported. Usually, determining reliable IFT values in a robust way is a challenge, mainly due to time effects on the IFT and the effects of multicomponent nature of the surfactant, the oil, and the brine.…”