Physicochemical Constraints on Surfactant Blends under Harsh Conditions and Evaluation of a Proposed Solution

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• 作者：Griselda Garcia-Olvera ; Teresa M. Reilly ; Teresa E. Lehmann ; Vladimir Alvarado
• 刊名：Energy & Fuels
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：31
• 期：1
• 页码：95-106
• 全文大小：635K
• ISSN：1520-5029

文摘

Chemical-enhanced oil recovery has been applied successfully in reservoirs with mild salinity and temperature conditions. Offshore reservoirs challenge chemical flooding, e.g., low-tension and foam flooding, because of the combined hardness and salinity of seawater along with the characteristics of the reservoir connate brine. These physicochemical conditions impose severe limitations on adequate phase behavior for most commercial surfactants. The purpose of this research is to analyze surfactant phase behavior for scenarios with seawater as the main carrying fluid for surfactant systems for harsh conditions similar to those in heavy-oil reservoirs in the Gulf of Mexico. We also aim at testing a recently developed surfactant characterization technique using a recently published NMR protocol [Garcia-Olvera et al., Energy Fuels, 2016, 30, 63]. In this technique, NMR spectra of surfactants, cosurfactants, and polymers are calibrated to enable analysis of individual components in chemical blends. Critical micelle concentration was estimated from further interpretation of the calibrated NMR data. Thermal stability and solubility for a family of ENORDET surfactants and an Alpha Foamer provided by two chemical companies were analyzed. Tests were conducted using a range of simulated connate brines, of up to 100 000 ppm of salinity and up to 20% of Ca–Mg hardness, and seawater compositions. Phase behavior experiments were run to determine which blend composition and brine salinity would enable the desired phase behavior. A medium-gravity oil thoroughly studied in our lab was selected for phase behavior studies. Finally, corefloods were completed to evaluate the additional oil recovery for surfactant–polymer and polymer evaluated scenarios. Some surfactants were disregarded for further analysis because of their lack of thermal stability, i.e., dropout from solution. In some cases, cosurfactants (e.g., N25) and cosolvents were added to increase solubility in surfactant blends with a high divalent ion content, which in some cases was insufficient to stabilize the blends. Phase behavior experiments show that some surfactants did not yield type III microemulsions and therefore were disregarded for low-tension flooding applications. NMR data for surfactants, cosurfactants, and polymers yielded good results to evaluate chemical concentrations even when the NMR spectra for different blend components overlaid significantly. Softening of high-salinity brines indeed improved microemulsion volume in the phase behavior tests, as demonstrated in the coreflooding results of up to 87% total recovery factor. However, this strategy is shown through geochemical analysis to be risky for more reactive reservoir lithologies, where dissolution and precipitation events are prompted by reduction in hardness in the injection brine.