Surfactant Systems for EOR in High-Temperature, High-salinity Environments

Abstract

ABSTRACT A systematic study was made of phase behavior of alkoxy glycidyl sulfonates (AGSs). These surfactants were screened with either NaCl-only brines or NaCl-only brines and n-octane at WOR ~1 for temperatures between approximately 85°C and 120°C. All test cases were free of alcohols and other co-solvents. Classical Winsor phase behavior was observed in most scans with optimal salinities ranging from less than 1% NaCl to more than 20% NaCl for AGSs with suitable combinations of hydrophobe and alkoxy chain type (ethylene oxide or propylene oxide) and chain length. Oil solubilization was high, indicating that ultralow interfacial tensions existed near optimal conditions. The test results for 120°C at WOR~1 have been summarized in a map, which might provide a useful guide for initial selection of such surfactants for EOR processes. Saline solutions of AGSs separate at elevated temperatures into two liquid phases (cloud point phenomenon), which may be problematic when they are injected into high-temperature reservoirs. An example is provided which indicates that this situation can be alleviated by blending suitable AGS and internal olefin sulfonate (IOS) surfactants, these being within Shell Chemical's ENORDETTM range of surfactants for EOR. Synergy between the two types of surfactant resulted in transparent, single-phase aqueous solutions for some blends, but not for the individual surfactants, over a range of conditions including in synthetic seawater. Such blends are promising because both AGS and IOS surfactants have structural features that can be adjusted during manufacture to give a range of properties to suit reservoir conditions (temperature, salinity and crude oil type).