Fluid-Fluid Interactions Inducing Additional Oil Recovery during Low Salinity Water Injection in Inefficacious Presence of Clay Minerals

One the most promising Enhanced Oil Recovery (EOR) methods, Low salinity water injection (LSWI) has faced several critical challenges, of which understanding the underlying mechanism is still of utmost importance. Here, we combine traditional coreflood experiments with several analytical tools to gain an insight into the mechanism of additional oil recovery by LSWI. Two crude oil samples with contrasting propensities to form microdispersion were chosen for coreflood experiments in a clay-rich sandstone core. Microdispersion is a term denoting the spontaneous formation of separated water phases within the crude oil phase by surface-active materials such as asphaltenes and/or carboxylic acids contributing to additional oil recovery by wettability alteration and crude oil swelling. Investigating the reasons behind the different responses to tertiary LSWI, it appeared that clay is not a decisive factor for low salinity effect (LSE) as previously believed. Additionally, surface charge evaluations and ionic composition of effluents showed that electrical double layer expansion and multi-ion exchange (MIE) mechanisms are not primary contributors to LSE. Extensive investigation by FT-IR spectroscopy and water content measurements suggests the underlying mechanism associated with LSWI is microdispersion formation by acidic materials (i.e., carboxylic acids and/or carboxylic functional groups of asphaltenes). The performance of tertiary LSWI, in terms of additional oil recovery, agreed well with the propensities of crude oils toward microdispersion formation. Experimental findings obtained herein contribute to resolve uncertainties around the mechanism of LSWI and look at reservoir eligibility for use of this EOR method.