Abstract
Low salinity flooding (LSF)- decreasing ionic strength to enhance oil production- is an Enhanced Oil Recovery (EOR) process currently being evaluated in industry and academia with first deployment beginning. A wettability modification is assumed to take place when decreasing the ionic strength. In this work we explore the effects of varying salinities from formation water down to very low salinity on brine permeability and on effluent composition. The following effects have been investigated: the presence and absence of oil in the core, the cation exchange capacity (CEC), mineral dissolution and cation stripping. The experimental component of this investigation consisted of continuous permeability measurements during flooding at various salinity steps and simultaneous collection of the effluent. The effluent was analyzed using Inductively Coupled Plasma (ICP elemental analysis). The CEC's of the rock exposed to the different salinities have also been measured. Scanning Electron Microscope (SEM) visual investigations have also been carried out.
During the flooding with several different brines, permeability variations were observed. The variation of the ionic composition of the effluent has allowed for:
identification and characterization of the temporary divalent cation stripping process
the framing of hypotheses about other possible mechanisms taking place in the core during LSF, such as:
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ion exchange between injected brine and the clays as the salinity decreased
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The role that CEC plays in the re-equilibration with the new salinity
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the CEC variation throughout the experiment at Sor
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mineral dissolution and clay deflocculation. The comprehensive suite of tools and techniques used here has given more insights into the mechanisms taking place when decreasing the ionic strength and their use can serve to improve the deployment of the technology, including the prevention of formation damage.
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