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Zwitterionic Surfactant for EOR in Tight Carbonate Reservoir: Physico-Chemical Interaction and Microfluidic Study
- Author / Creator
- Zhang, Zifan
Recently, during surfactant aided recovery processes for unconventional reservoirs, carboxybetaine based zwitterionic surfactants (CnDmCB) have attracted attention due to their good tolerance to high saline produced water, remarkable water solubility, and ultra-low interfacial tension (IFT) at extremely low concentrations. The objective of this work is to study the effect of CnDmCB and CnDmCB/co-solvents formulations on fluid-fluid and fluid-rock interactions in limestone and tight carbonate reservoirs at varying salinities. More specifically, these interactions correspond to IFT and zeta potential. Additionally, a microfluidic study was conducted to provide insight into the dominating mechanism for tight carbonate reservoirs using different types of surfactants.
The CnDmCB was prepared using different carbon chain lengths of 12, 14, 16, 18 of tertiary amines and confirmed by 1H NMR. In turn, the CnDmCB/co-solvent formulation consists of the previously described formulation plus four small molecular alcohols including 1-butanol, 1-pentanol, isoamyl, 1-octanol with fixed surfactant-to-co-solvent ratio. IFT measurements were initially conducted using the four mentioned surfactants under various concentrations in simulated formation water at varying salinities. Afterwards, the experiment was rerun using surfactant that exhibited the best performance in addition to the co-solvents. Zeta potential test was performed using three surfactants and two surfactants/co-solvents at a wide range of salinities for both the brine/oil and brine/rock systems. These results were compared to the original systems without any additions. Micromodel flood test was conducted in both the water-wet and oil-wet homogeneous porous media as well as the heterogeneous one to visualize the oil displacement pattern of flooding process based on the results of bulk experiments.
Results show that the IFT of CnDmCB reduces with the increasing carbon chain length except for C18DmCB due to its poor solubilization in the simulated formation water (SFW). The lowest IFT is up to 4.81*10-3 mN/m magnitude for 0.025 wt% C16DmCB at 100,000 ppm, contributing to the enhanced oil recovery. The additive co-solvents to C16DmCB have adverse effects in terms of IFT, and the magnitude differs from the alkyl chain lengths and structures. The zeta potential of oil droplets remains negative in SFW over the salinity range covered except the salinity of 200,000 ppm. The limestone surface is negatively charged at low salinities after which it becomes positive from 25,000 ppm. However, the surface charge of tight carbonate rock is positive overall due to the extra magnesium ions. Charge conversion from opposite to the same polarity takes place with the presence of all the tested surfactants indicating the potential for altering wettability. CnDmCB is found not applicable at the low salinity range with the limestone particles. However, the addition of co-solvents to CnDmCB may improve the magnitude of zeta potential among which C16DmCB/1-butanol is suggested. C16DmCB can be used alone considering economic applicability in most other cases with the limestone and tight carbonate samples. In the water-wet homogeneous micromodel, there exists a correlation between ultra-low IFT and higher tertiary oil recovery by the addition of CnDmCB. However, wettability alteration dominates the early stage while IFT reduction plays an essential role during the late time in the oil-wet porous media.
- Graduation date
- Fall 2019
- Type of Item
- Master of Science
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