Physico-Chemical and Micromodel Investigation of Low-Tension Waterflooding in Tight Reservoirs

• Author / Creator

  Nwani, Benedicta

• The existing controversies in the exact mechanism responsible for improved oil recovery during low-tension water flooding in rocks have portrayed the chemical enhanced oil recovery technique to be risky, hence less exploited in the field.
  This study evaluates experimentally, the effect of brine ionic composition, salinity and surfactant type on improved oil recovery in five different rocks - Botucatu outcrop sandstone, Indiana limestone outcrop core, Silurian dolomite outcrop core, Slave point reservoir core, and Evie shale. Commercially available surfactants (Nonylphenol ethoxylate, Sodium Olefin Sulfonate, and Dodecyl Trimethyl Ammonium Bromide) at 1% surfactant concentration in Sodium chloride, Calcium Chloride, and Synthetic formation brines at varying salinities ranging from 0 ppm, and 200,000 ppm is used for this study.
  Initially, fluid-fluid analyses were conducted via phase behavior, oil-brine electrokinetic, and interfacial tension measurements to understand the effect of the varying components on the oil-brine system. Based on the observed trend from the fluid-fluid analyses, a new brine was designed to further reduce the oil-brine interfacial tension with the non-ionic surfactant. Also, rock-fluid studies were conducted via rock-brine electrokinetic measurements, single phase spontaneous imbibition tests and micromodel flooding with specially designed and fabricated homogeneous and fractured micromodel which are representative of the rocks studied. Based on the understanding of rock-brine electrokinetic interaction in the outcrop carbonate cores, a newly designed brine was prepared and evaluated for an increased wettability alteration potential with the slave point reservoir core. The Single-phase spontaneous imbibition and micromodel flooding experiments were conducted to determine the dominating mechanism involved in recovery and correlate the rock-brine electrokinetic results with porous media experiments.
  Results indicate that the non-ionic surfactant although not able to alter wettability favorably, can reduce interfacial tension better than the other two surfactants. The non-ionic surfactant in the newly designed brine reduced the interfacial tension better than the base case scenario in the original synthetic formation brine. It was also observed that the wettability alteration potential in the newly designed brine was better compared to the original synthetic formation brine in the slave point core which implies that a common trend exits in similar carbonate cores.
  
  Single-phase spontaneous imbibition experiments with the Silurian dolomite core showed that expansion of the electrical double layer (EDL), rock dissolution and multi-component ion exchange are responsible for favorable wettability alteration, with the EDL mechanism occurring first. For the Evie shale core, the illite content of the rock and pore connectivity could have a significant impact on the imbibition results which could further explain the unusual imbibition profile observed during imbibition.
  In less heterogeneous rocks such as sandstones, the homogenous micromodel flooding results show that ion effect dominates recovery compared to the interfacial tension values. Contrarily, for heterogeneous or fractured rocks such as carbonates, the interfacial tension reduction plays a dominant role in improved oil recovery, especially for surfactants that are not able to alter wettability favorably.
  This study adds to the body of knowledge for surfactant slug design in rocks, suggests the dominant oil recovery mechanism in the analyzed rocks and projects the possibility of sodium ions as potential determining ions.

• Subjects / Keywords

  • smart water
  • surfactants
  • carbonate rocks
  • low salinity water
  • Tight reservoirs
  • zeta potential
  • micromodel

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-pcd1-fp18

• License

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