Effect of Brine Dilution and Surfactant Concentration on Spreading and Wettability

摘要

The interfacial phenomena of spreading and adhesion of fluidson rock surfaces have serious implications because of theirimpact on production strategy and oil recovery. The presentstudy reports new experimental data on the effect of brinedilution and surfactant addition on spreading and adhesionbehavior of Yates crude oil on dolomite surfaces. Spreadingand adhesion have been characterized through measurementsof oil-water interfacial tension (IFT) and dynamic (wateradvancingand receding) contact angles. The interfacialtension was measured using Computerized AxisymmetricDrop Shape Analysis (CADSA) Technique, which wascalibrated against the well-known du Nuoy Ring Technique.The Dual-Drop-Dual-Crystal (DDDC) Technique has beenused to measure dynamic contact angles.In order to study the effect of brine dilution, Yates reservoirbrine was mixed with deionized water (DIW) in variousproportions. For each diluted brine, crude oil-water IFT,water-advancing and receding contact angles were measured.The oil-water IFT initially decreased as the volume percent ofbrine in the mixture decreased. However, the IFT increasedwith further dilution of reservoir brine with DIW. Adecreasing trend was observed in the behavior of wateradvancingcontact angle with brine dilution. This indicatedthat the initial oil-wet nature of the system was changed tointermediate-wettability simply by diluting the reservoir brine.However, a strange behavior of spreading of crude oil dropagainst brine on the dolomite surface (with large waterrecedingcontact angles) was observed at certain brinedilutions. This spreading of crude oil appears to be related tointerfacial tension in a manner similar to Zisman'sobservations in solid-liquid-vapor systems.The use of surfactants to enhance oil recovery throughreduction in IFT is well known in the industry. However, this study examines the capability of certain surfactants to alterwettability in addition to reducing IFT. For the Yates reservoirrock-fluids system, an Ethoxy Alcohol surfactant altered thestrongly oil-wet nature (advancing angle of 158o) to water-wet(advancing angle of 39o) at a concentration of 3500 ppm.While the DDDC technique yielded significant changes inwettability due to surfactant addition, the Wilhelmy PlateTechnique remained insensitive throughout the range ofsurfactant concentrations. The practical significance of thisstudy is that it identifies two simple modes through surfactantaddition and brine dilution to alter wettability to minimizecapillary trapping of oil.