Role of Polar Species in Determining the Interfacial Tension of a Crude Oil/Water System

Interfacial tension (IFT) between crude oil and water is one of the critical properties that governs the multiphase flow in porous media. Measuring IFT in the laboratory is time-consuming and difficult, especially with live reservoir fluids. Tools and processes are unavailable to measure it downhole. Current reservoir simulators rely on empirical models to estimate the IFT. In general, these models overpredict IFT and do not account for the role of crude oil chemistry. The surface-active naphthenic acids (NAs) present in crude oil play a crucial role in governing IFT behavior at the oil/water interface and stabilizing in situ emulsions that pose operational challenges. Additionally, the NA concentration is challenging to determine without a wet-chemistry laboratory process. In this study, we used 22 crude oil samples from different fields to develop a model that can potentially be used for downhole IFT measurements. This research will help improve saturation height function modeling, enable more informed decisions on field development planning for newly drilled wells, and develop better production strategies with the older (or preexisting) ones. Several parameters were investigated related to the Gibbs-Langmuir model. The proposed model provides average universal parameters (Gamma(m) and K-L) related to the crude oil/water interface, enabling us to characterize the crude oil chemistry. Such a model can be used to account for the effect of acids on the crude oil interfacial tension. The acid concentration is used as an input parameter to better estimate the oil/water interfacial behavior. This model can potentially be used as a monitoring tool to avoid technical issues, such as in situ emulsification, corrosion, and scaling problems.

Automated summary

Interfacial tension (IFT) between crude oil and water is a critical property that affects multiphase flow in porous media. Measuring IFT in the laboratory is challenging, and tools for downhole measurement are currently unavailable. Existing reservoir simulators rely on empirical models that do not accurately account for crude oil chemistry. This study developed a potential model for downhole IFT measurement using crude oil samples from different fields. The model can improve saturation height function modeling, aid in field development planning and production strategies, and serve as a monitoring tool to prevent technical issues.