Standards Development

Scope

This document specifies a spinning drop method for measuring the interfacial tension between surfactant-based chemical flooding system and oil, especially for interfacial tension less than 10^-2 mN/m.

This document is applicable to surfactant-polymer (SP), alkali/salt-surfactant (AS), and alkali/saltsurfactant- polymer (ASP) flooding systems.

This document includes sections on principles, reagents and materials, instruments, procedures.

Purpose

Surfactant-based chemical flooding technology is one of the important methods to enhance oil recovery, especially for the displacement of residual oil in reservoirs after water flooding. Many field applications have been carried out in regions such as China, North America, South America, Asia- Pacific, and the Middle East. Daqing Oilfield in China is the world’s largest application base for ASP flooding, with a cumulative recoverable geological reserve of 306 million tons. Enhanced oil recovery by ASP flooding is more than 18% OOIP over that from water flooding with an annual oil production of over 4 million tons. Oil fields such as Cambridge in the United States, La Salina in Venezuela, Mangala in India, and AlKhalta in Oman have also increased the recovery by more than 18% OOIP. In Kuwait’s SAMA oil field, the residual oil saturation was reduced to 60% by ASP injection.

Reducing the interfacial tension between water and oil is the core mechanism for enhancing oil recovery by surfactant-based chemical flooding. According to the classical capillary number theory, the capillary number is inversely proportional to the interfacial tension, and the residual oil saturation decreases significantly with the increase of the capillary number. Both laboratory experimental studies and field application have confirmed that the reduction of interfacial tension has a significant impact on oil displacement efficiency. The capillary number during typical later waterflooding is in the range of 10^-7 to 10^-6. By reducing the oil-water interfacial tension to below 1×10^-2 mN/m (ultra-low) through the action of the flooding system, the capillary number could reach 10^-3 to 10^-2, which results in a remarkable reduction of residual oil saturation. Therefore, interfacial tension is an important parameter for surfactant-based chemical flooding system.

Phase behavior experiments can provide a complete picture of the phase behavior between the flooding system and oil (such as the type and formation area of microemulsions). Based on the rules of phase behavior, parameters such as surfactant concentration and salt concentration can be optimized. Typically, the interfacial tension of Winsor III type microemulsion can reach ultra-low levels. For flooding systems that cannot form Winsor III type microemulsion, the system needs to be screened based on interfacial tension. Using a simple and direct method to quickly pre-select systems that can achieve ultra-low interfacial tension, and then conducting in-depth studies on phase behavior and comprehensive performance, can significantly shorten the research time and optimization cycle of the surfactant-based chemical flooding system, improving work efficiency.

Currently, the methods for directly measuring interfacial tension include drop volume method, ring method, Wilhelmy plate method, and spinning drop method. The drop volume method can accurately measure interfacial tensions above 1 mN/m. When the interfacial tension reaches ultra-low levels, the deformation of the liquid drop is minimal, leading to significant errors. This method is mainly used in the pharmaceutical, cosmetic, and food emulsification industries. The ring method involves immersing a metal ring into a liquid and measuring the maximum force required to detach the ring from the liquid surface using a sensor. It is also only suitable for interfacial tensions above 1 mN/m and is primarily used in daily chemical products, pharmaceuticals, and water treatment. The Wilhelmy plate method is suitable for interfacial tensions above 10^-1 mN/m and is mainly used in the development of food and coating materials. The spinning drop method can accurately measure interfacial tensions below 10^-2 mN/m. It has the advantages of short duration, high accuracy, and the ability to continuously record dynamic changes. This method is particularly suitable for the development of chemical flooding formulations and the field of nanomaterial. Countries such as the United States, Canada, Germany, Norway, the United Kingdom, the Netherlands, France, and China have adopted the spinning drop method in the field of EOR. It provides core data to optimize oil displacement formulations and evaluate the compatibility of surfactant-based chemical flooding systems with reservoirs.

Establishment of an international standard for measuring ultra-low interfacial tension using the spinning drop method has the following significance: 1. It provides an internationally recognized experimental method to determine the interfacial tension of surfactant-based chemical flooding systems; 2. It can quickly screen flooding systems and shorten the formulation optimization cycle; 3. It offers important parameters for optimizing flooding systems, enabling the systems to achieve optimal performance. This is of great significance for ensuring the effectiveness of surfactant-based chemical flooding development and helps to realize the sustainable use of resources; 4. It forms a unified testing standard to facilitate quality supervision; 5. It lays the foundation for global chemical flooding industry communication and cooperation, promoting international technology sharing.