Abstract
Acid emulsions as aqueous acid in oil emulsions are used widely as either acid delayed systems or to clean up formation damages. The stability of emulsified acid blends at room and elevated temperatures is a crucial factor for a successful job execution. To predict the stability and reactivity so far mainly indirect methods, such as visual inspections or conductivity measurements, are used in the industry. These methods are often inaccurate and subjective. They can also lead to a wrong interpretation of acid emulsion stabilities, especially at elevated temperatures. In this study we are presenting a new method of stability determination of acid emulsions by the detection of the droplet size through static light scattering. Static light scattering (or laser diffraction) is a widely used particle sizing technique for materials ranging from several nanometers up to several millimeters in size. This is the typical size range of emulsions. The technique by itself is well-established, allows rapid measurements, and does not need an external calibration. By using this method, we were able to correlate the droplet size of acid emulsions with their stability and to study the influence of different parameters such as solvent, surfactants or temperature. Only the change of the solvent (e.g., from xylene to diesel) can have a tremendous influence on the stability of a 28% hydrochloric acid emulsion. The study of acid emulsions was executed with different solvents, surfactants, acid strengths, and temperatures. Through the direct determination of the acid emulsion stability by measurement of the droplet size, we are able to predict the emulsion stability at elevated temperatures very accurately. This method is also suitable for such emulsions that possess remarkably high acid strengths.
