Rheological and stability study of water-in-crude oil emulsions

Abstract

The formation of crude oil emulsion is a prevalent oilfield problem that can cause significant flow assurance issues during oil production, treatment and transportation. When they occur, emulsion problems are very difficult to solve and can lead to numerous operational problems like; creating high pressure drops in pipes and/or flowlines, production of off-specification crude oil and tripping of separation equipment. These emulsions can be very stable as a result of the presence of polar compounds, such as asphaltenes and resins, that play the role of natural surfactants and also because of the occurrence of many types of fine solids that can form resistant films at the crude oil/water interface. Solid particles also play significant roles in stabilizing emulsions. The water produced during oil production is either produced as free water, and so it will settle out fairly quickly, or the water may be combined with oil in the form of emulsions. This is more prevalent when producing oil from mature oilfields, where water production is relatively large. Under standard oilfield conditions the most common form of emulsion is a water-in-oil emulsion; a dispersion of water droplets in oil. In this work, the authors studied the consequence of different water-cuts and the presence of an emulsifier on the stability of water-in-oil emulsions. The rheological properties of W/O emulsions with different water cuts (10-50 v/v %) at different temperatures (25°C – 60°C) were studied. Rotational rheology and stability of the emulsions were studied on emulsions aged for 30 days. Generally, the results revealed that the presence of an emulsifying agent, difference in water content, shear rate and temperature significantly affect emulsion stability and rheological properties