The emulsion that is mixed with returned acidizing fluids and crude oil has strong stability, which may have a great influence on the crude oil dehydration and the safe operation of crude setting tank. The effects of temperature, demulsifier dosage, pH value, viscosity reducer dosage on the viscosity of emulsion and demulsification performance are studied, and the microscopic changes of emulsion at different times are observed. It is indicated by experiments that the viscosity of emulsion mixed with returned acidizing fluids and crude oil declines significantly firstly and then decreases gradually with the increasing temperature; when the temperature is lower than 40℃, the emulsion has stronger stability, however, between the temperature of 50-60℃, the dehydration rate does not increase significantly with the increasing temperature. So it is concluded that the best demulsification temperature is 50℃. It is also found that emulsion viscosity could be decreased by adding demulsifier, but not significantly; the more the dosage of demulsifier is, the better the demulsification performance is, and the dehydration rate is not remarkably increased when the demulsifier dosage is more than 150 mg/L. So it is concluded that the best demulsifier dosage is 150 mg/L. Moreover, it is beneficial for demulsification performance to adjust the returned acidizing fluids pH value to 6.0-7.0. With the increasing pH value, the oil water interface grows suddenly angular and the structure of crude oil after dewatering is more tight. Finally, the dehydrating speed is improved obviously by using viscosity reducer. These conclusions can be used as references to the demulsification and dehydration of emulsion that is flowed back early after the implementation of acidification.

returned acidizing fluids  /  emulsion  /  demulsification  /  dehydration rate