Abstract
The prediction of asphaltene precipitation is an important topic in petroleum industry. Reliable evaluation of the asphaltene stability requires representative samples and measurement using special high pressure equipment. Moreover, development project may involve many reservoirs with many different fluids. Even inside of a connected reservoir, the quality of the oil and the asphaltene can vary through a large scale and the investigation of each fluid in the representative conditions become very expensive and often impossible.
Many fast screening methods have been proposed so far. The De Boer’s diagram is one of the most useful methods. However, it takes into account only the properties of the hydrocarbon phase without any investigation on the asphaltene fraction : this method gives always pessimistic prediction of the risk of asphaltene precipitation. Other methods, colloidal instability index for example, are not consistent enough to be used for flow assurance issue.
Based on some relevant solubility properties of the asphaltene fractions, a new and easy way for screening asphaltene instability is proposed. Using PVT properties of the live oil and an easy asphaltene characterization procedure, this method allow limiting advanced investigation only to fluids which present a real risk of precipitation. The asphaltene characterization can be performed on dead oil samples.
If a precipitation risk is stated, additional tests, performed on pressurized representative samples or taking into account reorganization of asphaltenes from different fluids, will help to define the severity of the risk. For mitigation, a test set-up has been developed: it allows evaluating the efficiency of chemical additives to prevent plugging under flow conditions of fluids above the asphaltene precipitation threshold. Depending on the crude oil, the severity of the precipitation conditions, and the nature of the additive, the blocking of the capillary tube can be delayed or prevented.
