Method and system for determining asphaltene onset pressure using a using depressurization and pressurization

A system for determining asphaltene onset pressure of a formation fluid, the system comprising:

• a source for generating light that is transmitted through a sample of the formation fluid;
• a detector for detecting light transmitted through the formation fluid sample;
• a pressure control unit configured to vary pressure of the formation fluid sample;
• and
• a controller configured to determine the asphaltene onset pressure of the formation fluid using (i) intensity of the transmitted light detected during each depressurization of the formation fluid sample and (ii) intensity of the transmitted light at a plurality of fixed pressures.

A method for determining asphaltene onset pressure of a formation fluid, the method comprising:

• (a) transmitting light through a sample of the formation fluid;
• (b) decreasing pressure of the formation fluid sample;
• (c) detecting intensity of the transmitted light during depressurization;
• (d) identifying a change in intensity of the transmitted light during depressurization;
• (e) increasing pressure of the formation fluid sample to a fixed pressure;
• (f) detecting intensity of the transmitted light at the fixed pressure;
• (g) repeating processes (e) to (f) for a plurality of different fixed pressures;
• and
• (h) determining the asphaltene onset pressure of the fluid sample using (i) the intensity of the transmitted light during depressurization and (ii) the intensity of the transmitted light at each of the different fixed pressures.

A method for detecting asphaltene onset of a formation fluid, the method comprising:

• (a) transmitting light through a sample of the formation fluid;
• (b) detecting intensity of the transmitted light while decreasing pressure of the formation fluid sample;
• (c) detecting intensity of the transmitted light while increasing pressure of the formation fluid sample;
• and
• (d) detecting asphaltene onset within the sample by identifying a difference in intensity between transmitted light during process (b) and transmitted light during process (c).