Determining dew precipitation and onset pressure in oilfield retrograde condensate

A method for detecting dew precipitation in a sample of formation fluid located downhole in an oilfield reservoir, comprising:

• (a) illuminating the fluid sample downhole with fluorescence excitation light at a first excitation wavelength;
• (b) measuring fluorescence intensity emitted from the fluid sample under reduced pressure in a fluid sample cell to produce a measured intensity value;
• and
• (c) detecting dew precipitation when the measured intensity value is greater than a reference intensity value.

A tool for detecting dew precipitation in a fluid sample located downhole in an oilfield reservoir, comprising:

• a tool body including a fluid sample cell adapted to take a sample of formation fluid downhole in the oilfield reservoir;
• means for isolating a sample of formation fluid downhole;
• means for illuminating the sample downhole with fluorescence excitation light;
• means for repeatedly reducing pressure on the sample and measuring at least one characteristic of fluorescence emission from the sample;
• and
• means for detecting dew precipitation when a change is detected in a parameter that is a function of the at least one characteristic of fluorescence emission.

A tool for detecting dew precipitation in a fluid sample located downhole in an oilfield reservoir, comprising:

• a tool body including a fluid sample cell adapted to take a sample of formation fluid downhole in the oilfield reservoir;
• means for illuminating the fluid sample downhole with fluorescence excitation light at a first excitation wavelength;
• means for measuring fluorescence intensity emitted from the fluid sample under reduced pressure in a fluid sample cell to produce a measured intensity value;
• and
• means for detecting dew precipitation when the measured intensity value is greater than a reference intensity value.