Determining Formation Fluid Variation With Pressure

A method, comprising:

• operating a downhole tool within a wellbore adjacent a subterranean formation to pump fluid from the subterranean formation into the downhole tool while obtaining a series of fluid property measurements pertaining to the pumped fluid over a period of time, wherein the downhole tool is in communication with surface equipment located at a wellsite surface associated with the wellbore;
• and
• operating at least one of the downhole tool and the surface equipment to:
• estimate a first relationship between compressibility and pressure of the pumped fluid based on the series of fluid property measurements;
• measure a momentary optical density (OD) of the pumped fluid;
• and
• correcting the measured momentary OD based on the estimated first relationship.

A system, comprising:

• surface equipment located at a wellsite surface associated with a wellbore extending into a subterranean formation;
• a downhole tool operable within the wellbore to:
• communicate with the surface equipment;
• pump fluid from the subterranean formation into the downhole tool;
• and
• obtain a series of fluid property measurements pertaining to the pumped fluid;
• and
• at least one processor comprised by at least one of the surface equipment and the downhole tool, wherein the at least one processor is operable to:
• estimate a first relationship between compressibility and pressure of the pumped fluid based on the series of fluid property measurements;
• estimate a momentary formation volume factor (FVF) of the pumped fluid;
• estimate a second relationship between FVF and pressure of the pumped fluid based on the estimated first relationship and the estimated momentary FVF;
• measure a momentary optical density (OD) of the pumped fluid;
• and
• correcting the measured momentary OD based on the estimated first relationship.