Method and apparatus for determining a downhole fluid sample volume

A formation test tool for obtaining a downhole fluid sample from a formation of interest and returning the fluid sample to the surface of a well, comprising:

• a cylinder forming a fluid sample chamber therein;
• a piston sealingly movable within the cylinder and separating the fluid sample from a cushioning fluid;
• a fluid line fluidly connecting the formation of interest to the fluid sample chamber;
• a valve controlling fluid flow along the fluid line;
• and
• a sensor for detecting a position of the piston within the cylinder while at the surface of the well.

A method of determining the volume of the downhole fluid sample within a formation test tool at the surface, comprising:

• providing a cylinder forming a fluid sample chamber therein;
• providing a piston sealingly movable within the cylinder and separating the fluid sample from a cushioning fluid;
• fluidly connecting the formation of interest to the fluid sample chamber;
• controlling fluid flow from the formation of interest to the cylinder;
• and
• measuring a position of the piston within the cylinder at the surface to provide an indication of the volume of the fluid sample within the cylinder.