Downhole fluid analysis methods for determining viscosity

A downhole tool comprising:

• a pressure sensor to measure a first pressure of formation fluid within a flowline during a first pressure phase of a sampling operation, a second pressure of the formation fluid within the flowline during a second pressure phase of the sampling operation, a third pressure during a third pressure phase of the sampling operation, and a fourth pressure during a fourth pressure phase of the sampling operation;
• a viscosity sensor to measure a first viscosity of the formation fluid within the flowline during the first pressure phase of the sampling operation, a second viscosity of the formation fluid within the flowline during the second pressure phase of the sampling operation, a third viscosity during the third pressure phase of the sampling operation, and a fourth viscosity during the fourth phase of the sampling operation;
• and
• a controller configured to execute instructions stored within the downhole tool to determine a pressure-viscosity profile based on the measured first, second, third, and fourth viscosities and the measured first, second, third and fourth pressures, wherein determining the pressure-viscosity profile comprises fitting a curve to the first, second, third, and fourth viscosities and pressures.

A downhole tool comprising:

• a pressure sensor to measure pressures of formation fluid within a flowline;
• a viscosity sensor to measure viscosities of the formation fluid within the flowline;
• and
• a controller configured to execute instructions stored within the downhole tool to:
• initiate a sampling operation with the downhole tool disposed in a wellbore;
• measure a first viscosity and a first pressure in the flowline during a pumping phase of the sampling operation;
• measure a second viscosity and a second pressure in the flowline during a sample chamber filling phase of the sampling operation;
• measure a third viscosity and a third pressure in the flowline during a pressure build-up phase of the sampling operation;
• measure a fourth viscosity and a fourth pressure in the flowline during a probe retraction phase of the sampling operation;
• determine a viscosity-pressure profile based on the measured first, second, third, and fourth viscosities and pressures;
• and
• display a graphical representation of the viscosity-pressure profile.