Methods and apparatus for monitoring a property of a formation fluid

A method comprising:

• acquiring, in a downhole tool disposed in a borehole penetrating a subterranean formation, a sample of formation fluid from the formation;
• obtaining a first NMR measurement of the formation fluid sample using the downhole tool while the sample is in the downhole tool;
• using the first NMR measurement to determine a first viscosity value of the formation fluid sample in the downhole tool;
• providing heat energy to the formation fluid sample in the downhole tool;
• obtaining a second NMR measurement of the formation fluid sample using the downhole tool while the sample is in the downhole tool;
• using the second NMR measurement to determine a second viscosity value of the formation fluid sample in the downhole tool;
• and
• determining a relationship between a value indicative of an amount of energy provided to the formation fluid sample and viscosity of fluid in the formation based on at least the first and second viscosity values.

An apparatus for determining a parameter of a formation fluid, the apparatus configured for disposition in a borehole penetrating a subterranean formation, the apparatus comprising:

• a tool configured to be positioned in a borehole penetrating a subterranean formation, and further configured to make NMR measurements of a fluid sample obtained from the formation while the fluid sample is in the tool;
• a heating element configured to change a temperature associated with the formation fluid sample in the tool;
• and
• a controller coupled operatively with the tool and the heating element, wherein the controller is configured to determine a relationship between an amount of energy associated with changing the temperature of the formation fluid sample and a viscosity of the formation fluid sample.

A method to characterize a subterranean formation with a tool disposed in a borehole penetrating the subterranean formation, the method comprising:

• effecting a radial gradient of a characteristic of the formation;
• obtaining a first NMR measurement at a first selected location in the formation;
• obtaining a second NMR measurement at a second selected location in the formation, wherein at least one of the first selected location and the second selected location is located radially outward of a wall of the borehole;
• and
• using the first and second NMR measurements and the radial gradient of the characteristic to determine a relationship between NMR measurements and the characteristic of the formation.