Apparatus and method for analyzing well fluid sag

A method for measuring or analyzing dynamic sag in a fluid, said method comprising:

• providing a sample of said fluid in an elongated container inclined on a central pivotal axis;
• pressurizing said container and heating or chilling said container to simulate fluid environmental conditions;
• accommodating expansion and contraction effects of said pressure and temperature on said fluid in said container so that the center of mass of the fluid relative to said central pivotal axis is not changed due to said effects;
• imparting a controlled rate of shear to said fluid;
• monitoring the torque or moment about said central pivotal axis;
• detecting and measuring any change in said torque or moment over time;
• and
• relating said measurements to sag in the fluid.

A method for measuring or analyzing sag in a drilling fluid, said method comprising:

• providing a sample of said fluid in a elongated container with an inner, rotatable shear shaft and an annulus region in between for containing said fluid sample;
• coupling or engaging a rotator to said shaft for controllably rotating said shaft;
• immersing said container in temperature controlled pressurization fluid;
• inclining said continuously immersed container on a central pivotal axis with adjacent pistons to accommodate test fluid expansion and contraction due to any temperature adjustments and pressurization;
• rotating said shaft and imparting a controlled rate of shear to said fluid;
• detecting and measuring any change in moment about said pivotal axis over time;
• relating said measurements to quantify sag in said fluid.

A method for analyzing the dynamic sag phenomenon in a drilling fluid, or other solids bearing fluid, in a subterranean borehole, said method comprising:

• placing a sample of said fluid in an apparatus positioned on an incline with a pivotal support located at a central axis of said apparatus about which the apparatus can rotate or pivot;
• wherein the apparatus is associated with control circuitry and a self-integrating error accumulator that drives current such that the current adjusts to prevent said rotation about said pivot;
• applying pressure and adjusting temperature to approximate the pressure and temperature the fluid would encounter in said borehole;
• applying a controlled shear rate to said sample in said apparatus;
• monitoring and measuring the current at said pivot axis over time;
• and
• relating change in current to sag in said sample fluid.