Rheological test apparatus and method using a helical screw rheometer

摘要

A rheological test apparatus and method using a helical screw rheometer. The screw in the rheometer is driven by a hydraulic motor controlled by a proportioning valve. A pressure transducer provides a pressure signal at the outlet of the rheometer, and a solenoid valve is used to close the outlet downstream from the pressure transducer. In a test, fluid is flowed into the rheometer. With the screw stopped and the discharge closed, a static pressure is measured by the pressure transducer, and a computer means resets this to a zero reference value. The screw in the rheometer is then rotated at a constant speed with the discharge closed, and the dynamic pressure at the outlet is measured by the pressure transducer. Because the static pressure was zeroed, the dynamic pressure value is substantially equal to the differential pressure across the rheometer. The test is repeated for different speeds. In an alternate embodiment, the speed of the rheometer is varied over a period of time, and a series of dynamic pressure values are obtained which are substantially equal to a series of differential pressures across the rheometer for the corresponding speeds in the speed range. In both methods, the computer calculates, in response to the differential pressure values and speeds, the n' and k' parameters of a shear rate versus shear stress relationship of the fluid. Using these parameters, predictions of friction pressure loss and bottom hole treating pressure during a well fracturing treatment may be generated.