Methods for determining rheological quantities of a drilling fluid using apparent viscosity

摘要

Rheological quantities, such as shear stress, can sometimes be difficult to determine under extreme temperature and pressure conditions. In contrast, the relative rheology of a fluid can often be readily determined over a range of temperature and pressure conditions. The relative rheology can then be used to scale a rheological quantity of the fluid to a given temperature and pressure condition. Methods for scaling a rheological quantity can comprise: measuring an apparent viscosity of a drilling fluid at first, second and third reference temperature and pressure conditions; determining a rate of change in apparent viscosity with respect to temperature at a substantially equal pressure; determining a rate of change in apparent viscosity with respect to pressure at a substantially equal temperature; and scaling a rheological quantity from an initial set of temperature and pressure conditions to a final set of temperature and pressure conditions using the rates of change.

主权项

1. A method comprising:
measuring an apparent viscosity of a drilling fluid at a first set of reference conditions comprising a first reference temperature and a first reference pressure, at a second set of reference conditions comprising a second reference temperature and a second reference pressure, and at a third set of reference conditions comprising a third reference temperature and a third reference pressure; wherein at least two of the reference temperatures are substantially equal to one another and at least two of the reference pressures are substantially equal to one another, the reference temperatures and the reference pressures defining a calibration range; determining a rate of change in apparent viscosity with respect to temperature between two of the sets of reference conditions in which the reference pressures are substantially equal; determining a rate of change in apparent viscosity with respect to pressure between two of the sets of reference conditions in which the reference temperatures are substantially equal; and scaling a rheological quantity measured at an initial set of temperature and pressure conditions within the calibration range to a final set of temperature and pressure conditions within the calibration range, the scaling being calculated based upon the rate of change in apparent viscosity with respect to temperature and the rate of change in apparent viscosity with respect to pressure, thereby determining a calculated rheological quantity.