Variable diameter viscometer for evaluating well fluids

#This application is the National Stage of, and therefore claims the benefit of, International Application No. PCT/US2014/049273 filed on Jul. 31, 2014, entitled “VARIABLE DIAMETER VISCOMETER FOR EVALUATING WELL FLUIDS,” which was published in English under International Publication Number WO 2016/018405 on Feb. 4, 2016. The above application is commonly assigned with this National Stage application and is incorporated herein by reference in its entirety.

#This disclosure relates to evaluating well fluids, e.g., drilling fluids, production fluids, or other well fluids.

#Viscometers are used to measure rheological properties, e.g., viscosity, flow parameters, or other rheological properties, of fluids. A Couette viscometer can be operated to determine fluid viscosity based on a force required to turn an object in the fluid. Such a viscometer includes two co-axial cylinders (i.e., an inner cylinder and an outer cylinder) with a gap in between. A volume of the fluid to be tested is flowed in the gap and the two cylinders are rotated relative to each other. For example, the outer cylinder can be rotated at a predetermined speed while the inner cylinder is held stationary (or vice versa). The viscometer can measure the shear stress on the fluid as the outer cylinder rotates. A ratio of the shear stress to the shear rate, determined from the rotational speed of the outer cylinder, yields the viscosity of the fluid in the gap.

#FIG. 1 is a schematic diagram of a well system including a variable diameter viscometer.

#FIGS. 2A and 2B are schematic diagrams of a first implementation of the variable diameter viscometer.

#FIGS. 2C and 2D are schematic diagrams of a second implementation of implementation of the variable diameter viscometer.

#Like reference symbols in the various drawings indicate like elements.

#This disclosure describes a variable diameter viscometer for evaluating well fluids. In general, the viscometer includes a first portion and a second portion that is positioned adjacent to the first portion. The arrangement of the first and second portions results in a gap between the two portions. Rheological properties of fluids can be evaluated by flowing the fluid into the gap and then applying a shear on the fluid by moving the first portion and second portion relative to each other. The gap between the two portions of the viscometer described here can be varied without requiring that either of the two portions be removed or replaced. In some implementations, the gap can be varied during operation of the viscometer, e.g., while the two portions are moving relative to each other. The viscometer can be implemented to evaluate the viscosity of a well fluid that includes solid particles of different sizes. The viscometer can also be implemented to evaluate rheological properties of a continuous stream of fluid. For example, the fluid can continuously be flowed through the gap between the two portions. Different samples of the fluid that flow through the viscometer at different time instants can have different viscosities, e.g., due to the absence or presence of different sizes or volume fractions (or both) of solid particles (or other materials intentionally added or not) in the different samples. The viscometer can be implemented to continuously and in real-time adjust the gap between the two moving portions to determine the different viscosities of the different samples without requiring removal or replacement of one of the portions to adjust the gap to accommodate each sample.

#Implementations of the viscometer described here can enable evaluating rheological properties of fluids, e.g., well fluids or other fluids, with a wide range of viscosities without changing the viscometer's torsion spring. In addition, varying the gap in the viscometer can allow applying different shear rates to the fluids while maintaining a constant relative velocity between the two moving portions. For example, slurries with lost circulation material (LCM) that are sometimes too large to be evaluated using field viscometers can be evaluated using the viscometer described here. In another example, the viscometer described here can be implemented with components that can easily be removed from materials such as cements or resins after the materials have completely reacted or set up. In another example implementation, the viscometer can measure the viscosity of cutting laden drilling fluids such as those at a well flow line. The viscometer can be implemented to qualitatively approximate large solids volume content and size with materials such as cuttings, e.g., by coupling sensors, such as strain sensors, LVDT, RVDT, optical, ultrasonic, hall effect or other sensors, with the viscometer. The variable configuration allows the relative size of the two portions and thus capabilities to be changed in environmental conditions where a complete shut-down of an operation may be required for configuration changes in zones such as Class I Div 1. Velocity of one or more members may be varied to provide a shear rate range as well. In this rheometer design, both the gap and the relative velocity may be varied simultaneously to achieve a constant shear rate. In some fluids, this may be used to indicate the degree of shear thinning of the test fluid.