High-pressure linear viscoelasticity measurements

Date
2018
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Complex fluids from biological systems to polymeric solutions and gels experience elevated pressures due to environmental and processing conditions, which may impact the fluid performance. Tunable pressure-dependent fluid behavior is desirable for oilfield applications to optimize hydrocarbon recovery. Oilfield fluids are used to help transport and suspend solids, reduce friction pressure, and prevent fluid loss. Key to these fluid performance metrics is the fluid rheology. Depending upon the composition and flow conditions, the fluid can behave as a purely viscous or viscoelastic fluid. By selecting the composition, the flow properties can be optimized for specific functions, such as, suspending proppants to keep fractures open or retaining fluid downhole. ☐ High-pressure measurements may be performed using falling body, pressure-driven, and rotational devices. Falling body rheometers use a stationary object in a moving fluid or a stationary fluid with a mobile object to obtain viscosity measurements. Pressure-driven devices force a fluid through a capillary and obtain pressure drop and volumetric flow rate to obtain the viscosity. These techniques are restricted in the material properties that may be obtained and their application to non-Newtonian fluids. Rotational rheometers apply a shear or oscillatory stress or strain to the fluid to obtain viscoelastic properties, however, this technique is often pressure-limited. Overall, high-pressure viscoelastic measurements can be challenging for mechanical rheometers. ☐ To address these shortcomings, a passive microrheology experiment has been designed and validated to measure the linear viscoelasticity of complex fluids at high pressures. The apparatus incorporates a steel alloy sample chamber with dual sapphire windows into a simple diffusing-wave spectroscopy (light-scattering) device and is capable of both transmission and backscattering geometries. The measured light intensity correlation from the Brownian motion of polystyrene probe particles dispersed in the sample is interpreted using the Generalized Stokes-Einstein Relation to determine the material linear viscoelasticity. This high-pressure microrheology instrument is validated by measuring the viscosity change of water and 1-propanol over pressures from 0 to 172.4 MPag at ambient temperature. ☐ Complimentary mechanical and microrheology measurements are performed at ambient pressure on stimulation fluids containing a crosslinked guar gum biopolymer before the measurement is performed at elevated pressures. We investigate the effect of crosslinker density on rheological properties at frequencies up to 1 MHz and pressures of 200 MPag, expanding the accessible range of experimental conditions beyond those of existing rheological measurement techniques.
Description
Keywords
Applied sciences, Diffusing wave spectroscopy, High-pressure, Microrheology
Citation