Passive Wireless Pressure Gradient Measurement System for Fluid Flow Analysis.

Using distributed MEMS pressure sensors to measure small flow rates in high resistance fluidic channels is fraught with challenges far beyond the performance of the pressure sensing element. In a typical core-flood experiment, which may last several months, flow-induced pressure gradients are generated in porous rock core samples wrapped in a polymer sheath. Measuring these pressure gradients along the flow path requires high resolution pressure measurement while contending with difficult test conditions such as large bias pressures (up to 20 bar) and temperatures (up to 125 °C), as well as the presence of corrosive fluids. This work is directed at a system for using passive wireless inductive-capacitive (LC) pressure sensors that are distributed along the flow path to measure the pressure gradient. The sensors are wirelessly interrogated with readout electronics placed exterior to the polymer sheath for continuous monitoring of experiments. Using microfabricated pressure sensors that are smaller than ø15 × 3.0 mm3, an LC sensor design model for minimizing pressure resolution, accounting for sensor packaging and environmental artifacts is investigated and experimentally validated. A test setup, built to provide fluid-flow pressure differentials to LC sensors with conditions that mimic placement of the sensors within the wall of the sheath, is used to test the system. Experimental results show the microsystem operating over full-scale pressure range of 20,700 mbar and temperatures up to 125 °C, while achieving pressure resolution of <1 mbar, and resolving gradients of 10-30 mL/min, which are typical in core-flood experiments.

Ultra-stable CO2-in-water foam by generating switchable Janus nanoparticles in-situ.

HYPOTHESIS: The surface of silica nanoparticles (NP) may be covalently grafted with two amino ligands to balance colloidal stability and interfacial activity via formation of in situ Janus particles. The modified NP may be combined with a like-charged diamine surfactant to create ultra-stable CO2 foam at low NP concentrations. EXPERIMENTS: The NP colloidal stability was measured up to 80 °C in 230 g/L TDS brine with dynamic light scattering. The NP surface was characterized using zeta potential, TEM, TGA, conductometric and potentiometric titrations, NMR and interfacial measurement. CO2/brine foam was generated at 60-80 °C and 15 MPa and apparent viscosity was measured vs foam quality. The foam stability was measured in-situ with an optical microscope. FINDINGS: Upon adding only 0.1 wt% NP, ultra-stable CO2 foam was observed at 60 °C with a bubble coarsening rate 3 orders of magnitude lower than with surfactant alone. Foam bubbles were spherical with NP present, but became polyhedral for the much less stable surfactant-only foams. For this novel like-charged surfactant-NP system, the limited surfactant adsorption on the NP resulted in NP stabilized CO2 foam, while maintaining NP colloidal stability at high surfactant concentrations and high salinity, providing a new perspective of NP-surfactant design.