We demonstrate a gradient-index (GRIN) optofluidic waveguide using polydimethylsiloxane cured with a radial variation of temperature. The waveguide wraps the microfluidic channel and the GRIN profile localizes the light around it, making the device suitable for evanescent sensing applications. The fabricated waveguide shows good light confinement, with a propagation loss of 1.47 dB/cm at a wavelength of 632.8 nm.

Carbonate rock exhibits great diversity in composition, pore size, and surface wettability, all of which significantly affect oil recovery process. In this work, we studied the pore size distribution, porosity, and permeability of the rock sample from one of the Abu Dhabi offshore reservoirs. To characterize the rock sample, mercury intrusion porosimetry combined with microscopic techniques were used. A digital pore-throat network was reconstructed by processing x-ray images of the rock sample. In order to experimentally visualize liquid/solid interaction and flow patterns, a polydimethylsiloxane (PDMS) microfluidic device was fabricated with the same digital pore-throat network map. Both flooding experiment and numerical simulation were performed to quantify the permeability and multiphase flow behavior inside the rock. From the oil-water displacement experiment, irreducible oil trapped in dead-end pores and narrow throats can be clearly observed. Furthermore, the numerical Lattice Boltzaman (LB) simulation results show the influence of surface wettability on the oil trapping and saturation change. The absolute and relative permeability of oil-water system were calculated from the direct water flooding simulation results. Furthermore, a three multiphase flow was simulated and oil saturation was monitored in order to understand the mechanism of water-alternating-gas enhanced oil recovery. This paper provides a feasible solution, which takes advantage of the recently developed micromodel fabrication and simulation techniques, on systematic permeability characterization of heterogeneous carbonate rocks.

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