H024-01
Experimental Microfluidics and Computational Studies of Precipitation and Dissolution
Monday, 7 December 2020: 19:00
Virtual
James W Carey1, Joaquin Jimenez-Martinez2, Phong Nguyen3, Jeffrey Hyman4, Yu Chen4 and George Jr. Guthrie5, (1)Los Alamos National Laboratory, Earth & Environmental Sciences, Los Alamos, NM, United States, (2)ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland, (3)Los Alamos National Laboratory, Earth & Environmental Science Group, Los Alamos, NM, United States, (4)Los Alamos National Laboratory, Los Alamos, NM, United States, (5)Los Alamos National Laboratory, Earth & Environmental Scienc, Los Alamos, NM, United States
Abstract:
Direct observations of dissolution and precipitation in geomaterials are important to constraining reactive transport models. In this paper, we present results from two microfluidics studies conducted in limestone and Portland cement. The objective was to map and explain dissolution and precipitation processes due to single- or multi-phase flow of CO
2 and water. Tabular specimens of rock and cement were etched to form reactive channels, and experiments were performed under constant flow conditions at 8 MPa CO
2 pressure. Results were analyzed by profilometry comparing initial and final channel geometries. In experiments on limestone, we studied the effects of multi-phase flow. The channel system consisted of an inlet that branched at a single point into 4 curved sub-channels with widths of 250, 500, 750 and 1000 µm and a common depth of 150 µm along with a 1000-µm wide dead-end channel. Single-phase flow resulted in preferential dissolution characteristic of wormhole formation. Surprisingly, multiphase flow showed homogeneous dissolution. We conducted multiphase lattice Boltzmann simulations on the full 3D geometry of the channels demonstrating that homogenization was induced by competition between flow of supercritical CO
2 bubbles and water among the channels. The presence of bubbles also caused limited flow into the dead-end channels explaining observations of calcite precipitation.
Experiments on Portland cement were designed to investigate the competition between dissolution that opens and precipitation that closes flow channels. Single-phase, CO2-saturated water experiments were performed in a single, serpentine channel at flow rates between 1 and 20 µL/min. We investigated channel dimensions of 250x200, 500x415, and 1000x400 µm all with 100 mm length. Dissolution dominated the entire channel length in the high flow-rate experiments and the inlet region of the low flow-rate experiments. However, precipitation quantities increased along the length of the channels in the low flow-rate experiments showing a transition from opening to closing conditions as a function of channel hydraulic diameter and flow rate. The results were consistent with previous reactive transport models demonstrating that self-sealing occurs in fractured Portland cement during flow of CO2-saturated water.
