Abstract
AbstractEnzymatically induced calcite precipitation (EICP) in porous media can be used as an engineering option to achieve precipitation in the pore space, for example, aiming at a targeted sealing of existing flow paths. This is accomplished through a porosity and consequent permeability alteration. A major source of uncertainty in modeling EICP is in the quantitative description of permeability alteration due to precipitation. This report presents methods for investigating experimentally the time‐resolved effects of growing precipitates on porosity and permeability on the pore scale, in a poly‐di‐methyl‐siloxane microfluidic flow cell. These methods include the design and production of the microfluidic cells, the preparation and usage of the chemical solutions, the injection strategy, and the monitoring of pressure drops for given fluxes for the determination of permeability. EICP imaging methods are explained, including optical microscopy and X‐ray microcomputed tomography (XRCT), and the corresponding image processing and analysis. We present and discuss a new experimental procedure using a microfluidic cell, as well as the general perspectives for further experimental and numerical simulation studies on induced calcite precipitation. The results of this study show the enormous benefits and insights achieved by combining both light microscopy and XRCT with hydraulic measurements in microfluidic chips. This allows for a quantitative analysis of the evolution of precipitates with respect to their size and shape, while monitoring their influence on permeability. We consider this to be an improvement of the existing methods in the literature regarding the interpretation of recorded data (pressure, flux, and visualization) during pore morphology alteration.
Highlights
Enzymatically induced calcite precipitation (EICP) in porous media can be used as an engineering option to achieve precipitation in the pore space, for example, aiming at a targeted sealing of existing flow paths
The results of this study show the enormous benefits and insights achieved by combining both light microscopy and X-ray microcomputed tomography (XRCT) with hydraulic measurements in microfluidic chips
EICP as we employ it here, relies on the dissociation of urea into carbon dioxide and ammonium catalyzed by the enzyme urease, which is extracted from jack-bean meal (JBM)
Summary
Induced calcite precipitation is an engineering option which can be employed for a targeted sealing of flow paths in the subsurface as it might be necessary in geological gas storage in the presence of conductive faults (Ebigbo et al, 2010; Hommel et al, 2013; Phillips, Gerlach, et al, 2013; Phillips, Lauchnor, et al, 2013), for creating barriers for groundwater and containment of subsurface contamination (Cuthbert et al, 2013), and for soil stabilization and improvement of the mechanical soil properties (Hamdan & Kavazanjian, 2016; van Paassen et al, 2010; Wiffin et al, 2007). One of them is referred to as enzymatically induced calcite precipitation (EICP). In circumneutral environments regarding the pH value, ammonium (NH 4) and bicarbonate are the dominant products of hydrolysis, see Equation 1 (Mitchell et al, 2019). According to van Paassen (2009), the release of a proton (H+) during the calcium carbonate precipitation buffers the production of hydroxide during the hydrolysis, see Equation 2. On the pore scale, precipitated calcium carbonate leads to changes in pore morphology, and on a larger scale, after averaging, this corresponds to changes in the effective quantities porosity and permeability, WEINHARDT ET AL
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