The concentrations of nanoparticles present in colloidal dispersions are usually measured and given in mass concentration (e.g. mg/mL), and number concentrations can only be obtained by making assumptions about nanoparticle size and morphology. Additionally traditional nanoparticle concentration measures are not very sensitive, and only the presence/absence of millions/billions of particles occurring together can be obtained. Here, we describe a method, which not only intrinsically results in number concentrations, but is also sensitive enough to count individual nanoparticles, one by one. To make this possible, the sensitivity of the polymerase chain reaction (PCR) was combined with a binary (=0/1, yes/no) measurement arrangement, binomial statistics and DNA comprising monodisperse silica nanoparticles. With this method, individual tagged particles in the range of 60-250 nm could be detected and counted in drinking water in absolute number, utilizing a standard qPCR device within 1.5 h of measurement time. For comparison, the method was validated with single particle inductively coupled plasma mass spectrometry (sp-ICPMS).

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In this study, we introduce a stochastic method to delineate the mineral effective surface area (ESA) evolution during a recycling reactive flow-through transport experiment on a sandstone under geologic reservoir conditions, with a focus on the dissolution of its dolomite cement, Ca 1.05 Mg 0.75 Fe 0.2 (CO 3 ) 2 . CO 2 -enriched brine was circulated through this sandstone specimen for 137 cycles (∼270 h) to examine the evolution of in situ hydraulic properties and CO 2enriched brine−dolomite geochemical reactions. The bulk permeability of the sandstone specimen decreased from 356 mD before the reaction to 139 mD after the reaction, while porosity increased from 21.9 to 23.2% due to a solid volume loss of 0.25 mL. Chemical analyses on experimental effluents during the first cycle yielded a dolomite reactivity of ∼2.45 mmol m −3 s −1 , a corresponding sampleaveraged ESA of ∼8.86 × 10 −4 m 2 /g, and an ESA coefficient of 1.36 × 10 −2 , indicating limited participation of the physically exposed mineral surface area. As the dissolution reaction progressed, the ESA is observed to first increase and then decrease. This change in ESA can be qualitatively reproduced employing scanning electron microscopy-image-based stochastic analyses on dolomite dissolution. These results provide a new approach to analyze and upscale the ESA during geochemical reactions, which are involved in a wide range of geoengineering operations.

Coupled thermal-hydrological-mechanical-chemical (THMC) processes can significantly impact the long-term evolution of reservoir permeability, associated with geothermal energy extraction (

We present flow‐through experiments to delineate the processes involved in permeability changes driven by effective stress variations and mineral cement dissolution in porous rocks. CO2‐enriched brine is injected continuously into a tight sandstone under in situ reservoir conditions for 455 hrs. Due to the dolomite cement dissolution, the bulk permeability of the sandstone specimen significantly increases, and two dissolution passages are identified near the fluid inlet by X‐ray CT imaging. Prereaction and postreaction examinations of the effective stress law for permeability suggest that after reaction, the bulk permeability is more sensitive to pore pressure changes and less sensitive to effective stress changes. These observations are corroborated by Scanning Electron Microscopy and X‐ray CT observations. This study deepens our understanding of the effect of mineral dissolution on the effective stress law for permeability, with implications for characterizing subsurface mass and energy transport, particularly during fluid injection/production into/from geologic reservoirs.