# Dr. Jin Ma

###### Former PhD Student for Geothermal Energy and Geofluids

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Contact
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 Dominique Ballarin Dolfin Phone +41 44 632 3465 Email ballarin@ethz.ch

## Publications

Underlined names are links to recent or past GEG members

### REFEREED PUBLICATIONS IN JOURNALS

7.
Ma, J., M. Ahkami, M.O. Saar, and X.-Z. Kong, Quantification of mineral accessible surface area and flow-dependent fluid-mineral reactivity at the pore scale, Chemical Geology, 563, pp. 120042, 2021. [View Abstract]Accessible surface areas (ASAs) of individual rock-forming minerals exert a fundamental control on the maximum mineral reactivity with formation fluids. Notably, ASA efficiency during fluid-rock reactions can vary by orders of magnitude, depending on the inflow fluid chemistry and the velocity field. Due to the lack of adequate quantification methods, determining the mineral-specific ASAs and their reaction efficiency still remain extremely difficult. Here, we first present a novel joint method that appropriately calculates ASAs of individual minerals in a multi-mineral sandstone. This joint method combines SEM-image processing results and Brunauer-Emmett-Teller (BET) surface area measurements by a Monte-Carlo algorithm to derive scaling factors and ASAs for individual minerals at the resolution of BET measurements. Using these atomic-scale ASAs, we then investigate the impact of flow rate on the ASA efficiency in mineral dissolution reactions during the injection of CO2-enriched brine. This is done by conducting a series of pore-scale reactive transport simulations, using a two-dimensional (2D) scanning electron microscopy (SEM) image of this sandstone. The ASA efficiency is determined employing a domain-averaged dissolution rate and the effective surface area of the most reactive phase in the sandstone (dolomite). As expected, the dolomite reactivity is found to increase with the flow rate, due to the on average high fluid reactivity. The surface efficiency increases slightly with the fluid flow rate, and reaches a relatively stable value of about 1%. The domain averaged method is then compared with the in-out averaged method (i.e the “Black-box” approach), which is often used to analyzed the experimental observations. The in-out averaged method yields a considerable overestimation of the fluid reactivity, a small underestimation of the dolomite reactivity, and a considerable underestimation of the ASA efficiency. The discrepancy between the two methods is becoming smaller when the injection rate increases. Our comparison suggests that the result interpretation of the in-out averaged method should be contemplated, in particular, when the flow rate is small. Nonetheless, our proposed ASA determination method should facilitate accurate calculations of fluid-mineral reactivity in large-scale reactive transport simulations, and we advise that an upscaling of the ASA efficiency needs to be carefully considered, due to the low surface efficiency.

6.
Ma, J., L. Querci, B. Hattendorf, M.O. Saar, and X.-Z. Kong, The effect of mineral dissolution on the effective stress law for permeability in a tight sandstone, Geophysical Research Letters, 2020. [View Abstract]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 hours. 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. Pre- and post-reaction 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.

5.
Ma, J., L. Querci, B. Hattendorf, M.O. Saar, and X.-Z. Kong, Toward a Spatiotemporal Understanding of Dolomite Dissolution in Sandstone by CO2‑Enriched Brine Circulation, Environmental Science & Technology, 2019. [View Abstract]In this study, we introduce a stochastic method to delineate the mineral effective surface area (ESA) evolution during a re-cycling 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 ($\sim$270 hours) to examine the evolution of in-situ hydraulic properties and CO$_2$-enriched 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 $\sim$2.45 mmol~m$^{-3}$~s$^{-1}$, a corresponding sample-averaged ESA of $\sim$8.86$\times 10^{-4}$~m$^2$/g, and an ESA coefficient of 1.36$\times 10^{-2}$, indicating limited participation of the physically exposed mineral surface area. As the dissolution reaction progressed, the ESA is observed to first increase, then decrease. This change in ESA can be qualitatively reproduced employing SEM-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 geo-engineering operations.

4.
Xu, R.N., R. Li, J. Ma, D. He, and P.X. Jiang, Effect of Mineral Dissolution/Precipitation and CO2 Exsolution on CO2 transport in Geological Carbon Storage, ACCOUNTS OF CHEMICAL RESEARCH, 50/9, pp. 2056-2066, 2017. [View Abstract]Geological carbon sequestration (GCS) in deep saline aquifers is an effective means for storing carbon dioxide to address global climate change. As the time after injection increases, the safety of storage increases as the CO2 transforms from a separate phase to CO2(aq) and HCO3- by dissolution and then to carbonates by mineral dissolution. However, subsequent depressurization could lead to dissolved CO2(aq) escaping from the formation water and creating a new separate phase which may reduce the GCS system safety. The mineral dissolution and the CO2 exsolution and mineral precipitation during depressurization change the morphology, porosity, and permeability of the porous rock medium, which then affects the two-phase flow of the CO2 and formation water. A better understanding of these effects on the CO2 water two-phase flow will improve predictions of the long-term CO2 storage reliability, especially the impact of depressurization on the long-term stability. In this Account, we summarize our recent work on the effect of CO2 exsolution and mineral dissolution/precipitation on CO2 transport in GCS reservoirs. We place emphasis on understanding the behavior and transformation of the carbon components in the reservoir, including CO2(sc/g), CO2(aq), HCO3-, and carbonate minerals (calcite and dolomite), highlight their transport and mobility by coupled geochemical and two-phase flow processes, and consider the implications of these transport mechanisms on estimates of the long-term safety of GCS. We describe experimental and numerical pore- and core-scale methods used in our lab in conjunction with industrial and international partners to investigate these effects. Experimental results show how mineral dissolution affects permeability, capillary pressure, and relative permeability, which are important phenomena affecting the input parameters for reservoir flow modeling. The porosity and the absolute permeability increase when CO2 dissolved water is continuously injected through the core. The MRI results indicate dissolution of the carbonates during the experiments since the porosity has been increased after the core-flooding experiments. The mineral dissolution changes the pore structure by enlarging the throat diameters and decreasing the pore specific surface areas, resulting in lower CO2/water capillary pressures and changes in the relative permeability. When the reservoir pressure decreases, the CO2 exsolution occurs due to the reduction of solubility. The CO2 bubbles preferentially grow toward the larger pores instead of toward the throats or the finer pores during the depressurization. After exsolution, the exsolved CO2 phase shows low mobility due to the highly dispersed pore-scale morphology, and the well dispersed small bubbles tend to merge without interface contact driven by the Ostwald ripening mechanism. During depressurization, the dissolved carbonate could also precipitate as a result of increasing pH. There is increasing formation water flow resistance and low mobility of the CO2 in the presence of CO2 exsolution and carbonate precipitation. These effects produce a self-sealing mechanism that may reduce unfavorable CO2 migration even in the presence of sudden reservoir depressurization.

3.
Manceau, J.C., J. Ma, and R. Li, Two-phase flow properties of a sandstone rock for the CO2/water system: Core-flooding experiments, and focus on impacts of mineralogical changes, Water Resources Research, 51, pp. 2885-2900, 2015. [View Abstract]The two-phase flow characterization (CO2/water) of a Triassic sandstone core from the Paris Basin, France, is reported in this paper. Absolute properties (porosity and water permeability), capillary pressure, relative permeability with hysteresis between drainage and imbibition, and residual trapping capacities have been assessed at 9 MPa pore pressure and 28°C (CO2 in liquid state) using a single core-flooding apparatus associated with magnetic resonance imaging. Different methodologies have been followed to obtain a data set of flow properties to be upscaled and used in large-scale CO2 geological storage evolution modeling tools. The measurements are consistent with the properties of well-sorted water-wet porous systems. As the mineralogical investigations showed a nonnegligible proportion of carbonates in the core, the experimental protocol was designed to observe potential impacts on flow properties of mineralogical changes. The magnetic resonance scanning and mineralogical observations indicate mineral dissolution during the experimental campaign, and the core-flooding results show an increase in porosity and water absolute permeability. The changes in two-phase flow properties appear coherent with the pore structure modifications induced by the carbonates dissolution but the changes in relative permeability could also be explained by a potential increase of the water-wet character of the core. Further investigations on the impacts of mineral changes are required with other reactive formation rocks, especially carbonate-rich ones, because the implications can be significant both for the validity of laboratory measurements and for the outcomes of in situ operations modeling.

2.
Ma, J., D. Petrilli, and J.C. Manceau, Core scale modelling of CO2 flowing: identifying key parameters and experiment fitting, Energy Procedia, 37, pp. 5464-5472, 2013. [View Abstract]In this study, we propose to evaluate CO2-brine characteristics using core flooding experiment results with magnetic resonance (MR) imaging and a 1D numerical modelling approach along with a perspective on the role of CO2-brine characteristics on storage efficiency at the reservoir scale. MRI can be used to understand the pore structure and the flow characteristic of the drainage process more directly. The relative permeability curve which is the key parameter to field scale simulation can be obtained by the experiments. 1D numerical modelling is conducted to understand the results observed experimentally and the associated processes by using the parameters measured during the experiments. The modelling can explain the observed differences with the experiment through a sensitivity analysis and propose several set of parameters allowing a good match between experiments and models (history matching). It is shown that the combination method between the experiments and the modelling is a suitable method to understand the mechanism of CO2 geological storage. Moreover, the experiments can provide the validation to the modelling which is the important tool to predict the CO2 migration underground.

1.
Ma, J., R.N. Xu, and S. Luo, Core-scale Experimental Study on Supercritical-Pressure CO2 Migration Mechanism during CO2 Geological Storage in Deep Saline Aquifers, Journal of Engineering Thermophysics, 33, pp. 1971-1975, 2012. [View Abstract]Abstract To address the climate change and reduce the emission of CO2, CO2 storage in the deep saline aquifer is one of the promising technologies. The visualization experimental system was set up to investigate the CO2 migration mechanism during the displacement of supercritical CO2 and water inside the core rock. From the experimental system, the experiment measured porosity, calculated the relative permeability-water saturation curve the water distribution will be achieved. The porosity can be measured accurately using MR technique. The fraction of effective porosity and movable fluid can be calculated, according to the T2 curve from MR. The MRI for core slice with the injection ratio of CO2:H2O=3:1 shows remarkable buoyancy effect. Core-scale experimental study on supercritical-pressure CO2 migration mechanism during CO2 geological storage in deep saline aquifers. Available from: https://www.researchgate.net/publication/279937649_Core-scale_experimental_study_on_supercritical-pressure_CO2_migration_mechanism_during_CO2_geological_storage_in_deep_saline_aquifers [accessed Jun 7, 2017].