Vivek V Patil | University of Utah (original) (raw)

Papers by Vivek V Patil

AGU Fall Meeting Abstracts, Dec 1, 2020

Greenhouse Gases-Science and Technology, Mar 2, 2017

Injecting anthropogenic CO 2 into the subsurface is suggested for climate change mitigation. Howe... more Injecting anthropogenic CO 2 into the subsurface is suggested for climate change mitigation. However, leakage of CO 2 from its target storage formation is a concern. In the event of leakage, permeability in leakage pathways such as faults may get altered due to mineral reactions induced by CO 2-enriched water, thus influencing the migration and fate of the CO 2. An example of such fault permeability alteration is found in the Little Grand Wash Fault zone (LGWF), where the fault outcrops show fractures filled with calcium carbonate. To test the nature, extent, and time-frame of such fault 'self-sealing', we developed reactive flow simulations based on hydrogeological conditions of the LGWF. We measured LGWF water chemistry and conducted an x-ray powder diffraction (XRD) analysis of the fault-rock to constrain the model geochemistry. We hypothesized that the choice of parameters for relative permeability, capillary pressure, and reaction kinetics will have a huge impact on the fault sealing predictions. Simulation results showed that precipitation of calcite in the top portion of the fault led to a decrease in porosity of the damage zone from a value of 40% to ∼ 2%. Over a simulation time of 1000 years, porosity in the damage zone showed self-enhancing behavior in the bottom portion and self-sealing behavior in the top portion of the fault. We found that the results were most sensitive to the relative permeability parameters and the fault architecture. A major conclusion from this analysis is that, under similar conditions, some faults are likely to seal over time.

Environmental Engineering Science, Mar 1, 2021

Fault zones significantly influence the migration of fluids in the subsurface and can be importan... more Fault zones significantly influence the migration of fluids in the subsurface and can be important controls on the local as well as regional hydrogeology. Hence, understanding the evolution of fault porosity/permeability is critical for many engineering applications (like geologic carbon sequestration, enhanced geothermal systems, groundwater remediation, etc.), as well as geological studies (like sediment diagenesis, seismic activities, hydrothermal ore deposition, etc.). The highly heterogeneous pore structure of fault zones along with the wide range of hydrogeochemical heterogeneity that a fault zone can cut through make conduit fault zones a dynamic reactive transport environment that can be highly complex to accurately model. In this article, we present a critical review of the possible ways of modeling reactive fluid flow through fault zones, particularly from the perspective of chemically driven ''self-sealing'' or ''self-enhancing'' of fault zones. Along with an in-depth review of the literature, we consider key issues related to different conceptual models (e.g., fault zone as a network of fractures or as a combination of damaged zone and fault core), modeling approaches (e.g., multiple continua, discrete fracture networks, pore-scale models), and kinetics of water/rock interactions. Inherent modeling aspects related to dimensionality (e.g., one-dimensional vs. two-dimensional) and the dimensionless Damköhler number are explored. Moreover, we use a case study of the Little Grand Wash Fault zone from central Utah as an example in the review. Finally, critical aspects of reactive transport modeling like multiscale approaches and chemomechanical coupling are also addressed in the context of fault zones.

Water Resources Research, Mar 1, 2020

• Fault permeability evolution caused by CO 2-induced reactions can impact initial predictions of... more • Fault permeability evolution caused by CO 2-induced reactions can impact initial predictions of CO 2 migration. • Carbonate precipitation in near-surface faults was found to be the most likely selfsealing mechanism. • Pressure-temperature and cation concentration are the most important conditions impacting model predictions.

One of the greatest sources of uncertainty associated with forecasting subsurface CO2 storage cap... more One of the greatest sources of uncertainty associated with forecasting subsurface CO2 storage capacity, and associated trapping mechanisms, is permeability heterogeneity. And, an often-overlooked source of heterogeneity in permeability is the relative permeability function assumed, and its calibration. A seemingly common approach to relative permeability for CO2 storage simulation analyses, due to lack of information, is to assume a “typical” relative permeability function and assign parameters based on similar rock type and geologic setting. We evaluated how such a nearly-arbitrary approach to assigning relative permeability can impact forecasts of storage capacity, and mineralization trapping in particular. We developed and executed the same simulation model of a porous medium but with four different relative permeability curves (functions), and examined the evolution of gas saturation, calcite precipitation, and for a simulated fault, the fault porosity and fault sealing rate, for these different relative permeability formulations. Assigning one permutation as the “base case” for comparison, gas saturation varied considerably among the four models. But, substantial differences in predictions of calcite precipitation were even more compelling. Accordingly, porosity evolution in the base-case model showed a trend where precipitated minerals formed early on and then dissolved in later stages of the simulations. Specifically, a ‘dissolution front’ moved up depth along flow pathways over time. For simulations of a generic fault zone with a marked contrast in porosity and permeability, using different relative permeability assignments also impacted predictions of fault self-sealing rates. At the top of the fault, each formulation predicted different sealing rates. For example, a van Genuchten formulation forecasted fault-sealing at almost twice the rate as a Corey formulation. The upshot of these results is that relative permeability assignment is a critical variable that must be calibrated with care; otherwise, perhaps a simple linear formulation will be just as meaningful as any other.

Environmental Engineering Science, 2021

Injecting anthropogenic CO2 into a subsurface reservoir for sequestration will impact the reservo... more Injecting anthropogenic CO2 into a subsurface reservoir for sequestration will impact the reservoir significantly, including its geochemistry, porosity and permeability. If a fault or fracture penetrates the reservoir, CO2-laden brine may migrate into that fault, eventually sealing it via precipitation or opening it up via dissolution. The goal of this study was to identify and quantify such conditions of fault self-sealing or self-enhancing. We found that the dimensionless Damköhler number (Da), the ratio of reaction rate to advection rate, provides a meaningful framework for characterizing the propensity of (fault) systems to seal or open up. We developed our own framework wherein Damköhler numbers evolve spatiotemporally as opposed to the traditional single Da value approach. Our approach enables us to use the Damköhler for characterization of complex multiphase and multimineral reactive transport problems. We applied this framework to 1D fault models with eight conditions derived from four geologic compositions and two reservoir conditions. The four geologic compositions were chosen such that three out of them were representative of distinct geologic end-members (sandstone, mudstone and dolomitic limestone) and one was a mixed composition based on an average of three end-member compositions. The two sets of P-T conditions chosen included one set corresponding to CO2 in a gaseous phase ("shallow conditions") and the other corresponding to supercritical phase CO2 ("deep conditions"). Simulation results suggest that fault sealing via carbonate precipitation was a possibility for shallow conditions within limestone and mixed composition settings. The concentration of cations in the water was found to be an important control on the carbonate precipitation. The deep conditions models did not forecast self-sealing via carbonates. Sealing via clay precipitation is a likely possibility, but the 1000 year time-frame may be short for such. Model results indicated a range of Da values within which substantial reductions of fault porosity (meaning self-sealing) could be expected. A key conclusion suggested by the results of this study is that carbonate precipitation in the near-surface (top ~50-100 m) depths of a fault is the most likely mechanism of "self-sealing" for most geological settings.

Water Resources Research, 2020

In the Fake Court of the Carbon Capture and Storage ________________ ... Kristine Blickenstaff, W... more In the Fake Court of the Carbon Capture and Storage ________________ ... Kristine Blickenstaff, Wei Jia, Aleksandra Opara, Vivek Patil, Justin Wriedt, Oscar Zabala Counsels for the Petitioner ... UNIVERSITY OF UTAH CVEEN 7920: CARBON CAPTURE AND ...

... BRIEF Kristine Blickenstaff, Wei Jia, Aleksandra Opara, Vivek Patil, Justin Wriedt, Oscar Zab... more ... BRIEF Kristine Blickenstaff, Wei Jia, Aleksandra Opara, Vivek Patil, Justin Wriedt, Oscar Zabala Counsels for the Petitioner ... researching the specific task he or she was assigned. Vivek Patil is an advocate of the post-combustion carbon capture technology based on ...

Geochemical modeling is widely used for understanding the geo-chemical ramifications of injecting... more Geochemical modeling is widely used for understanding the geo-chemical ramifications of injecting anthropogenic CO 2 into subsurface aquifers for sequestration purposes. We develop a kinetic batch reaction model of CO 2 injection into an arkosic sandstone. The model is simulated in two very different simulators, TOUGHREACT and The Geochemist's Workbench. The goal is to characterize the effect of their differences on the results. We find that in both models that the evolution of pH and porosity over a 1000 years follow a similar trend. However, the models differ in the formation of secondary minerals. We postulate that this is due to the different mechanisms used by the two models for mineral formation. Treatment of CO 2 in a multiphase code (TOUGHREACT) versus that in a single-phase (GWB) can be another controlling factor. This work is meant to give an insight to geochemical modelers into the effects of the nature of simulators on the results.

Greenhouse Gases: Science and Technology, Mar 2, 2017

Injecting anthropogenic CO2 into the subsurface is suggested for climate change mitigation. Howev... more Injecting anthropogenic CO2 into the subsurface is suggested for climate change mitigation. However, leakage of CO2 from its target storage formation is a concern. In the event of leakage, permeability in leakage pathways such as faults may get altered due to mineral reactions induced by CO2-enriched water, thus influencing the migration and fate of the CO2. An example of such fault permeability alteration is found in the Little Grand Wash Fault zone (LGWF), where the fault outcrops show fractures filled with calcium carbonate. To test the nature, extent, and time-frame of such fault ‘self-sealing’, we developed reactive flow simulations based on hydrogeological conditions of the LGWF. We measured LGWF water chemistry and conducted an x-ray powder diffraction (XRD) analysis of the fault-rock to constrain the model geochemistry. We hypothesized that the choice of parameters for relative permeability, capillary pressure, and reaction kinetics will have a huge impact on the fault sealing predictions. Simulation results showed that precipitation of calcite in the top portion of the fault led to a decrease in porosity of the damage zone from a value of 40% to ∼2%. Over a simulation time of 1000 years, porosity in the damage zone showed self-enhancing behavior in the bottom portion and self-sealing behavior in the top portion of the fault. We found that the results were most sensitive to the relative permeability parameters and the fault architecture. A major conclusion from this analysis is that, under similar conditions, some faults are likely to seal over time. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

Acta Geotechnica

ABSTRACT Geochemical interactions of brine–rock–gas have a significant impact on the stability an... more ABSTRACT Geochemical interactions of brine–rock–gas have a significant impact on the stability and integrity of the caprock for long-term CO2 geological storage. Invasion of CO2 into the caprock from the storage reservoir by (1) molecular diffusion of dissolved CO2, (2) CO2-water two-phase flow after capillary breakthrough, and (3) CO2 flow through existing open fractures may alter the mineralogy, porosity, and mechanical strength of the caprock due to the mineral dissolution or precipitation. This determines the self-enhancement or self-sealing efficiency of the caprock. In this paper, two types of caprock, a clay-rich shale and a mudstone, are considered for the modeling analyses of the self-sealing and self-enhancement phenomena. The clay-rich shale taken from the Jianghan Basin of China is used as the base-case model. The results are compared with a mudstone caprock which is compositionally very different than the clay-rich shale. We focus on mineral alterations induced by the invasion of CO2, feedback on medium properties such as porosity, and the self-sealing efficiency of the caprock. A number of sensitivity simulations are performed using the multiphase reactive transport code TOUGHREACT to identify the major minerals that have an impact on the caprock’s self-sealing efficiency. Our model results indicate that under the same hydrogeological conditions, the mudstone is more suitable to be used as a caprock. The sealing distances are barely different in the two types of caprock, both being about 0.6 m far from the interface between the reservoir and caprock. However, the times of occurrence of sealing are considerably different. For the mudstone model, the self-sealing occurs at the beginning of simulation, while for the clay-rich shale model, the porosity begins to decline only after 100 years. At the bottom of the clay-rich shale column, the porosity declines to 0.034, while that of mudstone declines to 0.02. The sensitive minerals in the clay-rich shale model are calcite, magnesite, and smectite-Ca. Anhydrite and illite provide Ca2+ and Mg2+ to the sensitive minerals for their precipitation. The mudstone model simulation is divided into three stages. There are different governing minerals in different stages, and the effect of the reservoir formation water on the alteration of sensitive minerals is significant.

inproceedings by Vivek V Patil

We present an extensive hydrologic and reactive transport analysis of the Little Grand Wash fault... more We present an extensive hydrologic and reactive transport analysis of the Little Grand Wash fault zone (LGWF), a natural analog of fault-associated leakage from an engineered CO2 repository. Injecting anthropogenic CO2 into the subsurface is suggested for climate change mitigation. However, leakage of CO2 from its target storage formation into unintended areas is considered as a major risk involved in CO2 sequestration. In the event of leakage, permeability in leakage pathways like faults may get sealed (reduced) due to precipitation or enhanced (increased) due to dissolution reactions induced by CO2-enriched water, thus influencing migration and fate of the CO2. We hypothesize that faults which act as leakage pathways can seal over time in presence of CO2-enriched waters. An example of such a fault 'self-sealing' is found in the LGWF near Green River, Utah in the Paradox basin, where fault outcrop shows surface and sub-surface fractures filled with calcium carbonate (CaCO3). The LGWF cuts through multiple reservoirs and seal layers piercing a reservoir of naturally occurring CO2, allowing it to leak into overlying aquifers. As the CO2-charged water from shallower aquifers migrates towards atmosphere, a decrease in pCO2 leads to supersaturation of water with respect to CaCO3, which precipitates in the fractures of the fault damage zone. In order to test the nature, extent and time-frame of the fault sealing, we developed reactive flow simulations of the LGWF. Model parameters were chosen based on hydrologic measurements from literature. Model geochemistry was constrained by water analysis of the adjacent Crystal Geyser and observations from a scientific drilling test conducted at the site. Precipitation of calcite in the top portion of the fault model led to a decrease in the porosity value of the damage zone, while clay precipitation led to a decrease in the porosity value of the fault core. We found that the results were sensitive to the fault architecture, relative permeability functions, kinetic parameters for mineral reactions and treatment of molecular diffusion. Major conclusions from this analysis are that a failed (leaking) engineered sequestration site may behave very similar to the LGWF and that under similar conditions some faults are likely to seal over time.

Geochemical modeling is widely used for understanding the ramifications of injecting anthropogeni... more Geochemical modeling is widely used for understanding the ramifications of injecting anthropogenic CO2 into subsurface aquifers for geological sequestration. We develop a kinetic batch reaction model of CO2 injection into arkosic sandstone with a brine of 6% salinity. The reaction scenario is modeled in two different simulators, TOUGHREACT and The Geochemist’s Workbench (GWB). The goal is to characterize the effects of the inherently different workflows of these simulators on the results, in spite of having an identical initial reaction basis. The TOUGHREACT model is built with ECO2H, the equation of state for H2O-NaCl-CO2 system. The GWB model is built in the React module.
We find in the results of both the models that even though the evolution of pH over a period of 1000 years is qualitatively similar, it differs quantitatively. Also, there is a net decrease of 0.16% in the porosity from the TOUGHREACT model, while a net increase of 0.15% in porosity is seen in the GWB model. In addition, the results of the two models greatly differ in predicting the precipitation and dissolution of the secondary minerals. We postulate that this is due to the different mechanisms used by the two models for secondary mineral formation. GWB uses the principle of nucleation, whereas TOUGHREACT allocates a minimal surface area for facilitating precipitation of secondary minerals. By far, the biggest difference in the two models is the behavior of CO2 in a multiphase code (TOUGHREACT) versus a single-phase code (GWB). Results show that in the TOUGHREACT model, some of the injected CO2 exists as a separate supercritical phase, which is in contrast to the GWB model wherein CO2 exists only in the dissolved phase. The contributions of multiple aspects in the respective simulator frameworks such as calculation of fugacity coefficients, activity coefficients and aqueous speciation are investigated in this study.
This work gives a meaningful insight to geochemical modelers into the effects of the implicit framework of simulators.