15 results found
Spurin C, Roberts GG, O'Malley CPB, et al., 2023, Pore-Scale Fluid Dynamics Resolved in Pressure Fluctuations at the Darcy Scale, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276
Zahasky C, Murugesu MP, Kurotori T, et al., 2023, Quantification of the Impact of Acidified Brine on Fracture-Matrix Transport in a Naturally Fractured Shale Using in Situ Imaging and Modeling, Energy and Fuels, Vol: 37, Pages: 12101-12112, ISSN: 0887-0624
Understanding flow, transport, chemical reactions, and hydromechanical processes in fractured geologic materials is key for optimizing a range of subsurface processes including carbon dioxide and hydrogen storage, unconventional energy resource extraction, and geothermal energy recovery. Flow and transport processes in naturally fractured shale rocks have been challenging to characterize due to experimental complexity and the multiscale nature of quantifying continuum scale descriptions of mass exchange between micrometer-scale fractures and nanometer-scale pores. In this study, we use positron emission tomography (PET) to image the transport of a conservative tracer in a naturally fractured Wolfcamp shale core before and after the core was exposed to low pH brine conditions. Image-based experimental observations are interpreted by fitting an analytical transport model to fracture-containing voxels in the core. Results of this analysis indicate subtle increases in matrix diffusivity and a slightly more uniform fracture velocity distribution following exposure to low pH conditions. These observations are compared with a multicomponent one-dimensional reactive transport model that indicates the capacity for a 10% increase in porosity at the fracture-matrix interface as a result of the low pH brine exposure. This porosity change is the result of the dissolution of carbonate minerals in the shale matrix to low pH conditions. This image-based workflow represents a new approach for quantifying spatially resolved fracture-matrix transport processes and provides a foundation for future work to better understand the role of coupled transport, reaction, and mechanical processes in naturally fractured rocks.
Kurotori T, Murugesu MP, Zahasky C, et al., 2023, Mixed imbibition controls the advance of wetting fluid in multiscale geological media, ADVANCES IN WATER RESOURCES, Vol: 175, ISSN: 0309-1708
Kurotori T, Zahasky C, Gran M, et al., 2023, Comparative Analysis of Imaging and Measurements of Micrometer-Scale Fracture Aperture Fields Within a Heterogeneous Rock Using PET and X-ray CT, TRANSPORT IN POROUS MEDIA, Vol: 147, Pages: 519-539, ISSN: 0169-3913
Anto-Darkwah E, Kurotori T, Pini R, et al., 2023, Estimating Three-Dimensional Permeability Distribution for Modeling Multirate Coreflooding Experiments, SUSTAINABILITY, Vol: 15
Eckel A-ME, Liyanage R, Kurotori T, et al., 2023, Spatial moment analysis of convective mixing in three-dimensional porous media using X-ray CT images, Industrial and Engineering Chemistry Research, Vol: 62, Pages: 762-774, ISSN: 0888-5885
Dissolution trapping is one of the primary mechanisms of carbon dioxide (CO2) storage in deep saline aquifers. The determination of the realized rates of CO2 dissolution requires an understanding of the mixing process that takes place following the emplacement of CO2 into the formation. Owing to the difficulty of reproducing the time-dependent convective process in porous media, experiments so far have largely focused on 2D systems (e.g., Hele-Shaw cells) and used analogue fluid pairs with properties that differ from the subsurface CO2/brine system. Here, we present a novel experimental approach to investigate the evolution of the convective mixing process in 3D porous media (homogeneous packings of glass beads) using X-ray computed tomography (CT). We explore a range of Rayleigh numbers (Ra = 3000–55000) and observe directly the mixing structures that arise upon dissolution. We compute from the images the temporal evolution of the spatial moments of the concentration distribution, including the cumulative dissolved mass, the location of the center of mass, and the standard deviation of the concentration field. The scalings of the spatial moments suggest an impact of hydrodynamic dispersion on the longitudinal mixing. We propose a simplified representation of the mixing process by analogy with the 1D advection–dispersion model. This enables the estimation of the bulk advective velocity and the effective longitudinal dispersion coefficient for each bead packing. These estimates suggest that the presence of the finger pattern and the counter-current flow structure enhance the longitudinal spreading of the solute by roughly 1 order of magnitude compared to unidirectional dispersion of a single-solute plume.
Huang Z, Kurotori T, Pini R, et al., 2022, Three-Dimensional Permeability Inversion Using Convolutional Neural Networks and Positron Emission Tomography, WATER RESOURCES RESEARCH, Vol: 58, ISSN: 0043-1397
Huang Z, Kurotori T, Pini R, et al., 2021, Three-Dimensional Permeability Inversion Using Convolutional Neural Networks and Positron Emission Tomography
Kurotori T, Pini R, 2021, A general capillary equilibrium model to describe drainage experiments in heterogeneous laboratory rock cores, Advances in Water Resources, Vol: 152, Pages: 1-12, ISSN: 0309-1708
Macroscopic observations of two-phase flow in porous rocks are largely affected by the heterogeneity in continuum properties at length scales smaller than a typical laboratory sample. The ability to discriminate among therock properties at the origin of the heterogeneity is key to the development of numerical models to be used forprediction. Here, we present a capillary equilibrium model that represents spatial heterogeneity in dual-porosityporous media in terms of the capillary entry pressure, 1∕𝛼, and the irreducible wetting phase saturation, 𝑆ir. Bothparameters are used to scale local capillary pressure curves by using three-dimensional imagery acquired duringmulti-rate gas/liquid drainage displacements. We verify the proposed approach by considering the case studyof a dual-porosity limestone core and use the spatial variation in 𝑆ir as proxy for microporosity heterogeneity.The latter places potentially next-to-leading order controls on the observed fluid saturation distribution, whichis strongly correlated to the distribution of 1∕𝛼. While microporosity is by and large uniform at the observationscale on the order of 0.1 cm3, the spatial correlation of 1∕𝛼 is on the order of 1 cm and is therefore not statisticallyrepresented in the volume of typical laboratory core samples.
Wenning QC, Madonna C, Kurotori T, et al., 2021, Chemo-Mechanical Coupling in Fractured Shale With Water and Hydrocarbon Flow, GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276
Wenning QC, Madonna C, Petrini C, et al., 2021, X-ray CT imaging of displacement-and swelling-induced fracture aperture changes in clay-rich rock
The study of permeability in fracture shale is challenging because coupled processes of mechanical damage, flow, and self-sealing are largely affected by the abundance of clay mineral in such systems. Yet the understanding of the coupling of these processes is fundamental to successful implementation of subsurface energy and waste storage technologies. Here, we present experimental results that combine simultaneous X-ray Computed Tomography with shear-flow experiments to study fracture deformation, fluid sorption, and flow in shale. In both experiments, the average mechanical aperture increases with shear displacement under constant radial stress (1.5 MPa). Upon subsequent brine injection the aperture is reduced to below the initial mated state. Digital image correlation is used to quantify the divergent displacement of the two sample halves, which is likely caused by fluid sorption. Fracture aperture reduction and divergent displacement were not observed in a control experiment with decane. Thus, at low confining pressures, the self-sealing process in clay-rich shales is dominated by swelling, rather than creep, and can occur relatively quickly (< 30 minutes).
Kurotori T, Zahasky C, Benson S, et al., 2020, Description of chemical transport in laboratory rock cores using the continuous random walk formalism, Water Resources Research, Vol: 56, ISSN: 0043-1397
We investigate chemical transport in laboratory rock cores using unidirectional pulse tracer experiments. Breakthrough curves (BTCs) measured at various flow rates in one sandstone and twocarbonate samples are interpreted using the one-dimensional Continuous Time Random Walk (CTRW) formulation with a truncated power law (TPL) model. Within the same framework, we evaluate additionalmemory functions to consider the Advection-Dispersion Equation (ADE) and its extension to describe mass exchange between mobile and immobile solute phases (Single-Rate Mass Transfer model, SRMT). Toprovide physical constraints to the models, parameters are identified that do not depend on the flow rate. While the ADE fails systematically at describing the effluent profiles for the carbonates, the SRMT andTPL formulations provide excellent fits to the measurements. They both yield a linear correlation between the dispersion coefficient and the Péclet number (DL Pe for 10 < (Pe) < 100), and the longitudinal dispersivity is found to be significantly larger than the equivalent grain diameter, De. The BTCs of the carbonate rocks show clear signs of nonequilibrium effects. While the SRMT model explicitly accounts for the presence of microporous regions (up to 30% of the total pore space), in the TPL formulation the time scales of both advective and diffusive processes (t1(Pe) and t2) are associated with two characteristic heterogeneity length scales (d and l, respectively). We observed that l 2.5 × De and that anomalous transport arises when ld (1). In this context, the SRMT and TPL formulations provide consistent, yet complementary, insight into the nature of anomalous transport in laboratory rock cores.
Wenning QC, Madonna C, Kurotori T, et al., 2019, Spatial mapping of fracture aperture changes with shear displacement using X-ray computerized tomography, Journal of Geophysical Research: Solid Earth, Vol: 124, Pages: 7320-7340, ISSN: 2169-9313
The shearing of fractures can be a significant source of permeability change by altering the distribution of void space within the fracture itself. Common methods to estimate the effects of shearing on properties, such as aperture, roughness, and connectivity are incapable of providing these observations in‐situ. Laboratory protocols are needed that enable measurements of the spatial structure of the fracture aperture field in the medium, non‐invasively. Here, we investigate changes in rough‐walled Brazilian‐induced tensile fracture aperture distribution with progressive shear displacement in Westerly granite and Carrara marble using a novel X‐ray transparent core‐holder. The so‐called calibration‐free missing attenuation method is applied to reconstruct highly‐resolved (sub‐millimeter) fracture aperture maps as a function of displacement (0 to 5.75 mm) in induced fractures. We observe that shearing increases the core‐averaged fracture aperture and significantly broadens the distribution of local values, mostly towards higher apertures. These effects are particularly strong in Westerly granite and may be the result of the higher initial roughness of its fracture surfaces. Also, while the correlation length of the aperture field increases in both parallel and perpendicular directions, significant anisotropy is developed in both samples with the progression of shearing. The results on Westerly granite provide a direct indication that fracture aperture remains largely unaffected until 1~mm of displacement is achieved, which is important when estimating permeability enhancement due to natural and induced shear displacement in faults.
Zahasky C, Kurotori T, Pini R, et al., 2019, Positron emission tomography in water resources and subsurface energy resources engineering research, Advances in Water Resources, Vol: 127, Pages: 39-52, ISSN: 0309-1708
Recent studies have demonstrated that positron emission tomography (PET) is a valuable tool for in-situ characterization of fluid transport in porous and fractured geologic media at the laboratory scale. While PET imaging is routinely used for clinical cancer diagnosis and preclinical medical research—and therefore imaging facilities are available at most research institutes—widespread adoption for applications in water resources and subsurface energy resources engineering have been limited by real and perceived challenges of working with this technique. In this study we discuss and address these challenges, and provide detailed analysis highlighting how positron emission tomography can complement and improve laboratory characterization of different subsurface fluid transport problems. The physics of PET are reviewed to provide a fundamental understanding of the sources of noise, resolution limits, and safety considerations. We then layout the methodology required to perform laboratory experiments imaged with PET, including a new protocol for radioactivity dosing optimization for imaging in geologic materials. Signal-to-noise and sensitivity analysis comparisons between PET and clinical X-ray computed tomography are performed to highlight how PET data can complement more traditional characterization methods, particularly for solute transport problems. Finally, prior work is critically reviewed and discussed to provide a better understanding of the strengths and weakness of PET and how to best utilize PET-derived data for future studies.
Kurotori T, Zahasky C, Hosseinzadeh Hejazi SA, et al., 2019, Measuring, imaging and modelling solute transport in a microporous limestone, Chemical Engineering Science, Vol: 196, Pages: 366-383, ISSN: 1873-4405
The analysis of dispersive flows in heterogeneous porous media is complicated by the appearance of anomalous transport. Novel laboratory protocols are needed to probe the mixing process by measuring the spatial structure of the concentration field in the medium. Here, we report on a systematic investigation of miscible displacements in a microporous limestone over the range of Péclet numbers, . Our approach combines pulse-tracer tests with the simultaneous imaging of the flow by Positron Emission Tomography (PET). Validation of the experimental protocol is achieved by means of control experiments on random beadpacks, as well as by comparing observations with both brine- and radio-tracers (labelled with 11C or 18F). The application of residence time distribution functions reveals mass transport limitations in the porous rock in the form of a characteristic flow-rate effect. Two transport models, namely the Advection Dispersion Equation (ADE) and the Multi-Rate Mass Transfer (MRMT) model, are thoroughly evaluated with both the experimental breakthrough curves and the internal concentration profiles. We observe that the dispersion coefficient scales linearly with the Péclet number for both porous systems. The tracer profiles acquired on the rock sample are successfully described upon application of the MRMT model that uses two representative grain sizes and a fraction of intra-granular pore space that is independent of the fluid velocity. The analysis of the PET images evidences the presence of macrodispersive spreading caused by subcore-scale heterogeneities, which contribute significantly to the value of the estimated core-scale dispersivity. This effect can be significantly reduced upon application of the ‘dispersion-echo’ technique, which enables decoupling the effects of spreading and mixing in heterogeneous porous media. These observations are likely to apply to any laboratory-scale rock sample and the approach presented here provides a
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