Extraction of physically-realistic pore network properties from three-dimensional synchrotron microtomography images of unconsolidated porous media

Algorithms were implemented to obtain high resolution three-dimensional images using synchrotron microtomography. Morphological algorithms were developed to extract physically-realistic pore-network structure from unconsolidated porous media systems imaged using synchrotron microtomography. The structure can be used to correlate pore-scale phenomena with the pore structure and can also be incorporated into a pore-network model to verify existing models, understand, or predict transport and flow processes and phenomena in complex porous media systems. The algorithms are based on the three-dimensional skeletonization of the pore space in the form of nodes connected to paths. Dilation algorithms were developed to generate inscribed spheres on the nodes and paths of the medial axis to represent pore-bodies and pore-throats of the network, respectively. Pore-network structure is captured by three-dimensional spatial distribution of pore-bodies and pore-throats, pore-body and pore-throat size distributions, and the connectivity. Theoretical packings were used to verify the algorithms. Systems of glass bead and natural sand were used in this study to investigate the applicability of the algorithms. Additionally, porosity, specific surface area, and representative elementary volume (REV) analysis of porosity were calculated. The impact of resolution was investigated using perfect glass bead and natural sand systems. Finally, semivariograms and integral scale concepts were used as a tool to investigate the spatial correlation of the network. Results showed that microtomography is an effective tool to provide quantitative analysis of three-dimensional systems. The quality of the datasets depends on photon energy, photon flux, size and type of the sample, and the number of projections. The resolution has a significant impact on the construction of the medial axis and extraction of pore network parameters. This impact varies in its significance based on the system and the properties being calculated. Results highlighted the difficulty of creating a unique network from a complex, continuum pore space. Results showed that the algorithms developed are general in use and can be applied to any three-dimensional unconsolidated porous media system. Spatial correlation results showed that systems have different correlation behavior; therefore, it might be not correct if a correlation model is assigned a priori into a pore-network model

Impact of Ionic Strength on Colloid Retention in a Porous Media: A Micromodel Study

Release of deposited colloids in the soil porous media during two-phase flow poses potential health hazard due to the facilitated transport of contaminants towards groundwater reservoirs. Considerable uncertainties exist concerning the impact of ionic strength on pore-scale mechanisms of colloid mobilization during transient flow. This study aims to investigate the effect of ionic strength on colloid retention and mobilization using a glass micromodel. The behavior of Carboxylate modified Polystyrene latex particles of 5 ?m diameter in saline solution (i.e., 100 mM & 1 mM of NaCl at pH 10) was visualized with an optical microscope during saturated and twophase flow. We found that colloid aggregation and attachment on Solid-Water Interfaces (SWI) was increased with increase in ionic strength. CO2 injection into the saturated micromodel mobilized the previously attached colloids on SWI, retained at the Gas- Water Interfaces (GWI) due to capillary forces and thus were transported through the micromodel. Imbibition mobilize colloids from GWI and are transported or reattached on SWI depending on the ionic strength of pore water. The greater adhesive forces of colloids at higher ionic strength was resulted in thin film attachment during drainage and reattachment of colloids mobilized from GWI on SWI during imbibition. The acquired images showed the application of a micromodel for the visualization of colloid retention and re-mobilization through the porous media.This publication was made possible by partial funding from NPRP grant # NPRP8- 594-2-244 from the Qatar National Research Fund (a member of Qatar Foundation). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of funding agencies

Retention of Hydrophobic Colloids in Unsaturated Porous Media using Microfluidics

Water recharge wells can provide a solution for 3.5 billion people, living in regions suffering from water scarcity. Due to fines migration, freshwater wells that are used to recharge aquifers, often experience expedited deterioration. Colloidal clay fine particles can be mobilized from within aquifers due to hydrodynamic forces or the sweeping of gas-water interface (GWI). The released colloids concentration increases then starts to retain and clog at the pores within the aquifer formation. Although fines migration is responsible for decommissioning many recharge wells, yet there is a lack of pore scale observations that uncover clogging mechanisms within porous media. Thus, this study utilizes wide-field optical macroscopy and microfluidic models with pore morphology of sandstone, to investigate the clogging mechanisms of hydrophobic colloids. The aim is to discover how interfacial surfaces within porous media retain colloids. Hence imbibition and drainage of colloidal suspension were carried to vary water saturation. Flow experiments were imaged at a resolution of 1µm/pixel, while colloids diameter was 5 µm. Images were segmented into solid, water, gas and colloids. Then the amount of colloids retained on each interface was quantified. Findings revealed that hydrophobic colloids retained mainly on the GWI. For colloids suspension in deionized water, affinity of colloids to GWI was high enough to cause bubble stabilization. In both hydrophobic and hydrophilic porous media, colloids disconnected the gas phase to create larger GWI surface. More than 90% of hydrophobic colloids were cleaned from the media after drainage, uncovering an efficient remediation technique for water aquifer

TORT3D: A MATLAB code to compute geometric tortuosity from 3D images of unconsolidated porous media

Tortuosity is a parameter that plays a significant role in the characterization of complex porous media systems and it has a significant impact on many engineering and environmental processes and applications. Flow in porous media, diffusion of gases in complex pore structures and membrane flux in water desalination are examples of the application of this important micro-scale parameter. In this paper, an algorithm was developed and implemented as a MATLAB code to compute tortuosity from three-dimensional images. The code reads a segmented image and finds all possible tortuous paths required to compute tortuosity. The code is user-friendly, easy to use and computationally efficient, as it requires a relatively short time to identify all possible connected paths between two boundaries of large images. The main idea of the developed algorithm is that it conducts a guided search for connected paths in the void space of the image utilizing the medial surface of the void space. Once all connected paths are identified in a specific direction, the average of all connected paths in that direction is used to compute tortuosity. Three-dimensional images of sand systems acquired using X-ray computed tomography were used to validate the algorithm. Tortuosity values were computed from three-dimensional images of nine different natural sand systems using the developed algorithm and compared with predicted values by models available in the literature. Findings indicate that the code can successfully compute tortuosity for any unconsolidated porous system irrespective of the shape (i.e., geometry) of particles. 1 2017 Elsevier B.V.Scopu

Influence of Water Table Fluctuation on Natural Source Zone Depletion in Hydrocarbon Contaminated Subsurface Environments

Most of the prediction theories regarding dissolution of organic contaminants in the subsurface systems have been proposed based on the static water conditions and the influence of water fluctuations on mass removal requires further investigations. In this study, it was intended to investigate the effects of water table fluctuations on biogeochemical properties of the contaminated soil at the smear zone between the vadose zone and the groundwater table. An automated 60 cm soil column system was developed and connected to a hydrostatic equilibrium reservoir to impose the water regime by using a multi-channel pump. Four homogenized hydrocarbon contaminated soil columns were constructed and two of them were fully saturated and remained under static water conditions while another two columns were operated under water table fluctuations between the soil surface and 40 cm below it. The experiments were run for 150 days and relevant geochemical indicators as well as dissolved phase concentrations were analyzed at 30 and 50 cm below the soil surface in all columns. The results indicated significant difference in terms of biodegradation effectiveness between the smear zones exposed to static and water table fluctuation conditions. This presentation will provide an overview of the experimental approach, mass removal efficiency, and key findings.This publication was made possible by funding from NPRP grant # NPRP9-093-1-021 from the Qatar national research fund (a member of Qatar Foundation). We acknowledge that all the Gas Chromatography analyses were accomplished in the Central Laboratories unit, Qatar University

Statistical Analysis of the Effect of Water Table Fluctuation and Soil Layering on the Distribution of BTEX on Soil and Groundwater Under Anaerobic Condition

Crude oil, gasoline, and diesel fuel spills pollute groundwater in many coastal areas. BTEX is a hydrocarbon of concern due to its high-water solubility, which allows it to spread widely in the subsurface environment. The mobile phase of LNAPLs percolates through porous soil and accumulates above the water table. Subsurface geological, pollutant morphology, and hydrogeologic site features make natural attenuation difficult to understand. Texture and vertical spatial variability affect soil hydraulic properties and water and contaminant distribution in soil profiles. Changes in rainfall strength and frequency and increased water demand may increase groundwater level oscillations in the next century. Five sets of columns, including one soil column and one equilibrium column, were operated for 150 days. One of the columns was operated under a steady state condition (S), and four columns under transient water table condition. The stable column (S), and the Fluctuating column 1 (F1) contain homogenized soil, while the fluctuating columns 2, 3, and 4 contains heterogenous soil. ORP values at the middle of the columns varied cyclically with WTF. EC values affected greatly by fluctuation and temperature and the statistical test p-value 3.119e-10 0.05). Soil layering affects the attenuation of BTEX, as the peak concentrations for benzene occurred at second imbibition cycle for the homogeneous soil, while for the heterogeneous soil occurred between second and fourth imbibition cycles

Dynamic Imaging of Hydrate Specific Area Evolution during Xenon Hydrate Formation

Gas hydrates are ice-like structures formed under high pressure and low temperature conditions. They are considered as a potential energy source due to their abundance and the increase in energy demand worldwide. A fundamental understanding of hydrate formation and dissociation kinetics is essential in order to improve gas productivity from natural hydrates reservoirs. This paper investigates the evolution of hydrate specific area during the process of hydrate formation using dynamic 3D synchrotron microcomputed tomography. Xenon hydrate was formed inside a high-pressure low-temperature cell, filled with silica sand partially saturated with water. The cell has a height of 70.2 mm and an inner diameter of 9.7 mm, and is capable of sustaining an internal pressure of 150 MPa. During hydrate formation and dissociation, full 3D images are acquired at a time resolution of 45 seconds and a spatial resolution of 5.38 ?m/voxel. The reconstructed images were enhanced and segmented, and direct volume and surface area measurements were obtained. Initially, the specific area of hydrate increased with increasing hydrate saturation up to a certain hydrate saturation threshold (9% hydrate saturation). After this threshold, hydrate specific area started to decrease with increasing hydrate saturation. This is an indication that the small crystals of hydrates tend to merge and form larger crystals during the process of hydrate formation.This publication was made possible by partial funding from NPRP grant # NPRP8- 594-2-244 from the Qatar national research fund (a member of Qatar Foundation) and the Institute for a Secure and Sustainable Environment (ISSE), University of Tennessee- Knoxville, USA. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of funding agencies. This paper used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory (ANL) under Contract No. DE-AC02-06CH11357. The PSMT images presented in this paper were collected using the x-ray Operations and Research Beamline Station 13-BMD at Argonne Photon Source (APS), ANL. We thank Dr. Mark Rivers of APS for help in performing the SMT scans. We also acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the National Science Foundation, Earth Sciences (EAR-1128799), and the DOE, Geosciences (DE-FG02-94ER14466)

The Dependent Clogging Dynamics and Its Impact on Porous Media Permeability Reduction

The dynamics of fine particle entrapment, transport, and deposition within pore systems, particularly the ability of mobile fines to impair permeability within porous media, are critical to a variety of natural and manmade phenomena, impacting oil and gas recovery, slope stability, filter capacity, and the efficiency of lab-on-chip diagnostics in medical disciplines. According to the research, clogging of pore throats in the porous media is not a random process; clogged throats, in particular, modify flow conditions and promote subsequent clogging nearby which is called dependent clogging. Over the last several decades, significant efforts have been made to identify and parameterize the role of dependent clogging in permeability reduction, with studies applying a combination of physical investigation and numerical simulation to this objective. In this work, we deploy a coupled computational fluid dynamics-discrete element method-based framework to investigate fines migration and consequent pore-throat clogging within a geologically realistic pore system extracted from an x-ray microtomographic image of a sand pack. The analysis of the simulation results revealed a spatial correlation between the clogged throats, implying that throats in close proximity became clogged dependently around the same time. Furthermore, dependent clogging was observed to be more frequent than independent clogging and it impacts system permeability more efficiently. This suggests that the distribution of clogged throats has a significant impact on the system's permeability reduction other than the total number of clogged throats.This publication was supported by Qatar University Grant (QUHI-CENG-22/23-517)

Perturbation Solution of the Jackson’s Dusty Gas Model Equations for Ternary Gaseous Systems

A perturbation technique was used to obtain an approximate closed-form solution for the mass balance equations when the dusty gas model (DGM) is used to calculate total molar fluxes of components of ternary gaseous systems. This technique employed the straight-forward expansion method to the second-order approximation. Steady-state, isobaric, isothermal and no reaction conditions were assumed. The obtained solution is a set of equations expressed to calculate mole fractions as functions of dimensionless length, boundary conditions, properties of the gases and parameters of transport mechanisms (i.e., Knudsen diffusivity and effective binary diffusivity). Three different systems represent field and experimental conditions were used to test the applicability of perturbation solution. Findings indicate that the obtained solution provides an effective tool to calculate mole fractions and total molar fluxes of components of ternary gaseous systems

Use of 3D Images to Evaluate Formation Damage Induced by Montmorillonite Fines in Porous Media Systems

Formation damage costs oil and gas industry $140 billion/year in lost productivity, this is a key challenge to Qatar, the world's largest LNG exporter. During production from a well, multiphase flow foster drag forces to mobilize fine particles from within the subsurface. Fine' migration can alter the gas flow, clogging pores and disconnecting gas pathways. Understanding fines influence is a complex challenge due to the reservoirs' porous media heterogeneity. Microtomography of sand sediments provides a standardized approach to study the fines impact. X-Ray microtomography of two repacked sand cylinders was carried at Argonne National Lab synchrotron. Rounded silica sand was mixed with hydrophilic swelling montmorillonite clay. High and low fines concentrations were mix--ed with the sand then deposited into five layers. Initially, samples were fully saturated, then gas was injected, the sediments were scanned before and after injection. At first, fines were suspended in the brine, but after injection were retained on the gasbrine interface, and their concentration in the brine increased. Gas injection divided pores and throats, reducing their average size. Contrarily, main gas pathways increased in size but were disconnected in the sediment with high fines concentration. Fines caused increased capillary pressure and lowered the sediment permeability.This research was made possible by the National Priorities Research Program (NPRP) grant #NPRP8-594-2-244 from Qatar national research fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors. The SMT images were collected using the X-ray Operations and Research Beamline Station 13-BMD at Argonne Photon Source (APS), Argonne National Laboratory. The authors thank Dr. Mark Rivers of APS for help in performing the SMT scans. They also acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the National Science Foundation, USA, Earth Sciences (EAR-1128799), and the US Department of Energy (DOE) and Geosciences (DE-FG02-94ER14466). Use of the Advanced Photon Source, an Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory, was supported by DOE, USA under contract no. DE-AC02-06CH11357