Recent Submissions

  • Three-dimensional natural convection, entropy generation and mixing in heterogeneous porous medium

    Yang, Xiangjuan; Shao, Qian; Hoteit, Hussein; Carrera, Jesus; Younes, Anis; Fahs, Marwan (Advances in Water Resources, Elsevier BV, 2021-07-02) [Article]
    Three-dimensional (3D) natural convection (NC) processes in heterogeneous porous media and associated energy losses and mixing processes are still poorly understood. Studies are limited to two-dimensional domains because of computational burden, worsened by heterogeneity, which may demand grid refinement at high permeability zones for accurate evaluation of buoyancy forces. We develop a meshless Fourier series (FS) solution of the natural convection problem in a porous enclosure driven by thermal or compositional variations. We derive the vector potential formulation of the governing equations for vertical and horizontal heterogeneity of hydraulic conductivity and implement an efficient method to solve the spectral system with an optimized number of Fourier modes. 3D effects are induced either by heterogeneity or variable boundary conditions. The developed FS solution is verified against a finite element solution obtained using COMSOL Multiphysics. We evaluate entropy generation (viscous dissipation and mixing) indicators using FS expansions and assess how they are affected by heterogeneity. We define a large-scale Rayleigh number to account for heterogeneity by adopting an arithmetic average effective permeability. The FS solution is used to investigate the effect of the large-scale Rayleigh number and level of heterogeneity on NC processes and energy losses. Results show that increasing the Rayleigh number intensifies fluid flow, thus enhancing convective transfer, which causes a dramatic increase in total entropy generation. Both viscous dissipation and mixing (and thus chemical reactions in the solute transport case) increase. The third dimension effect, which also enhances flow and entropy indicators, is more pronounced at high Rayleigh numbers. Surprisingly, entropy variation indicators remain virtually unchanged in response to changes in heterogeneity, for fixed Rayleigh number, which we attribute to the arithmetic average permeability being indeed appropriate for NC in 3D. This study not only explores the effect of Rayleigh number and heterogeneity on natural convection processes and the associated entropy generation and mixing processes, but also provides a highly accurate solution that can be used for codes benchmarking.
  • Improving Formation Pressure Integrity Tests with Field-Wise Test Data Analysis and Hydraulic Impedance Testing

    Abilov, Elmir (2021-07) [Thesis]
    Advisor: Patzek, Tadeusz
    Committee members: Finkbeiner, Thomas; Ahmed, Shehab
    Drilling operations without issues and non-productive time are highly desired by operators. Circulation loss is one of the common issues faced during drilling when a formation is fractured by mud weight or by Equivalent Circulating Density (ECD) exceeding the formation fracture gradient. This makes it necessary to obtain information about in-situ stress and rock strength. Formation Pressure Integrity Tests (FPITs) determine directly the fracture pressure of the formation or test the formation for a safe drilling mud weight window and kick tolerance. Although FPIT is a routine test conducted before drilling each hole section, previous studies and field experience have demonstrated several problems and a lack of unique operational procedures for these tests. This study examines some of the main issues faced during operation and interpretation of FPITs and possible solutions to eliminate them. We generated a unique database of FPITs which includes all necessary technical and non-technical details about each test and analyzed the discrepancy between surface and downhole pressure data generated while conducting FPITs. We also analyzed pressure build-up behavior versus pumped fluid volume and its similarities with Casing Integrity Tests (CIT). Furthermore, we investigated pressure loss rates after shut-in, and the application of hydraulic impedance testing to improve test quality. Our analysis of the discrepancy trends indicated that Reservoir Drilling Fluid (RDF) causes more pressure transmission losses than Oil-Based Mud (OBM). We examined more than 50 tests based on pressure build-up behavior versus pumped fluid volume and obtained an empirical equation that only requires the measured depth to give an estimation for the pressure build-up rate. In addition, comparing CIT with FPIT based on pressure build-up rate shows similarities between the tests, and CIT build-up rate values can potentially be used as an initial assumption for FPIT build-up rate. Our findings reveal that pressure loss rate after pump-off is less than 6 psi/min in more than 65% of the Formation Integrity Tests (FITs). We also suggest to use Hydraulic Impedance Testing (HIT) method together with formation strength tests to give a qualitative indication of fracture initiation and a quantitative estimation of fracture dimensions.
  • Application of Physics-Informed Neural Networks to Solve 2-D Single-phase Flow in Heterogeneous Porous Media

    Alhubail, Ali (2021-07) [Thesis]
    Advisor: Hoteit, Hussein
    Committee members: Sun, Shuyu; Ahmed, Shehab
    Neural networks have recently seen tremendous advancements in applicability in many areas, one of which is their utilization in solving physical problems governed by partial differential equations and the constraints of these equations. Physics-informed neural networks is the name given to such neural networks. They are different from typical neural networks in that they include loss terms that represent the physics of the problem. These terms often include partial derivatives of the neural network outputs with respect to its inputs, and these derivatives are found through the use of automatic differentiation. The purpose of this thesis is to showcase the ability of physics-informed neural networks to solve basic fluid flow problems in homogeneous and heterogeneous porous media. This is done through the utilization of the pressure equation under a set of assumptions as well as the inclusion of Dirichlet and Neumann boundary conditions. The goal is to create a surrogate model that allows for finding the pressure and velocity profiles everywhere inside the domain of interest. In the homogeneous case, minimization of the loss function that included the boundary conditions term and the partial differential equation term allowed for producing results that show good agreement with the results from a numerical simulator. However, in the case of heterogeneous media where there are sharp discontinuities in hydraulic conductivity inside the domain, the model failed to produce accurate results. To resolve this issue, extended physics-informed neural networks were used. This method involves the decomposition of the domain into multiple homogeneous sub-domains. Each sub-domain has its own physics informed neural network structure, equation parameters, and equation constraints. To allow the sub-domains to communicate, interface conditions are placed on the interfaces that separate the different sub-domains. The results from this method matched well with the results of the simulator. In both the homogeneous and heterogeneous cases, neural networks with only one hidden layer with thirty nodes were used. Even with this simple structure for the neural networks, the computations are expensive and a large number of training iterations is required to converge.
  • Carbonate Acidizing: Modeling and Uncertainty Propagation Analysis

    Sahu, Qasim (2021-07) [Thesis]
    Advisor: Hoteit, Hussein
    Committee members: Alafifi, Abdulkader Musa; Vahrenkamp, Volker C.
    Reservoir stimulation is a common technique used to improve the productivity of carbonate reservoirs. One of the effective stimulation methods is carbonate acidizing. This process involves injecting a reactive fluid to dissolve the rock mineral, creating a conductive path for hydrocarbon flow. With the development of tight and unconventional reservoirs, stimulation has become more critical for optimal economic production. This study aims to simulate the dissolution of carbonate in matrix acidizing. A reactive transport model is implemented in a finite – element solver to simulate the initiation and propagation of the dissolution channel in the carbonate rock in a two – dimensional domain. We investigate the effect of varying the injection rate on the dissolution channel and the efficiency of the acidizing fluid. Next, we use polynomial chaos expansion to conduct uncertainty propagation analysis. These uncertainties may have a major impact on the predictability of the simulation model. We utilize the surrogate model and Sobol indices to identify the most significant parameter in the model. The analysis provides an assessment of how the uncertainty can propagate to the model’s response. Also, we utilize the surrogate model to calculate the univariate effect. The results showed that the dissolution channel and pore volume to breakthrough depends on the injection rate. Furthermore, the surrogate model reproduces the simulation model results for the 5 dissolution channel, the pore volume to breakthrough, and the effective permeability. The global sensitivity analysis shows that the acid capacity number is the most significant parameter for the pore volume to breakthrough with the highest Sobol index value. For effective permeability, the initial mean porosity is the primary source of uncertainty. The marginal effect calculated for the individual parameter correlates with the results from Sobol indices.
  • Semi-Analytical Solution to Assess CO2 Leakage in the Subsurface through Abandoned Wells

    Qiao, Tian (2021-07) [Thesis]
    Advisor: Hoteit, Hussein
    Committee members: Patzek, Tadeusz; Sun, Shuyu
    Geological storage is an effective approach capable of reducing greenhouse gases emissions at significant scales by storing the CO2 underground. Subsurface reservoirs with sealing caprocks can provide long-term containment for the injected CO2. However, the leakage is a major concern in most storage sites. The presence of abandoned wells penetrating the reservoir caprock may cause leakage flow paths for CO2 to the overburden. To access the leakage in the subsurface, an analytical model for the time-varying leaky well is needed. In this thesis, we propose a new semi-analytical approach based on pressure-transient analysis to model the behavior of leakage and corresponding pressure distribution in multiple wells multiple layers system. Current solutions either take approximations on essential operations or requires numerical inversion for the solution in the Laplace domain. In this work, we employ the superposition in time and space to solve the diffusivity equation in 2D radial flow to approximate the transient pressure in the reservoirs. We use numerical simulations to verify the proposed time-dependent semi-analytical solution. The results show good agreement in both pressure and leakage rates. Sensitivity analysis is conducted to assess different CO2 leakage scenarios to the overburden. The equivalent injection rate is also proposed to release the single-phase assumption so that the solution can recover identical results as two-phase numerical simulation in the far-field.
  • Analysis and Visualization of 3D pore networks in Pleistocene reef cores from Shurayrah Island (Al Wajh, N Red Sea)

    Oyinloye, Michael (2021-07) [Thesis]
    Advisor: Vahrenkamp, Volker
    Committee members: Alafifi, Abdulkader Musa; Sun, Shuyu
    The characterization of petrophysical properties such as porosity and permeability of carbonate reservoirs for understanding their heterogeneous nature is essential to enhance reservoir modelling and exploration. In the early development stages of carbonate rocks, early diagenesis features fundamental changes in the porosity and permeability systems which will likely yield enormous influence on the subsequent diagenesis, and hence the petrophysical properties of potential limestone reservoirs. From a Late Pleistocene (MIS5) reefal core limestone from Al Wajh, Shurayrah Island, Northern Red Sea, KSA, detailed petrographic image analysis of thin sections, laboratory measurements of porosity and permeability and x-ray computed tomography (CT) of core plugs and whole core sections, were used for the identification, analysis and visualization of the pore types, pore network and pore connectivity. Analyzed x-ray CT scan images reveal the pore types, pore network and pore connectivity in 2D and 3D. A separate in-depth facies and diagenesis study using thin section images coupled with x-ray CT image analysis, shows lithofacies and microfacies types control most of the early diagenesis hence porosity and permeability. This thesis hopes to open a pathway to understanding pore and pore throat structures as well as the porosity-permeability relationship in young carbonate rocks before deep burial to enhance reservoir modelling and characterization of analogues
  • Data-driven analysis of climate change in Saudi Arabia: trends in temperature extremes and human comfort indicators

    Odnoletkova, Natalia; Patzek, Tadeusz (Journal of Applied Meteorology and Climatology, American Meteorological Society, 2021-06-30) [Article]
    AbstractWe have analyzed the long-term temperature trends and extreme temperature events in Saudi Arabia between 1979 and 2019. Our study relies on the high resolution, consistent and complete ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). We evaluated linear trends in several climate descriptors, including temperature, dewpoint temperature, thermal comfort and extreme event indices. Previous works on this topic used data from weather station observations over limited time intervals and did not include temperature data for recent years. The years 2010-2019 have been the warmest decade ever observed by instrumental temperature monitoring and comprise the eight warmest years on record. Therefore the earlier results may be incomplete and their results no longer relevant. Our findings indicate that over the past four decades, Saudi Arabia has warmed up at a rate that is 50% higher than the rest of land mass in the Northern Hemisphere. Moreover, moisture content of the air has significantly increased in the region. The increases of temperature and humidity have resulted in the soaring of dew point temperature and thermal discomfort across the country. These increases are more substantial during summers, which are already very hot compared to winters. Such changes may be dangerous to people over vast areas of the country. If the current trend persists into the future, human survival in the region will be impossible without continuous access to air conditioning.
  • Impact of fracture geometry and topology on the connectivity and flow properties of stochastic fracture networks

    Zhu, Weiwei; Khirevich, Siarhei; Patzek, Tadeusz (Water Resources Research, American Geophysical Union (AGU), 2021-06-27) [Article]
    In a low permeability formation, connectivity of natural and induced fractures determines overall hydraulic diffusivity in fluid flow through this formation and defines effective rock permeability. Efficient evaluation of fracture connectivity is a nontrivial task. Here we utilize a topological concept of global efficiency to evaluate this connectivity. We address the impact of key geometrical properties of stochastic fracture networks (fracture lengths, orientations, apertures and positions of fracture centers) on the macro-scale flow properties of a shale-like formation. Six thousand different realizations have been generated to characterize these properties for each fracture network. We find that a reduced graph of a fracture network, which consists of the shortest paths from the inlet nodes (fractures) to all outlet nodes, contributes most to fluid flow. 3D fracture networks usually have higher global efficiency than 2D ones, because they have better connectivity. All geometrical properties of fractures influence quality of their connectivity. Aperture distribution impacts strongly global efficiency of a fracture network, and its influence is more significant when the system is dominated by large fractures. Fracture clustering lowers global efficiency in both 2D and 3D fracture networks. Global efficiency of 2D and 3D fracture networks also decreases with the increasing exponent of the power-law distribution of fracture lengths, which means that the connectivity of the system decreases with an increasing number of small fractures. Realistic fracture networks, composed of several sets of fractures with constrained preferred orientations, share all the characteristics of the stochastic fracture networks we have investigated.
  • Numerical study of fractured rock masses: Transverse isotropy vs. implicit joint-continuum models

    Shin, Hosung; Santamarina, Carlos (Elsevier BV, 2021-06-26) [Article]
    Fractures prevail mechanical behavior of a rock mass and confer an overall anisotropic response. Engineering analyses in the elastic regime often use transverse isotropy to model fractured rock masses with a single fracture set. An alternative implicit joint-continuum model combines the mechanical response of the intact rock and fractures by adding their compliance matrices. It can accommodate multiple fracture sets and non-linear fracture response. While the transverse isotropic model is inadequate to model fractured rock media because of its inherent assumptions on the continuity for all stress components, the implicit joint-continuum model is verified against the exact solutions of internal stress distributions and displacement field. The analysis of strip foundations using the implicit joint continuum approach shows that the maximum settlement and tilt will take place when the fracture set strikes quasi-collinear with the strip direction (θJ ≈ ±15°) and the fracture dip angle is either βJ ≈ 40° ± 10° or βJ ≈ 140° ± 10°.
  • A Corrected Cubic Law for Single-phase Laminar Flow through Rough-walled Fractures

    He, Xupeng; Sinan, Marwa; Kwak, Hyung; Hoteit, Hussein (Advances in Water Resources, Elsevier BV, 2021-06-19) [Article]
    Hydraulic properties of natural fractures are essential parameters for the modeling of fluid flow and transport in subsurface fractured porous media. The cubic law, based on the parallel-plate concept, has been traditionally used to estimate the hydraulic properties of individual fractures. This upscaling approach, however, is known to overestimate the fractures hydraulic properties. Dozens of methods have been proposed in the literature to improve the accuracy of the cubic law. The relative performance of these various methods is not well understood. In this work, a comprehensive review and benchmark of almost all commonly used cubic law-based approaches in the literature, covering 43 methods is provided. We propose a new corrected cubic law for incompressible, single-phase laminar flow through rough-walled fractures. The proposed model incorporates corrections to the hydraulic fracture aperture based on the flow tortuosity and local roughness of the fracture walls. We identify geometric rules relative to the local characteristic of the fracture and apply an efficient algorithm to subdivide the fracture into segments, accordingly. High-resolution simulations for Navier-Stokes equations, computed in parallel, for synthetic fractures with various ranges of surface roughness and apertures are then performed. The numerical solutions are used to assess the accuracy of the proposed model and compare it with the other 43 approaches, where we demonstrate its superior accuracy. The proposed model retains the simplicity and efficiency of the cubic law but with pronounced improvement to its accuracy. The data set used in the benchmark, including more than 7500 fractures, is provided in open-access.
  • Impact of particle shape on networks in sands

    Fei, Wenbin; Narsilio, Guillermo A.; van der Linden, Joost H.; Tordesillas, Antoinette; Disfani, Mahdi M.; Santamarina, Carlos (Computers and Geotechnics, Elsevier BV, 2021-06-19) [Article]
    Employing network science to understand particle interactions helps manufacture advanced materials with superior force transmission and heat transfer. However, knowledge of the dependence of networks on particle features such as shape is missing. This study computes particle shape ─ the average of three-dimensional sphericity and roundness, and multiscale network variables ─ degree, edge betweenness centrality and global clustering coefficient from unweighted/weighted contact and thermal networks ─ for three sands based on their X-ray computed tomography images. The dependence of network features on particle shape is explored for both individual particles and bulk sand samples. Results show that particle shape affects the degree in a network at sample and particle scales differently. In contrast, weighted edge betweenness centrality has a consistent inverse relationship with particle shape at both scales. The weighted edge betweenness centrality values from different samples consistently indicate that 20% of network edges (e.g., contacts) are responsible for 60% of the heat transfer in dry sands. Although unweighted edge betweenness centrality cannot reflect the heat transfer directly, it has a similar correlation with particle shape to the weighted feature. Global clustering coefficient from the thermal network increases in round particle packings and can indicate the mechanical rigidity of sands.
  • Quality Evaluation of Epoxy Pore Casts Using Silicon Micromodels: Application to Confocal Imaging of Carbonate Samples

    Hassan, Ahmed; Yutkin, Maxim; Chandra, Viswasanthi; Patzek, Tadeusz (Applied Sciences, MDPI AG, 2021-06-16) [Article]
    Pore casting refers to filling the void spaces of porous materials with an extraneous fluid, usually epoxy resin, to obtain a high-strength composite material, stabilize a fragile porous structure, produce a three-dimensional replica of the pore space, or provide imaging contrast. Epoxy pore casting may be accompanied by additional procedures, such as etching, in which the material matrix is dissolved, leaving a clean cast. Moreover, an epoxy resin may be mixed with fluorophore substances to allow fluorescence imaging. Our work aims to investigate and optimize the epoxy pore casting procedure parameters, for example, impregnation pressure. We use silicon micromodels as a reference to validate the key parameters of high-pressure resin impregnation. We demonstrate possible artifacts and defects that might develop during impregnation with resin, e.g., resin shrinkage and gas trapping. In the end, we developed an optimized protocol to produce high-quality resin pore casts for high-resolution 3D imaging and the description of microporosity in micritic carbonates. In our applications, the high-quality pore casts were acid-etched to remove the non-transparent carbonate material, making the pore casts suitable for imaging with Confocal Laser Scanning Microscopy (CLSM). In addition, we evaluate the quality of our etching procedure using micro-computed tomography (micro-CT) scans of the pre- and post-etched samples and demonstrate that the etched epoxy pore casts represent the pore space of microporous carbonate rock samples with high fidelity.
  • Effect of Soft Viscoelastic Biopolymer on the Undrained Shear Behavior of Loose Sands

    Noh, Dong-Hwa; Cha, Wonjun; Santamarina, Carlos; Cho, Gye-Chun; Kwon, Tae-Hyuk (Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers (ASCE), 2021-06-03) [Article]
    Soft viscoelastic biological products such as biopolymers and biofilms have recently garnered significant interest as alternative biogrout materials for ground improvement because of their nontoxic and biodegradable characteristics. However, the impact of soft gel-like viscoelastic pore fillers on the undrained response of treated soils remains poorly understood. This study involves undrained triaxial compression tests with concurrent shear wave velocity measurements of loose contractive sands treated with soft gelatin. The specimens experience two distinct loading-gelation sequences, either consolidation before gelation (CbG) or confinement after gelation (CaG). Results reveal that the shear wave velocity can be used as an indicator of the effective stress carried by the granular skeleton. The inclusion of the viscoelastic biopolymer hinders the contractive tendency, diminishes postpeak softening, and increases the undrained shear strength of loose contractive sands. These effects become more pronounced for stiffer biopolymers because they provide an enhanced skeletal support against chain buckling and contraction. The presence of biopolymers increases the normalized undrained shear strength from Su=σ 0o ¼ ∼0.1 to ∼1.4, particularly at low effective confining stress. The biopolymers alter the terminal state in the p0-q-e space. Therefore, critical states should be reconsidered for biopolymer-treated sands. The confinement-gelation sequence affects the effective stress supported by the granular frame and thus has pronounced effects on the undrained shear strength. This suggests the potential use of viscoelastic pore fillers as an effective treatment of loose sands prone to liquefaction
  • A semi-analytical approach to model drilling fluid leakage into fractured formation

    Albattat, Rami; Hoteit, Hussein (Rheologica Acta, Springer Science and Business Media LLC, 2021-05-22) [Article]
    AbstractLoss of circulation while drilling is a challenging problem that may interrupt operations and contaminate the subsurface formation. Analytical modeling of fluid flow in fractures is a tool that can be quickly deployed to assess drilling mud leakage into fractures. A new semi-analytical solution is developed to model the flow of non-Newtonian drilling fluid in fractured formation. The model is applicable for various fluid types exhibiting yield-power law (Herschel-Bulkley). We use finite-element simulations to verify our solutions. We also generate type curves and compare them to others in the literature. We then demonstrate the applicability of the proposed model for two field cases encountering lost circulations. To address the subsurface uncertainty, we combine the semi-analytical solutions with Monte Carlo and generate probabilistic predictions. The solution method can estimate the range of fracture conductivity, parametrized by the fracture hydraulic aperture, and time-dependent fluid loss rate that can predict the cumulative volume of lost fluid.
  • Mid-Holocene to present circum-Arabian sea level database: Investigating future coastal ocean inundation risk along the Arabian plate shorelines

    Khanna, Pankaj; Petrovic, Alexander; Ramdani, Ahmad Ihsan; Homewood, Peter; Mettraux, Monique; Vahrenkamp, Volker (Quaternary Science Reviews, Elsevier BV, 2021-05-05) [Article]
    The Arabian Peninsula has a unique setting to resolve how proximity to tectonically diverse plate margins, eustacy, and glacial isostatic adjustment (GIA) influences coastal sea level fluctuations. New 14C AMS and U series dating of coastal sediments from the western, southern, and eastern plate margins (Al-Wajh and Thuwal, Saudi Arabia; Bar Al-Hikman, Oman; Abu Dhabi, U.A.E) have been integrated with an archive of dated coastal sediments (n = 145, 31 locations). Each dated sample is recalibrated for its elevation based on a high-resolution coastal. DEM dataset, tidal and tectonic correction, and reservoir correction, to develop a new-suite of relative sea level (RSL) plots, separated into six tectonically distinct zones. A mid-Holocene highstand has been identified in most of the zones (1, 2, 4, 6), however, with complex spatial and temporal variability. No data is available for zone 3, whereas no Holocene highstand was observed in zone 5. The results suggest that eustacy, varying rates of vertical tectonic change (max 1 mm/year) and glacial isostatic adjustment (max 0.5 mm/year) were the major drivers of sea level fluctuations since Mid-Holocene albeit in different proportions along the different sections of Arabian shorelines. Furthermore, the topography of a shoreline, tidal range, and presence/absence of a coastal barrier also significantly influences the coastal inundation. Based on our findings, eastern Arabia will in the near future experience the largest coastal flooding (largest 0–10 m elevation area, > 2 m tidal amplitude, no barriers), followed by western (1–2 m tidal amplitude, discontinuous coral reef barriers) and southern Arabia shorelines (>3 m tidal amplitude, no barriers) shorelines. The presented insights are critical in supporting communities along the coasts of the Arabian Peninsula, who will have to cope with flooding from rising oceans over the next few decades due to climate change.
  • Bio-inspired Geotechnical Engineering: Principles, Current Work, Opportunities and Challenges

    Martinez, Alejandro; DeJong, Jason; Akin, Idil; Aleali, Ali; Arson, Chloe; Atkinson, Jared; Bandini, Paola; Baser, Tugce; Borela, Rodrigo; Boulanger, Ross; Burrall, Matthew; Chen, Yuyan; Collins, Clint; Cortes, Douglas; Dai, Sheng; DeJong, Theodore; Dottore, Emanuela Del; Dorgan, Kelly; Fragaszy, Richard; Frost, J. David; Full, Robert; Ghayoomi, Majid; Goldman, Daniel; Gravish, Nicholas; Guzman, Ivan L.; Hambleton, James; Hawkes, Elliot; Helms, Michael; Hu, David; Huang, Lin; Huang, Sichuan; Hunt, Christopher; Irschick, Duncan; Lin, Hai Thomas; Lingwall, Bret; Marr, Alen; Mazzolai, Barbara; McInroe, Benjamin; Murthy, Tejas; O'Hara, Kyle; Porter, Marianne; Sadek, Salah; Sanchez, Marcelo; Santamarina, Carlos; Shao, Lisheng; Sharp, James; Stuart, Hannah; Stutz, Hans Henning; Summers, Adam; Tao, Julian; Tolley, Michael; Treers, Laura; Turnbull, Kurtis; Valdes, Rogelio; van Passen, Leon; Viggiani, Gioacchino; Wilson, Daniel; Wu, Wei; Yu, Xiong; Zheng, Junxing (Géotechnique, ICE Publishing, 2021-04-26) [Article]
    A broad diversity of biological organisms and systems interact with soil in ways that facilitate their growth and survival. These interactions are made possible by strategies that enable organisms to accomplish functions that can be analogous to those required in geotechnical engineering systems. Examples include anchorage in soft and weak ground, penetration into hard and stiff subsurface materials and movement in loose sand. Since the biological strategies have been “vetted” by the process of natural selection, and the functions they accomplish are governed by the same physical laws in both the natural and engineered environments, they represent a unique source of principles and design ideas for addressing geotechnical challenges. However, prior to implementation as engineering solutions, the differences in spatial and temporal scales and material properties between the biological environment and engineered system must be addressed. Bio-inspired geotechnics research is addressing topics such as soil excavation and penetration, soil–structure interface shearing, load transfer between foundation and anchorage elements and soils, and mass and thermal transport, having gained inspiration from organisms such as worms, clams, ants, termites, fishes, snakes and plant roots. This work highlights the potential benefits to both geotechnical engineering through new or improved solutions and biology through understanding of mechanisms as a result of cross-disciplinary interactions and collaborations.
  • Semi-Analytical Solution to Assess CO2 Leakage in the Subsurface through Abandoned Wells

    Qiao, Tian; Hoteit, Hussein; Fahs, Marwan (Energies, MDPI AG, 2021-04-25) [Article]
    Geological carbon storage is an effective method capable of reducing carbon dioxide (CO2) emissions at significant scales. Subsurface reservoirs with sealing caprocks can provide long-term containment for the injected fluid. Nevertheless, CO2 leakage is a major concern. The presence of abandoned wells penetrating the reservoir caprock may cause leakage flow-paths for CO2 to the overburden. Assessment of time-varying leaky wells is a need. In this paper, we propose a new semi-analytical approach based on pressure-transient analysis to model the behavior of CO2 leakage and corresponding pressure distribution within the storage site and the overburden. Current methods assume instantaneous leakage of CO2 occurring with injection, which is not realistic. In this work, we employ the superposition in time and space to solve the diffusivity equation in 2D radial flow to approximate the transient pressure in the reservoirs. Fluid and rock compressibilities are taken into consideration, which allow calculating the breakthrough time and the leakage rate of CO2 to the overburden accurately. We use numerical simulations to verify the proposed time-dependent semi-analytical solution. The results show good agreement in both pressure and leakage rates. Sensitivity analysis is then conducted to assess different CO2 leakage scenarios to the overburden. The developed semi-analytical solution provides a new simple and practical approach to assess the potential of CO2 leakage outside the storage site. This approach is an alternative to numerical methods when detailed simulations are not feasible. Furthermore, the proposed solution can also be used to verify numerical codes, which often exhibit numerical artifacts.
  • Heat Flow in Fractured Rocks: Stress and Moisture-Dependent Thermal Contact Resistance

    Garcia, A.V.; Santamarina, Carlos (Geothermics, Elsevier BV, 2021-04-21) [Article]
    The thermal conductivity of fractured rock masses is an important parameter for the analysis of energy geosystems, yet, its measurement is challenged by specimen size requirements. Fluids within fractures have lower thermal conductivities than rock minerals and heat flow lines constrict through contacting asperities. Together, heat flow constriction and phonon boundary scattering cause an apparent temperature discontinuity across the fracture, typically represented as a thermal contact resistance. We investigate the thermal contact resistance in fractured limestone and its evolution during loading and unloading (σ’=10 kPa to σ’=3000 kPa) for clean and gouge-filled fractures, under both air-dry and water-saturated conditions. The fracture thermal contact resistance decreases during loading because of the increase in the true contact area, gouge and asperity crushing, and fracture filling by produced fines that contribute new conduction pathways. These processes convey high stress sensitivity and loading hysteresis to the fracture thermal contact resistance. Water fills the fracture interstices and forms menisci at mineral contacts that significantly improve heat conduction even in partially saturated rock masses. The rock mass effective thermal conductivity can be estimated by combining the intact rock thermal conductivity with measurements of the thermal contact resistance of a single fracture under field boundary conditions.
  • Impact of depositional and diagenetic features on petrophysical and rock mechanical properties in Arab-D reservoir equivalent upper Jubaila Formation, Saudi Arabia

    Chandra, Viswasanthi; Petrovic, Alexander; Khanna, Pankaj; Ramdani, Ahmad I.; Yalcin, Bora; Vahrenkamp, Volker; Finkbeiner, Thomas (Marine and Petroleum Geology, Elsevier BV, 2021-04-20) [Article]
    This paper presents a comprehensive analysis of multiscale geological, petrophysical and rock mechanical data acquired from 35 m of outcrop well core from the Late Jurassic (Kimmeridgian) Upper Jubaila Formation, Saudi Arabia. In this location the sequence is a typical shallow marine heterogeneous carbonate sequence and a direct analogue to a part of the prolific Arab D reservoir sequence in the subsurface towards the east. Four main lithofacies types were identified with a general shoaling upwards trend, varying from nodular bioturbated peloidal mudstone/wackestone facies to sharp-based intraclast-peloidal, skeletal rudstone/floatstone facies. The mineralogy in the upper section of the well cores is predominantly calcite, while the lower section is also comprised of some dolomite and quartz. Stratiform dedolomitization as a telogenetic overprint is only evident in the upper 18 m of the core and controlled by vertical flow of meteoric fluids. The core plug porosity distribution is lower than that of the subsurface equivalent reservoir zones, and is attributed to meteoric cementation. Thalassinoides burrow features in mudstone and wackestone facies in the upper sections of the core control horizontal permeability distribution at the centimeter to meter-scale. Micrite morphology and dedolomitization appear to be key controls on plug permeability, rock strength and sonic velocity. Based on the trends observed in compressive rock strength, p-wave velocity and plug porosity distributions, the cored section was divided into five main rock mechanical layers. Despite reduced porosity, the average compressive rock strength in the outcrop core is lower than that of the Arab-D subsurface equivalent rocks, indicating overall ‘weakening’ of the rock due to telogenetic processes and surface weathering.
  • The Geological Potential of the Arabian Plate for CCS and CCUS - An Overview

    Vahrenkamp, Volker; Alafifi, Abdulkader Musa; Tasianas, Alexandros; Hoteit, Hussein (SSRN Electronic Journal, Elsevier BV, 2021-04-09) [Article]
    Given allowable carbon emissions for reaching climate targets, CCS and CCUS are without alternatives to simultaneously maintain a supply of sufficient energy for the world and preventing stranded subsurface assets for hydrocarbon producing countries. Permanent storage of carbon dioxide (CO2) in deep subsurface formations is acknowledged as a scalable and achievable technology to contribute to the ongoing efforts of limiting CO2 emissions and possibly lead to the use of stored CO2 for geothermal energy generation. The sequestration processes include entrapping CO2 in saline aquifers and hydrocarbon reservoirs in its mobile phase and in basalts as carbonate minerals. So, what are then the geological subsurface opportunities in Arabia for CO2 sequestration? A high level assessment has been conducted to identify geological formations suitable for storing and utilizing CO2 on a large scale. Over the Arabian peninsula four significantly different geological terrains are likely suitable for CCS & CCUS: (1) An Eastern section of stacked Mesozoic aquifers along the coast and inland of the Arabian Gulf, (2) rift basins with deep saline aquifers along the Red Sea, (3) Cenozoic volcanic rocks inland of the Red Sea coast, and Proterozoic ultramafic rocks in the Arabian Shield, and (4) a fringe of Cretaceous obducted marine crust (ophiolites) in Northeastern Oman and the UAE.

View more