Recent Submissions

  • Fracture Permeability Estimation Under Complex Physics: A Data-Driven Model Using Machine Learning

    He, Xupeng; Zhu, Weiwei; Santoso, Ryan; Alsinan, Marwa; Kwak, Hyung; Hoteit, Hussein (SPE, 2021-09-15) [Conference Paper]
    Abstract The permeability of fractures, including natural and hydraulic, are essential parameters for the modeling of fluid flow in conventional and unconventional fractured reservoirs. However, traditional analytical cubic law (CL-based) models used to estimate fracture permeability show unsatisfactory performance when dealing with different dynamic complexities of fractures. This work presents a data-driven, physics-included model based on machine learning as an alternative to traditional methods. The workflow for the development of the data-driven model includes four steps. Step 1: Identify uncertain parameters and perform Latin Hypercube Sampling (LHS). We first identify the uncertain parameters which affect the fracture permeability. We then generate training samples using LHS. Step 2: Perform training simulations and collect inputs and outputs. In this step, high-resolution simulations with parallel computing for the Navier-Stokes equations (NSEs) are run for each of the training samples. We then collect the inputs and outputs from the simulations. Step 3: Construct an optimized data-driven surrogate model. A data-driven model based on machine learning is then built to model the nonlinear mapping between the inputs and outputs collected from Step 2. Herein, Artificial Neural Network (ANN) coupling with Bayesian optimization algorithm is implemented to obtain the optimized surrogate model. Step 4: Validate the proposed data-driven model. In this step, we conduct blind validation on the proposed model with high-fidelity simulations. We further test the developed surrogate model with newly generated fracture cases with a broad range of roughness and tortuosity under different Reynolds numbers. We then compare its performance to the reference NSEs solutions. Results show that the developed data-driven model delivers good accuracy exceeding 90% for all training, validation, and test samples. This work introduces an integrated workflow for developing a data-driven, physics-included model using machine learning to estimate fracture permeability under complex physics (e.g., inertial effect). To our knowledge, this technique is introduced for the first time for the upscaling of rock fractures. The proposed model offers an efficient and accurate alternative to the traditional upscaling methods that can be readily implemented in reservoir characterization and modeling workflows.
  • CO2 Leakage Rate Forecasting Using Optimized Deep Learning

    He, Xupeng; ZHU, Weiwei; Santoso, Ryan; Alsinan, Marwa; Kwak, Hyung; Hoteit, Hussein (SPE, 2021-09-15) [Conference Paper]
    Abstract Geologic CO2 Sequestration (GCS) is a promising engineering technology to reduce global greenhouse emissions. Real-time forecasting of CO2 leakage rates is an essential aspect of large-scale GCS deployment. This work introduces a data-driven, physics-featuring surrogate model based on deep-learning technique for CO2 leakage rate forecasting. The workflow for the development of data-driven, physics-featuring surrogate model includes three steps: 1) Datasets Generation: We first identify uncertainty parameters that affect the objective of interests (i.e., CO2 leakage rates). For the identified uncertainty parameters, various realizations are then generated based on Latin Hypercube Sampling (LHS). High-fidelity simulations based on a two-phase black-oil solver within MRST are performed to generate the objective functions. Datasets including inputs (i.e., the uncertainty parameters) and outputs (CO2 leakage rates) are collected. 2) Surrogate Development: In this step, a time-series surrogate model using long short-term memory (LSTM) is constructed to map the nonlinear relationship between these uncertainty parameters as inputs and CO2 leakage rates as outputs. We perform Bayesian optimization to automate the tuning of hyperparameters and network architecture instead of the traditional trial-error tuning process. 3) Uncertainty Analysis: This step aims to perform Monte Carlo (MC) simulations using the successfully trained surrogate model to explore uncertainty propagation. The sampled realizations are collected in the form of distributions from which the probabilistic forecast of percentiles, P10, P50, and P50, are evaluated. We propose a data-driven, physics-featuring surrogate model based on LSTM for CO2 leakage rate forecasting. We demonstrate its performance in terms of accuracy and efficiency by comparing it with ground-truth solutions. The proposed deep-learning workflow shows promising potential and could be readily implemented in commercial-scale GCS for real-time monitoring applications.
  • EM-Based 2D Corrosion Azimuthal Imaging using Physics Informed Machine Learning PIML

    Ooi, Guang An; Özakin, Mehmet Burak; Mostafa, Tarek Mahmoud Atia; Bagci, Hakan; Ahmed, Shehab; Larbi Zeghlache, Mohamed (SPE, 2021-09-07) [Conference Paper]
    In the wake of today's industrial revolution, many advanced technologies and techniques have been developed to address the complex challenges in well integrity evaluation. One of the most prominent innovations is the integration of physics-based data science for robust downhole measurements. This paper introduces a promising breakthrough in electromagnetism-based corrosion imaging using physics informed machine learning (PIML), tested and validated on the cross-sections of real metal casings/tubing with defects of various sizes, locations, and spacing. Unlike existing electromagnetism-based inspection tools, where only circumferential average metal thickness is measured, this research investigates the artificial intelligence (AI)-assisted interpretation of a unique arrangement of electromagnetic (EM) sensors. This facilitates the development of a novel solution for through-tubing corrosion imaging that enhances defect detection with pixel-level accuracy. The developed framework incorporates a finite-difference time-domain (FDTD)-based EM forward solver and an artificial neural network (ANN), namely the long short-term memory recurrent neural network (LSTM-RNN). The ANN is trained using the results generated from the FDTD solver, which simulates sensor readings for different scenarios of defects. The integration of the array EM-sensor responses and an ANN enabled generalizable and accurate measurements of metal loss percentage across various experimental defects. It also enabled the precise predictions of the defects’ aperture sizes, numbers, and locations in 360-degree coverage. Results were plotted in customized 2D heat-maps for any desired cross-section of the test casings. Further analysis of different techniques demonstrated that the LSTM-RNN could show higher precision and robustness compared to regular dense NNs, especially in the case of multiple defects. The LSTM-RNN is validated using additional data from simulated and experimental data. The results show reliable predictions even with limited training data. The model accurately predicted defects of larger and smaller sizes that were intentionally excluded from the training data to demonstrate generalizability. This highlights a major advance toward corrosion imaging behind tubing. This novel technique paves the way for the use of similar concepts on other sensors in multiple barriers imaging. Further work includes improvement to the sensor package and ANNs by adding a third dimension to the imaging capabilities to produce 3D images of defects on casings.
  • Fault Traces: Generation of Fault Segments and Estimation of Their Fractal Dimension

    Zhu, Weiwei; Yalcin, Bora; Khirevich, Siarhei; Patzek, Tadeusz (Lithosphere, GeoScienceWorld, 2021-08-27) [Article]
    Fault damage zones have a higher upscaled permeability than the host rock because of a higher fracture intensity therein. Fracture distribution in the damage zone depends highly on the geometry of fault segments. However, precise images of architectural elements of large-scale faults at depth are difficult to obtain by seismic acquisition and imaging techniques. We present a numerical method that generates fault segments at multiple scales from an imprecise fault trace based on the fractal properties of these segments. The generated fault segments demonstrate hierarchical self-similar architecture, and their lengths follow approximately a lognormal distribution. These characteristics are similar to real fault segments observed in outcrops and seismic surveys. An algorithm that covers fault segments accurately with the minimum number of circles is proposed to calculate the fractal dimensions for both natural and computer-generated faults. The fractal dimensions of natural and generated fault segments are similar and range between 1.2 and 1.4.
  • Fault Traces: Generation of Fault Segments and Estimation of Their Fractal Dimension

    Zhu, Weiwei; Yalcin, Bora; Khirevich, Siarhei; Patzek, Tadeusz (Lithosphere, GeoScienceWorld, 2021-08-27) [Article]
    Fault damage zones have a higher upscaled permeability than the host rock because of a higher fracture intensity therein. Fracture distribution in the damage zone depends highly on the geometry of fault segments. However, precise images of architectural elements of large-scale faults at depth are difficult to obtain by seismic acquisition and imaging techniques. We present a numerical method that generates fault segments at multiple scales from an imprecise fault trace based on the fractal properties of these segments. The generated fault segments demonstrate hierarchical self-similar architecture, and their lengths follow approximately a lognormal distribution. These characteristics are similar to real fault segments observed in outcrops and seismic surveys. An algorithm that covers fault segments accurately with the minimum number of circles is proposed to calculate the fractal dimensions for both natural and computer-generated faults. The fractal dimensions of natural and generated fault segments are similar and range between 1.2 and 1.4.
  • Natural Rock Fractures: From Aperture to Fluid Flow

    Cardona, Alejandro; Finkbeiner, Thomas; Santamarina, Carlos (Rock Mechanics and Rock Engineering, Springer Science and Business Media LLC, 2021-08-07) [Article]
    AbstractFractures provide preferential flow paths and establish the internal “plumbing” of the rock mass. Fracture surface roughness and the matedness between surfaces combine to delineate the fracture geometric aperture. New and published measurements show the inherent relation between roughness wavelength and amplitude. In fact, data cluster along a power trend consistent with fractal topography. Synthetic fractal surfaces created using this power law, kinematic constraints and contact mechanics are used to explore the evolution of aperture size distribution during normal loading and shear displacement. Results show that increments in normal stress shift the Gaussian aperture size distribution toward smaller apertures. On the other hand, shear displacements do not affect the aperture size distribution of unmated fractures; however, the aperture mean and standard deviation increase with shear displacement in initially mated fractures. We demonstrate that the cubic law is locally valid when fracture roughness follows the observed power law and allows for efficient numerical analyses of transmissivity. Simulations show that flow trajectories redistribute and flow channeling becomes more pronounced with increasing normal stress. Shear displacement induces early aperture anisotropy in initially mated fractures as contact points detach transversely to the shear direction; however, anisotropy decreases as fractures become unmated after large shear displacements. Radial transmissivity measurements obtained using a torsional ring shear device and data gathered from the literature support the development of robust phenomenological models that satisfy asymptotic trends. A power function accurately captures the evolution of transmissivity with normal stress, while a logistic function represents changes with shear displacement. A complementary hydro-chemo-mechanical study shows that positive feedback during reactive fluid flow heightens channeling.
  • Comparison of various reactive transport simulators for geological carbon sequestration

    Addassi, Mouadh; Omar, Abdirizak; Ghorayeb, Kassem; Hoteit, Hussein (International Journal of Greenhouse Gas Control, Elsevier BV, 2021-08-05) [Article]
    The capabilities of reactive transport modeling codes for geological carbon sequestration have improved significantly in the past decade. Comparing different geochemical modeling codes is crucial to identify modeling discrepancies, especially when experimental validation is not feasible. However, it is challenging to consistently get comparable results, as shown in previous studies where batch reaction of CO2 storage using different simulators sometimes resulted in significant discrepancies in their outputs. In this study, we introduce and demonstrate an approach to consistently produce comparable batch-reaction modeling of kinetically controlled CO2-water-rock interactions in PHREEQC, TOUGHREACT, and GEM, which are amongst the most widely used simulators for CO2 sequestration studies. The primary step is to assemble a thermodynamic database in PHREEQC format, with representative fluid properties for CO2-water interaction, and carefully convert it to the format of the other simulators. We use two case studies from the literature to demonstrate our method where good matches between the outputs of all three simulators were achieved, which was not previously attained. Furthermore, limiting the discrepancies in batch-reaction models provides a consistent baseline to study the coupled mechanisms of transport and chemical reaction, which was also successfully demonstrated with a one-dimensional reactive transport model in PHREEQC, GEM and TOUGHREACT.
  • 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.
  • Structural aspects, mechanisms and emerging prospects of Gemini surfactant-based alternative Enhanced Oil Recovery technology: A review

    Pal, Nilanjan; Hoteit, Hussein; Mandal, Ajay (Journal of Molecular Liquids, Elsevier BV, 2021-06-30) [Article]
    The design and development of chemical routes with fascinating physicochemical attributes comprise a major field of research in enhanced oil recovery (EOR). ‘Dimerization’ depicts a novel way to control structural assemblies and physicochemical properties, to achieve marked improvements in the chemical EOR process, and strategize oil recovery performance. There are immense possibilities for the diversification of gemini surfactant structure, which essentially consists of two identical or distinct amphiphilic units linked with a spacer group. Gemini surfactant molecules possess significantly lower critical micelle concentration (CMC) as compared to their monomeric counterparts, owing to their ability to self-aggregate at low dosages. Gemini surfactants exhibit a uniquely stable micellar structure, favorable interfacial behavior, rock-wetting character, viscoelasticity and cost-profitability. Gemini surfactant-assisted EOR solutions are expected to provide enhanced stability in comparison to conventional fluids, with the added advantage of minor operating investments and significant returns for petroleum producing companies. Gemini surfactants form an intermediary between conventional surfactants and polymeric materials, with desirable traits of both kinds of chemicals. Mechanisms associated with gemini surfactant-assisted EOR have been reported. In this review, the status, developmental trends and prospects of gemini (dimeric) surfactants, with respect to the needs of the petroleum industry have been elaborated. Though gemini surfactants have been used in numerous sectors, their application in EOR has been limited owing to unfamiliarity and commercial unavailability. Prospective gemini surfactant systems have been discussed herein to identify technical risks, calibrate reservoir simulation models, contribute to environmental responsibility and develop operating strategies to improve oil recovery/economics.
  • 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
  • Probabilistic Assessment of Slip Rates and Their Variability Over Time of Offshore Buried Thrusts: A Case Study in the Northern Adriatic Sea

    Panara, Yuri; Maesano, Francesco Emanuele; Amadori, Chiara; Fedorik, Jakub; Toscani, Giovanni; Basili, Roberto (Frontiers in Earth Science, Frontiers Media SA, 2021-05-31) [Article]
    When sedimentation rates overtake tectonic rates, the detection of ongoing tectonic deformation signatures becomes particularly challenging. The Northern Apennines orogen is one such case where a thick Plio-Pleistocene foredeep sedimentary cover blankets the fold-and-thrust belt, straddling from onshore (Po Plain) to offshore (Adriatic Sea), leading to subtle or null topo-bathymetric expression of the buried structures. The seismic activity historically recorded in the region is moderate; nonetheless, seismic sequences nearing magnitude 6 punctuated the last century, and even some small tsunamis were reported in the coastal locations following the occurrence of offshore earthquakes. In this work, we tackled the problem of assessing the potential activity of buried thrusts by analyzing a rich dataset of 2D seismic reflection profiles and wells in a sector of the Northern Apennines chain located in the near-offshore of the Adriatic Sea. This analysis enabled us to reconstruct the 3D geometry of eleven buried thrusts. We then documented the last 4 Myr slip history of four of such thrusts intersected by two high-quality regional cross-sections that were depth converted and restored. Based on eight stratigraphic horizons with well-constrained age determinations (Zanclean to Middle Pleistocene), we determined the slip and slip rates necessary to recover the observed horizon deformation. The slip rates are presented through probability density functions that consider the uncertainties derived from the horizon ages and the restoration process. Our results show that the thrust activation proceeds from the inner to the outer position in the chain. The slip history reveals an exponential reduction over time, implying decelerating slip-rates spanning three orders of magnitudes (from a few millimeters to a few hundredths of millimeters per year) with a major slip-rate change around 1.5 Ma. In agreement with previous works, these findings confirm the slip rate deceleration as a widespread behavior of the Northern Apennines thrust faults.
  • A Microneedles Balloon Catheter for Endovascular Drug Delivery

    Moussi, Khalil; Haneef, Ali A.; Alsiary, Rawiah A.; Diallo, Elhadj; Boone, Marijn Antoine; Abu-Araki, Huda; Al-Radi, Osman O.; Kosel, Jürgen (Advanced Materials Technologies, Wiley, 2021-05-28) [Article]
    Disorders of the inner parts of blood vessels have been significant triggers of cardiovascular diseases (CVDs). Different interventional methods have been employed, from complex surgeries to balloon angioplasty techniques to open the narrowed blood vessels. However, CVDs continue to be the lead cause of death in the world. Delivering a therapeutic agent directly to the inner wall of affected blood vessels can be a transformative step toward a better treatment option. To open the door for such an approach, a catheter delivery system is developed based on a conventional balloon catheter where a fluidic channel and microneedles (MNs) are integrated on top of it. This enables precise and localized delivery of therapeutics directly into vessel walls. Customizable MNs are fabricated using a high-resolution 3D printing technique where MN's height ranges from 100 to 350 µm. The MNs penetration into a synthetic vascular model is investigated with a computerized tomography scan. Ex vivo tests on rabbit aorta confirm the MN-upgraded balloon catheter's performance on real tissue. Delivery of fluorescent dye is accomplished by injecting it through the fluidic channel and MNs into the aortic tissue. The dye is observed at up to 180 µm of depth, confirming site-specific endovascular delivery.
  • Exploitation of Field Drilling Data with an Innovative Drilling Simulator: Highly Effective Simulation of Rotating and Sliding Mode

    Koulidis, Alexis; Kelessidis, Vassilios; Ahmed, Shehab (SPE, 2021-05-25) [Conference Paper]
    Drilling challenging wells requires a combination of drilling analytics and comprehensive simulation to prevent poor drilling performance and avoid drilling issues for the upcoming drilling campaign. This work focuses on the capabilities of a drilling simulator that can simulate the directional drilling process with the use of actual field data for the training of students and professionals. This paper presents the results of simulating both rotating and sliding modes and successfully matching the rate of penetration and the trajectory of an S-type well. Monitored drilling data from the well were used to simulate the drilling process. These included weight on bit, revolutions per minute, flow rate, bit type, inclination and drilling fluid properties. The well was an S-type well with maximum inclination of 16 degrees. There were continuous variations from rotating to sliding mode, and the challenge was approached by classifying drilling data into intervals of 20 feet to obtain an appropriate resolution and efficient simulation. The simulator requires formation strength, pore and fracture pressures, and details of well lithology, thus simulating the actual drilling environment. The uniaxial compressive strength of the rock layer is calculated from p–wave velocity data from an offset field. Rock drillability is finally estimated as a function of the rock properties of the drilled layer, bit type and the values of the drilling parameters. It is then converted to rate of penetration and matched to actual data. Changes in the drilling parameters were followed as per the field data. The simulator reproduces the drilling process in real-time and allows the driller to make instantaneous changes to all drilling parameters. The simulator provides the rate of penetration, torque, standpipe pressure, and trajectory as output. This enables the user to have on-the-fly interference with the drilling process and allows him/her to modify any of the important drilling parameters. Thus, the user can determine the effect of such changes on the effectiveness of drilling, which can lead to effective drilling optimization. Certain intervals were investigated independently to give a more detailed analysis of the simulation outcome. Additional drilling data such as hook load and standpipe pressure were analyzed to determine and evaluate the drilling performance of a particular interval and to consider them in the optimization process. The resulting rate of penetration and well trajectory simulation results show an excellent match with field data. The simulation illustrates the continuous change between rotating and sliding mode as well as the accurate synchronous matching of the rate of penetration and trajectory. The results prove that the simulator is an excellent tool for students and professionals to simulate the drilling process prior to actual drilling of the next inclined well.
  • 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.

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