Recent Submissions

  • Chemical Compositions in Salinity Waterflooding of Carbonate Reservoirs: Theory

    Yutkin, Maxim; Radke, Clayton J.; Patzek, Tadeusz (American Chemical Society (ACS), 2020-06-18) [Preprint]
    <jats:p>Higher oil recovery after waterflood in carbonate reservoirs is attributed to increasing water wettability of the rock that in turn relies on complicated surface chemistry. However, calcite mineral reacts with<br>aqueous solutions, and can alter substantially the composition of injected water by mineral dissolution. Care-<br>fully designed chemical and/or brine flood compositions in the laboratory may not remain intact while the<br>injected solutions pass through the reactive reservoir rock. This is especially true for a low-salinity waterflood<br>process, where some finely-tuned brine compositions can improve flood performances, whereas others cannot.<br>We present a 1D reactive transport numerical model that captures the changes in injected compositions dur-<br>ing water flow through porous carbonate rock. We include highly coupled bulk aqueous and surface carbonate-<br>reaction chemistry, detailed reaction and mass transfer kinetics, 2:1 calcium ion exchange, and axial dispersion.<br>At typical calcite reaction rates, local equilibrium is established immediately upon injection. Using an open-<br>source algorithm (Charlton and Parkhurst 2011), we present a design tool to specify chemical/brine flooding<br>packages that correct for composition alteration by carbonate rock.<br>Here, we present a comprehensive 1D reactive transport model and validate it against analytic solutions<br>for rock dissolution, ion exchange, and longitudinal dispersion, each considered separately. A companion paper<br>compares the proposed theory against experiments on core plugs of Indiana limestone that serve as high velocity<br>probes for reaction-controlled and mass-transfer-controlled dissolution. Finally, in another companion paper,<br>we give examples of how injected salinity compositions deviate from those designed in the laboratory for water-<br>wettability improvement based on contact angles, zeta potentials, surface charge densities, and ion exchange.<br>How to correct the design chemical packages for exposure to reactive rock is also discussed in there.</jats:p>
  • Extraction, Characterization, and Anticoagulant Activity of a Sulfated Polysaccharide from Bursatella leachii Viscera

    Dhahri, Manel; Sioud, Salim; Dridi, Rihab; Hassine, Mohsen; Boughattas, Naceur A.; Almulhim, Fatimah; Al-Talla, Zeyad; Jaremko, Mariusz; Emwas, Abdul-Hamid M. (ACS Omega, American Chemical Society (ACS), 2020-06-10) [Article]
    Bioactive compounds for drug discovery are increasingly extracted and purified from natural sources including marine organisms. Heparin is a therapeutic agent that has been used for several decades as an anticoagulant. However, heparin is known to cause many undesirable complications such as thrombocytopenia and risk of hemorrhage. Hence, there is a need to find alternatives to current widely used anticoagulant drugs. Here, we extract a sulfated polysaccharide from sea hare, that is, Bursatella leachii viscera, by enzymatic digestion. Several analytical approaches including elemental analysis, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and high-performance liquid chromatography–mass spectrometry analysis show that B. leachii polysaccharides have chemical structures similar to glycosaminoglycans. We explore the anticoagulant activity of the B. leachii extract using the activated partial thromboplastin time and the thrombin time. Our results demonstrate that the extracted sulfated polysaccharide has heparin-like anticoagulant activity, thus showing great promise as an alternative anticoagulant therapy.
  • The Key Factors That Determine the Economically Viable, Horizontal Hydrofractured Gas Wells in Mudrocks

    Haider, Syed; Saputra, Wardana; Patzek, Tadeusz (Energies, MDPI AG, 2020-05-08) [Article]
    <jats:p>We assemble a multiscale physical model of gas production in a mudrock (shale). We then tested our model on 45 horizontal gas wells in the Barnett with 12–15 years on production. When properly used, our model may enable shale companies to gain operational insights into how to complete a particular well in a particular shale. Macrofractures, microfractures, and nanopores form a multiscale system that controls gas flow in mudrocks. Near a horizontal well, hydraulic fracturing creates fractures at many scales and increases permeability of the source rock. We model the physical properties of the fracture network embedded in the Stimulated Reservoir Volume (SRV) with a fractal of dimension D < 2 . This fracture network interacts with the poorly connected nanopores in the organic matrix that are the source of almost all produced gas. In the practically impermeable mudrock, the known volumes of fracturing water and proppant must create an equal volume of fractures at all scales. Therefore, the surface area and the number of macrofractures created after hydrofracturing are constrained by the volume of injected water and proppant. The coupling between the fracture network and the organic matrix controls gas production from a horizontal well. The fracture permeability, k f , and the microscale source term, s, affect this coupling, thus controlling the reservoir pressure decline and mass transfer from the nanopore network to the fractures. Particular values of k f and s are determined by numerically fitting well production data with an optimization algorithm. The relationship between k f and s is somewhat hyperbolic and defines the type of fracture system created after hydrofracturing. The extremes of this relationship create two end-members of the fracture systems. A small value of the ratio k f / s causes faster production decline because of the high microscale source term, s. The effective fracture permeability is lower, but gas flow through the matrix to fractures is efficient, thus nullifying the negative effect of the smaller k f . For the high values of k f / s , production decline is slower. In summary, the fracture network permeability at the macroscale and the microscale source term control production rate of shale wells. The best quality wells have good, but not too good, macroscale connectivity.</jats:p>
  • Nano-characterization of silicon-based multilayers using the technique of STEM-EELS spectrum-imaging

    Anjum, Dalaver H.; Qattan, I. A.; Patole, Shashikant; Diallo, Elhadj; Wei, Nini; Heidbreder, Henry (Materials Today Communications, Elsevier BV, 2020-05-06) [Article]
    Silicon (Si) and its compounds are still actively being used by electronic and solar-energy industries. In this work, we focus on one-stop-instrument (OSI) for the characterization of silicon (Si)-based thin-films namely Si, silicon nitride (SiNx), and silicon oxide (SiO2). The goal of performing the characterization of Si-based compounds with OSI has been achieved by carrying out their nanoscale-characterization (Nano-Characterization) with a modern transmission electron microscope (TEM). The presented results demonstrate that TEM is proven to be a powerful OSI for carrying out the Nano-Characterization of Si-based multilayer stacks. It does that via electron microscopy imaging (EMI), and electron spectroscopic imaging (ESI) routes. The presented results show that while EMI allows imaging the structure and morphology of thin-films at nanoscale, the ESI, by combining imaging and spectroscopy techniques, enables distinguishing the pure Si regions from its oxide and nitride regions. Moreover, for the first time, we show that the ESI is sensitive enough to differentiate the crystalline Si regions from that of amorphous Si ones.
  • A Review of Integrated On-Board EV Battery Chargers: Advanced Topologies, Recent Developments and Optimal Selection of FSCW Slot/Pole Combination

    Metwly, Mohamed Y.; Abdel-Majeed, Mahmoud S.; Abdel-Khalik, Ayman S.; Hamdy, Ragi A.; Hamad, Mostafa S.; Ahmed, Shehab (IEEE Access, Institute of Electrical and Electronics Engineers (IEEE), 2020-05-06) [Article]
    Integrated on-board battery chargers (OBCs) have been recently introduced as an optimal/elegant solution to increase electric vehicle (EV) market penetration as well as minimize overall EV cost. Unlike conventional off-board and on-board battery chargers, integrated OBCs exploit the existing propulsion equipment for battery charging without extra bulky components and/or dedicated infrastructure. OBCs are broadly categorized into three-phase and single-phase types with unidirectional or bidirectional power flow. This paper starts with surveying the main topologies introduced in the recent literature employing either induction or permanent magnet motors to realize fully integrated slow (single-phase) and fast (three-phase) on-board EV battery charging systems, with emphasis on topologies that entail no or minimum hardware reconfiguration. Although, permanent magnet (PM) motors with conventional double-layer distributed winding layouts have been deployed in most commercial EV motors, the non-overlapped fractional slot concentrated winding (FSCW) has been the prevailing choice in the most recent permanent magnet motor designs due to its outstanding operational merits. Hence, a thorough investigation of the impact different FSCW stator winding designs have on machine performance under the charging process is presented in this paper. To this end, the induced magnet losses, which represent a challenging demerit of the FSCW, have been used to compare different topologies under both propulsion and charging operation modes. Based on the introduced comparative study, the optimal slot/pole combinations that correspond to the best compromise under both operational modes have been highlighted.
  • An advanced discrete fracture model for variably saturated flow in fractured porous media

    Koohbor, Behshad; Fahs, Marwan; Hoteit, Hussein; Doummar, Joanna; Younes, Anis; Belfort, Benjamin (Advances in Water Resources, Elsevier BV, 2020-05-06) [Article]
    Accurate modeling of variably saturated flow (VSF) in fractured porous media with the discrete fracture-matrix (DFM) model is a computationally challenging problem. The applicability of DFM model to VSF in real field studies at large space and time scales is often limited, not only because it requires detailed fracture characterization, but also as it involves excessive computational efforts. We develop an efficient numerical scheme to solve the Richards equation in discretely fractured porous media. This scheme combines the mixed hybrid finite element method for space discretization with the method of lines for time integration. The fractures are modeled as lower-dimensional interfaces (1D), within the 2D porous matrix. We develop a new mass-lumping (ML) technique for the fractures to eliminate unphysical oscillations and convergence issues in the solution, which significantly improves efficiency, enabling larger field applications. The proposed new scheme is validated against a commercial simulator for problems involving water table recharge at the laboratory scale. The computational efficiency of the developed scheme is examined on a challenging problem for water infiltration in fractured dry soil, and compared with standard numerical techniques. We show that the ML technique is crucial to improve robustness and efficiency, which outperforms the commonly used methods that we tested. The applicability of our method is then demonstrated in a study concerning the effect of climate change on groundwater resources in a karst aquifer/spring system in El Assal, Lebanon. Simulations, including recharge predictions under climate change scenarios, are carried out for about 80 years, up to 2099. This study demonstrates the applicability of our proposed scheme to deal with real field cases involving large time and space scales with high variable recharge. Our results indicate that the water-table level is sensitive to the presence of fractures, where neglecting fractures leads to an overestimation of the available groundwater amount. The proposed numerical approach is generic for DFM model and can be extended to different 2D and 3D finite-element frameworks.
  • Physical Scaling of Oil Production Rates and Ultimate Recovery from All Horizontal Wells in the Bakken Shale

    Saputra, Wardana; Kirati, Wissem; Patzek, Tadeusz (Energies, MDPI AG, 2020-04-21) [Article]
    A recent study by the Wall Street Journal reveals that the hydrofractured horizontal wells in shales have been producing less than the industrial forecasts with the empirical hyperbolic decline curve analysis (DCA). As an alternative to DCA, we introduce a simple, fast and accurate method of estimating ultimate recovery in oil shales. We adopt a physics-based scaling approach to analyze oil rates and ultimate recovery from 14,888 active horizontal oil wells in the Bakken shale. To predict the Estimated Ultimate Recovery (EUR), we collapse production records from individual horizontal shale oil wells onto two segments of a master curve: (1) We find that cumulative oil production from 4845 wells is still growing linearly with the square root of time; and (2) 6401 wells are already in exponential decline after approximately seven years on production. In addition, 2363 wells have discontinuous production records, because of refracturing or changes in downhole flowing pressure, and are matched with a linear combination of scaling curves superposed in time. The remaining 1279 new wells with less than 12 months on production have too few production records to allow for robust matches. These wells are scaled with the slopes of other comparable wells in the square-root-of-time flow regime. In the end, we predict that total ultimate recovery from all existing horizontal wells in Bakken will be some 4.5 billion barrels of oil. We also find that wells completed in the Middle Bakken formation, in general, produce more oil than those completed in the Upper Three Forks formation. The newly completed longer wells with larger hydrofractures have higher initial production rates, but they decline faster and have EURs similar to the cheaper old wells. There is little correlation among EUR, lateral length, and the number and size of hydrofractures. Therefore, technology may not help much in boosting production of new wells completed in the poor immature areas along the edges of the Williston Basin. Operators and policymakers may use our findings to optimize the possible futures of the Bakken shale and other plays. More importantly, the petroleum industry may adopt our physics-based method as an alternative to the overly optimistic hyperbolic DCA that yields an ‘illusory picture’ of shale oil resources.
  • Quantification of Photophysical Processes in All-Polymer Bulk Heterojunction Solar Cells

    Albalawi, Ahmed; Kan, Zhipeng; Gorenflot, Julien; Guarracino, Paola; Chaturvedi, Neha; Privitera, Alberto; Liu, Shengjian; Gao, Yajun; Franco, Lorenzo; Beaujuge, Pierre; Laquai, Frédéric (Solar RRL, Wiley, 2020-04-14) [Article]
    All-polymer solar cells lag behind the state-of-the-art in small molecule nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic solar cells (OSCs) for reasons still unclear. Herein, the efficiency-limiting processes in all-polymer solar cells are investigated using blends of the common donor polymer PBDT-TS1 with different acceptor polymers, namely P2TPD[2F]T and P2TPDBT[2F]T. Combining data from steady-state optical spectroscopy and time-resolved photoluminescence, transient absorption, and time-delayed collection field experiments, provides not only a concise but also quantitative assessment of the losses due to limited photon absorption, geminate and nongeminate charge carrier recombination, field-dependent charge generation, and inefficient carrier extraction. Although both systems exhibit a similar charge separation efficiency in the absence of external bias, charge separation is significantly enhanced in P2TPDBT[2F]T-based blends when biased. Kinetic parameters obtained via pulsed laser spectroscopy are used to reproduce the experimentally measured device current–voltage (J–V) characteristics and indicate that low fill factors originate either from nongeminate recombination competing with charge extraction, or from a pronounced field dependence of charge generation, depending on the acceptor polymer. The methodology presented here is generic and can be used to quantify the loss processes in BHJ OSCs including both all-polymer and small molecule NFA systems.
  • IoT-Based Supervisory Control of an Asymmetrical Nine-Phase Integrated on-Board EV Battery Charger

    Metwly, Mohamed Y.; Abdel-Majeed, Mahmoud S.; Abdel-Khalik, Ayman S.; Torki, Marwan; Hamdy, Ragi A.; Hamad, Mostafa S.; Ahmed, Shehab (IEEE Access, Institute of Electrical and Electronics Engineers (IEEE), 2020-04-01) [Article]
    Electric vehicles (EVs) play a major role in the evolution towards sustainable transportation. The integration of information and communication technology (ICT) into the electric vehicle (EV) charging process has witnessed rapid progress. Wireless communication between EVs has become commercially viable, supporting vehicle-to-sensor, vehicle-to-vehicle, and vehicle-to-internet regimes. However, EVs still have limited market penetration due to charging process constraints such as charging time and the availability of charging points. This paper considers an asymmetrical nine-phase smart integrated on-board charging (OBC) system with a reduced cost, size and weight. All the propulsion components are utilized in the charging process. Both zero machine average torque production and unity power factor operation at the grid side can simultaneously be obtained during the charging process. Additionally, no hardware reconfiguration is required to allow the transition between propulsion and charging modes for this system topology. Furthermore, the proposed integrated on-board charger is completely monitored, and the charging rate is controlled through a smartphone application via internet of things (IoT) technology, thus optimizing the user experience. A 1.5 kW prototype is implemented to validate the proposed system by rewinding a three-phase induction motor (IM).
  • Soil Response to Repetitive Changes in Pore-Water Pressure under Deviatoric Loading

    Park, Junghee; Santamarina, Carlos (Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers (ASCE), 2020-03-10) [Article]
  • Electroactive biofilms on surface functionalized anodes: the anode respiring behavior of a novel electroactive bacterium, Desulfuromonas acetexigens

    Katuri, Krishna; Kamireddy, Sirisha; Kavanagh, Paul; Ali, Mohammad; Peter, Connolly; Kumar, Amit; Saikaly, Pascal; Leech, Donal (Cold Spring Harbor Laboratory, 2020-03-06) [Preprint]
    Surface chemistry is known to influence the formation, composition and electroactivity of electron-conducting biofilms with however limited information on the variation of microbial composition and electrochemical response during biofilm development to date. Here we present voltammetric, microscopic and microbial community analysis of biofilms formed under fixed applied potential for modified graphite electrodes during early (90 h) and mature (340 h) growth phases. Electrodes modified to introduce hydrophilic groups (-NH2, -COOH and -OH) enhance early-stage biofilm formation compared to unmodified or electrodes modified with hydrophobic groups (-C2H5). In addition, early-stage films formed on hydrophilic electrodes were dominated by the gram-negative sulfur-reducing bacterium Desulfuromonas acetexigens while Geobacter sp. dominated on -C2H5 and unmodified electrodes. As biofilms mature, current generation becomes similar, and D. acetexigens dominates in all biofilms irrespective of surface chemistry. Electrochemistry of pure culture D. acetexigens biofilms reveal that this microbe is capable of forming electroactive biofilms producing considerable current density of > 9 A/m2 in a short period of potential induced growth (~19 h followed by inoculation) using acetate as an electron donor. The inability of D. acetexigens biofilms to use H2 as a sole source electron donor for current generation shows promise for maximizing H2 recovery in single-chambered microbial electrolysis cell systems treating wastewaters.
  • Estimation of Effective Permeability, Fracture Spacing, Drainage Area, and Incremental Production from Field Data in Gas Shales with Nonnegligible Sorption

    Eftekhari, B.; Marder, M.; Patzek, Tadeusz (SPE Reservoir Evaluation & Engineering, Society of Petroleum Engineers (SPE), 2020-03-04) [Article]
    In a previous work, we introduced a three-parameter scaling solution that models the long-term recovery of dry gas from a hydrofractured horizontal well far from other wells and the boundaries of a shale reservoir with negligible sorption. Here, we extend this theory to account for the contribution of sorbed gas and apply the extended theory to the production histories of 8,942 dry-gas wells in the Marcellus Shale. Our approach is to integrate unstructured big data and physics-based modeling. We consider three adsorption cases that correspond to the minimum, median, and maximum of a set of measured Langmuir isotherms. We obtain data-driven, independent estimates of unstimulated shale permeability, spacing between hydrofractures, well-drainage area, optimal spacing between infill wells, and incremental gas recovery over a typical well life. All these estimates decrease to varying extents with increasing sorption. We find that the average well with median adsorption has a permeability of 250 nd, fracture spacing of 16 m, 30-year drainage length of 79 m, and a 30-year incremental recovery of 67%
  • Methane hydrate-bearing sediments: Pore habit and implications

    Terzariol, Marco; Park, Junghee; Castro, Gloria M.; Santamarina, Carlos (Marine and Petroleum Geology, Elsevier BV, 2020-02-20) [Article]
    Hydrate-bearing sediments are relevant to the organic carbon cycle, seafloor instability, and as a potential energy resource. Sediment characteristics affect hydrate formation, gas migration and recovery strategies. We combine the physics of granular materials with robust compaction models to estimate effective stress and capillary pressure in order to anticipate the pore habit of methane hydrates as a function of the sediment characteristics and depth. Then, we compare these results to an extensive database of worldwide hydrate accumulations compiled from published studies. Results highlight the critical role of fines on sediments mechanical and flow properties, hydrate pore habit and potential production strategies. The vast majority of hydrate accumulations (92% of the sites) are found in fines-controlled sediments at a vertical effective stress between σ′z = 400 kPa and 4 MPa, where grain-displacive hydrate pore habit prevails in the form of segregated lenses and nodules. While permeation-based gas recovery by depressurization is favored in clean-coarse sediments, gas recovery from fines-controlled sediments could benefit from enhanced transmissivity along gas-driven fractures created by thermal stimulation.
  • Investigation of an Improved Polymer Flooding Scheme by Compositionally-Tuned Slugs

    Santoso, Ryan; Torrealba, Victor; Hoteit, Hussein (Processes, MDPI AG, 2020-02-07) [Article]
    Polymer flooding is an effective enhanced oil recovery technology used to reduce the mobility ratio and improve sweep efficiency. A new polymer injection scheme is investigated that relies on the cyclical injection of low-salinity, low-concentration polymer slugs chased by high-salinity, high-concentration polymer slugs. The effectiveness of the process is a function of several reservoir and design parameters related to polymer type, concentration, salinity, and reservoir heterogeneity. We use reservoir simulations and design-of-experiments (DoE) to investigate the effectiveness of the proposed polymer injection scheme. We show how key objective functions, such as recovery factor and injectivity, are impacted by the reservoir and design parameters. In this study, simulations showed that the new slug-based process was always superior to the reference polymer injection scheme using the traditional continuous injection scheme. Our results show that the process is most effective when the polymer weight is high, corresponding to large inaccessible pore-volumes, which enhances polymer acceleration. High vertical heterogeneity typically reduces the process performance because of increased mixing in the reservoir. The significance of this process is that it allows for increased polymer solution viscosity in the reservoir without increasing the total mass of polymer, and without impairing polymer injectivity at the well.
  • Development and field testing of a novel multifunctional drilling enhancement tool in a middle east field

    Abdel-Aal, Mohamed Ahmed; Mohamed, Fahd Mohamed; Abdelkader, Ahmed Galal; AbdulHamid, Mohammed; Koulidis, Alexis; Ahmed, Shehab (International Petroleum Technology Conference, 2020-01-11) [Conference Paper]
    Well drilling and wellbore conditioning typically involve multiple specialized drilling tools. Systematic application of such tools can be a challenge from a logistics and maintenance perspective, which eventually has an impact on the efficiency of the drilling process as well as the resulting wellbore condition. This paper presents a new multifunctional drilling tool developed to address such operational challenges. The tool’s effect on the drilling and logging process is illustrated through a field case study. The CRS is a multifunctional drilling tool able to Cut, Ream and Stabilize when installing in a BHA. It is envisioned as an integral bottom hole assembly (BHA) component replacing the uppermost stabilizer while selectively acting as a fixed blade cutter, roller-reamer, lateral vibration damper, friction reducer, stabilizer and/or key-seat wiper. The specific function is dependent on wellbore conditions and is passively activated or engaged during operation. The CRS was successfully field-tested in a middle east field late 2018. Offset well data were used to validate the effectiveness of the tool and provide recommendations for future development. An offset well was used as a benchmark for comparison to characterize CRS performance. The CRS replaced the stabilizer directly above the measurement while drilling (MWD) tools as part of the BHA used for drilling the interval from 1800 to 2520 meters. When compared to the offset well, the tool had no negative effect on trajectory or dogleg severity. Tight spots required significant back-reaming in the offset well during pull-out-of-hole (POOH). Using the CRS saved 63 hours of rig time when POOH due to the tool’s effective tight spot cutting capability. High torque fluctuations ranging between 2 to 13 klbs-ft were observed in the offset well while drilling formations mainly composed of sticky claystone and limestone. The resulting poor wellbore quality rendered significant logging challenges. The CRS’s ability to damp lateral vibration while engaging in its reaming function resulted in the mitigation of these challenges. Another innovative feature of the CRS’s reaming function is the complete elimination of cutter loss risk. The CRS body is, by far, the industry’s largest area bearing mounted reaming structure and its concentric design eliminates the possibility of it being lost in the hole. The CRS body rotates in response to lateral vibration and drill string whirl when in a vertical or deviated wellbore, effectively contributing to the damping of both vibration modes. The body acts as friction reducer at high deviations. The rotating body also translates on the tool mandrel when faced with a tight spot or pack-off. This translation is opposed by a unique spring assembly that can deliver full top drive torque to the body to cut through the formation.
  • Application of machine-learning to construct equivalent continuum models from high-resolution discrete-fracture models

    He, Xupeng; Santoso, Ryan; Hoteit, Hussein (International Petroleum Technology Conference, 2020-01-11) [Conference Paper]
    Modeling fluid flow in fractured media is of importance in many disciplines, including subsurface water management and petroleum reservoir engineering. Detailed geological characterization of a fractured reservoir is commonly described by a discrete-fracture model (DFM), in which the fractures and rock-matrix are explicitly represented by unstructured grid elements. Traditional static-based and flow-based upscaling methods used to generate equivalent- continuum models from DFM suffer from low accuracy and high computational cost, respectively. This work introduces a new deep-learning technique based on neural networks to accelerate upscaling of discrete-fracture models. The objective of this work is to automate the process of permeability upscaling from detailed discrete-fracture characterizations. We build an
  • Improving Reservoir Quality Prediction of Microporous Carbonates using a Multi-Scale Geophysical Data Analysis Approach

    Ramdani, Ahmad; Chandra, Viswasanthi; Finkbbeiner, Thomas; Khanna, Pankaj; Vahrenkamp, Volker (International Petroleum Technology Conference, 2020-01-11) [Conference Paper]
    Microporosity is volumetrically the most important porosity type in the giant carbonate reservoirs of Arabia and can significantly impact reservoir quality and ultimate oil recovery. Understanding the impact of microporosity on reservoir quality and accurately predicting the spatial distribution of microporosity at the reservoir scale is required to improve the recovery of remaining hydrocarbons from the reservoirs. Utilizing an integrated data analysis approach applied to multi-scale geological and geophysical datasets from micrometer scale SEM imagery to decameter scale seismic data, we predict the distribution of microporosity at the reservoir grid-block scale. We apply the proposed methodology to Arab-D reservoir equivalent outcrop data from the Upper Jubaila Formation, Saudi Arabia. Thirty-five meters of near-surface well core and a 600 m long 2D near-surface p-wave seismic reflection profile were acquired at the outcrop location. From the core, 106 plug samples are analysed to determine porosity and permeability, ultrasonic velocities, powder XRD compositions, and SEM data. With the seismic reflection data, we perform a near-surface colored inversion to obtain a high-resolution acoustic impedance image of the seismic data. The morphology of micrite crystals that host microporosity was characterized and quantified by analysing SEM data using machine learning image classification tools. We use the resulting data to derive robust statistical relationships between microporosity and texture of micrite microcrystals on centimetre scale geophysical properties with a Self-Organizing Map (SOM) approach for data clustering. A Differential Effective Medium (DEM) model enabled us to correlate acoustic impedance and porosity, and distribute porosity across the 2D seismic cross-section. The key depositional lithofacies identified from core descriptions are bioturbated mudstones intercalated by packstones and grain dominated rudstones and floatstones. Image-based machine learning classification results indicate that microcrystals that host microporosity in this formation were typically homogenous in size but varied in morphological aspects such as granularity and angularity. Based on data clustering results, granularity and angularity of microcrystals appear to be the dominant controls over the lab- measured geophysical properties. This effect is manifested as a simple log-linear relationship between porosity and permeability among the major depositional facies. The DEM fitting parameter effectively represents the velocity-porosity relationship and can be used to predict the distribution of porosity across a seismic cross-section. For the first time, an integrated multi-scale data methodology involving machine leaning tools is applied to the Late Jurassic Upper Jubaila Formation outcrop data. Although we demonstrate the proposed methodology using outcrop data, it can be applied to any subsurface reservoir zone dominated by microporosity.
  • 3D confocal imaging methodology optimized for pore space characterization of microporous carbonate reservoirs

    Hassan, Ahmed; Chandra, Viswasanthi; Yutkin, Maxim; Patzek, Tadeusz (International Petroleum Technology Conference, 2020-01-11) [Conference Paper]
    Microporous carbonates host a significant portion of the remaining oil-in-place in the giant carbonate reservoirs of the Middle East. Carbonates host wide range of pore sizes, however the key element influencing hydrocarbon flow is pore interconnectivity. We evaluate the use of confocal microscopy to image fluorescent epoxy pore casts of microporous carbonates. The acquired high-resolution 3D confocal images are used to gain invaluable insights on the interconnectivity between macroporosity and microporosity. We analyzed the sensitivity of quality of epoxy pore cast images to: fluorochrome selection, objective lens, and imaging medium by imaging standard fluorescent spherical beads. Guided by the sensitivity results, we acquired 3D images of the multi-modal pore space in an Indiana limestone sample with lateral- and axial-resolution of 0.36 µm and 2 µm, respectively. And we were able to identify the multi-scale pore types in the studied carbonate sample and highlight their interconnectivity.
  • Carbonate rocks: Matrix permeability estimation

    Cardona, Alejandro; Santamarina, Carlos (AAPG Bulletin, American Association of Petroleum Geologists AAPG/Datapages, 2020-01-04) [Article]
    Carbonate rocks store half of the world’s proven oil reserves. Genesis and postdepositional diagenetic processes define the porous network topology and the matrix permeability. This study compiles a database of porosity, specific surface, mercury porosimetry, and permeability values extracted from published sources and complements the database through a focused experimental study. Specific surface and porosity combine to estimate the pore size (Dsur). Permeability versus Dsur data cluster along a single trend with a slope of 2 in a log–log scale, which is in agreement with the Kozeny–Carman model. Discordant data points correspond to samples with dual porosity or broad pore-size distributions with long tails, where flow channels along larger interconnected pores. Indeed, the detailed analysis of all the porosimetry data in the database shows that permeability correlates best with the pore size D80, that is, the 80th percentile in pore-size distributions. Once again, the best fit is a power function in terms of (D80)2, analogous to Kozeny–Carman. The prediction uncertainty using D80 is one order of magnitude and has the same degree of uncertainty as more complex models and analyses. This observation suggests an irreducible uncertainty of one order of magnitude in permeability estimation from index properties such as porosity, mercury porosimetry, and specific surface probably resulting from specimen preparation effects, inherent physical differences in permeation versus invasion, and difficulties in data interpretation. These estimates of permeability are most valuable when specimens are limited to small sizes, such as cuttings.
  • Hybrid Modular Multilevel Converter with Arm-Interchange Concept for Zero-/Low-Frequency Operation of AC Drives

    Elserougi, Ahmed; Abdelsalam, Ibrahim; Massoud, Ahmed; Ahmed, Shehab (IEEE Access, IEEE, 2020) [Article]
    DC-AC Modular Multilevel Converter (MMC) is a promising candidate for high-power AC drive applications. The main challenge of operating the MMC in AC drive applications is its performance during low-frequency conditions, as high voltage ripple is associated with the low-frequency operation, which results in voltage stresses on the involved semiconductor devices. To keep capacitor voltages balanced and bounded in low-frequency operation, different techniques have been proposed in literature, which can be classified into software and hardware approaches. In this paper, a hybrid MMC with arm-interchange concept is proposed to ensure operating successfully during low-frequency conditions. The hybrid MMC consists of two-stages. The first stage is a front-end Integrated Gate Commutated Thyristor (IGCT)-based H-bridge converter, while the second stage is a Full-Bridge Sub-Module (FBSM)-based MMC, where FBSMs is able to generate positive, zero, and negative voltage states. Detailed illustration and design of the hybrid MMC are introduced. Simulation results of the proposed converter are presented to show the effectiveness during low-frequency and normal frequency conditions in AC drive applications. Finally, a scaled-down prototype is employed for experimental validation.

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