Recent Submissions

  • Time-lapse data matching using a recurrent neural network approach

    Alali, Abdullah A.; Kazei, Vladimir; Sun, Bingbing; Alkhalifah, Tariq Ali (GEOPHYSICS, Society of Exploration Geophysicists, 2022-05-19) [Article]
    Time-lapse seismic data acquisition is an essential tool to monitor changes in a reservoir due to fluid injection, such as CO2 injection. By acquiring multiple seismic surveys in the exact same location, we can identify the reservoir changes by analyzing the difference in the data. However, such analysis can be skewed by the near-surface seasonal velocity variations, inaccuracy and repeatability in the acquisition parameters, and other inevitable noise. The common practice (cross-equalization) to address this problem uses the part of the data where changes are not expected to design a matching filter and then apply it to the whole data, including the reservoir area. Like cross-equalization, we train a recurrent neural network on parts of the data excluding the reservoir area and then infer the reservoir-related data. The recurrent neural network can learn the time dependency of the data, unlike the matching filter that processes the data based on the local information obtained in the filter window. We demonstrate the method of matching the data in various examples and compare it with the conventional matching filter. Specifically, we start by demonstrating the ability of the approach in matching two traces and then test the method on a pre-stack 2D synthetic data. Then, we verify the enhancements of the 4D signal by providing RTM images. We measure the repeatability using normalized root mean square and predictability metrics and show that in some cases, our proposed method performed better than the matching filter approach.
  • The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud

    Abdelkader, Mohamed; Stenchikov, Georgiy L.; Pozzer, Andrea; Tost, Holger; Lelieveld, Jos (Copernicus GmbH, 2022-05-13) [Preprint]
    We employ the atmospheric chemistry general circulation model (EMAC) with gas phase, heterogeneous chemistry, and detailed aerosol microphysics to simulate the 1991 Pinatubo volcanic cloud. We explicitly account for the interaction of simultaneously injected SO2, volcanic ash, and water vapor and conducted multiple ensemble simulations with different injection configurations to test the simulated SO2, SO42-, ash masses, stratospheric aerosol optical depth, surface area density (SAD), and the stratospheric temperature response against available observations. We find that the SO2, SO42- masses and stratospheric aerosol optical depth (SAOD) are sensitive to the initial height of the volcanic cloud. The volcanic cloud interacts with tropopause and stratopause, and its composition is shaped by heterogeneous chemistry coupled with the ozone cycle. The height of the volcanic cloud in our simulations is also affected by dynamic processes within the cloud, i.e., heating and lofting of volcanic products. The mass of the injected water vapor has a moderate effect on the cloud evolution when volcanic materials are released in the lower stratosphere because it freezes and sediments as ice crystals. However, the injected water vapor at a higher altitude accelerates the oxidization of SO2 which is sensitive to the injected water vapor mass (via hydroxyl production and reaction rate). The coarse ash comprises 98 % of ash injection mass, which sediments within a few days, but aged sub-micron ash could stay in the stratosphere for a few months providing SAD for heterogeneous chemistry. The presence of ash accelerates the SO2 oxidation that leads to a faster formation of the sulfate aerosol layer in the first two months after the eruption and has to be accounted for in modeling the impact of large-scale volcanic injections on climate and stratospheric chemistry.
  • A fully explicit and unconditionally energy-stable scheme for Peng-Robinson VT flash calculation based on dynamic modeling

    Feng, Xiaoyu; Chen, Meng-Huo; Wu, Yuanqing; Sun, Shuyu (Journal of Computational Physics, Elsevier BV, 2022-05-10) [Article]
    Since the Peng-Robinson (PR) equation of state (EoS) has proven itself to be one of the most reliable EoS, especially in the chemical and petroleum industries, the flash calculation based on the PR EoS is considered to be a foundation for describing complex compositional flows and for evaluating hydrocarbon reservoirs. Compared to the traditional Pressure-Temperature (PT) flash calculation, the novel Volume-Temperature (VT) flash calculation has become more appealing due to its advantages, such as less sensitivity to primary variables like pressure or volume. However, previous numerical schemes of the VT flash calculation involved many complicated nonlinear systems, which makes convergence hard to achieve. To treat this challenge, a fully explicit and unconditionally energy-stable scheme is proposed in this work. It is known that the dynamic model for VT flash calculation can preserve both the Onsager's reciprocal principle and the energy dissipation law. By combining the dynamic model and the linear semi-implicit scheme, the moles and volume can be updated, with the advantage that the energy-dissipation feature can be preserved at a discrete level unconditionally. Then, with the convex-concave splitting approach and the component-wise iteration framework, the scheme becomes fully explicit. The scheme shows promising potential not only because it inherits the original energy stability to ensure convergence, but it also reduces the implementation burden significantly in some engineering scenarios. A lot of numerical experiments are carried out. The numerical results show good agreement with benchmark data and the energy decaying trend at a very large time step demonstrates the stability and efficiency of the proposed scheme.
  • Deposition and Radiative Forcing of Coarse and Fine Dusts over the Middle East and their Impact on Solar Energy Devices

    Mostamandi, Suleiman; Ukhov, Alexander; Engelbrecht, Johann; Shevchenko, Illia; Stenchikov, Georgiy L. (Submitted to Aeolian Research, Submitted to Elsevier, 2022-05-08) [Preprint]
  • Numerical investigations of the PUGA geothermal reservoir with multistage hydraulic fractures and well patterns using fully coupled thermo-hydro-geomechanical modeling

    Gudala, Manojkumar; Govindarajan, Suresh Kumar; Yan, Bicheng; Sun, Shuyu (Energy, Elsevier BV, 2022-05-06) [Article]
    The Puga geothermal reservoir is located in the south-eastern part of Ladakh (Himalayan region, India), and it is providing encouraging results towards heat production. We proposed an improved mathematical model for the fully coupled thermo-hydro-geomechanical model to examine the variations in the Puga geothermal reservoir at between 4500 m from the surface with three, four, and seven hydraulic fractures in the reservoir along with four-spot, five-spot, seven-spot, and nine-spot well patterns. The distribution of low-temperature region is found in each fracture, and it is low in the reservoir with seven hydraulic fractures. The changes in the rock and fluid properties are examined effectively. Thermal strain is dominated in the fractures, and mechanical strain is impressive in the rock matrix; it is dependent on the number of hydraulic fractures and well patterns. The thermal performance of the Puga reservoir is examined with the geothermal life, reservoir impedance, and heat power and found that the number of hydraulic fractures and well patterns are influenced significantly in the multistage modeling of the Puga geothermal reservoir. Thus, the proposed mathematical model can effectively evaluate and predict the variations that occur in the Puga geothermal reservoir with dynamic rock, fracture, and fluid properties.
  • Leveraging domain adaptation for efficient seismic denoising

    Birnie, Claire Emma; Alkhalifah, Tariq Ali (Energy in Data, 2022-05-03) [Conference Paper]
    The selection of training data for deep learning procedures dictates both the neural network's performance and its applicability to further datasets. Particularly in seismic applications, the selection is non-trivial with the common approaches of manually labelling field data or generating synthetic data both exhibiting severe limitations. The former in its inability to outperform conventional approaches required for the label generation and the later in its inability to properly represent future application data. Domain adaptation, through input features and label transformations, offers the potential to leverage on the benefits of both these approaches while reducing their drawbacks. In this work we illustrate how vital information from field data can be incorporated into a training procedure on synthetic data with the trained network successfully applied on the field data afterwards, despite large differences between the training and inference, i.e., synthetic and field, datasets. Furthermore, we illustrate how an inverse correlation procedure can be incorporated into the training procedure in an attempt to maintain the original wavefield properties.
  • StorSeismic: A new paradigm in deep learning for seismic processing

    Harsuko, Randy; Alkhalifah, Tariq Ali (arXiv, 2022-04-30) [Preprint]
    Machine learned tasks on seismic data are often trained sequentially and separately, even though they utilize the same features (i.e. geometrical) of the data. We present StorSeismic, as a framework for seismic data processing, which consists of neural network pre-training and fine-tuning procedures. We, specifically, utilize a neural network as a preprocessing model to store seismic data features of a particular dataset for any downstream tasks. After pre-training, the resulting model can be utilized later, through a fine-tuning procedure, to perform tasks using limited additional training. Used often in Natural Language Processing (NLP) and lately in vision tasks, BERT (Bidirectional Encoder Representations from Transformer), a form of a Transformer model, provides an optimal platform for this framework. The attention mechanism of BERT, applied here on a sequence of traces within the shot gather, is able to capture and store key geometrical features of the seismic data. We pre-train StorSeismic on field data, along with synthetically generated ones, in the self-supervised step. Then, we use the labeled synthetic data to fine-tune the pre-trained network in a supervised fashion to perform various seismic processing tasks, like denoising, velocity estimation, first arrival picking, and NMO. Finally, the fine-tuned model is used to obtain satisfactory inference results on the field data.
  • Recent cooling in the lower Pacific Ocean based on dynamically-consistent ocean syntheses

    Liao, Fanglou; Zhan, Peng; Wang, Xiao Hua; Liu, Zhiqiang; Hoteit, Ibrahim (Research Square Platform LLC, 2022-04-27) [Preprint]
    The thermal state from 1993–2017 in the lower Pacific Ocean (below 2 km) was investigated using two dynamically-consistent syntheses. We show a robust and bottom-intensified cooling. This Pacific cooling is mainly determined by the meridional heat exchange with the Southern Ocean and the vertical heat advection. The abyssal Pacific Ocean loses heat by way of westward heat advection in the northwest ocean. Mixing is found to play a negligible role. This study is to some extent consistent with a recent study that presented a deep Pacific cooling as an adjustment to the last Little Ice Age. However, it contradicts with most recent studies, which argued the abyssal Pacific Ocean was warming over the recent two decades. Our study suggests that special caution is needed when auditing variations in the deep ocean and more work is in need for a better understanding of the deep ocean state.
  • Shear wave velocity structure beneath Northeast China from joint inversion of receiver functions and Rayleigh wave phase velocities: Implications for intraplate volcanism

    Tang, Zheng; Julià, Jordi; Mai, Paul Martin; Mooney, Walter; Wu, Yanqiang (Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 2022-04-21) [Article]
    A high-resolution 3-D crustal and upper-mantle shear-wave velocity model of Northeast China is established by joint inversion of receiver functions and fundamental-mode Rayleigh wave phase velocities. The teleseismic data used to calculate receiver functions are collected from 107 CEA permanent sites and 118 NECESSArray portable stations. Rayleigh wave dispersion measurements are extracted from an independent tomographic study. Our model exhibits significant detail in S-wave velocity structure. Particularly, we observe a nearly constant S-wave velocity of 3.4-3.6 km/s from shallow to deep crystalline crust under the study area, which we attribute to a high thermal gradient. Some modestly positive S-wave velocity anomalies in the crust beneath the Songliao basin are interpreted as solidified late-Mesozoic mafic intrusions. In the upper mantle, we confirm the local presence of low velocity zones below the Changbai mountains and Lesser Xing’an mountain range, consistent with asthenospheric mantle upwelling models. Furthermore, moderately low shear velocities imaged beneath the Halaha and Abaga volcanoes indicate possible pathways of magma ascent through the lithospheric mantle from the asthenosphere. At a regional scale, the average lithosphere-asthenosphere boundary depth increases from ∼70 km under the greater Changbai mountains to ∼100 km below the Songliao basin, and reaches ∼110-120 km beneath the Greater Xing’an mountain range in the west. The conjectured dense mantle lid under the Songliao basin, characterized by fast S-velocities, may have prevented sub-lithospheric melts from migrating to the surface
  • Generalized multiscale finite element methods for the reduced model of darcy flow in fractured porous media

    Alotaibi, Manal; Chen, Huangxin; Sun, Shuyu (Journal of Computational and Applied Mathematics, Elsevier BV, 2022-04-19) [Article]
    In this work, we combine the generalized multiscale finite element method (GMsFEM) with a reduced model based on the discrete fracture model (DFM) to resolve the difficulties of simulating flow in fractured porous media while efficiently and accurately reducing the computational complexity resulting from resolving the fine scale effects of the fractures. The geometrical structure of the fractures is discretely resolved within the model using the DFM. The advantage of using GMsFEM is to represent the fracture effects on a coarse grid via multiscale basis functions constructed using local spectral problems. Solving local problems leads to consideration and usage of small scale information in each coarse grid. Besides, the multiscale basis functions, generated following GMsFEM framework, are parameter independent and constructed once in what we call offline stage. These basis functions can be re-used for solving the problem for any input parameter when it is needed. Combining GMsFEM and DFM has been introduced in other works assuming continuous pressure across the fractures interface. This continuity is obtained when the fractures are much more permeable than that in the matrix domain. In this work, we consider a general case for the permeability in both fracture and matrix domain using the reduced model presented in Martin et al. (2005). The proposed reduction technique has significant impact on enabling engineers and scientist to efficiently, accurately and inexpensively solve the large and complex system resulted from modeling flow in fractured porous media
  • Effect of dust on rainfall over the Red Sea coast based on WRF-Chem model simulations

    Parajuli, Sagar P.; Stenchikov, Georgiy L.; Ukhov, Alexander; Mostamandi, Suleiman; Kucera, Paul A.; Axisa, Duncan; Gustafson Jr., William I.; Zhu, Yannian (Copernicus GmbH, 2022-04-19) [Preprint]
    Water is the single most important element of life. Rainfall plays an important role in the spatial and temporal distribution of this precious natural resource and it has a direct impact on agricultural production, daily life activities, and human health. One of the main elements that govern rainfall formation and distribution is atmospheric aerosol, which also affects the Earth’s radiation balance and climate. Therefore, understanding how dust compositions and distributions affects the regional rainfall pattern is of crucial, particularly in regions with high atmospheric dust loads such as the Middle East. Although aerosol and rainfall research has garnered increasing attention both as an independent and interdisciplinary topic in the last few decades, the details of various direct and indirect pathways by which dust affects rainfall are not yet fully understood. Here, we explored the effects of dust on rainfall formation and distribution as well as the physical mechanisms that govern these phenomena, using high-resolution WRF-Chem simulations (~1.5 × 1.5 km) configured with an advanced double-moment cloud microphysics scheme coupled with a sectional 8-bin aerosol scheme. Our model-simulated results were realistic, as evaluated from multiple perspectives including vertical profiles of aerosol concentrations, aerosol size distributions, vertical profiles of air temperature, diurnal wind cycles, and spatio-temporal rainfall patterns. Rainfall over the Red Sea coast is mainly caused by warm rain processes, which are typically confined within a height of ~ 6 km over the Sarawat mountains and exhibit a strong diurnal cycle that peaks in the evening at approximately 6 pm local time under the influence of sea breezes. Numerical experiments indicated that dust could both suppress or enhance rainfall. The effect of dust on rainfall were calculated as total, indirect, and direct effects, based on 10-year August-average daily-accumulated rainfall over the study domain covering the eastern Red Sea coast. For extreme rainfall events (domain-average daily-accumulated rainfall of ≥ 1.33 mm), the total (6.05 %), indirect (4.54 %), and direct effects (1.51 %) were all positive (enhancement). At a 5 % significance level, the total and indirect effects were statistically significant whereas the direct effect was not. For normal rainfall events (domain-average daily-accumulated rainfall < 1.33 mm), the indirect effect enhanced rainfall (4.76 %) whereas the direct effect suppressed rainfall (-5.78 %), resulting in a negative net suppressing effect (-1.02 %), all of which were statistically significant. We investigated the possible physical mechanisms of the effects and found that the dust direct effects were mainly caused by the scattering (absorption) of solar radiation by dust. The surface cooling (warming) induced by scattering (absorption) weakens (strengthens) the sea breeze circulation, which decreases (increases) the associated landward moisture transport, ultimately suppressing (enhancing) rainfall. Our results have broader scientific and environmental implications. Specifically, although dust is considered a problem from an air quality perspective, our results highlight the important role of dust on sea breeze circulation and associated rainfall over the Red Sea coastal regions. Our results also have implications for cloud seeding and water resource management.
  • Future projection of the African easterly waves in a high-resolution atmospheric general circulation model

    Raj, Jerry; Bangalath, Hamza Kunhu; Stenchikov, Georgiy L. (Research Square Platform LLC, 2022-04-18) [Preprint]
    Simulating the features of the African Easterly Waves (AEWs), such as their westward propagation off the coast, is challenging for coarseresolution climate models. In this study, we use High-Resolution Atmospheric Model (HiRAM) to simulate AEWs and analyze their future projections by the end of the 21 st century. The simulations are performed globally at a horizontal resolution of ∼ 25km. The model uses shallow convective parameterization for moist convection and stratiform cloudiness. Future projections are conducted using representative concentration pathway 8.5. The AEWs are separated with respect to their periods as 3–5- and 6–9-day AEWs, and bandpass filtering is used to filter the waves from the mean flow. HiRAM simulates structure and propagation of the waves well; however, it tends to overestimate the associated precipitation. In the future, the AEW activity and intensity of the circulation will considerably increase. The northward extent of the AEW track also shows a significant increase in the future. The increased wave activity can be translated as more Atlantic hurricanes in the future because AEWs are the seed disturbances for cyclogenesis in this region.
  • Bulk and Interfacial Properties of Brine or Alkane in the Presence of Carbon Dioxide, Methane, and Their Mixture

    Nair, Arun Kumar Narayanan; Anwari Che Ruslan, Mohd Fuad; Ramirez Hincapie, Marcia Luna; Sun, Shuyu (Industrial & Engineering Chemistry Research, American Chemical Society (ACS), 2022-04-11) [Article]
    We present an overview of the molecular simulations performed to understand the two-phase behavior of brine or alkane in the presence of CH4, CO2, and their mixture at reservoir conditions. The simulation results of bulk and interfacial properties of these systems compared well with experimental data and theoretical estimates obtained using, for example, density gradient theory based on CPA (with Debye–Hückel electrostatic term) and PC-SAFT EoSs. Here, CO2 is preferentially dissolved in the water-rich or alkane-rich phase and enriched at the interface from the CH4/CO2 equimolar mixture. The fact that the interfacial enrichment in CO2 was much higher than that of CH4 explained the relatively steep decrease in the interfacial tension (IFT) with pressure in brine+CO2 and alkane+CO2 systems. IFTs of brine+CH4+CO2 and alkane+CH4+CO2 systems decreased with increasing mole fraction of CO2 in the CH4/CO2-rich phase. Solubilities of CH4 and CO2 in the water-rich phase decreased with the addition of salt (salting-out effect). This effect followed the order NaCl < CaCl2. IFTs of brine+CH4/CO2 systems linearly increased as the salt concentration increased. Here, the larger slopes in the presence of CaCl2 are due to stronger hydration and repulsion from the interface of Ca2+ ions. Solubilities of CH4 and CO2 in the alkane-rich phase generally decreased with increasing alkane size nc. These solubilities were relatively lower in the cycloalkane-rich phase, while linear and branched alkanes gave similar results. IFTs of alkane+CH4/CO2 systems increased as nc increased and a relatively high IFT was obtained in cycloalkane+CH4/CO2 systems.
  • Novel Misfit Functions for Full-waveform Inversion

    Chen, Fuqiang (2022-04) [Dissertation]
    Advisor: Peter, Daniel
    Committee members: Keyes, David E.; Ravasi, Matteo; Fomel, Sergey
    The main objective of this thesis is to develop novel misfit functions for full-waveform inversion such that (a) the estimation of the long-wavelength model will less likely stagnate in spurious local minima and (b) the inversion is immune to wavelet inaccuracy. First, I investigate the pros and cons of misfit functions based on optimal transport theory to indicate the traveltime discrepancy for seismic data. Even though the mathematically well-defined optimal transport theory is robust to highlight the traveltime difference between two probability distributions, it becomes restricted as applied to seismic data mainly because the seismic data are not probability distribution functions. We then develop a misfit function combining the local cross-correlation and dynamic time warping. This combination enables the proposed misfit automatically identify arrivals associated with a phase shift. Numerical and field data examples demonstrate its robustness for early arrivals and limitations for later arrivals.%, which means that a proper pre-processing step is still required. Next, we introduce differentiable dynamic time warping distance as the misfit function highlighting the traveltime discrepancy without non-trivial human intervention. Compared to the conventional warping distance, the differentiable version retains the property of representing the traveltime difference; moreover, it can eliminate abrupt changes in the adjoint source, which helps full-waveform inversion converge to geologically relevant estimates. Finally, we develop a misfit function entitled the deconvolutional double-difference measurement. The new misfit measures the first difference by deconvolution rather than cross-correlation. We also present the derivation of the adjoint source with the new misfit function. Numerical examples and mathematical proof demonstrate that this modification makes full-waveform inversion with the deconvolutional double-difference measurement immune to wavelet inaccuracy.
  • Effects of Membrane Structure on Oil–Water Separation by Smoothed Particle Hydrodynamics

    Liu, Jie; Xie, Xiaoping; Meng, Qingbang; Sun, Shuyu (Membranes, MDPI AG, 2022-03-31) [Article]
    Membrane has been considered an effective tool for oil–water separation. By using the smoothed particle hydrodynamics (SPH) method, the effects of membrane structure on fluid separation were studied thoroughly in this paper. The oil–water two-phase fluid was generated as particles, while the membrane was built with solid particles, which was able to select the fluid particles. In general, the developed SPH method in this paper can evaluate separation performance with different membrane shapes, pore size distributions, membrane thickness and fluid properties. We suggest to the industry a potential approach to promote separation based on our simulation results, including adding the external force in the selected direction and demulsification for the bulk phase liquid particles. The triangular membrane performs well with the conditions for various parameters, as a result of its insensitivity to inhibiting factors. The effectiveness and robustness of the proposed SPH scheme was validated by a number of numerical experiments, and we assessed the optimized membrane structure and operation manners in order to improve separation efficiency and long-term safety.
  • Present-day uplift of the East Kunlun Shan, Northern Tibetan Plateau

    Liu, Shaozhuo; Nocquet, Jean-Mathieu; Xu, Xiwei; Jonsson, Sigurjon; Chen, Guihua; Tan, Xibin; Klinger, Yann (Copernicus GmbH, 2022-03-28) [Preprint]
    Part of the 5-km high Tibetan plateau is undergoing eastward extension and crustal thinning, which might be the signature of a waning orogeny. However, the actual extent of such processes throughout the high plateau remains uncertain. Here, we examine the impact of tectonic, geodynamic, and climate-related surface processes on the vertical deformation monitored since 2007 by continuous Global Positioning System (GPS) across the East Kunlun Shan (EKS), the largest relief inside the Tibetan plateau. GPS measurements reveal 1-2 mm/yr uplift of the EKS relative to the 2-km-lower Qaidam Basin. However, the range-perpendicular shortening is limited at most to ~1 mm/yr, which is not adequate to drive the observed vertical motion. Instead, (1) the isostatic response to erosion and regional deglaciation since the last glacial period likely accounts for a significant fraction, up to 40%, of our GPS derived vertical rate, and (2) the EKS and its surrounding region to the south are probably still rising at ~1 mm/yr, rather than subsiding. Thus, our results show that this part of the northern Tibetan plateau is rising, demonstrating that the Tibetan Plateau is still actively growing, in contrast with previous models proposing the passive demise of the high plateau due to erosion and gravitational collapse.
  • CO2 injection and storage for geothermal power generation in hydrothermal reservoirs along the Red Sea of Western Saudi Arabia

    Yalcin, Bora; Ezekiel, Justin; Arifianto, Indra; Mai, Paul Martin (Copernicus GmbH, 2022-03-27) [Presentation]
    As an alternative to water, CO2 can be used for heat mining from geothermal reservoirs, while also trapping most of the injected CO2 underground. In addition, supercritical CO2 has higher mobility and heat capacity than water, rendering CO2 capture, utilization and storage (CCUS) in geothermal reservoirs a very attractive option in a circular carbon economy. CCUS is also in line with Saudi Vision 2030, which includes the strategic framework to reduce Saudi Arabia’s dependence on hydrocarbons and diversify its economy. The western coast of Saudi Arabia, where the young and high-heat-flow Red Sea rift basins are located, are considered suitable for geothermal heat extraction and CO2 storage. In this study, we explore the potential of CCUS for geothermal power generation and CO2 storage in the hydrothermal reservoirs of Al Wajh basin located on the Red Sea coast. Geological studies in Al Wajh basin report that the hot fluid bearing, thick, porous, siliciclastic formations, such as Al Wajh (formation’s top depth, TD= 3900 meters), Burqan (TD = 2880 m) and Jebel Kibrit (Umluj member with TD = 1930 m) are sealed by the overlying anhydrite (Kial) and salt formations (Mansiyah). We combine publicly available data with different resolution scales, such as satellite gravity, seismic sections and well-log information to build a 3D geologic model, which enables us to constrain the 3D gross rock volume and the Net-to-Gross ratio/distribution of the target hydrothermal reservoirs. A 3D temperature model shows that the average surface temperature in the region and the subsurface temperature gradient create formation fluid temperature of over 120o C at 3 km depth. We conduct reservoir simulation of coupled transport of formation fluid, injected non-condensable gas (CO2) and heat in heterogeneous 3D reservoir model, using CMG STARS. We then estimate the geothermal energy extracting capacity and storage efficiency of CO2 in the prospective hydrothermal reservoirs in the Al Wajh basin. Our study provides the first semi-realistic reservoir model and simulation study in Saudi Arabia for combined CO2-based geothermal power generation and CO2 storage potential at a designated target site. The work-flow we propose is transferable to other suitable hydrothermal reservoirs in different locations in Saudi Arabia, thereby enabling CCUS technology implementation along the Red Sea.
  • Epistemic uncertainty in fault geometry effects earthquake rupture behavior

    Zielke, Olaf; Aspiotis, Theodoros; Mai, Paul Martin (Copernicus GmbH, 2022-03-27) [Presentation]
    It is well established in the seismology community that geometric complexity plays an important role for a fault’s seismotectonic behavior. It affects the initiation, propagation and termination of an earthquake as well as influencing the stress-slip relationship, the size of fault segments, and the probability of multi-segment rupture. Consequently, fault geometric complexity is studied intensively and increasingly incorporated into computational earthquake rupture simulations. These efforts reveal a problem: While we may be able to constrain a natural fault’s geometry with a high level of detail at the surface (i.e., the fault trace), we cannot do the same for the buried portion of the fault -where most of the rupture takes place. How much does a fault’s seismotectonic behavior vary as a result of this epistemic uncertainty? We address this question computationally with a physics-based multi-cycle earthquake rupture simulator (MCQsim), enabling us to investigate how (for example) earthquake recurrence, slip accumulation, magnitude-frequency distribution, and fault segmentation vary (looking at the entire fault as well as individual locations on the fault) as function of our insufficient knowledge about the fault’s geometric complexity. To simulate fault geometric complexity, we generate 2-D random fields, using the “random midpoint displacement” method (RMD), representing the fault’s non-planar, self-similar geometry. The advantage of using RMD is that it allows us to create a 2-D random field while also keeping one or more of the field’s edges at a prescribed value. Hence, this approach allows us to generate a random field to represent fault roughness while also allowing us to incorporate what is known about the fault geometry (i.e., the fault surface trace, representing one of the random field’s edges). In doing so, we can investigate how the aforementioned seismo-tectonic parameters vary as a function of fault roughness uncertainty. For this purpose, we create 5000-year long earthquake catalogs for a 150x18km large strike slip fault that is parameterized by more than 40k fault cells (average cell size 0.07km^2), containing earthquakes with 3.5 < M < 7.8. We create these catalogs for 100 roughness realizations while keeping the simulated fault’s surface trace constant for all realizations. The results of these simulations will be presented in our presentation.
  • Study of interfacial properties of water + methane + oil three-phase systems by a simple molecular simulation protocol

    Yang, Yafan; Che Ruslan, Mohd Fuad Anwari; Sun, Shuyu (Journal of Molecular Liquids, Elsevier BV, 2022-03-25) [Article]
    A straightforward molecular simulation protocol has been proposed to study the interfacial properties of the three-phase fluid systems. With this protocol, the interfctcial tension (IFT) can be calculated based on the pressure tensor of the entire simulation box of the two-phase systems split from the three-phase system without calculating the debatable pressure tensor profile. Water + methane + oil (decane, hexadecane, and toluene) three-phase systems was studied at different temperatures (323–423 K) and pressures (up to around 20 MPa). Reasonable agreement was found among the results obtained from molecular simulation, density gradient theory with the cubic-plus-association equation of state, and available experimental data in the literature. The IFT of the aqueous phase + vapor phase in the three-phase systems is smaller than the IFT in water + methane two-phase systems. Importantly, the reduction of IFT of aqueous phase + vapor phase in the three-phase systems containing decane or hexadecane is moderate while that in the three-phase systems containing toluene is significant, which can be explained by the stronger enrichment of toluene in the interfacial region in contrast to that of decane or hexadecane. Meanwhile, methane accumulates in the interfacial region of the aqueous phase + decane/hexadecane-rich phase in the three-phase systems, which causes the reduction of IFT with pressure while the opposite pressure effect was reported in the water + decane/hexadecane two-phase systems. The interfacial properties of the oil-rich phase + vapor phase in the three-phase systems are hardly affected by water due to the small amount of dissolved water. Furthermore, the calculated spreading coefficient of different types of oil in contact with water + methane under three-phase conditions follows this order: toluene > decane > hexadecane.
  • Cycle-skipping mitigation using misfit measurements based on differentiable dynamic time warping

    Chen, Fuqiang; Peter, Daniel; Ravasi, Matteo (GEOPHYSICS, Society of Exploration Geophysicists, 2022-03-19) [Article]
    The dynamic time warping (DTW) misfit function has been employed for full-waveform inversion to mitigate the local minima issue. However, it is not a smooth measurement and can yield strong discontinuities in the adjoint source. Such a weakness hampers the convergence of waveform inversion to informative minima. We introduce a smooth DTW misfit function to remedy this shortcoming. The fundamental idea of the smooth DTW is to replace the {min} operator with its smooth relaxation. This replacement results in differentiable misfit measurements. Moreover, considering that the optimal warping plan indicates the traveltime difference between the observed and synthetic trace, we can construct a penalization term such that the penalized differentiable DTW distance highlights the traveltime difference further. Numerical examples demonstrate the advantage of the penalized differentiable DTW misfit function over the conventional non-differentiable one.

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