Browsing by Subject "Seismic"

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Acoustic characterization of encapsulated bubbles at sonic frequencies and elevated temperatures and pressures
(2015-08) Lindsey, Danika Catherine; Hamilton, Mark F.; Spratt, Kyle S
The acoustic effects of introducing small quantities of a highly compliant material into a much less compressible system are well understood. However for applications in geological formations, additional requirements regarding the size and robustness of the particles can present challenges. Additionally, the elevated pressures commonly encountered in downhole situations can cause a significant decrease in the level of contrast provided. To address this, resonance tube experiments were carried out in an attempt to identify suitable particles for this application. Physical parameters for the ideal particle are given, and the potential problem of acoustic attenuation in the rock formation is addressed.
Analysis of GPU-based convolution for acoustic wave propagation modeling with finite differences: Fortran to CUDA-C step-by-step
(2014-05) Sadahiro, Makoto; Stoffa, Paul L., 1948-; Tatham, R. H. (Robert H.), 1943-
By projecting observed microseismic data backward in time to when fracturing occurred, it is possible to locate the fracture events in space, assuming a correct velocity model. In order to achieve this task in near real-time, a robust computational system to handle backward propagation, or Reverse Time Migration (RTM), is required. We can then test many different velocity models for each run of the RTM. We investigate the use of a Graphics Processing Unit (GPU) based system using Compute Unified Device Architecture for C (CUDA-C) as the programming language. Our preliminary results show a large improvement in run-time over conventional programming methods based on conventional Central Processing Unit (CPU) computing with Fortran. Considerable room for improvement still remains.
An analysis of salt welding
(2010-05) Wagner, Bryce Hedrick; Jackson, M. P. A.; Cloos, Mark; Hudec, Mike; Steel, Ron; Sen, Mrinal; Peel, Frank
Salt can be removed by viscous flow and dissolution to form a salt weld. A complete weld forms when salt is completely removed by these processes. Where salt removal is incomplete, a partial weld forms. Though welds are frequently mentioned in the literature, the details of weld formation and the properties of salt welds are poorly understood. In Chapter 1, I use analytical and numerical models to quantify the role of viscous flow during salt welding. Where salt flow is limited by boundary drag against the salt contacts, evacuation is slow and up to ~50 m of salt will be left behind in a partial weld. Where salt flow is laterally unrestricted, a vanishingly thin (<< 1 m) smear of salt will remain. I conclude that layer-parallel wall rock translation or dissolution must act to remove any remnant salt to create a complete weld. In Chapter 2, I characterize partial welds containing halite and anhydrite on reflection seismic data by treating welds as thin beds. Below the temporal resolution of reflection seismic data, typically ~25-50 m for modern surveys with peak frequencies of ~10-30 Hz, reflections from the upper and lower evaporite contacts converge and interfere to form a single composite reflection. Thus, partial and complete welds are typically indistinguishable using travel-time differences alone. I then use amplitude information from synthetics and seismic examples to estimate remnant evaporite thickness. In Chapter 3, I investigate fluid flow near and through salt welds. I conclude dissolution during boundary flow can remove up to a few meters of salt per million years. Though dissolution plays a volumetrically insignificant but important role in weld formation, as runaway dissolution can create pathways for focused cross-weld migration of subsurface fluids. I identify features that influence cross-weld migration of subsurface fluids and then develop an empirical relationship between weld geometry and the tendency seal or leak hydrocarbons. I find that in the Campos Basin, offshore Brazil, salt welds containing remnant evaporites thinner than ~50 m that are broader than ~25 km2 in area are likely to leak.
Autoencoders for seismic model upscaling and facies identification
(2022-08-12) DeFabry, Cameron Mark; Sen, Mrinal K.; Cardenas, Meinhard B; Spikes, Kyle T
The research presented here focuses on the resolution enhancement of inverted seismic volumes and geological facies identification. In the first section I utilize a regularized neural network in the form of an autoencoder to improve the resolution of seismic models which were inverted for compressional wave impedance. In the second section, I focus on the utilization of autoencoders to classify spatially small geologic facies with inverted seismic models and a computed facies map. In section one I focus on the processing and inversion of seismic data from the 3D Penobscot field on the Scotian shelf to produce models for compressional wave impedance. The dataset is inverted using two different approaches, first using a deterministic method, and secondly using a stochastic method. The stochastically derived models have higher frequency content than the deterministic models and are used as the target for the task of resolution enhancement. An autoencoder is trained to recreate the stochastic models with a set of randomly chosen starting weights. During training the network attempts to create a feature map that correlates the low-resolution deterministic model to the high-resolution stochastic model by using the deterministic models as input data and the stochastic models as target data. Once training is complete the network is given the deterministic model as an input and asked to predict an output with the convolution filters learned by recreating the stochastic models. The result is a model of higher resolution than the original deterministic model, but lower resolution than the original stochastic model. In section two I characterize a seismic volume from the Marco Polo field collected in the Gulf of Mexico and then classify five distinct facies, a shale member, an oil sand member, a gas sand member, and discrete brine sand members corresponding to the sand units. The brine sand members were simulated through fluid substitution and then have their probabilistic properties derived through a rock physics template. Bayesian classification is used to create an initial facies map with the brine sands predicted with rock physics templates, and the remaining units predicted directly from the distributions inherent to the well log. Geologic units less than 600 meters in any direction were specifically targeted by converting the standard facies map into a binary facies map. This binary facies map was used as an input in an autoencoder along with two seismic volumes inverted for compressional wave impedance and Vp/Vs. The result is a trained network that can take inverted model inputs and produce a probabilistic output predicting the location of a given facies. Additionally, when provided with smoothed inputs, the autoencoder can produce outputs of a similar resolution to that of the original data, with a loss of performance noted in the probabilities displayed. This result, along with the result from section one are used to justify the claim that autoencoders can be effectively used for the tasks of seismic model upscaling and facies identification without the direct use of well log data as a network input. Convolutional layers provide a way of processing these data in a manner often seen in image recognition and enhancement problems. These networks are limited to the data they were trained on, so additional training would be required for use on separate datasets. The utilized methods though, should maintain their efficacy provided the appropriate training has taken place.
Development of a hydrate-gas-water static equilibrium model and analysis of three-phase stability
(2018-05) Leung, Ryan Wai-Hung; Daigle, Hugh
Recent evidence suggests that a three-phase stability zone exists at the base of gas hydrate stability (BGHS), where hydrate and gas may coexist due to the pore size distribution. We develop a three-phase stability zone model at static equilibrium based on the idea of minimizing interfacial energy. We use this model to produce three-phase saturations and study the effects of three-phase stability for two applications. The first application is related to the migration of gas from beneath sealing hydrate layers to the seafloor. A proposed mechanism for this upwards gas migration is the generation of fractures through the sealing hydrate sediment due to overpressures caused by the accumulation of gas on geologic timescales. Our study focuses on how the fracturing potential of a three-phase stability zone differs from a discrete BGHS, where hydrate is separated from gas by a sharp boundary. We model gas overpressures at Blake Ridge, Hydrate Ridge, and the Kumano Basin by incorporating mercury intrusion capillary pressure data with our three-phase stability model. Our results show that the overpressures in the three-phase stability model are smaller, reducing the potential for gas-driven fracturing. We also find that hydrate-bearing basins with shallower seafloor depths modeled with three-phase stability need much more methane to generate the overpressures that will initiate fractures. The second application of three-phase stability relates to the bottom-simulating reflection (BSR), which is a common negative polarity reflection in marine sediments that often follows the contour of the seafloor. Recent literature suggests that the BSR indicates the shallowest presence of gas, not the BGHS. This three-phase stability model has an impact on the seismic response of the BSR, and we study this effect by developing 1-D rock physics models of Blake Ridge. By varying the methane quantity and performing fluid substitution with three-phase saturation profiles, we generate synthetic seismograms and analyze the difference in two way travel time (TWTT). For comparison, we use the workflow for a parameter sensitivity model and an original-resolution model. Through this analysis, we find a relationship between the TWTT width of the BSR’s peaks and the methane abundance at the BGHS
Development of seismic fragility curves for earth dams in Texas, Oklahoma, and Kansas
(2023-07-25) He, Jingwen, Ph. D.; Rathje, Ellen M.; Gilbert, Robert; Kumar, Krishna; Clayton, Patricia; Savvaidis, Alexandros
The seismic performance of earth dams is important in geotechnical engineering because most of the earth dams in the United States were constructed before seismic codes and design criteria were implemented, and the consequences of a dam failure may be drastic. Seismic fragility models predict damage as a function of earthquake ground shaking, and can be used to assess the seismic risk within a given region or to quickly evaluate the possible damage after an earthquake. This research aims to develop seismic fragility curves for earth dams using regional ground motion and dam information in Central and Eastern North America (CENA). The proposed seismic fragility framework consists of two major components: (1) a seismic capacity model and (2) a seismic demand model. These two models are used together within a Monte Carlo simulation to compute the resulting fragility model. A dataset of earthquake case histories of dam performance was compiled and used to develop a seismic capacity model that considers variability between damage state and relative settlement (RS), which defines the engineering demand. A demonstrative example develops seismic fragility curves for a 20m generic dam geometry. To develop seismic fragility curves for generic earth dams in CENA, a total of 120 homogeneous dams and 222 clay core dam models were created to represent the earth dam geometries and soil properties in Texas. A suite of 39 ground motions were selected from the Texas, Oklahoma, and Kansas region to represent the ground motion characteristics in CENA. Seismic fragility curves were developed for earth dams as a function of dam height and dam type (i.e., homogenous, clay core). To study the effect of regional ground motion characteristics on seismic dam performance, three ground motion suites from two different regions and with different magnitude ranges were used to develop predictive models for RS. It was found that peak ground velocity (PGV) was the most efficient ground motion intensity measure (IM) in predicting RS and was the only IM that unified the RS prediction across ground motions from different regions and with different magnitude ranges.
Direct in-situ evaluation of liquefaction susceptibility
(2014-05) Roberts, Julia Nicole; Stokoe, Kenneth H.
Earthquake-induced soil liquefaction that occurs within the built environment is responsible for billions of dollars of damage to infrastructure and loss of economic productivity. There is an acute need to accurately predict the risk of soil liquefaction as well as to quantify the effectiveness of soil improvement techniques that are meant to decrease the risk of soil liquefaction. Current methods indirectly measure the risk of soil liquefaction by empirically correlating certain soil characteristics to known instances of surficial evidence of soil liquefaction, but these methods tend to overpredict the risk in sands with silts, to poorly predict instances of soil liquefaction without surface manifestations, and fail to adequately quantify the effectiveness of soil improvement techniques. Direct in-situ evaluation of liquefaction susceptibility was performed at a single site at the Wildlife Liquefaction Array (WLA) in Imperial Valley, California, in March 2012. The project included a CPT sounding, crosshole testing, and liquefaction testing. The liquefaction testing involved the measurement of water pressure and ground particle motion under earthquake-simulating cyclic loading conditions. The objective of this testing technique is to observe the relationship between shear strain in the soil and the resulting generation of excess pore water pressure. This fundamental relationship dictates whether or not a soil will liquefy during an earthquake event. The direct in-situ evaluation of liquefaction susceptibility approach provides a more accurate and comprehensive analysis of the risks of soil liquefaction. It also has the ability to test large-scale soil improvements in-situ, providing researchers an accurate representation of how the improved soil will perform during a real earthquake event. The most important results in this thesis include the identification of the cyclic threshold strain around 0.02% for the WLA sand, which is very similar to results achieved by other researchers (Vucetic and Dobry, 1986, and Cox, 2006) and is a characteristic of liquefiable soils. Another key characteristic is the 440 to 480 ft/sec (134 to 146 m/s) shear wave velocity of the soil, which are well below the upper limit 656 ft/sec (200 m/s) and an indication that the soil is loose enough for soil liquefaction to occur. The third significant point is that the compression wave velocity of the sand is greater than 4,500 ft/sec (1,370 m/s), indicating that it is at least 99.9% saturated and capable of generating large pore water pressure due to cyclic loading. These three conditions (cyclic threshold strain, shear wave velocity, and compression wave velocity) are among the most important parameters for characterizing a soil liquefaction risk and must all be met in order for soil liquefaction to occur.
Dynamic site characterization of TexNet ground motion stations
(2018-05-02) Yust, Michael Benjamin Schutt; Cox, Brady Ray, 1976-; Rathje, Ellem M
The TexNet Seismic Monitoring Program is an important part of monitoring and understanding the presence and cause of seismic activity throughout the state of Texas. The network covers wide variety of geologic conditions across the 58 new ground motion stations. Characterizing the seismic site conditions at each station is an integral step toward properly interpreting and understanding the seismic activity recorded by the network. Additionally, the large number of stations being examined for this project affords researchers a chance to evaluate the uncertainty of near (i.e. depths < 30 m) surface seismic site characterization. Shear wave velocity profiles (Vs) derived from both invasive/borehole and noninvasive/surface wave methods are acknowledged to contain uncertainties in the thickness and stiffness of each resolved layer. However, it is quite rare for these uncertainties to be quantified, or even discussed, in a meaningful way when Vs profiles are reported. As estimates of Vs uncertainty are often required in subsequent analyses (e.g., seismic site response, development of ground motion prediction equations, etc.), it is important that we develop means to quantify these uncertainties rather than assume them, as is commonly done at the present time. This thesis presents an example of attempts to quantify the epistemic uncertainty in Vs profiles and Vs30 values (average Vs over the top 30 m depth) derived from noninvasive active- and passive-source surface wave testing using multiple modal interpretations and inversion parameterizations as well as a summary of all the sites characterized in this project and comparisons to other characterizations methods (i.e., P-wave seismogram and geologic proxy).
Effect of a discrete three-phase methane equilibrium zone on the bottom-simulating reflection
(2016-12) Shushtarian, Arash; Daigle, Hugh
Marine gas hydrates are stable under conditions of low temperature and high pressure in the upper few hundreds of meters below the seafloor in a variety of geological setting. At a discrete horizon where thermodynamically favored phase switches from hydrate to gas, a characteristic seismic reflection referred as the bottom-simulating reflection (BSR) is produced. Furthermore, in sediments with a distribution of pore sizes, the gas and hydrate phases can coexist in pores of different sizes, giving a rise to three-phase equilibrium zone. This three-phase zone causes the BSR to have distinct characteristics that differ from those observed with a discrete phase boundary. The main objective of this thesis is to model the seismic response of a potential three-phase zone at the Walker Ridge Block 313H in the northern Gulf of Mexico. I modeled the BSR arising from this three-phase zone and analyzed the characteristics of the BSR and their relationships to the thickness and phase saturation within the three-phase zone. This was done by determining the elastic properties of the formation via rock physics models and their mathematical convolution with a seismic wavelet to create synthetic seismograms. Results show that the main factor for the intensity of the BSR is the abundance of the free gas in the three-phase zone. Free gas saturation as low as 5% in the three-phase zone is enough to make the BSR visible in synthetic seismograms regardless of the hydrate saturation. Results of this thesis are significant for resource prospecting based on seismic data, drilling hazard identification, as well as the importance of hydrate as a potential source of energy and its influence on the global climate. For seismic prospecting, the presence of a three-phase zone inferred from BSR characteristic indicates the minimum methane flux into the base of the hydrate stability zone, and can be used to infer whether sufficient methane is available to form hydrate. For drilling hazard identification, the BSR characteristic indicates a possible shallower occurrence of gas than would be estimated under the assumption of a discrete phase boundary.
Experimental and analytical investigations on bond of reinforcement and nonlinear response of reinforced concrete columns
(2020-12-01) Fawaz, Ghassan; Murcia-Delso, Juan; Bayrak, Oguzhan; Manuel, Lance; Clayton, Patricia; Hrynyk, Trevor
Bond of reinforcement has a major influence on the behavior of reinforced concrete (RC) structures. Even though bond has been extensively studied over the past decades, there are still a number of knowledge gaps requiring investigation. This dissertation presents three studies related to the basic bond behavior of reinforcement and the influence of bond-slip on the seismic response of RC columns. The first investigation characterizes the bond behavior of iron-based shape-memory alloy (Fe-SMA) bars. Fe-SMA reinforcement provides new opportunities for design and strengthening of concrete structures thanks to their shape memory effect. However, there is currently little data on its bond performance. Experiments were conducted to study the bond-slip behavior of ribbed Fe-SMA bars embedded in concrete specimens with different levels of passive confinement. Fe-SMA bars presented a similar bond performance as conventional reinforcement, but their bond strength was reduced with heat activation in low-confined specimens. An analytical model is also proposed to calculate the transfer length of Fe-SMA bars in prestressing applications. The second investigation proposes nonlinear finite element models to accurately simulate the cyclic response of RC columns, including the effect of bond-slip. Concrete is modeled using a triaxial constitutive model recently proposed in the literature. A commonly used uniaxial steel model is modified to account for low-cycle fatigue rupture using a phenomenological criterion. The bond-slip behavior of bars is modeled using a zero-thickness interface element and a bond stress-slip law that predicts bond deterioration caused by generalized slip demands, tensile yielding of steel, and concrete damage. The proposed models accurately predict the cyclic response and failure of previously tested column components. The third investigation focuses on the effects of strain penetration and bond modification on the lateral response of RC columns. Two large-scale column specimens were tested under cyclic loading. One specimen had conventional reinforcement details, while the other had headed bars that were partially debonded along the footing to alleviate strain concentrations. Both specimens formed plastic hinges and failed due to rupture of longitudinal bars. The specimen with partial debonding presented less damage and a larger deformation capacity. Experimental data indicated that the debonding strategy reduced peak tensile strains, and increased bar slip and fixed-end rotations. However, it also reduced the lateral load resistance of the column. Companion finite element analyses have indicated that the reduction in peak lateral strength is caused by lower steel stress demands when concrete cover fails.
Fast methods to model the response of fluid-filled fractures and estimate the fracture properties
(2018-11-21) Alulaiw, Badr Abdullah; Sen, Mrinal K.; Spikes, Kyle T; Fomel, Sergey; Grand, Stephen P; Foster, Douglas
Estimation of fracture orientation and properties has become an important part of seismic reservoir characterization especially in unconventional reservoirs because of the crucial role of fractures in enhancing the permeability in tight reservoirs. The presence of fluid inside the fractures affects their seismic response. Using equivalent medium theories, seismic wave signatures such as Amplitude Variation with Offset and azimuth (AVOz), Normal Moveout (NMO) correction and shear waves splitting have been used to detect the presence of gas-filled and fluid-filled fractures. These methods, however, are unable to specify the type of fluid inside the fractures and cannot be used for thin beds and complex geology where the subsurface properties change laterally. Hence, modeling the seismic waveform using numerical methods is inevitable. The main limitation of those methods is their high computation costs. In this dissertation, I focus on developing two fast numerical methods to model the response of fluid-filled fractures as well as one fast global optimization method to estimate the fracture properties. Although local optimization methods are computationally cheap, the probability of being trapped in a local minimum becomes high when the initial model is not close to the global minimum especially when applied to highly nonlinear problems. Quantum Annealing (QA) is a recent global optimization method that was shown to be faster than Simulated Annealing (SA) in many situations. QA has been recently applied to geophysical problems. In this research, I modify QA by proposing using a new kinetic term that helps QA converge faster to the global minimum. With a synthetic dataset, I illustrate that QA is faster than Very Fast Simulated Annealing (VFSA) using a highly non-linear forward model that computes the response of seismic Amplitude Variation with Angle (AVA) for spherical waves. Most AVA inversion algorithms are based on plane wave solutions whereas seismic surveys use point sources to generate spherical waves. Although the plane wave solution is an excellent approximation for spherical waves, this approximation breaks down in the vicinity of the critical angle. Here, I implement an AVA inversion method for three parameters (P-wave velocity, S-wave velocity and density) based on analytical approximation for spherical waves. In addition, I apply this algorithm to a 2D seismic dataset from Cana field, Oklahoma with the primary objective of resolving the Woodford formation. I compare the results with those obtained by a local optimization method. The results clearly demonstrate superior performance of the proposed inversion method over that of local optimization. Specifically, the inverted images show clear delineation of the Woodford formation. For a reservoir containing vertical and rotationally invariant fractures, the linear slip model characterizes the reservoir using four properties: two elastic properties describing the isotropic host rock and two fracture properties – normal ΔN and tangential ΔT fracture weaknesses. This model, however, ignores the pore porosity effect on the anisotropy and hence the fracture properties might be inaccurate. In this work, I estimate the fracture properties as well as pore porosity using a new expression for the stiffness tensor for a porous fractured medium. I use the ray-Born approximation to calculate the seismic response of a laterally varying porous reservoir and QA to estimate the fracture properties. Using numerical experiments, I compare the inversion results from both unconstrained and constrained simultaneous (PP and PSV components) seismic inversion as well as constrained inversion using only the PP component. I explain the importance of including a constraint to mitigate the effect of the equivalence problem between ΔN and porosity. Unlike the unconstrained inversion, the estimated properties from the constrained inversion are acceptable. Also, I illustrate that the simultaneous constrained inversion is more robust than using the PP component alone. I apply this algorithm to a 3D multicomponent seismic dataset acquired in Saudi Arabia. The estimated fracture orientation agrees with those obtained in previous studies using borehole image logs, oriented cores, drilling observation and seismic in the same area. Also, the computed porosity using available well logs matches the inverted porosity very well. Computationally cheap analytical methods and equivalent medium theories available to model seismic wavefields diffracted by multiple fluid-filled fractures are not capable of handling complex fracture models or wave multi-scattering. Hence, using expensive numerical methods is inevitable. The advantages of boundary element method (BEM) over domain methods, such as finite difference and finite element methods, include the ease of handling irregular fracture geometry and reduction of the problem dimensions making the computation fast. Moreover, BEM models the complete wavefield including multiples, reverberations and refracted waves inside the fractures. The downside of BEM is that the computation cost increases rapidly whenever we increase the number of boundary elements making these methods computationally inefficient to model a large number of 2D cracks or 3D fractures. By combining the Indirect Boundary Element Method (IBEM) and a Generalized Born Series (GBS), I propose a new algorithm that can compute the response of 3D fluid-filled fracture sets effectively. In addition, when I consider equally spaced fractures that have the same geometry within a fracture set, computation can be performed even more rapidly. I compare the wavefield obtained using this approximation in five numerical experiments with those obtained from IBEM and show that the results are accurate in many situations.
Feasibility of isotropic inversion in orthorhombic media : the Barrett unconventional model
(2016-05) Yanke, Andrew James; Spikes, Kyle; Sen, Mrinal K; Fomel, Sergey B
Geophysicists often relegate shale reservoirs as having higher symmetries (e.g., transversely isotropic (TI) or isotropic) than what reality demonstrates. Routine application of TI (or even isotropic) algorithms to orthorhombic media neglects the associated errors because we never know the true model in practice. This thesis evaluates the viability of isotropic post-stack and pre-stack seismic inversion to orthorhombic media using the SEAM Barrett Unconventional Model, the most realistic depositional model to date. The Barrett Model contains buried topography, simulated stratigraphy, and designated reservoir zones with orthorhombic anisotropy. I inverted the Barrett data volume for isotropic elastic property cubes, which I compared to the model volume in each symmetry-plane of an orthorhombic medium. If the stacked seismic data contained only the near offsets, post-stack inversion resolved acoustic impedances that closely matched the true model both within and outside of the reservoir zones at all well locations. Anisotropy most affected the far offsets, so muting them predictably enhanced the post-stack inversion. I maintained all offsets for pre-stack inversion, but a parabolic radon filter eliminated nonhyperbolic behavior (rather than nonhyperbolic moveout analysis) at far offsets. The pre-stack impedance attributes adequately described the vertical heterogeneity of the true model at a cross-validation well, but the inverted values increasingly relied on the initial model with depth. The inverted density estimates experienced notable oscillations relative to the initial model, particularly where steep contrasts in elastic properties occurred. Mismatch of the inverted elastic properties at the well locations can be attributed to noise, thin layering effects, band limitation, steep contrasts in elastic properties, AVO behavior stacked into the data, an inaccurate starting model, and the effects of anisotropy. The most significant sources of error include small-scale reflectivity and comprehensive filtering of nonhyperbolic phenomena. Away from the well locations, the isotropic inversion gave no visual indication of reservoir geobodies, but it sufficiently described the elastic property variations near reservoir mid-sections. Moreover, I showed that the inverted elastic properties differ from their orthorhombic models by no more than 35%. The greatest misfits occurred near reservoir contacts and geobody locations. The computed impedance models in each symmetry-plane have distinctive differences, but isotropic inversion dismisses these variations entirely. I conclude that isotropic inversion should not be a surrogate for orthorhombic methods in data preconditioning and quantitative reservoir characterization.
Geologic characterization and modeling for quantifying CO₂ storage capacity of the High Island 10-L field in Texas state waters, offshore Gulf of Mexico
(2019-09-12) Ramirez Garcia, Omar; Chuchla, Richard J. (Richard Julian); Meckel, Timothy Ashworth
Carbon dioxide capture and storage (CCS) is a promising technology for mitigating climate change by reducing CO₂ emissions to the atmosphere and injecting captured industrial emissions into deep geologic formations. Deep subsurface storage in geologic formations is similar to trapping natural hydrocarbons and is one of the key components of CCS technology. The quantification of the available subsurface storage resource is the subject of this research project. This study focuses on site-specific geologic characterization, reservoir modeling, and CO₂ storage resource assessment (capacity) of a depleted oil and gas field located on the inner continental shelf of the Gulf of Mexico, the High Island 10L field. lower Miocene sands in the Fleming Group beneath the regional transgressive Amphistegina B shale have extremely favorable geologic properties (porosity, thickness, extent) and are characterized in this study utilizing 3-D seismic and well logs. Key stratigraphic surfaces between maximum flooding surfaces (MFS-9 to MFS-10) demonstrate how marine regression and transgression impact the stacking pattern of the thick sands and overlying seals, influencing the overall potential for CO₂ storage. One of the main uncertainties when assessing CO₂ storage resources at different scales is to determine the fraction of the pore space within a formation that is practically accessible for storage. The goal of the modeling section of this project is to address the uncertainty related to the static parameters affecting calculations of available pore space by creating facies and porosity geostatistical models based on the spatial variation of the available data. P50 values for CO₂ storage capacity range from 37.56 to 40.39 megatonnes (Mt), showing a narrow distribution of values for different realizations of the geostatistical models. An analysis of the pressure build-up effect on storage capacity was also performed, showing a reduction in capacity. This research further validates the impact of the current carbon tax credit program (45Q), applied directly to the storage resources results for the High Island field 10L using a simple NPV approach based on discounted cash flows. Several scenarios are assessed, where the main variables are the duration of the applicability of the tax credit, number of injection wells, and total storage capacity. Results are measured in terms of the cost of capture required for a project to be economic, given previous assumptions.
Interactions between sedimentation and deformation in the Kumano forearc basin (Japan) and the Malargue foreland basin (Argentina)
(2017-01-06) Ramirez, Sebastian Gabriel; Gulick, Sean P. S.; Horton, Brian K., 1970-; Hayman, Nicholas W; Milliken, Kitty L; Marrett, Randall
Forearc and foreland basins are ubiquitous along most convergent plate boundaries, with the geometries and contents of their sedimentary packages representing a direct record of the processes that control plate subduction and orogen growth. This project evaluates the evolution of a forearc basin in the Nankai margin of southwest Japan, and a foreland basin in western Argentina, with the ultimate goal of improving our understanding of how large-scale sedimentary systems respond to regional tectonic inputs, such as changes in plate convergence rate and subducting slab angle. The sediments of what today constitutes the Kumano forearc basin began depositing during the Pliocene in a thrust-bound, actively deforming outer accretionary wedge setting. 3D reflection seismic analysis allows to define a series of unconformity-bound packages that represent the dynamic and gradual stabilization of the inner portion of the wedge, ultimately leading to fast forearc sedimentation since ~2 Ma. The process of wedge stabilization was linked to activity along a large out-of-sequence thrust that bounds the forearc basin on its seaward side. U-Pb detrital zircon provenance results, interpreted using multidimensional scaling (MDS), show that within both the basin and the upper accretionary prism sediments were largely sourced from local rivers flowing into the Nankai margin. During the late Miocene, prism sediments had a dominant source similar to the modern Yodo River, suggesting a period of highly oblique subduction and diminished frontal accretion. Upon Pliocene forearc basin initiation, terrigenous input from the Kumano River accounted for most of the basin fill, with secondary contributions from possible reworked upper accretionary prism sediments and longitudinal gravity flows transporting sediment from rivers located farther to the northeast. These sediment provenance results highlight the highly variable distribution –both in time and space- of wedge-top sedimentation in accretionary systems, which recent work has shown may be a critical factor controlling the internal structure of submarine accretionary wedges. In the Malargüe basin, Neogene synorogenic sediments show that modern Andean fold-thrust belt (FTB) tectonic inversion and regional uplift began at ~20 Ma with the deposition of the Agua de la Piedra Formation. The younger, ~10.5 Ma Loma Fiera formation represents a second event of regional compression characterized by a shift toward coarser, cobble-dominated conglomeratic facies. It coincides with a marked increase in volcanic activity in the frontal sector of the FTB, and with evidence of generalized slip along several thick- and thin-skin structures, suggesting a possible linkage with a flat-slab event that may have simultaneously affected an over 200 km long segment of the fold-thrust belt during the mid-late Miocene.
Multiazimuth velocity analysis using velocity-independent seismic imaging
(2011-05) Burnett, William Andrew, 1983-; Fomel, Sergey B.; Stoffa, Paul L., 1948-
Multiazimuth seismic data contains information about how the Earth’s seismic response changes with azimuthal direction. Directional-dependence of the seismic response can be caused by anisotropy or heterogeneity, associated with subsurface features such as fractures, stresses, or structure. Characterizing azimuthal variations is done through velocity analysis, which provides a link between an acquired data set and its image, as well as between the image and subsurface geology. At the stage which conventional velocity analysis is applied, it is difficult to distinguish the geologic cause of observed azimuthal velocity variations. The inability to distinguish the similar effects of anisotropy and heterogeneity leads to positioning errors in the final image and velocity estimates. Regardless of the cause, azimuthally variable velocities require at least three parameters to characterize, as opposed to the conventional single-parameter isotropic velocity. The semblance scan is the conventional tool for seismic velocity analysis, but it was designed for the isotropic case. For multiple parameters, the semblance scan becomes computationally impractical. In order to help address the xiissues of geologic ambiguity and computational efficiency, I develop three methods for multiazimuth seismic velocity analysis based on “velocity-independent” imaging techniques. I call this approach, velocity analysis by velocity-independent imaging, where I reverse the conventional order of velocity estimation followed by image estimation. All three methods measure time-domain effective-velocity parameters. The first method, 3D azimuthally anisotropic velocity-independent NMO, replaces the explicit measurement of velocity with local slope detection. The second method, time-warping, uses local slope information to predict traveltime surfaces without any moveout assumption beforehand, and then fit them with a multiparameter velocity model. The third method, azimuthal velocity continuation, uses diffraction image focusing as a velocity analysis criterion, thereby performing imaging and velocity analysis simultaneously. The first two methods are superior to the semblance scan in terms of computational efficiency and their ability to handle multi-parameter models. The third method is similar to a single multi-parameter semblance scan in computational cost, but it helps handle the ambiguity between structural heterogeneity and anisotropy, which leads to better positioned images and velocity estimates.
Nonlinear modeling of Texas highway bridges for seismic response-history analysis
(2016-12) Prakhov, Vyacheslav Oleksiyovich; Clayton, Patricia M.; Williamson, Eric B., 1968-
A recent increase in the number of earthquakes across the state of Texas has raised concerns about seismic performance of highway bridges in the state inventory, the vast majority of which were not explicitly designed to withstand earthquake loading. Potential causes of seismic damage include column shear failure due to low transverse reinforcement rations and non-seismic detailing, girder unseating due to excessive bearing deformation or instability, deck pounding, and others. The objective of the study is to develop bridge numerical models for nonlinear response-history analysis taking into consideration Texas-specific design and detailing practices. Using the models developed, the fragility of Texas bridges can be analyzed and systematically quantified, allowing state highway officials to efficiently identify the bridges most likely to be damaged after an earthquake. Component models for all major bridge parts were developed for this study, including the superstructure, deck joint, bearing, bent, foundation, and abutment. The models were developed based on past experimental, analytical, and numerical work from the literature, accounting for the mass, stiffness, and damping properties of each bridge component. Damage was accounted for using nonlinear hinge models capable of simulating stiffness-degradation and hysteretic behavior based on specific properties and expected limit states of each bridge component. Finally, a MATLAB script was developed to assemble bridge component models into full bridge models depending on user input of geometric and material properties of an individual bridge sample.
Parameter selection in seismic data analysis problems
(2021-05-10) Decker, Luke Adam; Fomel, Sergey B.; Arbogast, Todd; Ghattas, Omar; Foster, Douglas; Wheeler, Mary
Seismic imaging is an essential tool for non-invasive subsurface evaluation. It enables Earth scientists to create a picture of the planet's interior, predicting the rocks and structures that lie below. This can enable characterization of tectonic margins to better understand the deep history of the planet, delineation of aquifers to provide water, and the safe and economic exploration for commercial oil and gas accumulations for energy production. To generate these images numerous observations of the subsurface are taken and they are transformed to a common domain where observations of the same point in the subsurface overlay. These transformations typically are linear on the observed data and usually depend on a parameter related to seismic wave propagation, like the speed at which a seismic wave travels through the subsurface, in a non-linear manner. Selecting and determining these parameters is a crucial step in the generation of seismic images. Using inaccurate parameters in the transformations involved in seismic data processing results in seismic images that are distorted, inaccurate representations of the subsurface. Because these parameters are related to seismic wave propagation, their values can provide insight into the composition of the Earth's interior, including the rocks or fluids present. In this dissertation, I present methods for accurately determining those parameters and how they may be used to efficiently generate accurate, well resolved images of the Earth's interior. I show how dynamic time warping may be used to create an operator which efficiently corrects for the blurring and distortion present in seismic images caused by seismic anisotropy, or wave propagation speed changing with the direction of travel, while simultaneously characterizing and quantifying that anisotropy. I demonstrate how slope-decomposed seismic images may be transported along their characteristics in a process called oriented velocity continuation to efficiently generate a suite of images over a range of plausible migration velocities, and how oriented velocity continuation may be used with seismic diffraction imaging to determine migration velocity. The use of oriented velocity continuation is further expanded on to generate a framework for probabilistic diffraction imaging using a collection of weights computed from slope-decomposed images that represent the probability of a correctly imaged diffraction existing at a point in space for a given migration velocity, while simultaneously outputting the most likely migration velocity at each point in space. This method generates seismic images with significantly improved signal to noise ratios compared to conventional approaches. Finally, I formulate a variational method for picking an optimal surface representing how a parameter evolves in space from a volume representing the quality of fit for different parameter values based on iteratively minimizing a functional. I prove that minimizers for that functional exist, and that an iterative method will converge to a minimizer in an infinite dimensional setting. The method is applied using continuation, or graduated optimization, to avoid local minima and used to determine seismic velocities as a component of seismic processing workflows and perform automatic interpretation of a seismic horizon.
Parametric collapse evaluation of steel moment resisting frames with fuse connections
(2022-08-12) Gilroy, Joseph; Engelhardt, Michael D.; Clayton, Patricia M.; Kallivokas, Loukas; McManus, Patrick
Recent research has investigated a low damage seismic design concept for steel moment resisting frames (MRFs): the moment resisting fuse connection. Fuse connections are moment resisting connections that yield prior to the beam or column they connect. The connection acts as an easily repairable structural fuse of the seismic system instead of the beam, which is the typical fuse in a steel moment resisting frame designed to resist seismic loads, which can be very challenging and costly to repair after an earthquake. In most proposed fuse connections, energy dissipation is achieved by means of connection component yielding or friction slip. In AISC 358-16 (AISC, 2016c), the first prequalified fuse connection was added to the specification: the Simpson Strong-Tie™ Yield-Link® (SST-YL) connection. Although the connection has shown sufficient strength and ductility at large levels of drift to reach prequalified status, there is some concern that steel MRFs with optimized fuse connections will not have the typical overstrength of traditional steel MRFs, which are usually controlled by drift limits rather than strength requirements. This concern raises the question: Are steel moment resisting frames with fuse connections adequately designed to prevent sidesway collapse during earthquakes when using typical seismic performance factors (R = 8, C [subscript d] = 5.5, and Ω₀ = 3.0) for steel special moment resisting frames (SMRFs)? To investigate this concept, four three-bay steel special moment resisting frames with fuse connections were designed using provisions in ASCE7-16 (ASCE, 2017), AISC 341-16 (AISC, 2016a), AISC 360-16 (AISC, 2016b), and AISC 358-16s20 (AISC, 2020) with steel SMRF seismic performance factors. These frames were 2 stories, 4 stories, 6 stories, and 8 stories in height. These four archetypes were also redesigned with modified capacity design requirements more comparable to typical steel MRFs for a total of four design cases. These designs were evaluated using the FEMA P-695 methodology (FEMA, 2009) to determine if they have adequate collapse capacity. Different post-yield behaviors and failure criteria were modeled to determine their effect on system collapse capacity. Nonlinear pushover and response history analyses were done using OpenSEES (McKenna et al., 2010). The results of this investigation support that the seismic performance factors for typical SMRF frames are appropriate for use in SMRFs with fuse connections. However, there are several sources of uncertainty that require further investigation and research to determine to what extent this conclusion is accurate, particularly for new fuse connections that may be proposed. Suggestions for future research into numerical modeling and analysis of SMRFs with fuse connections are presented.
Seismic and stratigraphic interpretation of the Morichito Subbasin, eastern Venezuelan basin
(2008-08) Salazar, Migdalys Beatriz; Fisher, W. L. (William Lawrence), 1932-; Moscardelli, Lorena Gina, 1977-
The Morichito Subbasin is a southwest-northeast oriented depocenter that is located in the Eastern Venezuelan Foreland Basin (EVFB). The Morichito Subbasin covers an approximate area of 1,000 km² between the Serranía del Interior fold and thrust belt and the Pirital High. This basin was formed during the Neogene as the result of complex transpressional interactions between the Caribbean and South-American plates. Previous studies have tried to address the tectonostratigraphic significance of the Morichito Subbasin but about 1,800 km² recently acquired 3D seismic volumes allowed us to expand our understanding of this subbasin. The relevance of the Morichito Subbasin lies in the fact that it provides a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in this portion of the EVFB. This work presents the tectonostratigraphic evolution of the Morichito Subbasin by defining four sequences (Units I to IV). These units were defined based on the integration of well logs and biostratigraphic information with geomorphological interpretations that were performed using 3D seismic data. Unit I (E. Miocene to M. Miocene) was deposited in shallow marine environments (the Carapita Formation) and its areal coverage extends to the south, beyond the boundaries of the Morichito Subbasin suggesting that Unit I pre-dates the formation of the Pirital High. Unit II (M. Miocene) is composed of alluvial fan deposits (the Morichito Formation) that were derived from the Serranía del Interior fold and thrust belt; pinch-out relationships against the Pirital High indicates that Unit II was contemporaneous with the Pirital thrusting event. Units III (L. Miocene to E. Pliocene) and IV (E. Pliocene to Recent) are composed of shallow marine and fluvial deposits (Las Piedras and Mesa Formations). These two units represent the final phases of basin infilling when tectonic activity and subsidence were at lower rates
Seismic and well log data integration using data-matching techniques
(2018-05-03) Bader, Sean Stephen; Fomel, Sergey B.
Relating well log data to seismic data is an important step in integrated reservoir characterization studies. Traditionally, an interpreter uses well log data, which has high vertical resolution but little lateral coverage, to understand amplitude variations in seismic data, which has lower vertical resolution than well logs but high spatial coverage. The process of calibration is referred to as a seismic-well tie. Several problems arise with the assumptions of conventional seismic-well tie workflows. The seismic-well tie involves generating a reflectivity series from available sonic and density logs acquired at the well, which inherently assumes all wells have a sonic and density log available along the entire length of the well. In many cases, this assumption is not valid as the number of wells drilled often out-numbers the number of sonic and density logs acquired. Common procedures to account for missing well logs in seismic-well ties are to use a time-depth relationship from a nearby well or use an empirical relationship to estimate the missing well log from an available well log. These methods provide constructive solutions. However, variations in structure, stratigraphy or missing/incomplete well logs can result in inaccurate seismic-well ties. In this thesis, I propose a method that predicts missing well log data by first estimating the shifts that align well logs with a reference type log. Once in this stratigraphically correlated, or `relative geologic time,' domain, I interpolate the missing well log data from available logs of the same type. The resulting well log is consistent with available well data and is not distorted by structural or stratigraphic variations. Once complete well log suites are estimated for each well, I focus on improving the efficiency and consistency of multiple seismic-well ties. The seismic-well tie typically involves a subjective and labor-intensive workflow that depends on the interpreter's experience and intuition. I introduce an automatic workflow using local similarity to match the synthetic with the real seismic trace. The advantage of using local similarity to compute the seismic-well tie is that consistent, repeatable, seismic-well ties are achieved. I generate a global log property volume by interpolating log data along local seismic structure and perform blind well tests to verify the accuracy and consistency of seismic-well ties. I apply this workflow to a 3D seismic dataset with 26 wells and achieve consistent, accurate and reproducible seismic-well ties. Combining the results of the well log interpolation and seismic-well tie I can generate a time-to-depth relationship for each well regardless of the initial well log suite. As a result, it is possible to generate log property volumes that integrate the high spatial coverage of seismic data with information from well log data. Well log data can also provide a useful source of information during velocity model building for depth migration. Using concepts and workflows described previously, I show that the mis-tie between a modeled synthetic and real seismic trace is related to an inaccurate migration velocity. Furthermore, this information can be used to update the migration velocity model such that modeled synthetic seismograms, the seismic image, migration velocities and well log velocities become consistent.