Browsing by Subject "Seismic response"
Now showing 1 - 5 of 5
- Results Per Page
- Sort Options
Item Estimation of dry-rock elastic moduli based on the simulation of mud-filtrate invasion effects on borehole acoustic logs(2007-08) Odumosu, Tobiloluwa Boladun; Torres-Verdin, CarlosReliable estimates of dry-rock elastic properties are critical to accurately interpreting the seismic response of hydrocarbon reservoirs. These estimates are needed as input for Biot-Gassmann fluid substitution calculations used in a wide range of applications for present-day reservoir characterization. We describe a new method for estimating elastic moduli of rocks in-situ by simulating the effect of mud-filtrate invasion on resistivity and acoustic logs. Simulations of mud-filtrate invasion account for the dynamic process of fluid displacement and mixing between mud-filtrate and hydrocarbons. The calculated spatial distributions of electrical resistivity are matched against resistivity logs by adjusting the underlying petrophysical properties. We then perform Biot-Gassmann fluid substitution on the twodimensional spatial distributions of fluid saturation with initial estimates of dry-bulk (kdry) modulus and shear rigidity ([Greek small letter mu]dry) and a constraint of Poisson's ratio (ν) typical of the formation. This process generates two-dimensional spatial distributions of compressional and shear-wave velocities, and density. Subsequently, sonic waveforms are simulated to calculate shear-wave slowness. Initial estimates of the dry-bulk modulus are progressively adjusted using a modified Gregory-Pickett (1984) solution to Biot's (1956) equation to estimate a shear rigidity that converges to the log value of shear-wave slowness. The constraint on Poisson's ratio is then removed and a refined estimate of the dry-bulk modulus is obtained by both simulating the acoustic log (monopole) and matching the log-derived compressional-wave slowness. This technique leads to reliable estimates of dry-bulk moduli and shear rigidity that compare well to laboratory core measurements. The resulting dry-rock elastic properties can be used to calculate seismic compressional-wave and shear-wave velocities devoid of mud-filtrate invasion effects for further seismic-driven reservoir characterization studies.Item The seismic response to fracture clustering : a finite element wave propagation study(2014-05) Becker, Lauren Elizabeth; Spikes, KyleCharacterizing natural and man-made fracture networks is fundamental to predicting the storage capacity and pathways for flow of both carbonate and shale reservoirs. The goal of this study is to determine the seismic response specifically to networks of fractures clustered closely together through the analysis of seismic wavefield scatter, directional phase velocities, and amplitude attenuation. To achieve this goal, finite element modeling techniques are implemented to allow for the meshing of discontinuous fracture interfaces and, therefore, provide the most accurate calculation of seismic events from these irregular surfaces. The work presented here focuses on the center layer of an isotropic model that is populated with two main phases of fracture network alteration: a single large-scale cluster and multiple smaller-scale clusters. Phase 1 first confirms that the seismic response of a single idealized vertically fractured cluster is distinct crosscutting energy within a seismogram. Further investigation shows that, as fracture spacing within the cluster decreases, the depth at which crosscutting energy appears exponentially increases, placing it well below the true location of the cluster. This relationship holds until 28% of the fractures are moved from their uniformly spaced locations to random locations within the cluster. The vertical thickness of the cluster has little effect on the location or strength or the crosscutting signature. Phase 2 shows that, although clusters of more randomly spaced fractures mask crosscutting energy, a marked decrease in amplitude coinciding with a bend in the wavefront produces a heterogeneous anisotropic seismic response. This amplitude decay and heterogeneous anisotropy is visible until cluster spacing drops below one half of the wavelength or the ratio of fractured material to matrix material within a cluster drops below 37%. Therefore, the location of an individual fracture cluster can be determined from the location of amplitude decay, heterogeneous anisotropy, and crosscutting energy. Furthermore, the density of the cluster can be determined from the degree of amplitude decay, the angle of heterogeneous anisotropy, and the depth of cross-cutting energy. These relationships, constrained by limits on their detectability, can aid fracture network interpretation of real seismic data.Item Sensitivity of seismic response to variations in the Woodford Shale, Delaware Basin, West Texas(2010-12) Shan, Na; Tatham, R. H. (Robert H.), 1943-; Sen, Mrinal K.; Spikes, Kyle T.; Ruppel, Stephen C.; Ogiesoba, Osareni C.The Woodford Shale is an important unconventional oil and gas resource. It can act as a source rock, seal and reservoir, and may have significant elastic anisotropy, which would greatly affect seismic response. Understanding how anisotropy may affect the seismic response of the Woodford Shale is important in processing and interpreting surface reflection seismic data. The objective of this study is to identify the differences between isotropic and anisotropic seismic responses in the Woodford Shale, and to understand how these anisotropy parameters and physical properties influence the resultant synthetic seismograms. I divide the Woodford Shale into three different units based on the data from the Pioneer Reliance Triple Crown #1 (RTC #1) borehole, which includes density, gamma ray, resistivity, sonic, dipole sonic logs, part of imaging (FMI) logs, elemental capture spectroscopy (ECS) and X-ray diffraction (XRD) data from core samples. Different elastic parameters based on the well log data are used as input models to generate synthetic seismograms. I use a vertical impulsive source, which generates P-P, P-SV and SV-SV waves, and three component receivers for synthetic modeling. Sensitivity study is performed by assuming different anisotropic scenarios in the Woodford Shale, including vertical transverse isotropy (VTI), horizontal transverse isotropy (HTI) and orthorhombic anisotropy. Through the simulation, I demonstrate that there are notable differences in the seismic response between isotropic and anisotropic models. Three different types of elastic waves, i.e., P-P, P-SV and SV-SV waves respond differently to anisotropy parameter changes. Results suggest that multicomponent data might be useful in analyzing the anisotropy for the surface seismic data. Results also indicate the sensitivity offset range might be helpful in determining the location for prestack seismic amplitude analysis. All these findings demonstrate the potentially useful sensitivity parameters to the seismic data. The paucity of data resources limits the evaluation of the anisotropy in the Woodford. However, the seismic modeling with different type of anisotropy assumptions leads to understand what type of anisotropy and how this anisotropy affects the change of seismic data.Item The role of the floor system in the seismic response of steel gravity framing(2019-05-09) Donahue, Sean Michael; Engelhardt, Michael D.; Helwig, Todd Aaron, 1965-; Clayton, Patricia; Williamson, Eric B; Taleff, Eric MThe flexural response of composite clip angle connections to cyclic inter-story drift was experimentally investigated in this test program. Testing was performed on a cruciform sub-assembly with W21x55 girders framing in to a W12x96 column with varied clip angle details. A composite slab was cast atop the girders with different construction details. The flexural response of the connection was then monitored as the system was subjected to simulated gravity loads, and rotations of the test column, simulating the inter-story drift expected in a seismic event. The experiments showed that typical simple shear connections can contributed significant lateral resistance to a structure in the displacements seen in a seismic event. There are many potential load-carrying mechanisms present in a composite shear connection that are typically neglected in current design, including bearing of the concrete slab on the column, binding between the flanges of the girder and column, tensile reactions in the reinforcement within the floor slab, and lateral restraint of the floor slab due to the surrounding bays of the structure. These mechanisms can work together to produce force couples, allowing the connection to develop significant flexural resistance at high rotations. Analysis of the parameters that control the response of these mechanisms is presented, and the ability of these connections to contribute to the seismic resistance of the structure is discussed.Item Topographic amplification of seismic motion(2017-05) Poursartip, Babak; Kallivokas, Loukas F.; Assimaki, Dominic; Demkowicz, Leszek F.; Manuel, Lance; Stokoe II, Kenneth H.; Tassoulas, John L.Seismic hazard assessment relies increasingly on the numerical simulation of ground motion, since recent advances in numerical methods and computer architectures have made it ever more practical to obtain the surface response to idealized or realistic seismic events. The key motivation stems from the need to assess the performance of sensitive components of the civil infrastructure (nuclear power plants, bridges, lifelines, etc.), when subjected to realistic scenarios of seismic events. To date, most simulation tools rely on a flat-earth assumption, which ignores topography and its effects on seismic motion amplification. In an attempt to narrow the gap between modeling and physical reality, in this dissertation we study systematically the effects topographic features have on the surface motion when compared against motion obtained using a at-surface assumption. To this end, we discuss first an integrated approach that deploys best-practice tools for simulating seismic events in arbitrarily heterogeneous formations, while also accounting for topography. Specifically, we describe an explicit forward wave solver based on a hybrid formulation that couples a single-field formulation for the computational domain with an unsplit mixed-field formulation for Perfectly-Matched-Layers (PMLs or M-PMLs) used to limit the computational domain. We use spectral elements for spatial discretization, and an efficient Runge-Kutta explicit solver for time integration. Due to the material heterogeneity and the contrasting discretization needs it imposes, we also use an adaptive Runge-Kutta-Fehlberg time-marching scheme to optimally adjust the time step so that the local truncation error rests below a predefined tolerance. To account for the seismic load, we use the Domain- Reduction-Method to introduce the incoming seismic motion in the computational domain whenever the introduction of the actual seismic source would make the computational domain unnecessarily large. Lastly, we couple the DRM with the PMLs to complete the seismic motion simulation engine. Using the developed toolchain, we then report results of parametric studies involving idealized topographic features, which show motion amplification that depends, as expected, on the relation between the topographic features' characteristics and the dominant wavelength. More interestingly, we also report motion de-amplification patterns. Given the prevalence of lower dimensionality models for seismic risk assessment, we also report on the effects model dimensionality has in the presence of heterogeneity and topography. The results reported herein, support the thesis that, for purposes of seismic risk assessment, topography and heterogeneity are best treated when fully accounted for in three-dimensional models. Even this is only a first and necessary step towards higher fidelity modeling of seismic motion effects.