No description available.

No description available.

Temporal and spatial variability makes locating zones of seepage difficult using traditional point measurements. The goal of this project was to employ 2D electrical resistivity, 3D electrical resistivity, and time-lapse resistivity to improve our understanding of how small-scale heterogeneity controls seepage. We collected underwater electrical resistivity data along the southwest shore of Mirror Lake, NH, as part of a multi-year assessment of the utility of geophysics for mapping groundwater seepage beneath lakes. We found that resistivity could predict out-seepage. A line collected perpendicular-to-shore along the lake bottom starting 27-m off shore and continuing 27-m on shore (1-m electrode spacing) showed the water table dipping away from the lake, the steep gradient indicative of high out-seepage in this area. Resistivity could also broadly delineate high-seepage zones. An 80-m line collected parallel to shore using 0.5-m electrode spacing was compared with measurements collected the previous year using 1-m electrode spacing. Both data sets show the transition from high-seepage glacial outwash to low-seepage glacial till, demonstrating reproducibility. However, even the finer 0.5-m electrode spacing was insufficient to resolve the heterogeneity well enough to predict seepage variability within each zone. In two sections along this 80-m line, one over glacial outwash, the other over till, we collected 14 parallel lines of resistivity, 13.5-m long and spaced 1-m apart to form a 13.5 x 13-m data grid. These lines were inverted using two methods: 1) individually using a 2-D inversion program and then interpolated to create a 3-D volume and 2) they were jointly inverted to create a 3-D volume. Examination of resistivity slices through these volumes highlights the heterogeneity of both these materials, suggesting groundwater flow takes indirect flow paths. However, only when there was a strong contrast in resistivities (the till section) could a possible groundwater flow path be identified. Time-lapse resistivity was used to determine the effect of the top layer of fine sediments. A 13.5-m long time-lapse resistivity survey was completed in the glacial till using 0.5-m electrode spacing showed that disturbing only a few millimeters of superficial sediments produced up to a 6% change in resistivity. This change was accompanied by changes in seepage, indicating that the fine layer of sediments is a major control on seepage patterns. This project showed that combining several electrical resistivity methods provides a better understanding of subsurface heterogeneity and aids in the placement of point measurements. However, in such heterogeneous material the goal of predicting seepage variation still remains difficult. / Geology

Thesis (Ph. D.)--California Institute of Technology, 1962. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/24/2010. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

<p>Reservoir properties are mainly determined based on well log information. However, wells in most reservoirs are sparse and widely spread compared to the size of the reservoir. Seismic data is thus one of the most important complementary sources of information used to build 3D models of hydrocarbon reservoirs. The need for a high quality reservoir description starts as soon as a discovery is made. In the appraisal phase, hydrocarbons in place and the amount of recoverable reserves are estimated based on the reservoir model. Improved structural models are also needed in optimal well placement during the production and development phase of a reservoir. Knowledge about saturation and pressure distributions in a reservoir are valuable both in the exploration and development phase of a reservoir. This knowledge is used to evaluate the size of a field, determine an optimal drainage pattern, and decide on optimal well design to reduce risks for blow-outs and damage on production equipment. Reducing uncertainty in reservoir property estimates from seismic data have large economic impact on the development of a hydrocarbon reservoir.</p><p>Quantitative reservoir property information can be obtained either through direct estimates of reservoir properties from seismic data or through estimates of elastic properties (velocities and densities) that are related to reservoir properties. The relationship between physical properties of rocks and fluids and P-wave seismic data are often empirical and non-unique. This leads to large uncertainties in reservoir models derived from pressure wave seismic data alone. Since shear waves do not propagate through fluids, combined use of pressure wave seismic data and shear wave seismic data might increase our ability to derive fluid and lithology properties from seismic data. One way to obtain information about shear wave velocities over a large area is to acquire multicomponent seismic data (for instance x, y, and z component geophone data). Parts of this thesis focus on methods to combine the information from multicomponent seismic data with pressure wave (hydrophone) seismic data. In this way we improve the accuracy in the estimates of pressure wave velocity, shear wave velocity and density in the subsurface.</p><p>To obtain information about changes in reservoir parameters like fluid saturation and pore pressure during production, comparisons between different vintages of seismic data acquired over the field can be performed. Differences in the seismic signal from the same area over a time period (time-lapse seismic data) can be interpreted as changes in reservoir properties. Benefits of improved reservoir characterization include ability to locate bypassed oil and mapping of fluid fronts. This leads to saved costs due to reduced number of misplaced wells, and increased production because of optimized well placement. In the early days of seismic reservoir monitoring, the analyses were qualitative, e.g. to identify undrained areas, analyzing the sealing capacity of faults, and detect drainage patterns. Today, time-lapse seismic analysis is still mainly qualitative. To be able to obtain more quantitative estimates of changes in reservoir properties from the time-lapse seismic data, we need to establish links between the rock parameters and the seismic data. I have used both time-lapse surface seismic data and time-lapse multicomponent seismic data to estimate production related changes in fluid saturation and pressure.</p><p>Finally, to be able to utilize rock physical information obtained from seismic reservoir characterization in reservoir modelling, information about uncertainties in the estimates are essential. One way to do this is to use deterministic models (rock physics models) that relates reservoir properties to seismic data, and assume that the model parameters are independent. However, the variables in these estimations are inherently dependent and should be treated as such. By formulating the problem in a Bayesian framework, dependencies between the different variables and spatial dependencies can easily be included. I have used both deterministic uncertainty analysis and Bayesian estimation methods to quantify uncertainties in the estimates.</p>

Reservoir properties are mainly determined based on well log information. However, wells in most reservoirs are sparse and widely spread compared to the size of the reservoir. Seismic data is thus one of the most important complementary sources of information used to build 3D models of hydrocarbon reservoirs. The need for a high quality reservoir description starts as soon as a discovery is made. In the appraisal phase, hydrocarbons in place and the amount of recoverable reserves are estimated based on the reservoir model. Improved structural models are also needed in optimal well placement during the production and development phase of a reservoir. Knowledge about saturation and pressure distributions in a reservoir are valuable both in the exploration and development phase of a reservoir. This knowledge is used to evaluate the size of a field, determine an optimal drainage pattern, and decide on optimal well design to reduce risks for blow-outs and damage on production equipment. Reducing uncertainty in reservoir property estimates from seismic data have large economic impact on the development of a hydrocarbon reservoir. Quantitative reservoir property information can be obtained either through direct estimates of reservoir properties from seismic data or through estimates of elastic properties (velocities and densities) that are related to reservoir properties. The relationship between physical properties of rocks and fluids and P-wave seismic data are often empirical and non-unique. This leads to large uncertainties in reservoir models derived from pressure wave seismic data alone. Since shear waves do not propagate through fluids, combined use of pressure wave seismic data and shear wave seismic data might increase our ability to derive fluid and lithology properties from seismic data. One way to obtain information about shear wave velocities over a large area is to acquire multicomponent seismic data (for instance x, y, and z component geophone data). Parts of this thesis focus on methods to combine the information from multicomponent seismic data with pressure wave (hydrophone) seismic data. In this way we improve the accuracy in the estimates of pressure wave velocity, shear wave velocity and density in the subsurface. To obtain information about changes in reservoir parameters like fluid saturation and pore pressure during production, comparisons between different vintages of seismic data acquired over the field can be performed. Differences in the seismic signal from the same area over a time period (time-lapse seismic data) can be interpreted as changes in reservoir properties. Benefits of improved reservoir characterization include ability to locate bypassed oil and mapping of fluid fronts. This leads to saved costs due to reduced number of misplaced wells, and increased production because of optimized well placement. In the early days of seismic reservoir monitoring, the analyses were qualitative, e.g. to identify undrained areas, analyzing the sealing capacity of faults, and detect drainage patterns. Today, time-lapse seismic analysis is still mainly qualitative. To be able to obtain more quantitative estimates of changes in reservoir properties from the time-lapse seismic data, we need to establish links between the rock parameters and the seismic data. I have used both time-lapse surface seismic data and time-lapse multicomponent seismic data to estimate production related changes in fluid saturation and pressure. Finally, to be able to utilize rock physical information obtained from seismic reservoir characterization in reservoir modelling, information about uncertainties in the estimates are essential. One way to do this is to use deterministic models (rock physics models) that relates reservoir properties to seismic data, and assume that the model parameters are independent. However, the variables in these estimations are inherently dependent and should be treated as such. By formulating the problem in a Bayesian framework, dependencies between the different variables and spatial dependencies can easily be included. I have used both deterministic uncertainty analysis and Bayesian estimation methods to quantify uncertainties in the estimates.

No description available.

The problem of inferring the velocity field is central to exploration seismology. Conventional velocity analysis is based on the hypothesis that reflection traveltime is a hyperbolic function of the distance between the source and the receiver. This is basis upon which interval velocities are obtained using Dix's equation for a horizontally layered model and Shah's equation for a dipping layered structure. However, in laterally inhomogeneous areas, traveltimes do not follow hyperbolae, hence, hyperbola based velocity estimation techniques fail in such areas. Although many sophisticated techniques, such as tomography, migration and model based velocity analysis can be used to obtain accurate velocity fields from seismic data in such areas, these methods are very computationally expensive. In this thesis, a simple, quicker and accurate velocity estimation technique is proposed. This technique does not abandon conventional velocity analysis, but gives further processing to stacking velocity data provided by conventional techniques. The new technique is based on the hypothesis that stacking slowness variations due to lateral interval slowness anomalies can be represented by the outputs of a linear impulse response system. The inputs of the system are the interval slowness anomalies. The system is space invariant for a horizontally layered model, but is space variant for a dipping layered model. A pre-determined background model is required to compute the linear system. Since the linear system is space invariant for a horizontally layered model and space variant for a dipping layered model, there are two schemes for velocity estimation for these two cases. In horizontal geology, the relationship between stacking slowness variations and interval slowness anomalies can be expressed by a set of linear equations in the wavenumber domain. The singular value decomposition method is used to solve the set of linear equations to obtain interval slowness anomalies from stacking slowness variations. In dipping geology, the relationship between stacking slowness variations and interval slowness anomalies cannot be written as a set of linear equations in the wavenumber domain. Interval slownesses must in this case be derived in the least square sense. Basis functions are introduced to construct interval slowness anomalies. Once the interval slowness anomalies have been estimated, interval slownesses (and hence velocities) are obtained by adding these to the background interval slownesses. Finally, the sensitivity of the linear system to data errors and model errors is investigated through a series of synthetic examples, the applications of these velocity estimation techniques and suggestions for further studies of the linear system are discussed

<p> Roat&aacute;n Island is the largest of the Bay Islands of Honduras. These islands form an emergent crest off the Caribbean coast of Honduras called the Bonacca Ridge. The Bartlett Trough to the north and subsequent Bonacca Ridge were likely formed due to the transform fault system of the Motagua-Swan Islands Fault System. This fault system forms the tectonic plate boundary between the North American and Caribbean plates. Although the timing and kinematics are poorly constrained, the Bay Islands and the Bonacca Ridge were likely uplifted due to transpression along this left-lateral strike-slip system. With limited regional exposures along the adjacent tectonic boundary, this study aimed to present a structural interpretation for Roat&aacute;n. This new interpretation is further explained through regional considerations for a suggested geologic history of the northwestern Caribbean. </p><p> In order to better constrain the kinematics of uplift and exhumation of Roat&aacute;n Island, structural, gravity, and magnetic surveys were conducted. Principal attention was directed to the structural relationship between the geologic units and their relationship to one another through deformation. Resulting geologic cross-sections from this study present the metamorphic basement exposed throughout the island to be in a normal structural order consisting of biotite schist and gneiss, with overlying units of chlorite schist, carbonate, and conglomerate. These units have relatively concordant strike and dip measurements, consistent with resultant magnetic survey readings. Additionally, large and irregular bodies of amphibolite and serpentinite throughout the island are interpreted to have been emplaced as mafic and ultra-mafic intrusions in weakness zones along Early Paleogene transform system fault planes. </p><p> The interpretation and suggested geologic history from this study demonstrate the importance of transpressive tectonics both local to Roat&aacute;n and regionally throughout geologic history. Consideration of this interpretation will help to further constrain regional studies over the northwestern Caribbean.</p>