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Collaborating Authors
2006 SEG Annual Meeting
ABSTRACT Common depth point (CDP) data can be naturally redatumed below salt with a vertical seismic profile (VSP) Green's function. In this case only VSP and CDP data are required and no velocity model is needed. Here both the Kirchhoff single-arrival datuming and multi-arrival (asymptotic) datuming (KMAD) methodologies are applied to SEG/EAGE salt model data and acceptable redatuming results are achieved. It shows that both of these methods can be used to redatum CDP data beneath the salt without knowing the velocity model of the salt body or overburden. However, the multi-arrival datuming method provides a more accurate datuming result than the single-arrival datuming method. The benefit of this method is that redatumed CDP data can be used, in principle, to more clearly image reflectors beneath the salt.
ABSTRACT We propose a tomography algorithm to enhance the resolution of 3D velocity model building. Our algorithm uses a fat ray instead of the conventional asymptotic ray. Compared to conventional ray tomography, the resulting tomography matrix is far less sparse. Thus, while the new matrix may still be ill-conditioned, much less model regularization is required to produce a well-posed system. In turn this should lead to a higher resolution tomographic update. A subsalt velocity analysis test on the Sigsbee 2a model shows promising result; we also apply the fat ray technique to well-tie tomography that estimates anisotropy parameters.
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (0.96)
ABSTRACT In a gas storage reservoir, the seismic monitoring of the gas bubble expansion or contraction as a function of injection or withdrawal is very attractive for reservoir management. However, the accuracy with which small seismic changes have to be measured for the monitoring of a gas bubble in a shallow gas storage reservoir requires seismic surveys with an excellent degree of sensitivity, such as can be found in borehole seismic surveys. A promising borehole seismic technique for reservoir monitoring is the use of permanently installed seismic sensors in wellbores. Yet, the effectiveness of distributed permanent seismic sensors in well can be limited by signal contamination induced by the borehole and the well completion. Repeatability is recognized as one major issue for improving the time-lapse seismic approach. To maximize repeatability, several walkaway VSP surveys using a permanent in-well fiber optic seismic system were acquired at different cycles of gas injection and withdrawal. Different configurations were tested to reduce the amplitude of undesirable tube waves and to enhance the signal-to-noise ratio. Finally, the results show that time-lapse VSP might be an efficient tool for gas reservoir monitoring.
- Europe (0.47)
- North America > United States (0.17)
Determination of a Seismic And Engineering Consistent Petro-elastic Model For Time-lapse Seismic Studies: Application to the Schiehallion Field
Floricich, Mariano (Heriot-Watt University) | MacBeth, Colin (Heriot-Watt University) | Stammeijer, Jan (Shell UK Exploration and Production) | Staples, Rob (Shell UK Exploration and Production) | Evans, Andrew (Shell UK Exploration and Production) | Dijksman, Niels (Shell UK Exploration and Production)
ABSTRACT A relationship between pressure and saturation changes in the reservoir and the corresponding time-lapse seismic signatures is determined from measurements of the produced fluids and downhole pressures at a number of wells. The results from this process also provide an insight into the governing parameters for the rock and fluid physics model which are then compared directly to conventional petro-elastic predictions. The methodology is applied to the Schiehallion field where it is found that the responses to water replacing oil, and gas breakout, follow the predictions of Gassmann fairly accurately. However, the sensitivity of the seismic to increases in pressure is observed to be roughly half as strong as that estimated from standard core plug measurements.
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- Europe > United Kingdom > Atlantic Margin > West of Shetland > Faroe-Shetland Basin > Judd Basin > Block 204/25 > Greater Schiehallion Field > Schiehallion Field (0.99)
- Europe > United Kingdom > Atlantic Margin > West of Shetland > Faroe-Shetland Basin > Judd Basin > Block 204/20 > Greater Schiehallion Field > Schiehallion Field (0.99)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Four-dimensional and four-component seismic (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)
ABSTRACT The goal of seismic tomography is to estimate a velocity model, so that migration produces an optimum image. Velocity models derived from seismic data using tomography suffer from non-uniqueness, but in general, the resolution of the model depends on the measurements used and the parameterization of the model. Unfortunately, the more measurements we use in the tomography, and the greater degree of freedom we allow in the model, the costlier it becomes to accomplish the task. Our goal is to balance the demands of optimizing the velocity model against the costs of picking, QC'ing and inverting the measurements. The data acquired during the Wide Azimuth Towed Streamer (WATS) field trial over the Mad Dog field in the Gulf of Mexico provided a unique opportunity to compare results from three different tomography experiments. In the first experiment we ran tomography based on single parameter residual moveout using a narrow azimuth subset of our wide azimuth data. In the second experiment we used the same data, but used tomography based on multiparameter residual moveout. As expected this second velocity model contained higher resolution details than the first. In the final experiment we used the entire wide azimuth dataset applying tomography based on multiparameter vector-offset residual moveout. Our study showed that using all of the data provided a better velocity model in the areas with complicated structures than either of the approaches above. Thus, although costly, the tomography that incorporates all of the data provides a higher resolution velocity model that should be used to obtain the best imaging results.
- North America > United States > Louisiana (0.31)
- North America > United States > Gulf of Mexico > Central GOM (0.25)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Green Canyon > Block 826 > Mad Dog Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Green Canyon > Block 825 > Mad Dog Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Green Canyon > Block 782 > Mad Dog Field (0.99)
ABSTRACT In chalk reservoirs such as the Ekofisk Field, fluid flow and geomechanical effects combine to change both the location and properties of the reservoir and overburden. Pore pressure and fluid saturation changes cause reservoir compaction and perturb the elastic properties of the reservoir rocks. The overburden responds to the compaction with piston-like seafloor subsidence and length changes (strains). These overburden strains change the seismic velocity. The resulting velocity changes are observed on time-lapse seismic data as time-shifts that accumulate though the overburden. These processes are being monitored by GPS surveys of the production facilities, repeat logging of radioactive marker bullets, repeat bathymetry surveys, core sample analysis, and time lapse seismic data. The goal of this paper is to combine these measurements to better understand the relationship between overburden strains, changes in overburden velocity, and resulting time-lapse time-shifts.
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Tor Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Ekofisk Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > Block 2/8 > Valhall Field > Tor Formation (0.99)
- (3 more...)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Integration of geomechanics in models (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
ABSTRACT In wave-equation reflection tomography, the finite frequency content of data leads to interference effects in the process of medium reconstruction, which are ignored in traditional ray theoretical implementations. We consider inverse scattering of body waves to develop a method of wave-equation migration velocity analysis. We follow a frequency-domain implementation, and emphasize the multi-scale aspects underlying the velocity estimation.
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.87)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (0.69)
ABSTRACT Interbed multiple reflections contain valuable information about the subsurface reflectivity distribution that can complement information obtained from primary reflections and free-surface multiples. In this report two methods are developed and used to migrate interbed multiples. The first method applies Fermat's principle to find the specular reflection point along the interbed multiple generating interface; the second method sums all the diffractions bouncing off the multiple generating interface. The first method is more computationally efficient, while the second method utilizes the full Fresnel zone along the interbed multiple generating interface. Numerical tests with synthetic VSP data and field data show that interbed multiples can illuminate areas below salt and can image salt boundaries. One challenge is that interbed multiple reflections are usually weak, thus the interbed multiple generating interface needs to be strong, and the reflector to be imaged also must be strong in order to generate noticeable interbed multiple reflections.
ABSTRACT The Integrated Ocean Drilling Program''s (IODP) Site Survey Data Bank (SSDB) is a growing online collection of data in support of 65 active proposals for drilling targets in many of the major ocean basins. Initially developed to support the international review of drilling proposals, access to the collection will be opened to the public for further research, publication and education. In addition, since drilling does not always go according to even the best of plans, the authoritative versions of all the data for a site can be of great value on board the vessel when a decision needs to be made in real time.
Monitoring And Modeling Production-Induced Surface Deformation
Herring, T.A. (Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology) | Hager, B.H. (Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology) | Sarkar, S. (Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology)
Monitoring and Modeling Production-Induced Surface Deformation T. A. Herring, B. H. Hager, and S. Sarkar, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 We examine methods of monitoring surface deformations in a producing oil and gas field, and the numerical modeling of these deformations. Our analysis uses seven years of annually repeated precise leveling which reveals the vertical deformation of the field and three years of Global Positioning System (GPS) measurements that reveal both horizontal and vertical deformations. The GPS measurements are carried out with a combination of continuously operating receivers and set of periodically measured benchmarks. There are five continuously operating receivers with one located outside of the thought-to-be deforming region and four inside the deforming region. Forty-five additional sites that are close to the precise leveling benchmarks were initially measured about every two weeks using three "roving" GPS receivers and recently have been measured every quarter.