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Collaborating Authors
2010 SEG Annual Meeting
Summary High seismic repeatability is critical to the monitoring program of the Naylor Field because of the small timelapse effect related to CO2 injection into a depleted gas reservoir (Naylor). To understand the effect of changing ground conditions on repeatability, we conducted so-called “micro-array” investigation of the near-surface layers at this site. A feature of the injection test site area is the nearsurface karst topography. In such geological terrain, a change in water table level can influence the seismic response and cause changes in the seismic wave scattering pattern. Hence the aim of micro-array measurements was to determine the properties of the near surface layers during the wet and dry seasons. This could help us understand and ultimately predict the seismic response and hence survey repeatability at a given site. Measurements of seismic response due to near surface property changes (seasonal) could help optimise the design of time lapse surveys which ultimately yields improved survey differencing. Measured elastic properties of the near surface are used to produce seismic response and predict repeatability as a function of the variable soil conditions. Comparison of numerical and field data is finally used to verify the validity of this approach. In this study we investigated the variation of elastic properties of both top soil and the deeper rugose clay-limestone interface as a function of water depth level. Such tests in fact simulate the measurements conducted in dry and wet seasons and help evaluate the effect of these seasonal variations on the seismic signature, which is then analysed in terms of non-repeatability. In this study, we use both micro-borehole (micro VSP) and micro-refraction arrays to analyse directional properties of the near-surface. Finally, numerical tests were performed with calibrated soil parameters.
- Geology > Rock Type > Sedimentary Rock (0.91)
- Geology > Geological Subdiscipline > Geomechanics (0.70)
- Oceania > Australia > Victoria > Otway Basin (0.99)
- Oceania > Australia > South Australia > Otway Basin (0.99)
- North America > Canada > Alberta > Naylor Field > Icg Shelter Naylor 7-33-97-25 Well (0.99)
- Oceania > Australia > Western Australia > North West Shelf > Carnarvon Basin > Barrow Basin > Victoria Field > Flag Formation (0.91)
Summary Automatic common image gather (CIG) event picking and tomography inversion are the main stream tools in velocity model building for prestack depth imaging projects. The conventional CIGs are typically in the offset domain, output from a ray based Kirchhoff migration. This kind of CIGs suffers from migration artifacts due to the multiarrival problem when the velocity model contains strong lateral variations. These artifacts cause difficulties in tomography. The CIGs in subsurface angle domain are, however, artifact-free. With the help of wide azimuth acquisition and high performance computers, the 3D CIGs indexed by reflection angle and azimuth angle (ADCIGs) are now available within the output of reverse time migration (RTM). It brings new opportunities to observe the azimuthal dependent structural attributes and to refine subsurface model building. However, the automatic seismic event picking and tomography in angle domain face new challenges. In this abstract we address some implementation and application issues of automatic picking and tomography inversion on 3D angle domain CIGs. We have implemented our automatic picking and inversion tools for the 3D full azimuth ADCIGs. We demonstrate the efficiency and robustness of our algorithms using a Gulf of Mexico real data application.
- North America > Mexico (0.35)
- North America > United States (0.25)
SUMMARY In thrust-fold belt tectonic settings (e.g., the Canadian Foothills), conventional acquisition and (prestack time) pro- cessing of seismic data is often inadequate in producing an ac- curate sub-surface image. The presence of steep dips and large lateral velocity contrasts require both prestack depth migration methods and suitable seismic survey design (e.g., acquiring long offsets). As such, an accurate velocity model is required. A superior method of velocity model estimation, Waveform Tomography, can then be used to improve the sub-surface im- age. We apply this approach to 2-D, long-offset data acquired in the Canadian Foothills.
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (1.00)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
Summary Reliable seismic imaging of gas accumulations in the shallow subsurface underneath the platforms in the Forties field will mitigate drilling risks and reduce drilling cost. We chose to use Ocean Bottom Seismometers for the ability to operate safely and efficiently in a busy oilfield. The resulting seismic image allows us to pay extra care during drilling of wells where gas is likely to be encountered. Conversely, we can avoid rigging the gasdiverter line when no gas is expected. The resulting operations are therefore optimized in terms of safety and costs.
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 21/10 > Forties Field > Forties Formation (0.99)
- Europe > United Kingdom > UKCS Field (0.97)
Summary A key factor in current 4D seismics is to repeat all acquisition parameters in order to enhance production effects in the final 4D image. For marine data this has led to strong focus on reducing geometrical mispositioning between different 4D seismic vintages. In this study we show that the current level of geometric repeatability has reached a point were seismic migration remediates the effect of mispositioning on the final 4D image. Further improvement of 4D quality requires better attenuation of traditional 3D noise like diffracted multiples and side scattering.
- Europe > Norway > Norwegian Sea > Halten Terrace > PL 128 > Block 6608/10 > Norne Field > Tofte Formation (0.99)
- Europe > Norway > Norwegian Sea > Halten Terrace > PL 128 > Block 6608/10 > Norne Field > Not Formation (0.99)
- Europe > Norway > Norwegian Sea > Halten Terrace > PL 128 > Block 6608/10 > Norne Field > Ile Formation (0.99)
- (8 more...)
4D Seismic Monitoring of CO2 Sequestration Based Upon Spectral-element And Adjoint Methods: Comparison of Acoustic, Elastic And Poroelastic Theories
Morency, Christina (Department of Geosciences, Princeton University) | Luo, Yang (Department of Geosciences, Princeton University) | Tromp, Jeroen (Department of Geosciences and Program in Applied and Computational Mathematics, Princeton University)
SUMMARY The key issues in CO2 sequestration monitoring involve accurate monitoring, from the injection stage to prediction & verification, of CO2 movement over time for environmental considerations. A natural non-intrusive monitoring technique is referred to as “4D seismics”, which involves 3D time-lapse seismic surveys. The success of monitoring the CO2 movement is subject to a proper description of the physical properties of the structure. We realize time-lapse migrations comparing acoustic, elastic, and poroelastic simulations of 4D seismic imaging to characterize the storage zone, based solely upon the first arrival traveltime anomaly arising from the injection of CO2. This approach highlights the influence of using different physical theories on interpreting seismic data, and, more importantly, on extracting the CO2 signature from the seismic wave field. Simulations are performed using a spectral-element method, which allows for highly accurate results. Biot’s equations are implemented to account for poroelastic effects. The sensitivity of observables to the model parameters is quantified based upon finite-frequency sensitivity kernels calculated using an adjoint method.
- North America > United States (0.47)
- Europe (0.31)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/9 > Sleipner Field > Draupne Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/8 > Sleipner Field > Draupne Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/6 > Sleipner Field > Draupne Formation (0.99)
- North America > United States > New Mexico > San Juan Basin > Media Field (0.97)
Summary During the last five years elastic prestack waveform inversion has been applied on a number of case studies. Recently isotropic elastic prestack waveform inversion has been extended to VTI anisotropic prestack waveform inversion. The case studies in this presentation refer to development of onshore oil and gas fields in North America. Seismic inversion has been deployed to derisk the drill locations and also generate improved reserve estimates prior to drilling. Prestack waveform inversion estimates elastic parameters by matching the seismic waveforms on each gather with the NMO correction removed over the complete zone of interest. In one particular case study we have compared a prestack waveform inversion with the results of an angle stack inversion.
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic modeling (1.00)
- Management > Professionalism, Training, and Education > Communities of practice (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (1.00)
ABSTRACT Being a highly compacted chalk reservoir, Ekofisk is a well known example of a field showing strong time lapse effects; as a result of compaction, the water bottom has subsided by over 9 m since the start of production in 1971. Five 4D seismic surveys have been shot on the area to improve understanding of reservoir behaviour. For instance, these multiple monitors sampled the evolving distribution of water and the effects of fault compartmentalisation on reservoir fluid flow. Although an extensive use of the time shift estimated at the top of the reservoir has been made in the past, it has so far been difficult to invert for subtle time lapse effects within the reservoir and therefore to identify which part of the reservoir undergoes 4D changes with sufficient accuracy and confidence. When several seismic vintages are available, it is possible to improve the precision of the inverted 4D attributes by performing an inversion that minimises at the same time the differences between all possible combinations of pairs of datasets. This sort of multi-vintage warping enables improved images showing 4D changes within the Ekofisk reservoirs to be obtained. These images can improve the reservoir understanding on a scale, where a number of slides, slumps and debris flows create a rather heterogeneous three-dimensional pattern and sometimes make fluid flow understanding and correlation between wells problematic.
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (0.90)
- 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 > PL 018 > Block 2/5 > Greater Ekofisk Field > Tor Field > Tor Formation (0.98)
- (7 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (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)
SUMMARY Wavefield inversion tries to minimise the difference between real and modelled seismic data, which means that its success relies in the accuracy of the wave equation solver used in the process. Then, the wave equation solver should take elastic phenomena into account in order to compare its results with real field data. The purpose of our project was to develop a 3D wavefield tomography algorithm with an elastic wave equation solver in order to recover elastic properties. First formulations of the elastic inverse problem were published more than 20 years ago (Tarantola (1986); Mora (1987)), but only recently the computational resources needed to apply it to 3D have become available.
SUMMARY Brine substituting for a light oil in a reservoir production scenario is analyzed with synthetic seismograms to assess the feasibility of using time-lapse or change in compressional attenuation as a monitoring technique. In light of the large relative changes in intrinsic attenuation observed in the laboratory due to brine substitution, time-lapse attenuation observations are an attractive monitoring tool. When fluid substitution occurs, we show quantitatively that time-lapse apparent attenuation is dominated by the change in intrinsic attenuation rather than scattering attenuation, so that we are still able to extract the proper time-lapse intrinsic attenuation. Although apparent attenuation is sensitive to receiver separation and random noise, we are still able to predict time-lapse intrinsic attenuation for these synthetic traces.