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Results
Calibrating 3D VSP Image area with Finite Difference Modeling – A Case Study in Gulf of Mexico
Rollins, Francis (BP) | Sandschaper, J. R. (BP) | Li, Qingsong (BP) | Ye, Fiona (BP) | Chakraborty, Samarjit (BP)
Summary Accurately predicting the effective image area of a 3D VSP can be a difficult task to accomplish. The creation of a field wide Finite difference earth model at the Mad Dog Field provided the opportunity to perform forward modeling of an already existing 3D VSP in order to calibrate expectations of image area on possible future VSP acquisition. The acquired 3D VSP, which had recently been reprocessed, was modeled by conducting acoustic wave equation forward modelling and migrated with reverse time pre-stack depth migrations (RTM) and wave equation migrations (WEM) of the synthetic data. These data were then stacked and compared to the images from the acquired VSP. At first look, the finite difference model VSP image area was much larger than the image area of the acquired VSP. One problem was that the RTM produced a much more extensive image both above and below the receivers, a function of the algorithm being able to handle both upgoing and down-going energy. The WEM, however, could handle only up-going energy, and produced an image closer in appearance to the VSP processed image. Although the acquired VSP was processed with a reverse time migration, the down-going energy contribution was much less robust than that of the modeled data; this could be due to the velocity model errors in the real world case. Differences between the acquired VSP and the modeled WEM may also be due to velocity model errors in the actual VSP processing. With both migration types, it became apparent that the modeled image areas would likely be interpreted as being significantly more extensive than the actual realized image. However, through detailed inspection, it was possible to determine which areas of the modeled image needed to be discounted. This ultimately resulted in a predicted image that was very similar to the actual VSP image. These learnings were subsequently applied to the modeling of a planned VSP acquisition in a different well, and impacted both the source pattern design and the expected image. Introduction The Mad Dog Field is a giant subsalt field in the Gulf of Mexico, discovered by BP in 1998. The field started producing in 2005. The field lies beneath the edge of the Sigsbee Escarpment in 4000 to 7000 feet of water approximately 190 miles south of New Orleans
- North America > United States > Gulf of Mexico > Central GOM (0.76)
- North America > United States > Louisiana > Orleans Parish > New Orleans (0.26)
- 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)
Understanding and Improving the Subsalt Image at Thunder Horse, Gulf of Mexico
Hartman, Ken (BP) | Chakraborty, Samarjit (BP) | Nolte, Bertram (BP) | Gou, Weiping (CGG) | Sun, Qingqing (CGG) | Chazalnoel, Nicolas (CGG)
Summary Subsalt imaging at the Thunder Horse Field in the Gulf of Mexico is challenging primarily because the salt canopy, overlying roughly 75% of the structure, greatly distorts subsalt illumination and causes imaging and resolution problems. Since the Thunder Horse discovery, advancements in seismic acquisition techniques and imaging technologies have significantly improved subsalt images. The latest successful application is from a tilted transverse isotropy (TTI) reverse time migration (RTM) project combining two wide azimuth towed streamer (WATS) data sets and three narrow azimuth towed streamer (NATS) data sets. The addition of an extra WATS data set and the application of the recent imaging technologies are key contributors to the dramatic structural image improvements with better defined three-way events and a higher signal-to-noise ratio (S/N). Introduction The Thunder Horse Field has been producing since 2008 and is located in the south-central part of the Mississippi Canyon protraction area in the Gulf of Mexico. A large overlying allochthonous salt body causes rapid spatial and temporal changes in illumination and image quality, making interpretation difficult, especially near the steeply dipping three-way closure against the salt stock. During the course of discovery and development, BP has made continuous efforts to better understand and improve Thunder Horse’s subsalt image with new seismic data sets and more advanced imaging technologies (Pfau et al., 2002; Ray et al., 2002, 2005; Gherasim et al., 2012). The latest successful TTI RTM project with two WATS data sets and three NATS data sets is the continuation of this effort to improve Thunder Horse subsalt images. This project aimed to improve the structural image in poorly illuminated areas and to maximize the usable vertical and horizontal resolution for well targeting and planning. The latest image shows a dramatic improvement over the previous TTI RTM image produced in the 2012 project for three reasons. First, the additional WATS data in the NE-SW direction illuminated some key areas that the NW-SE WATS and three NATS surveys did not. Second, the majority of the NATS traces were migrated rather than just used to infill missing traces in the NW-SE WATS shot gathers, as was done in 2012. Finally, more advanced imaging workflows and technologies were used to address specific problem areas in the data. Shot patch-based angle gather illumination weighting (AGILW) and input data selection technologies, which were applied in this project, effectively attenuate noise while preserving signal. Specular imaging using RTM dip gathers also helped enhance the S/N. We also discovered one of the reasons for frequency loss underneath the salt.
- North America > United States > Gulf of Mexico > Central GOM (0.69)
- North America > Canada > Alberta (0.45)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Mississippi Canyon > Block 822 > Thunder Horse Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Mississippi Canyon > Block 778 > Thunder Horse North Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Mississippi Canyon > Block 778 > Thunder Horse Field (0.99)
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