Integrated Interpretation in the Deepwater Gulf of Mexico: Examples from the TGS-NOPEC Phase 45 Deepwater Reconnaissance Program

Brian Anderson and Phillip Pappano, Jr., LCT; Dr. David Hall and Robert Brooks, TGS-NOPEC

Along with the explosion in seismic activity in deep water areas of the Gulf of Mexico, the application of high resolution gravity and magnetic data has also increased dramatically. The proper application of these data can result in enhanced seismic velocities, truly integrated geologic models, and decreased exploration risk.

Using new interpretation case studies from the TGS-NOPEC Deep Water Reconnaissance Program, the power of incorporated gravity constraints on deep water interpretations can be clearly demonstrated. Since the Phase 45 program is comprised of long regional lines, a clearer view of the deep regional structure may also be interpreted from the data.

The acquisition of high resolution gravity and magnetic data, in conjunction with both 2D and 3D seismic surveys has now become a normal procedure in the Gulf of Mexico. Several hundred OCS blocks of recently acquired high resolution gravity and large areas of high resolution aeromagnetic data now exist in the Gulf of Mexico and more acquisition is in progress. The use of high resolution gravity in seismic velocity analysis, and the use of velocity grids for localized, focused density input to gravity models are now commonly used. A brief review of instrumentation, costs, and integrated workstation software applications is provided to set the framework for the interpretation of a localized salt feature is provided from the Phase 45 area.

Workstation applications now in use facilitate the direct transfer of data and models between seismic and gravity/magnetic modeling software systems. A demonstration of these tools is included in the presentation. The ongoing 15.0 second seismic data is being recorded with a 6,000 meter cable and in areas where the overlying horizontal salt is limited deep reflectors between 8.0 and 10.0 seconds can be mapped. Based on similar occurring reflectors in the Mississippi Canyon- Viosca Knoll area and ties to wells in those areas, these deep reflectors are tentatively identified as lower Eocene carbonates or MCU (Mid Cretaceous Unconformity). In the Main Pass- Viosca Knoll area these reflectors are at approximately 4.0 to 6.0 seconds and deepen rapidly to the southwest toward upper Mississippi Canyon and Grand Isle. In areas of better data quality, salt pillows can be seen, as well as secondary welds that extend from the interpreted MCU up into the shallow part of the section where horizontal injection occurs. In some areas, there is a deeper band of reflections approximately 200 to 500 ms below the interpreted MCU that could be basement. Regional interpretations of this surface could add significantly to information related to the formation of the Gulf of Mexico basin and the interplay between structure, stratigraphy, and sand deposition in the overlying tertiary.