- Copyright © 2001 Society of Exploration Geophysicists
Texaco has drilled more than 100 wells surrounding a piercement salt dome in Vermilion Bay Field, southern Louisiana (Figure 1). Cumulative production in the field exceeds 270 billion ft3 gas and 4 million b/o since the discovery well was drilled on 23 July 1939. Early drilling around the dome clearly indicated that the salt structure has a pronounced overhang 5000–8000 ft below the surface. Accuracy in determining the location of the salt flank adjacent to each proposed new well is important to development of hydrocarbon reservoirs trapped in a narrow band against the salt. The producing horizon exceeds 70° angle of dip, which pushed seismic data to its interpretable limit in the vicinity of the proposed wells. For every 100 ft that the salt contact approaches a proposed well bore, this equals 275 ft of structure lost—and a less desirable prospect. If drill pipe becomes stuck due to encountering salt, additional costs can cause the well to be abandoned. The cost of sidetracking a well, for any reason, adds approximately US$1 million to the total cost. Changing the drilling-mud system adds approximately US$500 000.
This study, the Salt Dome Visualization project, resulted in an extremely accurate interpretation of the Vermilion Bay salt body. 3-D visualization yielded a quick way to review proposed drilling locations and to select the optimum position of future well paths. IESX GeoViz 3-D visualization software performed the precise analysis and interpretation required in the project. Benefits included reducing the risk of encountering salt, allowing the use of a lower cost drilling-mud program, and reduced risk of stuck drill-pipe.
Experience using salt proximity surveys and well logging
The most recent 3-D seismic survey was acquired in the mid-1990s. In 1999 the survey was prestack depth migrated using the best velocity model available. The quality of the data was poor …