The use of 3D seismic and computer-aided exploration (CAEX) workstations-as it has elsewhere in the oil and gas exploration industry-has transformed the way Mobile Bay operators explore for hydrocarbons and select bottomhole production locations.
Although the largest Norphlet reservoirs were discovered before 3D was widely used, Mobil's 1995 well, 95-5, and its final bottomhole location-with a sidetrack 700 ft east of the initial location-illustrate how 3D and CAEX are improving Norphlet results.
Mobil's 95-5 well illustrates the effects of 3D seismic data on well placement. Mobil spudded the well in July 1994, deviated 7,400 ft east from a rig located outside the Mobile Bay shipping fairway on Tract 94. The initial well was tested in May 1995 and judged capable of producing 50 MMcfd.
Three-dimensional seismic data were used to clarify the top and base of Norphlet and show the geologic depth cross section of the well. Conventional 2D seismic could be relied on only to supply information on structural position. Using the extremely fast computing power of the CAEX workstation allowed integration of the 3D data with geologic data to pinpoint a bottomhole location.
The well was sidetracked to a location 8,100 ft east of the rig to maximize both structural height and stratigraphic thickness. It reached TD in October 1995.
Moving the well 700 ft east of its original bottomhole location improved the porosity from 11.7% to 12.8% and markedly improved the well's productivity. The sidetracked well tested at 77.3 MMcfd. Production averaged 70 MMcfd during the 2 months following start-up in November 1996.
The increased productivity improves the economics dramatically. The added 20 MMcfd boosts cash flow by $20,000/day at a wellhead netback price of $1/Mcf. An incremental $6 million/month will pay for a substantial amount of 3D seismic data and drilling rig time.
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