Current development of the Jolliet Field, located offshore Louisiana in the Flexure Trend, is a joint effort of Conoco Inc.'s exploration and production personnel. Interpretation of the complex geology was aided by 3-D seismic data, and a new-generation tension leg well platform was developed to produce this relatively small oil field economically in 1760 feet of water.
When production commences in 1989, Jolliet Field will be in the deepest water of any oil field producing to a platform. It is, located in Green Canyon Block 184, 170 mi 1es southwest of New Orleans, in what has come to be known as the Flexure Trend. The 1ocati on is shown in Figure 1.
The Flexure Trend is not a single geologic entity but is somewhat arbitrarily defined by a series of oil and gas discoveries in the Gulf of Mexico, seaward from-the present-day shelf-slope break, in water depths between 600 and 3000 feet. The productive trend extends along the Gulf Coast slope for more than 450 mi 1es from the central Texas coast eastward to the Cretaceous shelf edge. Potentia1 reserves may be as high as 2 billion barrels of oil equivalent.
Until the early 1970s, industry activity along the offshore Gulf Coast was limited to the shallow-water shelf area. Sands were believed to be deposited primarily from deltaic systems and restricted to the shelf. With the first leasing of nominated acreage on the slope in 1974, exploration was extended into this previously undrilled area. Results of the initial drilling indicated thick sequences of sands deposited, at least locally, over the shelf edge during sea-level lowstands. The sands were deposited as fans, fan channels, or distal turbidites in a deepwater environment.
Jolliet is one of several Flexure-Trend discoveries. Currently, it is estimated that more than 40 significant discoveries have been made, although additional delineation drilling will be required on many to determine economic limits. The discovery locations are shown in Figure 2. Oil and gas have been found in Miocene, Pliocene, and Pleistocene sands, all of which are productive on the shelf in shallower waters.
Prospects along the Flexure Trend are related to sediment loading, deep-seated faulting and/or salt tectonics. The remobilization of the Jurassic Louann salt is a major factor in the distribution and thickness of the sands over much of the slope area. The salt becomes more prominent farther to the south in the deeper water and generally appears as lenses, tongues, or layers.
Hydrocarbons have been found in the classic types of features, including fault closures, faulted anticlinal structures, salt flanks, and stratigraphic traps. Future discoveries are conceivable from underneath the salt layers where most present-day seismic data are poor. The hydrocarbon migration pathways into many Flexure-Trend reservoirs are believed to be the result of deep-seated faulting; the source of the oil and gas is thought to be from the older, possibly Cretaceous, sediments.
