Gulf Coast "Sub-Salt" Play Exploration Strategies
Authors: Pratsch J.-C. 
Published: October 2008

Successful exploration strategies in the New offshore Gulf CoastMio-Plioceneoil And gas (" Sub-Salt-) play will include the Entire Petroleum System involvedfrom pre- Miocene sourcebed deposition onward. On The shelf, primaryaccumulations occurred In pre-Late Miocenetime and reservoirs; in Deep-waterareas, hydrocarbon generation, Migration and entrapment occurred just Duringthe last few million years. In both Scenarios, deep (pre-Miocene) structuralConfiguration is decisive for the selection Of most prospective acreage blocks, using Established regional hydrocarbon migration Principles..

INTRODUCTION

About 11 billion Bbls oil and over 130 Trillions gas have been reported asRecoverable proved reserves in Federal Waters, Louisianaand Texas shelf (MMS,1993). in addition, 4.0-5.0 billion Bbls Oil (potentially recoverable) havebeen Discovered in deep-water areas of the U.S. Gulf Coast province (pressreports 1994)" Of these reserves, some 7.5 billion oil and 65.0 trillion Cftgas occur in Pleistocene And Pliocene reservoir son the northern Gulf Coastshelf (MMS,1993).

The present" old" play on the Louisiana/Texas shelf concentrates on Miocene toPleistocene sandstones; this Play today is at a rather mature stage Today downto a depth of about 15,000feet. However, a new " Sub-Salt" oil and gas play Liesbelow this level of past exploration. This new play has been suspected or hopedFor by many for more than 25 years, but Industry just preferred toexplore. Elsewhere rather than to establish the full Reserve potential of theGulf Coast Petroleum Systems. Improved knowledge from New stratigraphic, geochemical and finally Reflection-seismidcatabases during the Last10-15yearsthen led to an improved Understanding of chances and risks. Relatively recently first successes were Obtained with two major oildiscoveries on The Louisianashelf: fahogany, 1993, and Teak, 1994.

It is at this point that our discussion on Exploration strategies scones intoplace: How do we best explore for the targets in The new play? We will discusshere mainly Exploration on the Gulf Coast shelf. The Geological dimensions inthis discussion Are the over-all basinal region and basin wide? Explorationstrategies, not the single 5,000-acres acreage blockor the single Drillingprospect. Figure 1 schematically Illustrates the main geological points of thediscussions.

THE PLAY

The " new" (" Sub-Salt") play on the Gulf Coast shelf involves Miocene and EarlyPliocene sand stones in structural and Stratigraphic traps; they lie below andin The area of the Polio/Pleistocene Depocenter, located on the lower southernThird of the Louisianashallow-watershelf. Future exploration depth here isanywhere between about 12,500 and 730,000ft (Figure1).

All of the oil and about 2/3 of the gas in The " old" shallower play on the GulfCoast Shellfire thermally matures but occur in Thermally immature reservoirsections. Some (about 1/3 of the accumulated gas) is Of shallow biogeniclow-temperatureorigin (" Biogenic"). Source beds for all oil and most gas are ofPaleogeneand Late Jurassic ages on the Northern Gulf Coast shelf (Sassen, 1991;Wagered al, 1994); additional Cretaceous Source beds may also occur (Sassen,1990). Indicated then is a major vertical and Lateral hydrocarbon migrationprocess Operating in the region; thermally mature Oil and gas have migrated asmuch as 45,000 Feet vertically and as much as 30 miles Laterally (Pratsch,1993).