The Risk/Reward Balance in Subsalt Exploration: How Teamwork and Technology are Improving the Odds
Authors: Coffelt R.M. , Fox J.F. 
Published: October 2008

The recent discoveries in the subsalt trend Offshore Louisiana are examples of how teamwork And technology can open up a new frontier in a maturely explored basin. Several key relationships had to succeed before the subsalt plan could become reality: Partnerships between companies with different experience, expertise and viewpoint; Regional understanding of the basin geology coupled with a detailed understanding of salt tectonics; Integrated teams of engineers, geoscientists, and other specialists to handle new drilling problems; Proper application of new seismic imaging technology; and Support for key research, both internal and external.

Electively managing these relationships has helped the risk/reward balance, allowing the subsalt to be an economic venture. The high entry cost of subsalt wells, basin-wide 2D and 3D seismic databases, and the technologies employed (such as 3D depth migration), would be prohibitive without the possibility of significant discoveries and large reserves. Also, the challenge of managing such diverse talents and personalities involved with the key relationships is demanding. By properly utilizing the innovative ideas of these specialists, and applying leading edge technologies, true value is being generated for the share holders of the companies involved in the play.

The discoveries of Mahogany and Teak have generated not only excitement in the Gulf Coast oil industry, but on Wall Street and in Washington as well. The possibility of another major frontier in the United States could revitalize the domestic oil industry. But this new play brings additional competition, which brings added challenges. Continued wise utilization of creative people's talents and new technologies will be necessary to reap the true rewards of this play.

The Subsalt Play

The salt province offshore Louisiana is part of the larger Gulf Coast Geosyncline that is dominated by salt tectonics, growth faults, and clastic dominated Tertiary sedimentation (Fig. 1). The province is known for its prolific production of hydrocarbons, and has remained one of the hottest drilling provinces in the world. The offshore Louisiana basin is also one of great geologic complexity with future treasures waiting to be discovered, as is proven by the recent discoveries in the subsalt play. Without this complexity, how else could such a heavily drilled province hold so much future potential?

The basin contains massive quantities of Jurassic salt that has mobilized and formed complex structures. Until recently, most of the mobilization was believed to have been vertical, with the less dense plastic salt rising through sediment that was deposited above it. We now know that there is also a strong horizontal component to the salt movement, and that horizontal salt sheets cover over 30% of the offshore Louisiana shelf. The horizontal emplacement mechanism is what creates the subsalt play. In other basins world wide there have been presalt plays, where drilling through salt has encountered large reserves beneath the salt. The difference is that in the presalt play, the rocks beneath the salt are older.