AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Deepwater renaissance on the Atlanic Margins

Abstract

Many deepwater drilling records were set in the Campos Basin of Brazil in the mid 1980’s with the discovery of the giant Tertiary Marlim Oil field. This heroic exploration, paced by deep water efforts in the Gulf of Mexico opened up a new field of enterprise for the Industry. This arrived in West Africa in the late 1990s with the discovery of the Ceiba field in Equatorial Guinea. This was followed in 2007 by the giant Jubilee field, thought to be a solely stratigraphic trap at base of slope, but subsequently found to have a structural component to both deposition and trap. Many wells exploring constrained channel systems on both sides of the Atlantic were subsequently drilled, searching for sands in up-dip bypass-traps. A context of conjugate-margins, where source rocks if not geology might be translatable was sought yet this has found limited commercial success, because this trapping style is very difficult to image with any technology. However, a new energy has appeared in the industry as number of key wells drilled recently in North West Africa have started to open the door to a low risk deep water play that has achieved stunning success to date (Tortue-1, Marsuin-1, Terranga-1, Yakaar-1) and looks set to draw the industry into exploring a new play type down on the basin floor, that will spread all along the West African margin. Previous to this Petrobras’s discoveries in Brazils Sergipe basin (Barra, Moita Bonita etc) and later Exxon’s discoveries in Guyana (Liza, Snoek) have shown that not only can the deep water be incredibly rewarding, with fast development opportunities, but it is also as rich with oil as it is gas. Deep water drilling capability has improved steadily over the last 70 years, mostly during times where oil price has been below $50/bbl. This improvement in technology is occurring whilst costs are dramatically falling. The basin floor fans that have always been beyond capability are now in sight. At the same time, seismic technology has improved probably faster than any other oil-industry related technology, with multiple elimination techniques and deghosting now standard. As the industry is pushing forward with new technologies and models – surprises are occurring. Unexpected heat-flow distribution across crustal structural architecture, unexpected source rocks and constraints on the ages of those and recognition of the role of contourite currents in mixed systems for the distribution of porosity and permeability on the basin floor are bringing challenges , but in equal measure new opportunities. Additionally a number of basins from Mauritania to Namibia, and Guyana to Argentina have been de-risked in terms of source rock presence and effectiveness. The combination of operational excellence and improvement, and the understanding of geoscience through technology and inspiration sets a scene heralding in a new age of exploration on the slopes and Basin floor of the Atlantic Margins. In this new age, smarter seismic, smarter geoscience models and de-risking tools, and enhanced drilling techniques will be employed that will open the margin to explore a new scale of play that was never accessible before: the base-of-slope and basin floor fans of the South Atlantic, where prospect resource potential (both oil and gas) is created and determined by plate scale geometries. This regional play fairway and its main characteristics are illustrated in this talk by a series of seismic examples derived from an extensive 2D seismic dataset.