Petroleum Implications of Gravity Tectonics

De Clarens, Philippe, Bernard Pironon, Total, Paris la Defense Cedex, France

The majority of deep offshore reserves to date have been found where salt or shale tec­tonics plays a role. The regional scale structural fabric also plays a significant role in the location of the discoveries. These two statements can be compared with the current under­standing of the driving mechanisms inferred in gravity tectonics. Each gravity driven sys­tem is controlled by interactions of the mechanical property of the decollement, the sedi­mentary loading and the basal slope geometry. At regional scales, the structural closures can result from various combinations of several gravity driven systems, which in them­selves can be simple. The deformations occur permanently during long periods but during shorter time intervals they are enhanced by regional tectonics and sedimentary events. The propagation of the deformation and the area it affects are different on salt and shale. The detachment levels can successively or alternatively act as a source rock interval (when shaly) or regional or local barriers to hydrocarbons migration (when below the decolle­ment). Above the detachment, the history of the sliding can control the location of the source rocks and the reservoirs, and also the internal architecture of the reservoirs, with respect to the structural closures. After burial, the size of the drainage areas above the decollement is linked to the style and the history of the deformation. The main objective of this talk is to illustrate, with data from various deep offshore basins, the way in which grav­ity tectonic concepts can provide useful guidelines to interpret petroleum processes and search for new plays.