Petroleum Implications of Gravity Tectonics
De Clarens, Philippe, Bernard Pironon,
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.