Influence of tectonic on the petroleum sys- tem of Wessex Basin Guillermo GIACOMI, Stanislas PAUTHIER, Éric DEVILLE, Pierre-Yves DÉ- QUIREZ, Jean-Claude HEIDMANN Petroleum Geosciences, Promotion 2016 IFP School, 232 Avenue Napoléon Bonaparte – 92852 Rueil-Malmaison Abstract: The Wessex basin displays a remarkable combination of renowned geological features. It comprises a near-continuous sequence of Permian, Triassic, Jurassic, Cre- taceous and Tertiary rock exposures that represents almost 300 million years of earth history. This report focuses on the study of petroleum system present in the Wessex Basin in order to determine how tectonics may have controlled the development of it. Indeed, stratigraphy, petroleum system elements and processes were led by two major tectonic events: an extensive phase of Permian to Cretaceous and a compressive phase. The paleostructures such as normal faults, were first allowed to bury enough Lias source rocks in the Purbeck area and thus to generate type II hydrocarbons. Subsequently, sandstones reservoirs of Sherwood (Triassic) and Bridport (Toarcian) were filled by hy- drocarbons that have migrated through the faults. These were then trapped by the tilted fault blocks created during the extensional phase. Keywords: Wessex basin • Petroleum system • Structural • Extensive system Corresponding author: guillermo.giacomi.2016@ifp-school.com - stanislas.pauthier.2016@ifp- school.com Introduction The Wessex Basin is one of a system of linked Mesozoic basins that cross southern England (Fig. 1), the Channel and Northern France. The Wessex Basin covers more than 20,000 km 2 of southern England, principally within the counties of Dorset and Hampshire, and extends offshore into the Eng- lish Channel. It is a significant petroleum province, containing a fairly complete sequence of Permian to Cretaceous sediments, within which are source rocks for petroleum generation, reservoir rocks in which oil may accumulate, and seals to keep oil accumulations in place. The complex tectonic his- tory of the basin has allowed burial of source rocks into the zone of oil generation, and also led to the formation of traps for oil accumulation. The basin contains Wytch Farm, the largest known onshore oilfield in Western Europe, and larger than most UK offshore fields. Two much smaller fields (Wareham and Kimmeridge) also produce oil in the basin, and a series of oil seep- ages are known in outcrops on the Dorset coast. Fig. 1: Location map indicated the area of inter- est (Underhill and Stoneley, 1998).