Tectonic evolution of the Penglai 7-6 structure and its implications for petroleum exploration in a releasing bend of a strike-slip fault system, Tan-Lu fault zone, east China

The Penglai 7-6 (PL7-6) structure is located on the Tan-Lu fault zone, a huge fault zone in east Asia. Tectonism of the Tan-Lu fault zone produced complex structural deformation and was an important factor in petroleum accumulation. Three-dimensional seismic data were employed to document the structural geometry and evolutionary process of the PL7-6 structure, and implications for petroleum exploration in a releasing bend of a strikeslip fault system were discussed. Systematic analysis of the seismic data indicates that the main fault (the BD2 fault) of the Tan-Lu fault system slipped right-laterally during the Cenozoic. Strike-slip movement of the BD2 fault peaked during deposition of E(1-2)k to E(3)d(3), and decreased largely in intensity during E(3)d(1-2) deposition. In the Neogene and Quaternary, the BD2 fault was reactivated. Formation of the Bodongnan low uplift is related to the connection between the Bodongnan low uplift (N) and Bodongnan low uplift (S). The Bodongnan low uplift (N) is represented by an anticline produced by strike-slip movement of the BD2 fault, and the Bodongnan low uplift (S) is represented by the relatively uplifted strata in the vicinity of an extensional fault (the BD3 fault). The PL7-6 structure developed above a releasing bend formed by the subsequent strike-slip movement of the curved BD3 fault. Orientations of the shallow faults in the PL7-6 structure are not only associated with the lower BD3 fault, but also controlled by the basement high. Unlike traditional releasing bends that are generally disadvantage to petroleum accumulation due to the lower structural elevation in the center, the releasing bend in the PL7-6 structure is favorable for petroleum accumulation because of the three reasons: (1) adjacent to generative kitchens, (2) located on a regional structural high, and (3) served by the releasing-bend-related faults acting as conduits for vertical petroleum migration.