Sequence Stratigraphy Model and Episodic Generation and Accumulation of Oil-gas Reservoirs in Laizhouwan Sag,Bohai Gulf Basin

Laizhouwan sag is one of the typical rift lacustrine basins in the Bohai Gulf Basin. Due to tectonic movement, palaeotopography and palaeoclimate, the sequence stratigraphy models of Laizhouwan sag are composed of lowstand, transgressive, highstand and fluvialsystem tracts. Tectonic movement is the direct cause of episodic hydrocarbon accumulation of Laizhouwan sag and the neotectonicmovement or late-stage tectonization determines whether the hydrocarbon reservoirs formed at early stage can preserve well or not in thesag. The partial crude oil of reservoirs that formed by being migrated and accumulated at early Paleogene is biodegraded due to the topsedimentary cover of Dongying Formation, which is the upthrow side of the main faults in strike-slip structural belt, Laizhouwan sag, isexposed to denudation caused by the tectonic uplift of Jiyang Depression in Late Paleogene. As a result, the oil and gas were poured inNeogene is preserved and formed reservoirs. Therefore, it is predicted that the downthrow side of main fault in the strike-slip structuralbelt and the central uplift zone are most favourable for oil and gas accumulation.