--> Hydrocarbon Accumulation Model of Large-Scale Anticline Structure in Strike Slip-Extension Complex Tectonic Area and Exploration Significance: A Case Study of Laizhouwan Sag in Bohai Bay Basin

International Conference & Exhibition

Datapages, Inc.Print this page

Hydrocarbon Accumulation Model of Large-Scale Anticline Structure in Strike Slip-Extension Complex Tectonic Area and Exploration Significance: A Case Study of Laizhouwan Sag in Bohai Bay Basin

Abstract

Laizhouwan sag which clamped between the two branches of the Tan-Lu Strike slip faults is an important exploration area in Bohai Bay basin. In Cenozoic, affected by the superimposition of regional rift faulting activity and dextral slip pull-apart activity, here forms a series of large-scale anticline structures, which have characteristics of bigger scale, steeper amplitude and better migration-accumulation condition compared with anticline structures in conventional rifted basins. Up to now, 80% of oil discovery lies in this kind of structures in Laizhouwan sag. By deeply analyzing the tectonic origin and petroleum migration-accumulation system of the the anticline structures, two different hydrocarbon accumulation models are generalized: vertical accumulation model of reversal anticline structure and lateral accumulation model of drape anticline structure. The vertical accumulation model mainly exists in the steep zone and strike slip transfer zone, which are adjacent to the oil source area; High amplitude and big-scale reversal anticlines are formed by the superposition of the early regional rift faulting activity and the late strike-slip transpression activity; And also due to the superposition stress, this kind of anticline has many faults of various scales, which look like flower shape in section; Hydrocarbon vertically migrates along these faults which cutting in source rocks and efficiently accumulates in the anticline traps; These reservoirs usually are featured with deep-shallow complex accumulation and high-abundance. Lateral accumulation model mainly exists in the slope belt which far away from the oil source area; The early extensional faulting and differential settlement dominates the formation of large drape anticline, and late strike slip activity developes massive faults in the anticline; Hydrocarbon migrates long distance from deep depression area to slope low potential area through faults, sandbodies and unconformity surfaces, forming the stepped passage system; Therefore, the large drape anticline trap in slope is the final destination of accumulation; This kind of reservoirs usually have a single oil-bearing formation and mainly accumulates in shallow layers. In recent years, many large-scale anticline oil fields have been found here with reserve of 150 million cubic meters and also the exploration success ratio reachs 90% under the guidance of the two models, which are also a great help to the exploration in other similar areas.