Research On The Fault Systems Evolution And Its Effact On The Hydrocarbon Accumulation In The Baiyun Sag, Pearl River Mouth Basin

Baiyun sag is the biggest sag in Pearl River Mouth basin, lying in deep-waterarea in the north of South China Sea. This area is an important place for the studies ofsome international leading subjects, such as tectonic belts of shelf-break, crust-mantle,sequence stratigraphy and the deep water fan. It is important to research on the faultsystems evolution to speed up the exploratory progress in the deep water region.In this paper, the character of fault systems is studied by use of 2D seismic dataexplanation as a basic method; The formation and evolution process of fault systemsis probed by means of analyzing stress field of congjugate faults, typical fault growthindex and activity ratio, and large structural evolution sections; By summing up thelaw of hydrocarbon migration in northern slope of Baiyun sag, associated with thetime of trap forming and the analysis of fault systems activity state, the control effectsof fault systems to the migration and accumulation of hydrocarbon are expounded.The main conclusions as follows:1. During faulting, the minimal principal stress was NNW-SSE in the Baiyun sag;during the faulting transition period, it departured towards east, which was NNE-SSW;during sagging, it was NNW-SSE again.2. Firstly, the concept of fault activity ratio is quoted in the Baiyun sag.Combining growth index, the paper has a qutantitative study on typical faults'activities. It indicates that fault activity can be divided into three climax periods andtwo quiet periods: Palaeocene (or earlier)-early Oligocene, early Miocene-middleMiocene, late Miocene and middle-late Oligocene and Pliocene.3. Baiyun sag fault systems evolution can be divided into six stages: (1) riftingperiod; (2) faulting period; (3) expanding period of the South China Sea; (4) faultingtransition period; (5)depression period; (6)shelf slope period. 4. By studying the nature and time of faulting activity, it is deemed that trapformation is controlled by strike-slip faults and their rotation action.5. Two models are established, one is a multiple delivery system model with afault as the boundary, the other is an explosion delivery system model with a sourcefault in the sag.6. All over the Baiyun sag, 10.SMa is the most important period for oil migrationand trap formation, and reservoir formation is controlled by fault systems.