Structural Deformation And Its Effects On Hydrocarbon Accumulation In The Songnan Low Uplift,Qiongdongnan Basin

The Qiongdongnan basin is a extensional basin of Cenozoic located in the north of South China Sea,which is one of the important places for oil and gas research in deep water.The study area of this paper is in the middle of the Qiongdongnan basin,including the Songnan low uplift and its adjacent area.This area is the most significant research fields of deep-water oil and gas exploration in the Qiongdongnan basin.In recent years,many wells have been drilled in the Songnan low uplift,some of which have resources.This shows a good exploration prospect.In this paper,under the guidance of the theory of oil and gas basin structure,we have studied the structural deformation characteristics and its effects on hydrocarbon accumulation through the interpretation of seismic data and drilling data in study area.We have also analyzed structure of the Songnan low uplift,evolution and deformation characteristics of faults.Then we establish the hydrocarbon accumulation model with the effect of faults in study area.The results show that: The Songnan low uplift began to develop from the early Oligocene to the middle Miocene,during which the structural activity was strong.Under the influence of multi-stage tectonic movement,the low uplift in the Songnan has a large structural difference from west to east.The area can be divided into western,central and eastern parts.There are a lot of faults of Paleogene in the Songnan low uplift.In the profile,the forms of single-strand faults are mostly shovel-type and plate-type normal faults,and multiple faults can be combined into domino,inverse "Y",stepped,shovel fan and other structural types.On the plane,the single fault is shown as linear,arc and "S"-shaped,and multiple faults are formed into parallel combination,cross combination,echelon combination and broom combination.In addition,according to the combination method of extensional structural styles,a variety of typical structural styles,such as horst and graben,half graben,warped block and sliding fault order,can be identified on the Songnan low uplift.Based on quantitative calculation of the main fault activity in the study area and analysis of balanced section,the evolution of the Songnan low uplift can be roughly divided into three stages: the early rift stage,the middle depression stage and the late post-rift subsidence stage.There are mainly two types of structural traps developed in the Songnan low uplift: faulted anticline and faulted nose.According to the matching relationship between fault activity and hydrocarbon accumulation,the faults in the Songnan low uplift and adjacent areas are divided into three types: oil source fault,reservoir control fault and other faults.Based on the results above,the hydrocarbon accumulation model of the Songnan low uplift is mainly manifested as "long distance source-lateral-compound migration".