Structural Feature And Hydrocarbon Accumlation Of Paleogene In Tong Cheng District,Jinhu Depression

Tongcheng District belonging to Jinhu Depression is characteristic of complex structure where develops of different and widely-developed faults and complicated structure styles.There is a close relation between structure and hydrocarbon accumulation.The thesis researched structural features and genesis,studied structural controlling in hydrocarbon accumulation and regularity of hydrocarbon accumulation on the basis of 3D seismic explanation and guided by theories about structural analysis and petroleum geology.Bounded by Tongcheng Fault,many of faults in high evolution degree are in Eastern-Tongcheng area,many of faults in low evolution degree are in Western-Tongcheng area,Northern-Tongcheng area has both.The combination type of fault is parallel-aligned,skew-type,broom-like,?-like in the plane and is y-like,graben-horst-type,faulted-steps-type,negative flower structure on profile.Extensional structure style is primary and the reverse tilting fault block is the most common style.Tongcheng Fault is characterized by normal fault and strike-slip fault,reverse fault only in southern of it.According to fault activity analysis by fault throw and development of faults,we identified four fault activity types including I1 which long-lived,I2 which late-lived,II which late-lived and only developed above T30 reflecting layer,III which early-lived.The regularity of fault activity varied in different geological era,fault segment and structural area.The peak activity occurred during Sanduo sedimentation period.The I1 type faults are common in Eastern-Tongcheng area,I1 type faults develop more in Western-Tongcheng area,II type and III type faults are concentrated in Northern-Tongcheng area.The analysis of structural evolution sections showed that structural morphology started to form during Funing sedimentation period,finalized during Funing sedimentation period and gradually stabilized afterwards.The feature of structural evolution varied in different structural area resulted by different activity types and genesis of faults.Structural formation influenced by regional stress and basement faults.Basement faults on both sides of Tongcheng Fault have distinctive differences.Tongcheng Fault was a transfer fault which played a role in structural accommodating by NW-SE extension which before Middle Eocene,grew and had properties of passive strike-slip and active strike-slip by near SN extension which from Middle Eocene to eve of Sanduo Movement,the plane of south of it reversed and seemed like reverse fault caused by near EW compression which during Sanduo Movement.Meanwhile,different faults and extensional structure style formed in district.The numerical simulation for the ancient structural stress field proved the rationality of structural evolution.Tongcheng District is adjacent to Dongyang sub-sag,Longgang sub-sag and Chajian sub-sag.Hydrocarbon source and reservoir condition are fine in the district.Funing Formation is mainly hydrocarbon production strata.Structure features controlled formation of traps and hydrocarbon migration and accumulation.Fault-nose and fault-block traps formed near tilting fault blocks,large sliding faulted steps and strike slip structure.Large traps were controlled by I1 faults.Traps are best in Eastern-Tongcheng area,good in Northern-Tongcheng area and not good in Western-Tongcheng area.Hydrocarbon migration direction decided by rolling topography.Faulted steps in Eastern-Tongcheng area and Yang-2,Tian-62 well area in Northern-Tongcheng area are favorable directional zone.The activity of faults in accumulation period and lithology juxtaposition are main influence factors that controlled effectiveness of traps and hydrocarbon accumulation.Finally,limit of fault activity in accumulation period and degree of lithology juxtaposition sealing were determined,beneficial targets were indicated according to all accumulation conditions.