Fault And Controlling Function Of Hydrocarbon Accumulation In The Fangzheng Fault Depression

Fracture plays an essential role in oil and gas accumulation. Fangzheng fault depressionis located in the east of songliao basin, it’s the northern section in the middle of yi-shu grabenwhich is the northern extension of tanlu fault. Under the influence of tectonic movement,there’s a large number of fracture, and a lot of oil and gas reservoirs were located in thevicinity of fracture. According to the latest geological data and seismic data interpretationresults, from the fracture geometry and the formation mechanism，the evolution history offracture were researched, and the fracture system were divided, and then the controlling ofhydrocarbon accumulation were analyzed. The research shows:Vertical fangzheng fault depression can be divided into initial fault depression structurallayer, intensive fault depression structural layer, fault sag structural layer and shrinking faultdepression structural layer four structural layers; Based on the partition of structural layer,fault can be divided into upper and lower two sets of fault system by the bottom ofbaoquanling formation, fracture geometry is different between the two; Fracture experiencedthree intensive activity period: xinancun and wuyun formation sedimentary period,baoquanling formation sedimentary early period and fujin formation sedimentary early period;The formation and evolution history of fracture is three great stage：strike-slipping extensionaldeformation from xinancun and wuyun formation to dalianhe formation sedimentary period，interim tensile shearing in deformation baoquanling formation sedimentary period，transpressional deformation in fujin formation sedimentary period; based on the formationperiod，variability characteristics and formation mechanism of fangzheng fault depression,fracture system can be divided into six types：early strike-slipping extensional fault (typeⅠ)interim tensile shearing fault (type Ⅱ), late transpressional fault (type Ⅲ), earlystrike-slipping extensional and interim tensile shearing fault (type Ⅳ), interim tensileshearing and late transpressional fault (type Ⅴ)，early strike-slipping extensional and interimtensile shearing and late transpressional fault (type Ⅵ).Fault controlling of hydrocarbon accumulation were showed：①vertical migration of oiland gas was controlled by faults connected with source rocks, the activity of fault providedmethod that was transport condition for the migration of oil and gas when source rocksdischarged hydrocarbons;②faulted thickness directly affect the vertical sealing of cap rock, ifit’s within a certain range, oil and gas could be sealing under the cap rock;③footwall ofreverse faults is advantageous space for oil and gas accumulation, it is conducive to trap formation, reverse faults also provide effective sealing condition, together with unconformityand lithology up-dip pinch-out can form compound reservoir;④the lateral sealing of faultsensured the hydrocarbon accumulation effectively, the level of hydrocarbon accumulation wascontrolled by the former.