Studies On Hydrocarbon Accumulation Conditions Of The South Slope Belt In Bonan Sag

Located on Zhanhua depression,Bonan sag,is a third class negative element in Jiyang depression.Multi-type sedimentary facies were developed during the deposition period of Southern slopes in Paleogene,which sand body distribution were complicated,with factors of series of activity,multistage reservoir formation,multi-accumulation.Thus it due to relatively complicated reservoiring condition,which constraint further exploration and deployment in this region.Based on this,this paper comprehensively using seismic,drilling,logging and testing data,guiding by theoretical knowledge such as sedimentology,reservoir geology,petroleum geology,conducts sedimentary reservoir,oil source correlation,time period of accumulation,the regularity of accumulation elements research on Southern slopes of Bonan sag,by which guide the exploration and deployment in this area.The research results show that palaeogene of the study area can be divided into three second-order sequences including Ek to early Sha4,late Sha4 to early Sha2,late Sha2 to Ed,in which develops many types of the sedimentary facies,such as alluvial fan,fluvial,nearshore subaqueous fan,fan delta,braided river delta,turbidite fan,coastal shallow-lake and semideep lake facies.etc.Provenance distance and the type of the sedimentary facies show regular variation with the changes from lowstand system tract(LST),transgressive system tract(TST)to highstand system tract(HST)in different second-order sequences;Overall,being medium pore and medium permeability reservoir,the clastic reservoir has generally better physical properties,while carbonate reservoir is ultra-low porosity and ultra-low permeability reservoir on the whole.The study area contain composite reservoir that controlled by structure and lithology,oil and gas of which main from late Sha4 and Sha3 of Bonan sag,few from Sha3 of Gunan sag.Integrated hydrocarbon history,reservoir saturated pressure and the fluid package body data analysis,it confirmed two oil and gas charging stages and three stages of reservoir formation exist in research district.Dongying Formation is the first oil and gas charging stage,of which oil from late Sha4 of Bonan sag,with oil of slopes from Sha4 of Luojia&Kenxi and Sha3 of negative structure of Sanhecun formed in this period.Guantao Formation is the earlier stage and Minghuazhen Formationang is the later of the second oil and gas charging stage,of which oil from Bonan sag and Sha3 of Gunan sag.Negative structure conclude three types of "network blanket","early accumulation" side direction and "unconformity" mixed direction,while slopes conclude conduit systems of “T”,which composed of fault and sand.With the dfferences in sources,accumulation stages and forms,the accumulation patterns are different between negative ang slopes structure.According to the patterns of play factor,we wonder to grasp the key elements of the hydrocarbon accumulation.Negative structural belt of Sha3 in Sanhecun conducts early accumulation elements reverse,while slopes of Luojia&Kenxi carry out sand body refined description and analysis of fault sealing,according to which the exploration and deployment has achieved good results.Finally,the results guide the exploration and deployment effectively in this area.