The Characteristics Of Archeozoic Buried Hill Reservoir Fractures In The Area Of Bohai Bay Basin

Bohai bay basin is the great basin that has the highest degree in oil and gas enrichment of our country.After the years of exploration,has successfully developed multiple archaeozoic buried hill reservoirs and achieved good results in studying the fracture types,attitude,reservoir physical properties and descriptions.But with the deepening of the development,exposed the buried hill fracture formation mechanism was not unified,control factors was not clear,that reasonable restricted oil field production.Under the background of the research literature,analyzed the tectonic framework of the basin and explored the evolution process that accord to the main line which combine the forth Cenozoic basement and the Cenozoic tectonic.Combined with core observation and well logging interpretation,divided the plains into different strata groups including plain formation of quaternary,ming town formation of Neogene,dongying formation of paleogene,shahejie formation and the archaeozoic.Based on the core chip and outcrop observation,the rocks can be divided into gneiss and cataclasite.The gneiss is given priority to with biotite plagioclase gneiss,monzonitic granitic gneiss and biotite two-feldspar gneiss,the cataclasite is given priority to hemp qualitative cataclastic rock and broken porphyry.Minerals in the highest content of plagioclase,up to 42%,followed by quartz and potassium feldspar.With field outcrop,core and imaging logging fracture identification as the basis,the study showed that the fracture was given priority to structural fractures and then were weathered fracture and dissolution fractures,as high as60;fracture aperture concentrated in the 0.5mm to 1mm,and has the great open nature;high angle oblique fracture has the greatest density,but well-blocks fracture density are difference;the fracture strike is given priority to EW,NE and NW;the effective fractures are given priority to the open inclined cracks which forming in the later periods,the next is half pack of vertical fracture,the worst is the early horizontal fracture.The fractures which move towards to NNW and NNE were formed early,and the fractures which move towards to NE and NW were formed late.Overall,there are large difference between each well-block fracture characteristics.Through the study on thestructure,lithology and fracture characteristics of the basin,found that the internal control factors include the rock properties,the external factors include weathering,dissolution,unconformity surface,tectonic stress,palaeogeomorphology and fault structures.Though the comprehensive analyzing,found that the main controlling factors include lithology,tectonic stress and fracture structures.Found that the lithology impacts the difficulty of the fracture development,the stress cracks control the advantage direction and distribution,the fault structures control the regional characteristics of fractures.And found that the favorable reservoirs distribute at the east and northeast of the basin and are zonal distribution along the major faults which toward to west to the north and the high positions of structures.After the comprehensive analyzing and comparison of parameters,14 parameters were selected.According to the attribute characteristics of each parameter,the comprehensive evaluation index system after the 14 parameters were given a quantitative evaluation.Using the analytic hierarchy process to get the weight of each parameter.Based on the evaluation index system,the internal wellblock of jinzhou south buried hill and bohai bay basin developed buried hill oil field were evaluated,which got a good evaluation result.