Research On Tight Oil Accumulation Mode Of The Chang 6 Oil-Bearing Formation In The Southeastern Of Ordos Basin

Based on previous research results,making use of data of the core,slice,well-logging,drilling,analysis and testing,applying sedimentary petrology,structural geology,petroleum geology,logging geology,reservoir geology and other discipline theories,the paper studies the accumulation mode of light oil with the example of the Chang 6 oil-bearing formation in the southeastern of Ordos Basin and acquires the following understanding.The layer of the Chang 6 oil-bearing formation in the study area is stable with a thickness distribution of 123~137m and has a relatively small sand body size which has stripped distribution with SW-NE direction.The structural elevation distribution shows-60~240m,which is characterized by the monocline from northwest to southeast.The denudation thickness of the tectonic uplift in the late early Cretaceous period is over 1300m.The reservoir rock types of the Chang 6 oil-bearing formation is mainly feldspar sandstone,secondly the lithic arkose,and mainly develops dissolved pores and residual intergranular pores.The porosity of the reservoir was 8.7%on average,the permeability was 0.44mD on average,so it belonged to the tight reservoir,which was controlled by compaction,cementation and dissolution,the porosity reduction rate was about 65%by compaction and about 24%by cementation,and dissolution pore increasing by about 10%.The total organic carbon content of Chang 7 oil-bearing formation ranges from 0.45%to 3.35%,with an average of 1.80%.It belongs to good source rocks.The vitrinite reflectance is 0.75%~1.0%,with an average of 0.93%.It reaches the mature stage.The cumulative oil production intensity of the Chang 7 source rock is 31 mg HC/g TOC,and the cumulative oil discharge intensity reaches 2.04 kg HC/m~3 rock.There are numbers of sand bodies and the characteristics of lateral contiguous and multi-layered distribution in the Chang 6oil layer formation,and composes the lens traps and diagenetic traps to the quasi-continuous distribution mode.The fluid inclusions are mainly divided into quartz healing crack occurrence,feldspar particles and increasing the secondary side.The uniform temperature distribution of the inclusions is unimodal,and the main range is 80-130?,with an average of about 107.2?.The accumulation time of tight oil is in the distribution range of 170-110 Ma.The filling time starts from the middle and late Jurassic and lasts the end of the late early Cretaceous,with a coupling relationship of“first tight and then accumulated”.The residual pressure of hydrocarbon generation in Chang 7 oil-bearing formation is 12~16MPa.The three-dimensional network system of sand bodies and fractures constitutes the main channel of petroleum migration.There is the tight oil accumulation mode of lower generation,upper storage and overpressure-driven type established in the Chang 6 oil-bearing formation.