塔东南坳陷侏罗系层序地层分析与油气前景

Study of Sequence Stratigraphy in Mesozoic Southeast Tarim Foreland Basin

塔东南盆地发育侏罗系陆相煤系地层和白垩系红层 ,勘探程度低。为研究中生代地层的分布和对比 ,沉积特征及勘探方向 ,重点对侏罗系进行了露头层序地层学分析。建立了五个三级层序。层序 1以正旋回的冲积扇或辫状河相为主 ,储集条件良好 ,层序 2发育正旋回及反旋回的三角洲相 ,具有良好储集条件 ,上部有较好的生油岩 ,层序3为反旋回的三角洲相及湖相韵律层 ,是良好生油层和盖层 ,层序 4为正旋回的河流相 ,层序 5为正旋回的干旱气候下冲积扇相 ,可形成次生溶孔发育的良好储层。塔东南侏罗系分布广泛 ,有良好的油气前景 ,是重要的含油气层系。

Tarim basin is a large,complex and multicycle basin, and has a complex geologic evolution history.Nevertheless,little is known about the geology of the Southeast Tarim basin.With the development of oil, people pay more attention to Mesozoic stratum exposed on basin margin.There develop Jurassic terrestrial coal measure strata and Cretaceous red beds.The present paper aims at analysing Jurassic system by use of sequence stratigraphy to study Mesozoic stratum distribution,contrast,sedimentary character,and to build up pattern of sequence stratigraphy.Using unconformity as main mark of different sequences,it shows Jurassic makes up a second order sequence,which represents a structural subsidence uplift process.Inside Jurassic,lacustrine invasion onlap and basinmargin exposure truncation can differentiate the third order sequence,which represents a relative water invasion water regression process. Sequence I subface is a regional erosion unconformity.It because of appearance on piedmont thrust belt on field outcrop is fault contact and bottom development incomplete.The sequence consists of alluvial fan facies or braided river facies with positive cycle.Its storage condition is good.Sequence 2 subface is lacustrine invasion onlap surface land alluvial fan facies is replaced by delta facies.Delta plain consist of braided river sequence with positive cycle.Delta front and lacustrine facies consist of prograding sequence with counter cycle.The sequence have good storage condition.Its upper part is a coal measure strata and it has fairly good oil source rock.Sequence 3 subface is lacustrine invasion onlap surface.The sequence consists of delta facies with counter cycle and rhythmic unit of lacustrine facies.At this moment lacustrine invasion is the largest .It takes shape of condensed section of deep lake facies.That is good oil source bed and overlying formation.Sequence 4 subface is basin margin truncation surface.That consists of river facies with positive cycle.At this moment,the lake is with small scope,climate change arid and hot.Sequence 5 subface is basin margin truncation surface.Its top surface is regional unconformity,which consists of alluvial fan facies with positive cycle in arid climate.It can become good reservoir that develops secondary dissolved porosity. Jurassic in southeast Tarim basin distributes extensively with a great thickness.It has good hydrocarbon, potential,and is also major hydrocarbon bearing sequence.In Sequence 3,condensed section of deep lake and semi deep lake is the most favorable oil source rock.Moreover,it is a regional overlying formation.Sequence 1 and 2 one of the most profitable exploration horizons since sequcence 5 and lower Cretaccous Kezileqiapu Formation is reservoir,and lacustrine shale and gypsum layer in Kezileqiapu Formation is its caprock .