Volcanostratigraphy Framework And Eruption Patterns In Carboniferous Of The Surrounding Areas Of Pen 1 Well West Sag,Junggar Basin

Large structures and volcanic rocks are developed in the Carboniferous system on the surrounding areas of Pen 1 Well West Sag,Junggar Basin,with favorable reservoir formation conditions.However,the volcanic rocks in the study area have complex lithology and rapid changes.At present,the research on volcanic rock reservoirs in this area is not deep enough.In this paper,the Carboniferous volcanic rocks in the surrounding areas of Pen 1 Well West Sag in Junggar Basin were studied.Different lithology and lithofacies in this area were identified and divided by using core data,casting thin section identification,rock pricipal and trace element tests,combined with logging response characteristics of core section in drilling.Based on the analysis of single well facies,the correlation of connected well profiles and the interpretation and analysis of seismic data,the spatial distribution law and volcanic eruption patterns of the Carboniferous volcanic stratigraphic mechanism in this area are clarified,in order to provide reference for the exploration and development of the carboniferous volcanic rock reservoir in the surrounding areas of Pen 1 Well West Sag,Junggar Basin.The results of the study are as follows: 1.Through core observation and microscopic thin section identification,three major lithology types of volcanic lava,pyroclastic rocks and sedimentary pyroclastic rocks are identified in the study area.Lithology is complex.The Shixi and Mobei areas are mainly medium-acid,with eight lithology types developed: andesite,dacite,rhyolite,dacite tuff,dacite volcanic breccia,andesitic volcanic breccia and andesitic cryptoexplosive breccia.2.There are four kinds of volcanic facies and six kinds of subfacies in the study area.The main lithofacies are intermediate-acid overflow facies and explosive facies,while the basic overflow facies and volcanic channel facies are less developed.The subfacies are mainly the middle and lower subfacies of the intermediate-acid overflow facies,air-fall subfacies of the explosion facies.In addition,the upper subfacies of the intermediate-acid overflow facies,the plate lava flow subfacies of the basic overflow facies and the pyroclastic flow deposit subfacies of the explosion facies are also developed.3.The Carboniferous volcanic strata in the study area can be divided into three cycles according to the abrupt changes of lithology and lithofacies combination and lithofacies sequences.In this study,the third cycle,as the main research horizon,can be divided into four eruption periods.The volcanic activities of the first three eruption periods increased gradually and the volcanic activities of the last period significantly weakened.4.Due to the different properties of magma,volcanic edifices in the study area can be divided into three types,called stratovolcanic edifice formed by intermediate-acid magma,mound superimposed volcanic edifice and shield basic volcanic edifice formed by basic magma.5.The volcanic eruptions in the study area are affected by the properties of the original magma and controlled by faults.Two different models of volcanic eruption are formed,namely,central eruption and fissure eruption.The volcanic edifice of central eruption are arranged as a string of beads along the fault.The volcanic edifices of fissure eruption are arranged as a belt along the fault zone.