Origin Of High-Quality Reservoirs Of The Lower Part Of Xishanyao Formation In Taibei Sag,Turpan-Hami Basin

The research shows that many sandstone reservoirs in the world still develop high-quality reservoirs with relatively high porosity and high permeability under the background of overall low porosity and low permeability.It is of great theoretical and practical significance to clarify the genetic mechanism of high-quality reservoirs for pre-drilling evaluation of mid-deep and deep sandstone reservoirs,prediction of high-quality reservoirs and improvement of economic petroleum reserves.At present,the petroleum exploration fields in Turpan-Hami Basin are gradually changing from the adjusted structural petroleum reservoirs in the ring Sub-sag of middle and shallow layers to the lithologic petroleum reservoirs in the inner Sub-sag of mid-deep and deep layers.transitioning from tunable structural petroleum.The lower part of Xishanyao Formation is an important petroleum exploration horizon for lithologic reservoirs in the Sub-sag.However,due to its rapid sedimentary phase transformation and strong reservoir heterogeneity,the development law and genetic mechanism of high-quality reservoirs are unclear,which severely restricts the large-scale exploration and development of petroleum in the lower part of Xishanyao Formation.This thesis takes the lower part of Xishanyao Formation of the Middle Jurassic in Taibei Sag,Turpan-Hami Basin as the research object,comprehensive utilization of core observation and description,scanning electron microscopy(SEM),thin section identification,physical testing,particle-size analysis,X-ray diffraction analysis(XRD),mercury injection,constant velocity mercury injection test and fluid inclusion and other technical means are comprehensively used to follow the research idea of"characterizing the difference phenomenon-exploring the internal mechanism-summarizing the distribution law".In the characterization of sandstone reservoir sedimentology and petrological characteristics,determine the lower limit of reservoir effective porosity and normally primary pore evolution trend line.The characteristics of physical properties,microscopic pore structure,diagenesis and diagenetic equivalence of different types of reservoirs are clarified.The controlling factors of reservoir physical property differential evolution are analyzed,the formation mechanism of high-quality reservoirs is revealed,and the plane distribution law of high-quality reservoirs is predicted.The main achievements and understandings are as follows:The sedimentary period of the lower part of Xishanyao Formation was mainly controlled by the north and south provenance,and fan delta front,braided river delta front and lacustrine sedimentary system were identified.From the first member to the second member of the Xishanyao Formation,the braided river(fan)inner delta front-lacustrine depositional system evolved to the braided river(fan)outer delta front-lacustrine depositional system.The multistage superimposed channel and mouth bar thick sandbodies constitute primary reservoirs.The rock types of the lower part of the Xishanyao Formation in Taibei Sag are feldspathic litharenite sandstone and litharenit sandstone with low to medium compositional and textural maturity.It is a typical ultra-low porosity and ultra-low permeability clastic reservoir.Four anomalously high porosity zones are developed in the Xishanyao Formation at burial depths of 2100?2400 m,2800?3150 m,3250?3700 m and 3800?4100 m.The reservoir space in anomalously high porosity reservoirs are mainly primary intergranular pores and dissolution pores;the reservoir space of normal evolution high porosity reservoir is mainly secondary dissolution pores,followed by micropores,and the content of residual intergranular pores is less;the reservoir space of normal evolution low porosity reservoir is mainly micropore and dissolution pores,and there is almost no intergranular pores.The sandstone reservoirs in the lower part of Xishanyao Formation are currently in the mesogenetic stage A₂,and there are mainly four types of diagenetic facies:strong carbonate cementation facies,strong compaction weak dissolution facies,medium compaction middle dissolution facies and strong dissolution facies.Among them,the diagenetic facies assemblages of high-quality reservoirs are medium compacted dissolved phase and strong dissolved phase.Strong compaction is the main factor leading to the deterioration of reservoir physical properties,accounting for76.4%on average.The cementation of clay minerals and carbonate further destroys the reservoir physical properties.The high energy thick sandbodies are the material basis for the formation of aomalously high porosity reservoir and normal evolution of high porosity reservoir.The late detachment nappe tectonic activity is the key to the preservation of primary pores in sandstone reservoir,and the organic acid dissolution is the fundamental reason for the formation of high-quality reservoir.The lower part of Xishanyao Formation can be divided into four types,?and?are relatively high-quality reservoirs,which are mainly distributed in Shenquan-Huoyanshan-Qiketai area,as well as Kekeya and Qiquanhu area in the northern part of Taibei Sag.From the first member to the second member of the Xishanyao Formation,the distribution of high-quality reservoirs is similar,but the development scale gradually decreases.The research results of this thesis can provide theoretical geological basis for the exploration and development of middle and deep lithologic reservoirs in Taibei Sag of Turpan-Hami Basin,and have reference significance for the study of the genetic mechanism of high-quality reservoirs under similar geological background.