准噶尔盆地吉木萨尔凹陷芦草沟组混合细粒岩沉积微相

准噶尔盆地吉木萨尔凹陷二叠系芦草沟组成为页岩油气勘探的重点区块,开展精细混积岩沉积层序及其相关研究具有十分重要的理论及实践意义。利用岩心、薄片、扫描电镜、测井曲线、XRF及XRD等资料,结合岩心相及其组合分析、测井曲线最小二乘法拟合和岩性随机模拟等技术,开展层序地层格架及沉积微相识别,建立研究区混积细粒岩沉积微相模式。研究发现:①芦草沟组可划分为5个中期旋回、9个短期旋回、33个超短期旋回。中期旋回对应段级别,短期旋回相当于一个砂组或小层(含多个单砂层),超短期旋回大体对应于单层;②研究区目的层为一套咸化湖泊-三角洲沉积体系,岩性复杂,在各种沉积作用共同影响下,形成由细粒碎屑岩、碳酸盐岩、泥岩构成的混积细粒岩层。识别了储集层沉积微相类型,主要包括砂坝、前三角洲泥、砂滩、混合滩、云坪及湖相泥微相等;③吉木萨尔凹陷芦草沟组甜点段主要分布在P2l22上段及P2l12上段。综合分析提出吉木萨尔凹陷芦草沟组陆源碎屑-碳酸盐岩混合细粒岩沉积模式。基准面上升时,沉积环境由三角洲外前缘砂坝和浅湖砂滩沉积向浅湖-半深湖混合滩和云坪沉积转变,随着基准面继续上升至最大可容纳空间,深水环境黑灰色泥岩大面积沉积;基准面下降时,主要发育浅湖-半深湖混合滩和云坪沉积,随着基准面继续下降,发育浅湖亚相砂滩沉积和三角洲前缘砂坝沉积。

Study on sedimentary microfacies of mixed fine-grained rocks in Lucaogou Formation,Jimsar Sag,Junggar Basin

The composition of the Permian Lucaogou Formation in Jimsar Sag,Junggar Basin is a key block for shale oil and gas exploration. It is of great significance to carry out the study of fine mixed rock sedimentary sequences and related research. Using core,thin section,scanning electron microscope,well logging curve,XRF,XRD and other data,combined with core phase and its combination analysis,log curve least squares fitting and lithology random simulation,etc.,the sequence stratigraphic framework and sedimentary microfacies identification established a microfacies model of mixed fine-grained sediments in the study area.(1)Lucaogou Formation can be divided into 5 medium-term cycles,9 short-term cycles and 33 ultra-short-term cycles. The medium-term cycle corresponds to the segment level,and the short-term cycle is equivalent to one sand group or small layer(including multiple single sand layers),and the ultra-short-term cycle generally corresponds to a single layer.(2)The target layer of the study area is a salt lake-delta sedimentary system with complex and variable lithology. Under the joint influence of mechanical,chemical,biological and other sedimentary effects,a mixed fine-grained rock formation composed of fine-grained clastic rocks,mudstones and carbonate rocks is formed. The sedimentary microfacies types of the reservoir mainly include sand dam,prodelta mud,sand bank,mixed bank,dolomitic flat and lacustrine mud.(3)The dessert section of Lucaogou Formation in Jimsar Sag is mainly distributed in the Upper p2122 and p2112.The sedimentary model of terrigenous clastic-carbonate mixed fine-grained rocks in Lucaogou Formation is put forward. When the datum surface rises,the sedimentary environment changes from the delta outer leading sand dam and the shallow lake sand bank sediment to the shallow lake-semi-deep lake mixed bank and dolomitic flat sediment,and a large area of black gray mudstone is deposited as the datum surface continues to rise to the maximum accommodating space;When the datum is declining,the shallow lake-semi-deep lake mixed bank and dolomitic flat sediment are mainly developed. As the datum continues to decline,shallow lake subfacies sand bank and delta front sand dam deposits are developed.