柴北缘团鱼山地区石门沟组含煤段三角洲沉积特征

柴北缘团鱼山地区中侏罗统石门沟组含煤段砂体分布广、厚度大,有可能成为良好的油气储层。通过岩心观察、粒度及测井曲线分析,并利用频率曲线、概率累计曲线、C-M图分析、散点图分析等对各微相沉积粒度特征及水动力环境进行精细研究。结果表明:石门沟组主要为三角洲相沉积,进一步可划分为三角洲平原、三角洲前缘、前三角洲3种亚相和水上分流河道、水上分流河道间、水下分流河道、水下分流河道间、河口坝及席状砂6种沉积微相; C-M图表现为典型的牵引流沉积特征,席状砂、分流河道间、河口坝主要集中在QR段,搬运方式以递变悬浮为主,水下分流河道集中于QPPO段,以跳跃搬运方式为主,三角洲平原水上分流河道集中于PO-ON段,滚动组分较多,以跳跃搬运方式为主;砂岩总体向上变粗,呈逆粒序特征;席状砂、河口坝、水下分流河道微相概率累计曲线均为2段式,以跳跃组分为主,三者曲线斜率依次变小,沉积颗粒分选变差,水动力增强;水上分流河道微相水动力最强,概率累计曲线为3段式,以跳跃组分为主,存在滚动组分,曲线斜率最小,分选最差。

Sedimentary characteristics of Shimengou-Formation coal-bearing-interval delta in Tuanyushan area in the northern margin of Qaidam Basin

The sandbodies in Middle-Jurassic Shimengou-Formation coal-bearing interval in Yushan area in the northern margin of Qaidam Basin are characterized by the wide distribution and a large thickness, which may become a good oil and gas reservoir. Through the core observation, the particle size and log curve analyses and moreover with the help of the frequency curve, probability accumulation curve, C-M map analysis, scatter plot analysis, etc., the granularity characteristics and hydrodynamic environments of each microfacies were studied in detail. The study achievements show that Shimengou-Formation is mainly the delta facies deposit, which can be further divided into three sub-phases: delta plain, delta front and front delta and moreover the six sedimentary microfacies: water distributary channel, water distributary interchannel, underwater distributary channel, underwater distributary interchannel, river mouth bar and sheet sand. C-M shows the typical traction-flow sedimentary features;the sheet sand, the distributary channel and the mouth bar are mainly concentrated in QR Interval, the graded suspension is the main transporting mode;the underwater distributary channel is concentrated in QP-PO Interval with the jumping transportation as the main form, the delta-plain water distributary channel is concentrated in PO-ON Interval, the rolling component is much more, but the jumping transportation is still the main form;in general, the sandstone becomes coarser upward and presents the reverse grain order;the micro-phase probability cumulative curves of the sheet sand, mouth bar and underwater distributary channel are all two-staged with the jumping component as the main form, and the slopes of the three curves become smaller, the sorting of the sedimentary particle is deteriorated and the hydrodynamic force is enhanced;the hydrodynamics of the water distributary channel micro-facies is the strongest, the probability cumulative curve can be divided into 3 segments, which is mainly composed of the jumping component, there are rolling components, the slope of the curve is the least, the sorting is the worst.