草湖凹陷东部T—J层序地层与沉积体系

TRIASSIC-JURASSIC SEQUENCE STRATIGRAPHY AND SEDIMENTARY SYSTEM IN EASTERN CAOHU SAG

根据地层基准面旋回原理,通过对地质、钻井、测井及地震等资料的综合分析,将草湖凹陷东部地区的三叠系—侏罗系地层划分为5个长期地层旋回(相当于Ⅲ级层序),从下向上依次为:T-LSC1,T-LSC2,T-LSC3,J-LSC1和J-LSC2,均为陆源碎屑层序。在层序划分和建立层序地层对比格架的基础上,识别出了4种类型的沉积体系:半深湖—深湖沉积体系、滨浅湖—三角洲沉积体系、滨浅湖—扇三角洲沉积体系和泛滥平原沉积体系,并分析了各旋回沉积体系的构成。综合分析生、储、盖条件后提出,T-LSC3旋回下部和T-LSC2旋回是本区最有利的储集层段;就相带而言,三角洲和扇三角洲砂体是较为有利的储集层段。

According to the principles of stratigraphic datum cycle, five long-term stratigraphic cycles (corresponding to sequences of Grade Ⅲ) are recognized in Triassic-Jurassic strata in eastern Caohu sag through comprehensive analyses of the geologic, drilling, logging and seismic data. They are, from bottom to top, T-LSC1,T-LSC2,T-LSC3,J-LSC1 and J-LSC2 respectively, all of which are terrigenous clastics sequences. Based on sequence division and stratigraphic correlation, 4 sedimentary systems are recognized, including semi-deep-deep lake, shore-shallow lake-delta, shore-shallow lake-fan delta and flood plain. The components of sedimentary systems in each cycle are analyzed. On the basis of comprehensive analyses of source, reservoir and cap rocks conditions, it is believed that vertically the T-LSC2 and lower T-LSC3 cycles are the most favorable reservoirs in the study area, while sandbodies of delta and fan delta facies are relatively favorable reservoirs in respect of facies belt.