Study On Sequence Stratigraphy And Depositional Systems Of Shahejie Formation In Xiaolongwan-Jiangzhangsi Area Of Eastern Depression

This paper established the sequence boundaries of Shahejie Formation in Xiaolongwan-Jiangzhangsi region of eastern depression,Liaohe Basin with the synthetic analysis of seismic,geology,drilling and logging data using the theory of classic sequence stratigraphy and high-resolution sequence stratigraphy.Through the VSP synthetic records combining with structural evolution feature of the eastern depression,the sequence stratigraphy framework of Shahejie Formation is established in Xiaolongwan-Jiangzhangsi region.Based on single well facies analysis and sedimentary facies analysis,the sedimentary evolution characteristics is studied and then favorable clastic rock reservoir is predicted.Combined with the oil and gas accumulation conditions and main controlling factors analysis,the favorable exploration area is determined in the study area.In this paper,five third-order sequence boundaries(SB)of Shahejie Formation are identified including two regional unconformity surfaces and three deposition transformation surfaces,and maximum flooding surfaces(MFS)are identified in the middle-shallow layer.Then four third-order sequences are divided in target stratum.Framework in study area is established on the basis of well-seismic regional profiles been correlated.Through logging facies and seismic facies analysis,six types of sedimentary facies of Shahejie formation in the work area is determined,namely fan delta,braided delta,nearshore subaqueous fan,river,alluvial plains,alluvial fan and lacustrine.Vertically,the depositional evolution from single source to multiple origins;Short axis source is rich and fan sand bodies develops well.Long axis of the river alluvial plain also develops during the deposition of the upper interval of the third member of Shahejie Formation.The sedimentary body in Steep slope zone was characterized by the inheritance,mainly fan-delta.Overall,the sediment system has the character such as multi-provenances and multi-types of reservoir.Reservoir is predicted using post-stack impedence inversion technique under the control of sequence framework and sedimentary system.Clastic rock reservoir is get after filting out the volcanic reservoir.The logging curve intersection chart analysis shows VSH curve is most sensible to lithology.Using acoustic curve and VSH curve to compose a pseudo-acoustic curve to do the wave impedance inversion,the results show that sandstone reservoir developed mostly in the upper third-member of Shahejie Formation and the first-member and second-member of Shahejie Formation.Sandstone reservoir developed poor in the low and middle of third-member of Shahejie Formation.Reservoir mainly locates in central northwest and southeast area of the first-member and second-member of Shahejie Formation and maily locates in central area of the upper third-member of Shahejie Formation.The reservoir distribution is mainly affected by the distribution of sedimentary facies.Finally,the configuration of generating rock,reservoir and cap in the study area and the hydrocarbon accumulation conditions were analyzed.The main controlling factors of hydrocarbon accumulation is identified.Then this paper makes prediction of the favorable zones for subtle reservoir exploration in the area.It points out that braided delta front and nearshore subaqueous fan are favorable sand body types for lithologic trap exploration,and Jiazhangsi depression and Jiadong fault zone are favorable exploration area for tectonic lithologic trap and lithologic trap.