The Research On Sedimentary Microfacies Of The Lower Member Of Yanan Formation In The Southern Of Ansai, Ordos Basin

Ordos basin as the second largest basin in our country, rich in oil and gas resources.This paper combines the general geology,basic data such as core data,logging data,according to the lower member of Yanan Formation Yan10、Yan9、Yan8,research on stratigraphic division and correlation、sedimentary facies type、the sedimentary facies distribution and the sandstone spread,and based on the study of sedimentary microfacies,combined with physical data and oil production test data,predict the favourable region.This paper researched stratigraphic division and correlation of three reservoir group,Yan 10、Yan 9、Yan 8,and detailed description the formation thickness、lithological and electrical characters of this reservoir group based on method of the key bed、the method of formation thickness and sedimentary cycle method,analyzed the change of purpose layer in the transverse direction through connecting-well section.Through integrated analysis of petrologic characteristics、core description、logging data,the author holds that Yan 10 oil-bearing belongs to braided river subfacies, channel sandbars sedimentary micro-facies widely distributed and floodplain sedimentary micro-facies distributed in southern area;Yan 9、Yan 8 oil-bearing belongs to delta front subfacies,including underwater distributary channel、underwater river-bay、frontal sheet sand and mouth bar sedimentary micro-facies. Yan 10 oil-bearing develops EW trending sand body effected by Gan-Shaan paleochannel,the sand bodies of Yan 9、Yan 8 oil-bearing are too thin, developing three NE-SW subaqueous distributary channel sand.Yan 10、Yan 9、Yan 8 oil-bearing of the study area all develop nose-like structure,and its location、scale having some inheritance,mainly distribution in nearby G17-Q6010 well and G22-Q52 well. The lower member of Yanan Formation of this study area is structural-lithologic reservoir,and its main controlling factors is sedimentary micro-facies and nose-like structure.By analysis that our study area has two pool-forming pattern, slope area fluvial facies and delta front pool-forming pattern.Based on the unfold character sandstones,characteristics of pore permeability,reservoir distribution and characteristics of top structural,we preduct the favorable area of Yan 10、Yan 9、Yan 8 oil-bearing,and select eight favorable area,which provides the basis for exploration and development in the future.