Geological Study On Low Permeability Reservoir In Triassic Yanchang 8th Formation In The North Of Zhenjing Area

As the world 's oil and gas exploration and development situation of increasingly serious,the status of the low permeability reservoir is more and more important.But the permeability reservoir has its special geological characteristics,as poor physical property,sediment low maturity,small pore throat radius,low matrix permeability,large difference of diagenetic,strong stress sensitivity,crack development and strong heterogeneity,etc,make its development rule is different from conventional reservoir and hard to predict.Therefore,make detailed description of the low permeability reservoir geological characteristics is important to find out its oil and gas accumulation regulation.The Yanchang 8th formation in the north of Zhenjing area in Ordos basin is an typical low and very low permeability reservoir.Its formation is flat and structure is simple.Although it has more than 10 years exploration,its sand body distribution characteristics and residual oil enrichment regulation is still unclear.This paper take the chang 81 reservoir as example,according to the geological date,combined using the method of development geology and reservoir engineering,started from the stratigraphic division and correlation,studied its geology characteristics as sedimentary microfacies,micro characteristic and heterogeneity.Combined with the dynamic production data,this paper analyzed its remaining oil distribution and controlling factors from aspects of geological and development.The results showed that,the reservoir of chang 81 could be identified microfacies types as underwater distributary channel,tributary bay,branching mouth bars and distal bar.The reservoir experienced complicated and strong diagenesis after deposited which made its low porosity and permeability,and made its pore structure complexed,its pore throat small,and secondary porosity developed.It has strong heterogeneity within the layer and on the plane,but weak heterogeneity between layers.The residual oil distribution mainly controlled by sedimentary microfacies,and partly controlled by reservoir heterogeneity factors such as physical differences,micro structure and interlayer,which made the remaining oil enriched in the main microfacies and complicated in local.