The Favorable Reservoir Distribution Of Chang 8 Formation In Fuxian Exploratory Area,Ordos Basin

The Ordos Basin has an abundant supply of coal,oil and gas resources,which is an important energy base in China.Fuxian exploratory area of Yanchang oilfield is located in the southeast of Ordos Yishan slope of the basin,insufficient in exploration,is still in the zone evaluation and trap exploration stage.After decades of exploration and development,it is generally considered that the Mesozoic Triassic Yanchang formation is the most important reservoir basin,and Chang 8 reservoir of Yanchang formation is the main oil-bearing formation in Fuxian exploratory area.This paper,depending on the applying of cores,well logging and mud logging data,realizes the fine stratigraphic division covering the Chang 8 oil reservoir setin Fuxian exploration area.combined with the regional geological background,the sedimentary microfacies in the study area is determined,and its development characteristics is studied.By making full use of various analytical and testing methods,the reservoir is depicted in terms of the petrology,physical characteristics,pore structure characteristics and diagenetic characteristics.considering the sedimentary facies and reservoir characteristics helps further delineation of favorable reservoir area.Based on sedimentary cycles,the Chang 8 reservoir of Yanchang Formation is divided into 2 small layers.Based on the principle of thickness stratigraphy and the use of marker beds,the stratigraphic correlation is refined to reveal the characteristics of the top surface of Chang 8 reservoir.The geotecture of the study area is basically consistent with the regional geological background thatit is agentle monocline which has been inclined to the west by north,with several nose like uplift structures.The sedimentary facies in the study area are mainly delta front subfacies deposits,with underwater distributary channels,underwater distributary Bay,estuary sand bar,underwater natural dyke and other sedimentary microfacies well developed,and turbidite is also found.There are 4 main channels wandering from NorthEast to South West,and the development of sand body is controlled by the characteristics of the sedimentary microfacies distribution,which is generally consistent with the distribution of the channel distribution.Fuxian exploratory area,the rock type of Chang 8 reservoir is mainly feldspathic lithic sandstone and lithic feldspar sandstone.reservoir space is mainly composed of the original intergranular pores,secondly dissolution pores and occasionally micro cracks.The diagenesis of clastic rock has included compaction,cementation and dissolution.There are three main types of the pore-throat combination,respectively medium pore with narrow throat,small pore with narrow throat and tiny pore with micro-narrow throat.Referring to the previous reservoir evaluation criteria,combined with the actual situation,the Chang 8 reservoir group is divided into 3 types: class?,class ? and class ? reservoir,of which the reservoir is the main reservoir.With the help of the research results of sedimentary characteristics and reservoir discription,the favorable reservoir range is delineated abiding by the reservoir evaluation criteria.The favorable reservoirs are mainly distributed in the fine and thick underwater distributary channel sand bodies,estuarine sand bodies and some turbidite sand bodies.