The major gas pay zone lies in the 8th member of the Upper Paleozoic Lower Shihezi Formation(He 8 member)

eastern part of Sulige region

Ordos basin.Its reservoir architecture acts as a predominant geological factor for oil/gas distribution.Targeting at Tianshengqiao outcrop in Fugu county in eastern Ordos Basin

similar to eastern Sulige region in provenance and sedimentary setting

we finely studied the architecture of the outcropped sand body

which can offer critical information for the establishment of geological model of eastern Sulige region.Based on the outcrop survey

pe-trographic investigation

architecture analysis and fine measurement of sand body volume

combined with the sedimentary and petrologic analyses

we recognized twelve types of lithofacies in the braided river deposits of He 8 member.Six levels of architecture interfaces were classified within the reservoirs

namely composite channel-belt

single channel-belt

single sand body

silty layer accompanied with accretion

bed set

single bed and laminae.Six reservoir architecture units are indentified

that is

channel filling(CH)

longitudinal bar(LB)

diagonal bar(DB)

transverse bar(TB)

abandoned channel(ACH) and overflow deposits(OF).Among these

sand bar is a dominant reservoir architecture unit.The thickness of longitudinal bar ranges between 2.5m and 5.8m with the width/thickness ratio varying from 27.6 to 37.7; the thickness of diagonal bar ranges between 2.2m and 6m with a width/thickness ratio varying from 38.4 to 42.1; while the thickness of transverse bar ranges between 1.5m and 3.6m with a width/thickness ratio varying from 47.0 to 61.8.Based on the analyses of different architecture units

we summed up the spatial superimposition patterns of the reservoir

established the 3D architecture model of braided river composite sand body in the He 8 member of Tianshengqiao outcrop in Fugu county

both of which will provide geological evidences in the fine description of He 8 member in eastern Sulige region.