Sandy braided river deposits have excellent physical properties

thus are important oil/gas reservoirs.In order to demonstrate the lithofacies and architectural characteristics of the sandy braided river reservoirs

and quantify the geometric properties and physical properties of architectural units

a systematic study for outcrops of sandy braided river deposits in the Middle Jurassic Yungang Formation in the Datong Basin has been conducted on the basis of outcrop observation

detailed interpretation of architectures

and laboratory analysis.Seven types of lithofacies in five associations have been identified.Five typical architectural units were identified in the sandy braided river deposits

including channel (CH)

channel bar (CB)

point bar (PB)

abandoned channel (ACH)

and overflowing sediments (OF).Among these architectural units

the channel and channel bar are the main architectural units with accumulative distribution frequency up to 78%.The thickness of channels ranges from 2.5 m to 6.5 m

width/thickness ratio is about 25-30

and the average porosity is 7.1%.The thickness of channel bars ranges from 2.5 m to 7.0 m

width/thickness ratio is about 30-35

and the average porosity is 7.8%.During the same depositional period

four basic combination types of the architectural units developed in the sandy braided river

namely CH-OF

CH/ACH-PB

CH-CB-CH

and CH/ACH-PB-OF.The spatial distribution of the architectural units in the different depositional periods is characterized by superposition or repetition of these four basic combination types in vertical and lateral.Channel and channel bar are the major reservoir types in the sandy braided river deposits

but the scale and physical properties of the later are better than the former.