The 8

th

Member of the Shihezi Formation and the 1

st

Member of the Shanxi Formation of the Upper Paleozoic in Sulige gasfield are mainly of fluvial facies

and the crosscutting and superimposition of multiple-stage channels resulted in a large "braided river system" in geologic history.According to different sedimentary environments and sedimentation characteristics

the braided river system can be divided into superimposed zone

transitional zone and inter-channel zone.This study deepens and develops the concept and deposit connotation of the braided river system

establishes a sedimentary hierarchy of sedimentary facies-braided river system-braided river system zone

and proposes multiple-parameter quantitative classification standards for Sulige's braided river system.Through integrated analysis of core

logging and drilling data

it is concluded that braided river system zone is the key geological factor for sedimentation and reservoir characteristics of Sulige gasfield

as it strongly controls the sedimentary microfacies distribution and scale

sand bodies' superimposition style and effective sand bodies' type and centralization.The superimposed zones of the braided river system feature in highly develo-ped and large channel bars

superimposition of multiple stage sand bodies and clustering of effective sand bodies

thus is the favorable facies zone for gas production.In transitional zone

channel filling is more developed and effective sand bodies are mainly distributed in isolation in space.In contrast

the inter-channel zone is characterized by scattered and sparse sand bodies

thus its exploitation potential is poor.In addition

the criteria of geological target selection for horizontal wells are set up for the superimposed zone and transitional zone of braided river system respectively

and horizontal well trajectory is optimized

providing a more reliable basis for geo-steering while drilling of horizontal wells.