The main gas-bearing horizons in Daniudi gas field of Ordos basin is the Upper Carboniferous Taiyuan

Lower Permian Shanxim and Xiashihezi Formations.Stratigraphic division and correlation are difficult because of rapid change of fluvial facies

sparse well pattern

and large project area in the field.Single stratigraphic division and correlation method failed to work effectively.At the very beginning of the study

there were several schemes as for how to solve the problems.As a result

a composite method of stratigraphic classification and correlation suitable for complicated sedimentary environment are developed by integrating the marker bed method(introducing coal seams as markers and supplementary horizon markers)

the isopach method(the same layer having similar thickness) in adjacent wells

the sequence stratigraphy method

and the dense well pattern analysis method(i.e.

applying knowledge obtained from analysis of dense well pattern to sparse well pattern).By doing that

this paper presents a new scheme of stratigraphic division and correlation

which have been used successfully in real practice and achieved a unified understanding of the formations in the study area.