Abstract:

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.

Key words: marker bed, isopach method, sequence, stratigraphic division and correlation, coal seam, Daniudi gas field, Ordos Basin