Identification of lithology and lithofacies type and its application to Chang 7 tight oil in Heshui area, Ordos Basin

The characteristics of lithology and lithofacies in Chang 7 tight oil in Heshui area, Ordos Basin, were studied by such means as core observation, traditional thin section analysis, conventional logging and imaging logging processing, combined with general physical analysis. Chang 7 tight oil reservoir is mainly sandstone caused jointly by sandy debris flow, turbidity current and slump, and source rocks are mainly mudstone and oil shale. According to grain size parameters, Chang 7 tight oil is further divided into six kinds of lithology and lithofacies, i.e., fine sandstone of sandy debris flow, fine sandstone of turbidity current, siltstone of turbidity current, fluxoturbidite, mudstone of semi-deep water or deep water and oil shale. According to conventional logging and imaging logging scaled by core data, the authors established the evaluation criteria of well logging identification in different kinds of lithology and lithofacies, realized the identification and classification of lithology and lithofacies in a single well on the longitude, and further explored the relationship between different kinds of lithology and lithofacies and TOC content as well as brittleness index. Finally oil-gas testing data and oil-gas interpretation results were combined to illuminate the quantitative control of lithology and lithofacies on physical property and oil-gas possibility of tight oil reservoir. The study of lithology and lithofacies of tight oil can lay the foundation for the further analysis of lithogenous phase and pore structure as well as the prediction of high quality reservoir. It can also provide theoretical guidance and technical support for the comprehensive assessment of Chang 7 tight oil and the prediction of favorable zones for oil-gas reservoir development.