A Study on Sedimentary Microfacies of Benxi Formation and Its Controlling Effect on Gas Enrichment in Yanchang District of Ordos Basin

This paper studies sedimentary microfacies and sand body distribution of Benxi Formation in Yanchang District of Ordos Basin on the basis of field materials, core data, logging curves and former proofs. Holding Results have shown that the sedimentary microfacies mainly evolves from barrier coast despositionaldepositional system and shelf despositionaldepositional system, it and can be classifiesd into seven types, including them into sand flat, mixed flat, muddy flat, mud-ashy flat, barrier sand dam, lagoonal mud and muddy shelf, among which barrier sand dam and sand flat are the framework sand body for gas reservoir, whose occurrence is totally controlled by the distribution of sedimentary facies belt. The major gas-producing reservoir of Benxi Formation which is Jinci sandstone is originated from barrier sand dam and tidal sand flat, with the main sand dam distributing in NNE-SSW direction. Small sand dams are distributed sporadically while sand flat extends in NNW-SSE direction. In conclusion, the development districts of both barrier sand dam and sand flat are favorable target areas for gas exploration in Benxi Formation.