The Gas-bearing System And Sedimentary Control From Benxi To Shanxi Formation In Middle Part Of Hedong Coalfield

The sedimentary environment,sequence stratigraphic framework,gas-bearing system and sedimentary control of the strata from the Benxi to Shanxi formation are studied in the northeastern margin of Ordos Basin based on the theories and methods of sedimentary petrology,sequence stratigraphy,petroleum geology,logging geology,and organic geochemistry,etc,according to the data of sixty logging-while-drilling,cores,gas logging and analysis.Three types of sedimentary facies including carbonate tidal flat,barrier bar lagoon and shallow water delta,five subfacies and eight microfacies are recognized from Benxi to Shanxi formation in the study area and their characteristics are summarized as well.By identifying sequence boundary and sequence stratigraphic correlation,Benxi to Shanxi formation in the study area are divided into twelve third-order sequences,and the sequence stratigraphic framework is established.Besides,the paleogeography evolution is searched for in the sequence stratigraphic framework.The regularity of the development of mudstone containing siderite is found out.In the coal bearing rock series,4 layers of stable water-gas barrier are identified,which mainly developed near the maximum sea surface.Applying the water barrier layer as the restriction,Benxi to Shanxi formation can be divided into four first-degree gas systems and several second-degree gas systems combined with the vertical variation of gas content.The sedimentary control of gas-bearing system is discussed and the controlling effects generated by sequence stratigraphic framework and sedimentary environment on the development regularity of coal source rocks,gas content characteristics,reservoir distribution law,physical properties change of coal measures sandstone,development law of water-gas barrier are clarified.