Study On Sedimentary Facies Of Taiyuan Formation In Daniudi Gas Field

We analyzed the individual well microfacies by applying modern sedimentological methods and observation of drilling cores. On the basis of geological, logging and drilling materials, we enlarged the profiles to cover the whole area by correlation of well tie. Not only did we study the sedimentary microfacies types, sedimentary characteristics and sedimentary enviornment of reservoir of Taiyuan formation in Daniudi Gas Field, but we also studied the distributional pattern of sedimentary systems and sand bodies. By studying the regional tectonic evolution of basin, the sedimentary model of this basin was established. The sedimentary origin and controlling factor of the key research area were studied, and the master controlling factor of reservoir was clear, too. After researching the lithofacies paleogeology of this area, sedimentary evolutional history and the main controlling factor of gas accumulation, we could provide scientific theordial criteria of next exploration strategy and forecast beneficial reservoir sand bodies and interested zone.According to the observation and careful description of drilling cores of 10 wells of Taiyuan formation in Daniudi Gas Field, we recognized 10 types of bedding and 16 types of lithofacies. By drilling core characteristics, the observation of thin slices of 7 wells under microscope and the logging materials, we recognized 3 types of sedimentary facies, 6 types of sedimentary subfacies and 13 types of sedimentary microfacies. We held the viewpoint that Tai 1 member developed barrier island-tidal flat sedimentary system, and Tai 2 member developed braided-delta front sedimentary system, which challenged the conception that Taiyuan formation developed barrier island-tidal flat sedimentary system only.On the basis of the research before, we made 9 synthetic figures of individual well sedimentary facies, 8 well ties including 4 horizontal profiles and 4 vertical profiles, 2 sedimentary facies ichnographs. We analyzed the sedimentary facies of Taiyuan formation vertically and horizontally and held the viewpoint that the main controlling factor of sedimentary facies of Taiyuan formation is the terrigenous supply. The trend of barrier island of Tai 1 member is northeast-southwest direction. Tidal flat and lagoon deposits develop landwards. The trend of underwater distributary channel of Tai 2 member is northeast-southwest direction. The main channel goes through the work area, mouth bar and sand sheet develop at the end of the channel.According to the statistics of physical property distribution of 261 drilling core samples and the observation of 23 thin slices, we conclude that the reservoir of Taiyuan formation in the work area is low-porosity and low-permeability. The physical properties of sand bodies of microfacies differ a lot. The good reservoirs are mouth bar, tidal channel and underwater distributary channel. The main factor deciding whether the reservoir is effective is the depth of sand bodies. The depth of sand bodies of underwater distributary channel, tidal channel and barrier bar are relatively thick, the depth of sand bodies of mouth bar are less thick, the depths of sand bodies of sand sheet and sand flat are thin.According to the statistics of physical properties of every major microfacies, distribution of sandstone depth, sedimentary microfacies ichnographs, and the statistics of the gas testing wells of Tai 1 and Tai 2 member, we conclude that the beneficial zones of Tai 1 member are located at these places where tidal channels and barrier bars distribute, while the beneficial zones of Tai 2 member are located at these places where underwater distributary channels distribute.