Sedimentary Characteristics and Source-sink Process of Fan Delta in Nantun Formation of Beixi Area in Baer Depression

Abstract

Fan delta is a very important oil and gas gathering place of continental faulted basin, to establish an accurate and reliable fan delta depositional model is of great value to predict dominant reservoir group. With the comprehensive application of core, earthquake and logging data, the typical fan delta depositional system developed in the Baer sag of the Nantun formation has been clearly defined by the fine depiction of the internal sedimentary units and phase marks of the fan. It can be subdivided into 3 subphases and 11 types of microfacies. The fan delta plain subfacies developed 3 kinds of microfacies, namely plain distributary channel microfacies, plain distributary channel microfacies, plain natural dyke microfacies. There are 6 types of microfacies developed in the fan delta front subfacies, namely, the main channel microfacies of the leading edge of the front, the microfacies of the subaqueous distributary channel in the front edge, the front edge mat microfacies, the sandstone microfacies of the estuarine dam, the sandstone microfacies of the far sand bar and the inter subaqueous microfacies of the leading edge. There are 2 kinds of microfacies in the delta facies, namely, the front delta siltstone microfacies and the front delta mudstone microfacies. The fan delta deposits in the Nantun formation of the Baer sag are mainly developed in the Beixi slope zone, the Huoduomoer tectonic belt, the Suderte tectonic belt, and so on, which are close to the steep slope of the basin margin or the control fault. According to the different characteristics, two sedimentary models of steep slope and steep slope are established.