Detailed description of the sedimentary reservoir of a braided delta based on well logs

The sedimentary reservoir of Lower Cretaceous Bashijiqike Formation in Kuqa depression was studied by making full use of core observation as well as conventional and image logs. The results show that the Bashijiqike Formation was formed in the sedimentary facies zone of braided delta front subfacies, of which the underwater distributary channel and mouth bar depositional microfacies constitute the main framework of sandbodies. A suite of recognition models for typical lithologies and sedimentary structures were built by core-log calibration methods. Then the well logging recognition and division standards were built, and the control of depositional microfacies on reservoir quality was discussed. The depositional microfacies were further divided into lithologies and lithofacies such as medium-grained sandstones of underwater distributary channel and fine-grained sandstones of underwater distributary channel based on the medium grain size and compositional maturity index. In addition, the logging evaluation methods of medium grain size and compositional maturity index were built. At last, the vertical distribution law of lithologies and lithofacies in single wells were figured out by making full use of image logs, shapes of conventional logs and core observations as well as the logging calculation of medium grain size and compositional maturity index. The research results lay a solid foundation for detailed description of sedimentary reservoir as well as the natural gas exploration and development in the future.