Distributary channel type and high-quality reservoirs in tight sandstone—A case study on the outcrops and reservoirs of Xujiahe formation in Western Sichuan Basin

Abstract

The distributary channels in shallow-water delta are well-developed in tight sandstone. There are few studies on the channel type and diagenetic differences among them. To illustrate the relationship between channel types and high-quality reservoirs, this study summarizes the lithofacies types and sequences in the second member of the Xujiahe Formation. We use core data, outcrops, and modern sediments observation, scanning energy spectrum, and rock thin sections. The lithofacies can be divided into 15 types, and there are four types of vertical lithofacies sequence. Lithofacies sequences are different in lithofacies, channel scale, reservoir porosity and permeability, and so forth. They are formed in various hydrodynamic environments. With the continuous bifurcation of the channels, the width and depth of the channels are decreasing, forming different lithofacies sequences. Four types of distributary channels are classified. The characteristics of these channels are described, and the sedimentary models are established. Distributary channel types are related to the diagenetic process. Channel type I and the bottom of type II develop moderate compaction–dissolution diagenetic facies, the middle and upper parts of type II and type III can develop strong compaction, moderate compaction–dissolution, or strong cementation diagenetic facies, and type IV can develop strong compaction diagenetic facies. High-quality reservoirs are developed in limitedly distributed in distributary channels of type I and type II, and part of type III. This study provides a useful view for evaluating high-quality reservoirs based on distributary channel types.