Characteristics and controlling factors of deep to ultra-deep tight-gas clastic reservoirs in the Junggar Basin

To explore favorable deep to ultra-deep tight-gas clastic reservoirs in the Junggar Basin, we investigate the developmental characteristics, storage space types, changes in physical properties, and controlling factors of these reservoirs using data from drilling, logging, thin-section observation, and assays. Key findings are as follows: (1) Favorable deep to ultra-deep tight-gas clastic reservoir rocks in the basin are mainly of deltaic conglomerates and sandstones, which are dominated by fine-, medium-, and medium-to fine-grained conglomerates/sandstones and can be classified as lithic sandstones. Of these, gravels and sandstone detritus consist primarily of tuffs, and the cements are dominated by calcite, with locally enriched zeolite. (2) The storage spaces consist of pores and fractures, dominated by pores. Accordingly, the storage spaces can be categorized into three types: pore, fracture, and mixed pore-fracture types. The pores are mainly primary residual and secondary dissolution pores, with the latter being predominant, while the fractures are composed mainly of diagenetic compaction-induced micro-fractures and tectonic fractures, (3) forming three secondary pore zones vertically. (4) Major factors governing the favorable reservoirs include rock composition, constructive diagenesis, and anomalously high pressure, which jointly control the development and distribution of favorable deep to ultra-deep tight-gas clastic reservoirs in the Junggar Basin.