Diagenesis and reservoir property variations of tight sandstone with burial depths ranging from shallow to ultra-deep in the Kuqa Depression, Tarim Basin, China

Abstract

The Lower Cretaceous Bashijiqike Formation, which is an important gas exploration target in the Kuqa Depression, Tarim Basin, China, is an excellent case illustrating the diagenesis and reservoir property variations of tight sandstone with burial depths ranging from 3500 m to 8000 m. Thus, integrated approaches incorporating thin-section petrographic characterization, mineral morphology and identification, X-ray diffraction analysis, reservoir property tests, and fluid inclusion analysis were applied to investigate the diagenesis and reservoir property variations of Bashijiqike sandstone with different burial depths. The main findings of this study were as follows. (1) Diagenesis of the Bashijiqike sandstone with a burial depth of less than 5000 m was mainly characterized by kaolinite, colloidal quartz, euhedral quartz, and the dissolution of feldspar, whereas diagenesis of the sandstone with a burial depth of more than 5000 m was primarily distinguished by albite, dolomite, calcite, illite, and chlorite. (2) The porosity and permeability rapidly decreased as the burial depth increased within the range of less than 5000 m, while they slowly decreased as the burial depth increased within the range of more than 5000 m, indicating that the reservoir properties have a nonlinear correlation with the burial depths ranging from 3500 m to 8000 m. (3) During the late stage of the Himalayan movement, the enhanced compaction of Bashijiqike sandstone with the increased burial depth resulted in a decrease in the number of intergranular pores, whereas the dissolution of feldspar and quartz led to the formation of secondary pores. Taken together, the findings of this study indicate that the Himalayan movement after the Neogene resulted in burial depth variations with regard to the studied sandstone, which represents the key controlling factor for both its diagenesis and its reservoir properties.