Diagenesis and its controlling factors of Lower Donghetang Formation tight sandstone reservoir in Bachu area, Tarim Basin, China.

The tight sandstone reservoir of the Donghetang Formation underwent complex diagenetic processes for which the controlling factors remain unknown. Here, we present a case study of the lower member of this formation and show that this part of the reservoir consists mostly of lithic quartz sandstone with poor physical characteristics. Using core observation, thin section identification, electronic microprobe, scanning electronic microscopy, X-ray diffraction, and inclusion fluorescence microscopy, we identified five major diagenetic processes: compaction, cementation, dissolution, metasomatism, and hydrocarbon charging. Compaction and cementation have negative effects on petrophysical properties (referred to porosity and permeability of sandstone in this paper), and dissolution improves these properties. Diagenesis is affected by the depositional environment, and clastic constituents control compaction and dissolution; burial history and the geotemperature field control diagenesis at the macroscopic scale, while hydrocarbon charging affects the degree of cementation and dissolution. As oil saturation increases, the percentage of calcareous cements decreases and the development of secondary dissolved pores improves. [ABSTRACT FROM AUTHOR]