Analysis of factors affecting the reservoir quality of deepwater gravity flow tight sandstone: a case study of the Chang 6 oil reservoir of the Yanchang Formation in the Huaqing area, China

• Published in: Arabian journal of geosciences 2022-02, Vol.15 (3), Article 229
• Main Authors: Chen, Zhaobing, Fu, Ling, Zhou, Chuangfei, Gao, Jianrong, Liu, Xinshe, Chen, Xinjing, Zhu, Yushuang, Chen, Yuhang
• Format: Article
• Language: English
• Subjects: Analysis; Complexity; Deep water; Diagenesis; Earth and Environmental Science; Earth science; Earth Sciences; Grain size; Gravity; Gravity flow; Mica; Natural gas exploration; Oil; Oil and gas exploration; Oil exploration; Oil reservoirs; Original Paper; Permeability; Porosity; Reservoirs; Sandstone; Sedimentary rocks; Throats
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-021-09321-3

Unconventional tight sandstone reservoirs resulting from deepwater gravity flows have attracted much attention from the oil and gas exploration community. In this paper, we conducted a systematic analysis on the influencing factors of reservoir quality in a deepwater gravity flow tight sandstone in the Chang 6 oil layer of the Yanchang Formation in the Huaqing area of the Ordos Basin, China, using casting thin section analysis, EPMA, QEMSCAN, SEM, particle size analysis, nano-CT tests, and MICP and CVMI experiments. The results show that the matrix and detrital mica contents and the grain size sorting differences control the compactness of the original deposition of tight sandstone. The low content of the matrix (less than or equal to 7%) and detrital mica (less than or equal to 8%) have a positive effect on the preservation of original pores. Diagenesis is the reconstruction of the original reservoir quality, which increases the complexity of reservoirs and is the key controlling factor of reservoir quality. The diagenetic index, Q, can favorably characterize the diagenesis and compactness of reservoirs. Under the combined influence of the sedimentary environment and diagenesis, the deepwater tight sandstone reservoir with complex pore throat structure is formed. The micropore throat structure is a key factor influencing the permeability of reservoirs. The correlation is poor between the permeability and porosity of deepwater tight sandstone. The permeability is mainly controlled by the effective throat radius and the ratio of the pore throat radius.