Physical simulation experiment of tuffaceous dissolution effect in sandstone reservoirs: a case study of Paleogene Wenchang Formation in Huizhou and Lufeng area, Pearl River Mouth Basin

Abstract

Tuffaceous sandstone reservoirs of Paleogene Wenchang Formation in Huizhou and Lufeng area of Zhu I Depression, Pearl River Mouth Basin were selected, and core-scale fluid-rock interaction simulation experiments were designed and carried out to explore the dissolution and modification effect of acidic fluid on tuffaceous components in clastic reservoirs during burial process and its controlling factors. The dissolution characteristics and physical property response characteristics of sandstone reservoirs under different fluid flow rates and tuffaceous contents before and after the experiments were compared and analyzed through microscope observation, fluid composition analysis, physical property characterization and other methods. The results showed that tuffaceous dissolution was common in acidic fluid environment, but the intensity of tuffaceous dissolution and the response of reservoir physical properties were different under different experimental conditions. Among them, the openness and closure of diagenetic system determined the intensity of tuffaceous dissolution. Under the same rock and acidic fluid conditions, the amount of tuffaceous dissolution in the high flow rate open system was higher than that in the closed system, and the dissolution products in the closed system tended to precipitate, which was not conducive to the preservation of dissolution pores. In addition, the content of tuffaceous components significantly affected dissolution effect, the tuffaceous-rich sandstone would not be conducive to dissolution porosity, while the tuffaceous-containing sandstone and tuffaceous-poor sandstone could increase dissolution porosity, and tuffaceous-containing sandstone has higher dissolution efficiency. Overall, in the reservoirs with relatively moderate to low contents of tuffaceous components, the open diagenetic system in the shallow-middle burial stage is most conducive to the development of dissolution pores of tuffaceous components. After the late stage of acidic fluid dissolution and modification, it is easier to form secondary dissolution-type high-quality reservoirs. This study is of great significance for the prediction of dissolution-type reservoir sweet spots in different areas.

Keywords

• tuffaceous dissolution and modification
• diagenetic system
• dissolution simulation experiment
• huizhou and lufeng area
• zhu i depression
• pearl river mouth basin