Volume 35: CCUS Technologies for the Carbon Neutrality: Part III

Experimental Study on Wettability Changes of CO2 Flooding in Tuff Sandstone Reservoir Hongda Hao, Bihua Xian, Song Deng, Jirui Hou, Xiaopeng Yan, Chaowei Li, Shuo Yang

Abstract

The composition of tuffaceous sandstone is complex, and it is easy to react with CO2, resulting in significant changes in wettability during CO2 flooding. However, the change mechanism for wettability is still unclear. Therefore, researches are carried out in laboratory to study the wettability change mechanism during CO2 flooding in a tuffaceous sandstone reservoir. A high temperature and high pressure reactor is used to establish a reaction environment of CO2-water-minerals, the maximum temperature is 65℃, and the maximum pressure is 20 MPa. The changes of wettability, mineral composition and mineral morphology of tuffaceous sandstone reservoir rock samples were measured by contact angle meter, EDS energy spectrometer and scanning electron microscope (SEM). The SEM results show that the mineral morphology changes significantly after CO2 contacted with the tuffaceous rock, from the original smooth and flat surface to a large corrosion pit on the surface. The contact angle increases by an average of 18.77° after CO2-water-mineral reactions, and the wettability changes from strong water-wet to neutral-wet. The mineral composition also changes significantly after CO2-water-mineral reactions, which is mainly manifested by the increase of Al content with a maximum increase of 142%, and the decrease of Si and K content with a maximum decrease of 32% and 54%, respectively. The change mechanism of wettability is mainly due to the transform of mineral potassium feldspar to kaolinite, and the temperature and pressure will further promote the growth of kaolinite. The innovation is to study the reaction of CO2, water and minerals for the tuffaceous reservoir, and the mechanism of wettability change are revealed by the CO2-water-mineral reactions. And the influence of wettability change on miscible CO2 flooding recovery are also studied in this paper.

Keywords Tuffaceous sand, CO2-water-rock reaction, wettability, mineral composition, Mineral morphology