Experimental Study on the Wettability of Longmaxi Formation Shale in the Sichuan Basin, China

Abstract

Abstract The wettability of conventional reservoirs have been extensively studied in the past. However, Shale is rich in organic matter, composed of many mineral components in complex relationships, and contains pores of various scales from micrometer to nanometer, so it is very difficult to evaluate the wettability of shale. In this study, low field nuclear magnetic resonance (NMR) was used to test the water wettability of shale and a new mixed wettability model was built to quantitatively calculate the organic matter contact angle and evaluate the water wettability of organic matter. The experimental results show that the surface of the shale exhibits complex non-uniform mixed wettability, both oil-wet and water-wet; with the increase of soaking time, the water wettability of shale enhances significantly and the equilibrium time of water imbibition is 5-10 days; the average contact angle of water with organic matter is 75.2°, indicating water can enter organic matter pores, but at weaker capacity than entering inorganic pores. The research results are helpful for making clear the micro mechanism of the action between fracturing fluid and shale reservoir and designing fracturing scheme.