EXPLORING THE WETTABILITY CHARACTERISTICS OF ARGILLACEOUS SILTSTONE WITH IMBIBITION AND NMR TECHNIQUE FOR MARINE RESERVOIR EXPLOITATION

The argillaceous siltstone reservoirs in South China Sea involves a wide variety of fossil resources, such as gas hydrate, marine oil, natural gas, and other mineral resources. The argillaceous siltstone with mixed wettability characteristics is easily dispersed in water, and it is difficult to study the wettability of argillaceous siltstone based on water imbibition technique. In this work, an innovative method is proposed to demonstrate the mixed wettability based on imbibition and nuclear magnetic resonance (NMR) technique. The contact angle results show that the affinity of argillaceous siltstone for oil is stronger than that for water. However, the imbibition volume of water is much larger than that of oil. The oil imbibition curve is linear, while water imbibition curve has a two-stage feature. This difference can be explained by the expansion of clay, where more water wet surfaces are exposed to the liquid, leading to changes in wettability. In addition, the coexistence of organic matter and inorganic clay minerals results in a mixed wetting characteristic. Based on NMR technology, a micro wettability index is proposed to quantitatively characterize the micro wettability heterogeneity. The micro water (or oil) wettability index of micropores (0.01−10 ms) is approximately equal to 0.5, indicating the mixed wettability. The micro water wettability index of mesopores (10−500 ms) is approximately equal to 1.0, indicating strong water wettability. These pores or cracks may be induced by clay minerals expansion. The micro oil wettability index of macropores (> 500 ms) is approximately equal to 1.0, indicating strong oil wettability, which is resulted from significant accumulation of organic debris enrichment. It is of great significance to improve the exploration and exploitation efficiency of mineral resources in the South China Sea.