AN IMPROVED GRAIN FLOTATION APPROACH TO DETERMINING THE WETTABILITY OF LACUSTRINE SHALE OIL RESERVOIRS

Wettability is one of the most important factors controlling the occurrence, migration and sustainable production of shale oil, but is not yet fully understood for fine-grained shale with a wide range of maturation. In this study, to minimize the heterogeneity of compositions and pore structures in shales on the wettability results, a range of granular shale samples from Second Member of Kongdian Formation (Ek₂) in Cangdong Sag of Bohai Bay Basin was selected to investigate the wetting characteristics using grain flotation method and liquid-liquid extraction (LLE) technique with different fluids (deionized water, brine, n-decane, toluene, dimethylformamide, kerosene, and shale oil). In the grain flotation tests, a clear positive relationship is observed between floating fraction (on 0 vol.% solution surface; ranging from 1.2 to 100 %) and S₁ (from pyrolysis tests), indicating strongly oil-wet characterization of samples with higher S₁ values (> 2 mg/g). A slight effect of particle size on LLE results are shown by using quartz grains with various particle size ranges. More importantly, the surface area fraction of organic matter increases with shale particle size decrease, which may be the main reason for a significant increase of oil-wet fraction.

Acknowledgements: This work was funded by the National Natural Science Foundation of China (No. 41672251 and 41830431).