Experimental study on the wettability and adsorption characteristics of Longmaxi Formation shale in the Sichuan Basin, China

• The spontaneous imbibition rate of water for the LF shales is higher than the oil.
• The methane adsorption capacity of the Kerogen is much larger than the pure minerals.
• The water molecules will reduce the methane adsorption capacity on the Kerogen.
• The methane adsorption capacity on the mixed minerals can be approximately equal to the sum of the methane adsorption capacity on the pure minerals calculated by the mass ratios.
• The mixed wettability, the influence of the water on the methane adsorption capacity and water-induced cracks should be considered in the water blocking damage evaluation system.

In this paper, the core shale samples from the Lower Longmaxi Formation (LF) in the southwest of the Sichuan Basin of China are carried out laboratory experiments to investigate the wettability and adsorption characteristics. The influences of the wettability on the development of the shale gas reservoirs were discussed. And the influences of the kerogen and the pure mineral on the methane adsorption capacity were discussed. The differences between the methane adsorption capacity of the pure mineral and the mixed minerals were also discussed. The results show that the spontaneous imbibition rate of the LF shale samples tended to rise firstly and then become stable with the increasing of the time; The spontaneous imbibition rate of water was higher than the spontaneous imbibition rate of oil; The methane adsorption capacity on the kerogen and the pure minerals first increased rapidly and then increased slowly and tended to be stable with the increasing of the pressure; The methane adsorption capacity on the kerogen was much larger than the different pure minerals; And among the different pure minerals, the order of the methane adsorption capacity is that: illite > chlorite > quartz; The water molecules would reduce the methane adsorption capacity on the Kerogen; The methane adsorption capacity of the mixed minerals can be approximately equal to the sum of the methane adsorption capacity of the pure minerals calculated by the mass ratios. The water blocking damage in the shale formation can’t be assessed according to the water blocking damage evaluation system of the conventional oil and gas reservoirs. The mixed wettability, the influence of the water on the methane adsorption capacity and water-induced cracks should be considered in the water blocking damage evaluation system of the shale reservoir.