Study On Characteristics And Influencing Factors Of Spontaneous Imbibition Of Shale

Shale gas reservoirs with abundant gas stored in both free and adsorbed state have recently received much interest.Shale reservoirs are generally developed using hydraulic fracturing techniques.Due to the special pore structure of shale gas reservoirs,the spontaneous imbibition characteristics are different from the conventional reservoirs.At present,researchers always use intact rock samples as samples to study the imbibition and single experimental methods,resulting in insufficient understanding,and less research on shale powder imbibition.Imbibition experiments were carried out using intact shale,and pore connectivity and fluid mobility were analyzed by the imbibition curve.The results show that the experimental shale connectivity is good and the liquid in the tiny pores forms non-Darcy flow.The effects of microcracks were studied by repeated spontaneous imbibition experiments.The experiments showed that microcracks had a great influence on the initial imbibition process.The analysis of spontaneous imbibition of parallel bedding and vertical bedding showed that the bedding direction often forms the dominant channel of imbibition,and a new anisotropic index formula is proposed.From the relationship between the imbibition rate and the contact angle,it is found that the infiltration rate is inversely proportional to the contact angle,and the closer the angle of the contact angle is,the more similar the infiltration rate is.A shale powder imbibition device was designed using shale powder as an experimental sample,and a spontaneous imbibition experiment was carried out under the air-oil and the air-water system.The experimental results show that the oil uptake is higher than the water uptake,but the rate of water imbibition is higher than the rate of oil imbibition,the phenomenon is further explained by LLE method and wettability index method.Based on the imbibition experiment of intact rock samples and the conventional normalization model,considering the influencing factors of imbibition,a new spontaneous imbibition time-free time scale model and a normalized recovery model are proposed,which can highly fit the experimental data.