Abstract
At present,the stimulation technique involving soaking after fracturing of shale gas reservoirs has received increasing attention.In this study,gas-water displacement experiments were carried out to simulate the contact state between the fracturing fluid and the shale during the soaking stage after hydraulic fracturing of the shale gas reservoir.By using low-field nuclear magnetic resonance to dynamically monitor the occurrence state of the methane in shale cores,the changes in the masses of the methane in different occurrence states were calculated.Furthermore,the displacement of the adsorbed methane in the shale by the fracturing fluid was studied.In addition,the influences of the fracturing fluid's salinity and the shale clay content and type on the displacement process were also analyzed.The results of this study show that the fracturing fluid has a stronger adsorption on clay minerals than that of methane,so it can replace the adsorbed methane in the shale.Compared with pure fracturing fluid solution,the high salinity fracturing fluid solution containing cations has a stronger adsorption on the clay minerals in the shale,and thus,it has a stronger displacement ability.The mineral composition of the shale reservoir also has an important influence on the displacement efficiency.The higher the content of clay minerals with high adsorption capacities,the more adsorbed methane is replaced.The results of this study are important for gaining a better understanding of the stimulation technique involving soaking after fracturing of shale gas reservoirs and for optimizing the design of soaking.
NSTL