Adsorption of water in organic matter, clay minerals and deep gas-bearing reservoir: Insights from experimentation and molecular simulation

In this research, the isothermal curves for water molecule adsorption in gas-bearing reservoir were obtained through gravimetric adsorption experiment. The adsorption performances of water molecule on the three individual components of organic matter, illite and montmorillonite were analyzed through molecular simulation method. Then, combining experiment and molecular simulation results, the adsorption mechanism of water on gas-bearing reservoir was discussed. The findings reveal that at the small loading range, primary adsorption regulated through surface functional groups predominates during the adsorption process. At the large loading range, secondary adsorption determined through water cluster formation within inner pore space plays a crucial role. Under high pressure, inner pore structure possesses an obviously stronger effect on water adsorption than surface functional groups. The effect for water on gas transport is primarily attributed to the formation of water cluster during secondary adsorption. For organic matter, water molecule adsorption only appears in the area near the two sides of pore wall. For clay minerals, water molecule adsorption occurs both in the central area and two sides of nanopore. The uptake for water molecule on organic matter is significantly lower than those on clay minerals. Clay minerals dominate water adsorption on gas-bearing reservoir. The mode for water adsorption on gas-bearing reservoir differs from those on organic matter and clay minerals. Water molecules retained on clay minerals are more difficult to desorb, which has the more obvious effect on the pore connectivity of gas-bearing reservoir and the ultimate gas production behavior.