Effects of hydrophilic and hydrophobic nano-CaCO3 on kinetics of hydrate formation

The invasion of drilling fluids during well drilling through gas hydrate-bearing sediments may seriously damage gas hydrate stability and distort well-logging identification and evaluation in exploration and production of gas hydrate reservoirs. Adding nanoparticles into drilling fluids can be an efficient method to reduce fluid invasion. However, nanoparticles may induce hydrate formation in wells, which will block annulus and lead to safety accidents. Therefore, suitable nanoparticles used for hydrate drilling should be clarified first. This study addressed this issue by experimentally investigating the influence of hydrophilic and hydrophobic nano-CaCO3 on CH4 hydrate formation in a dynamic system. We performed a series of experiments by using nano-CaCO3 (1.0-6.0 wt%) with different particle sizes (20, 70, and 700 nm) at 3.0 degrees C and 6.0 MPa. The macroscopic kinetic parameters of hydrate formation were obtained. The results show that hydrophobic nano-CaCO3 particles promote hydrate formation, while hydrophilic ones can inhibit hydrate formation at certain particle sizes and concentrations. This is mainly due to the different surface wettability, resulting in the different distribution of water and gas molecules in fluids. The hydrophilic nano-CaCO3 with the particle size of 20 nm and addition of 3.0 wt% has the strongest inhibition effect under the given experimental conditions. In comparison with ultrapure water, the induction time is increased by about 38%, while the formation amount and rate are decreased by about 13% and 18%, respectively. This work will provide valuable ideas and references for the design of deepwater drilling fluid using nanoparticles, and also provide insight into revealing the formation and evolution mechanism of hydrate deposits at the micropore or even nanopore scale.