Role of chemical cementation and hydration inhibition on wellbore stability in hydrate bearing sediment: Experimental and molecular dynamics simulation studies

Abstract

As a sustainable alternative energy source, natural gas hydrate exploitation is limited by the risk of wellbore instability. The hydrate is usually distributed in unconsolidated shallow sediment with high clay content. A modified polyvinyl alcohol was proposed as a novel drilling fluid additive that could increase wellbore stability through chemical cementation and hydration inhibition. Under the action of modified polyvinyl alcohol, the linear expansion rate of the in situ deep-sea soil core was reduced from 18% to 1.9%, which remained the original shape after immersion for 24 h. The adsorption behavior was studied by atomic force microscopy, contact angle measurement and molecular dynamics simulations. The adhesion force was increased from 143.07 to 391.13 kcal/mol on the illite surface compared to the quartz surface by introducing positive functional groups in the modification process. The hydration peak decreased from 4.39 to 3.68 on the illite surface by occupying the interaction site between the rock surface and water molecules. This study provides a new method to ensure the safety of drilling and exploitation of natural gas hydrate and the development of drilling fluid additives for hydrate bearing sediment.