NMR based experiment of fluid invasion to natural gas hydrate reservoir and hydrate dissociation inhibition mechanism

Abstract

Hydrate dissociation inhibition has an important bearing on drilling safety for natural gas hydrate exploitation. A low-field NMR-based experimental method is developed for characterizing the hydrate dissociation inhibition effect during fluid invasion to hydrate-bearing sediment. The hydrate core sample is prepared by excess-gas method, and deionized water or hydrate dissociation inhibitor solution was injected at constant flow rate. In the presence of hydrate dissociation inhibitor, the invasion area is significantly reduced, and invasion fluid saturation was kept at 30 % instead of 80 % compared to water. Experimental techniques were used to reveal hydrate dissociation inhibition mechanism. Hydrate dissociation inhibitor at 1 % can reduce the thermal conductivity of aqueous solution from 0.5870 W·m−1·K−1 to 0.5710 W·m−1·K−1 at 4 °C, and increase the low-temperature apparent viscosity from 1 mPa·s to 10 mPa·s, reducing the heat and mass transfer ability of drilling fluid with hydrate reservoirs. The surface tension of water was decreased from 72.8 mN·m−1 to 59.94 mN·m−1, which is conducive to the multi-point adsorption of inhibitors at the hydrate interface. The water activity was reduced from 1.000 to 0.985, showing little effect on the equilibrium temperature of hydrate phase. This work showcases the significance of hydrate dissociation inhibition during fluid invasion to hydrate-bearing sediment.