An investigation of interaction of drilling fluids with gas hydrates in drilling hydrate bearing sediments

Natural gas hydrates, preserved in deep ocean sediments, are supposed to be the future hydrocarbon source of energy. The possibility of gas production from natural gas hydrate bearing sediments (NGHBS) has been scrutinized by many researchers. Thermal stimulation, depressurization and use of thermodynamic inhibitors are three main proposed approaches to produce gas from the hydrates. When drilling through NGHBS, these mechanisms may cause wellbore instability and other drilling hazards such as severe mud gasification, low quality logging and cementing, casing collapse due to high pressure gas accumulation behind the casing, casing subsidence due to NGHBS failure and consequently instability of the ocean floor. In this study, the mechanism of thermal stimulation was studied. An experimental set up was designed and manufactured to investigate hydrate behavior when it comes in contact with warmer drilling fluids. Several muds with different additives were tested to investigate which properties are responsible for wellbore integrity maintenance. For this intention, linear temperature distribution in the hydrate was recorded for near distance from hydrate mud contact and the hydrate dissociation rate was calculated. The purpose was to reduce the heat flux of the drilling fluid into the hydrate using relevant additives or by altering the mud circulation rate. Experimental results were validated by a hydrate dissociation model to obtain viable assessment for designing prospective exploration wells. (C) 2014 Elsevier B.V. All rights reserved.