Abstract
The characteristics of drilling fluid invasion into hydrate-bearing sediments (HBS) would trigger geological risks. However, invasion mechanisms and formation responses during drilling the gas hydrate reservoirs, still remain poorly understood. Thus, we develop a three-dimensional (3-D) numerical model to investigate the invasion process in drilling hydrate with and without hydrate dissociation. This model model deals with the changes of pressure and temperature induced hydrate dissociation in near-wellbore region and subsequent influence on the process of drilling fluid invasion. The results indicate that the invasion of drilling fluid induces changes in pressure and temperature fields, with a gradual decrease from wellbore to the formation. The cumulative filter volume increases while the invasion velocity decreases gradually over invasion time. Besides, the increase of temperature and decrease in drilling fluid pressure can promote the dissociation of hydrate. Moreover, characteristics and mechanisms of drilling fluid invasion into hydrate reservoirs are analyzed based on the numerical results. The optimization strategies and drilling technology are discussed to prevent hydrate dissociation and control geological risks during drilling hydrate.
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