Drilling Through Gas Hydrates Formations: Managing Wellbore Stability Risks

Abstract

As hydrocarbon exploration and development moves into deeper water and onshore arctic environments, it becomes increasingly important to quantify the drilling hazards posed by gas hydrates. To address these concerns, a 1D semi-analytical model for heat and fluid transport in the reservoir was coupled with a numerical model for temperature distribution along the wellbore. This combination allowed the estimation of the dimensions of the hydratebearing layer where the initial pressure and temperature can dynamically change while drilling. These dimensions were then used to build a numerical reservoir model for the simulation of the dissociation of gas hydrate in the layer. The bottomhole pressure (BHP) and formation properties used in this workflow were based on a real field case. The results provide an understanding of the effects of drilling through hydratebearing sediments and of the impact of drilling fluid temperature and BHP on changes in temperature and pore pressure within the surrounding sediments. It was found that the amount of gas hydrate that can dissociate will depend significantly on both initial formation characteristics and bottomhole conditions, namely mud temperature and pressure. The procedure outlined suggested in this work can provide quantitative results of the impact of hydrate dissociation on wellbore stability, which can help better design drilling muds for ultra deep water operations.