Drilling Through Gas-Hydrate Sediments: Managing Wellbore-Stability Risks

Abstract

Summary 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 semianalytical 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 hydrate-bearing 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 hydrate-bearing sediments (HBS) 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 in the paper can provide quantitative results of the impact of hydrate dissociation on wellbore stability, which can help in better design of drilling muds for ultradeepwater operations.