Drilling Through Gas-Hydrate Sediments: 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 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.

Wellbore Stability Problems in Deepwater Gas Wells

“…For deepwater gas wells, there is the possible of gas hydrate formation, if no hydrate prevention is implemented, due to the low temperature and high-pressure conditions of the environment as well as the coexistence of gas and water inside the wellbore [36] [37] [38]. The presence of water is the main cause of gas hy-World Journal of Engineering and Technology drate formation, the first step in solving this problem is to use a proper oil-based mud or synthetic based mud for drilling to reduce water production from the invaded mud filtrate.…”

Geohazards and Ocean Hazards in Deepwater: Overview and Methods of Assessment

“…Birchwood et al, 2006;Freij-Ayoub, 2007;Salehabadi, 2009;Khabibullin, 2011) and to plan for possible formation over-pressures, and gas release from the hydrate zone during drilling; additives can be added to the drilling fluids to inhibit hydrate formation in the pipelines, or chemically stabilize hydrates near the well bore. Birchwood et al, 2006;Freij-Ayoub, 2007;Salehabadi, 2009;Khabibullin, 2011) and to plan for possible formation over-pressures, and gas release from the hydrate zone during drilling; additives can be added to the drilling fluids to inhibit hydrate formation in the pipelines, or chemically stabilize hydrates near the well bore.…”

Fundamental Investigation of the Effects of Modified Starch, Carboxymethylcellulose Sodium, and Xanthan Gum on Hydrate Formation under Different Driving Forces

“…It is crucial, for safety, to efficiently prevent and control various risks while drilling [11]. During drilling in gas hydrate-bearing sediments, hydrate phase transformations occur due to the change of temperature and pressure conditions in the well and/or around the wellbore, which results in different safety problems [12]. Shallow gas and hydrate decomposition gas permeate into drilling fluid in the well [13,14], changing the properties of the drilling fluid and forming hydrates.…”