Experimental study of the drilling process in hydrate-bearing sediments under different circulation rates of drilling fluid

Abstract

Natural gas hydrate (NGH) is widely considered a potential alternative to traditional energy resources. Some countries are trying to exploit and utilize NGH. However, due to the sensitivity of the hydrate, and a lack of exploitation experience with the NGH, drilling in hydrate reservoirs is considered risky. In order to understand the disturbance effects of drilling fluid with different circulation rates on the hydrate-bearing sediments during the drilling process, a novel hydrate drilling experimental apparatus was used to study the drilling process in the hydrate-bearing sediments. Four drilling experiments were carried out in consolidated sediments containing Tetra-n-butyl ammonium bromide (TBAB) hydrate. The drilling fluid injection rate ranges from 500 to 1800 g/min. The results show that hydrate dissociation can be induced by the circulation of relatively high-temperature drilling fluid when drilling in hydrate-bearing sediments, and that the hydrate dissociation rate is greatly influenced by the circulation rate of the drilling fluid. The drilling fluid invasion area has a maximum as the experiment progresses. Increasing the drilling fluid circulation rate can enhance the sediment temperature rise rate, enlarge the hydrate dissociation region, and increase cumulative TBAB production. Drilling fluid with a relatively low circulation rate is beneficial to wellbore stability. These findings will provide help with drilling design suitable for hydrate-bearing sediments, and provide a scientific basis for achieving safe drilling in hydrate-bearing sediments.