Multiphase flow behavior in deep water drilling: The influence of gas hydrate

Abstract

Hydrate phase transition may bring hidden dangers for well control safety, even accidents of blowout happen in deep water drilling. Accurate calculation of all the drilling parameters is of great importance for well control safety. In this study, the mathematic models of transient heat transfer and multiphase flow have been established with the consideration of hydrate phase transition. Furthermore, the position where hydrate formation is most likely to occur was predicted with the proposed models, and the factors affecting hydrate formation region were also analyzed. Finally, the analysis of the effect of gas hydrate phase transition on some important parameters in well control, such as the pit gain, gas void fraction, and bottom hole pressure, is presented. The results show that hydrates form near the mud line during the drilling and shut‐in stage, but the hydrate formation region will be narrowed as well killing start. Additionally, the hydrate formation region decreased with the increase of flow rate and increased with the increasing shut‐in time, hydrate inhibitors, and riser insulation are presented to prevent hydrate blockage. More importantly, the gas void fraction and pit gain decrease due to the formation of hydrates, leading to the gas kick early detection not timely and gas kick more “hidden.”

A novel model for calculating critical droplet entrainment rate of gas well considering droplet deformation and multiple parameters

“…For the multi-phase pipe flow, the friction coefficient calculation formulae vary with the flow pattern. 39 When the gas and water phases are in a critical liquid removal state, the flow pattern in the wellbore is an annular mist flow. 40 Yu Xichong 41 suggested that the calculation method for the friction coefficient of monophasic flow could be applied to obtain the friction coefficient between the fluid and pipe wall in a multi-phase pipe flow, including stratified, annular, and slug flows.…”

“…Equation () indicates that the friction coefficient of the gas‐liquid two‐phase pipe flow is required in the calculation of the critical droplet entrainment rate. For the multi‐phase pipe flow, the friction coefficient calculation formulae vary with the flow pattern 39 . When the gas and water phases are in a critical liquid removal state, the flow pattern in the wellbore is an annular mist flow 40 .…”

Investigation on Methane Hydrate Formation in Water-based Drilling Fluid

“…The exploration process faces serious drilling risks caused by the deep-water environment. Due to the appropriate temperature and pressure which meet the conditions for gas hydrate formation in deep-water oil and gas exploitation, gas hydrate formation in drilling pipelines has been a major problem which strictly restricts the safe and efficient exploitation of deep-water oil and gas. − …”

“…In view of increasingly stringent environmental protection rules, water-based drilling fluids have been gradually used instead of oil-based drilling fluids during oil and gas exploitation. This may increase the possibility of hydrate formation in the drilling fluid. ,,,− When drilling in deep-water fields, free gas may invade the wellbore annulus. As the gas and drilling fluids flow in the annulus, gas hydrates may continue to form and accumulate under appropriate temperature and pressure conditions, as seen in Figure , which leads to changes in the drilling fluid’s performance and interruption of the normal drilling operation.…”

“…If the pressure and temperature conditions have changed such that they no longer meet the conditions for the stable existence of hydrate, the free gas which formed from the hydrate decomposition would continue to affect the performance of the drilling fluid. The formation of gas hydrates also changes the rheological properties of the drilling fluids, in which density and viscosity both increase. , Hydrates can form anywhere in pipelines, such as in choke lines, drilling risers, blowout preventers, and subsea wellheads, resulting in challenges for well control and even serious drilling accidents. , Breaking the temperature–pressure conditions with the drilling fluid circulation is unavoidable, which then leads to the gas hydrates’ likely decomposition. The free gas and water produced by the decomposition of gas hydrates would also change the drilling fluids’ properties, and accidents, such as a blowout, can happen if the pressure in the wellbore is not controlled in a safe operating range.…”