Study On Hydrate Generation Pattern Under Deepwater Gas Well Intervention Operation

Deepwater gas well intervention operations are unplanned deepwater gas well operations such as those required for well management during deepwater operations or when a well failure occurs.The deployment of deepwater gas well intervention tools can lead to unforeseen risks in deepwater gas wells,including damage to the wellbore structure and blockage of the pipeline by hydrate formation.Since the fluid in the wellbore is influenced by both the deep sea and the formation,it is in a complex environment,and the risk of the intervention tool lowering process is large.There is a lack of models for temperature and pressure redistribution in the wellbore under deepwater gas well intervention and quantitative prediction of hydrate plugging in the wellbore.To address these problems,this paper summarizes previous studies on temperaturepressure coupling in the wellbore in the context of deepwater gas well intervention operations,introduces the intervention operation as an operating condition,and establishes a distribution model of temperature-pressure coupling under deepwater gas well perturbation by combining the perturbation law of intervention operation on wellbore temperature and pressure.In order to quantitatively describe the temperature and pressure field change law of intervention operation with pressure in deepwater gas well wireline and continuous tubing and the effect of intervention operation on hydrate generation in the wellbore.Based on the commonly used temperature and pressure calculation models and hydrate generation prediction models in the wellbore of deepwater gas wells,a model is developed to calculate the temperature and pressure fields in the wellbore under the intervention operation of deepwater gas wells,and the effects of the intervention operation on the temperature and pressure distribution in the wellbore are explored in three directions,including gas well production,tool lowering speed and tool lowering size,respectively.Based on the temperature and pressure variation pattern in the wellbore under the intervention operation of deepwater gas wells,it is found that the gas well production and tool lowering size will lead to the change of temperature and pressure in the wellbore,but the lowering tool speed will not lead to the change of temperature and pressure in the wellbore.Based on this temperature and pressure law,we also conducted a study on hydrate generation under different intervention conditions,and explained how gas well production,tool lowering speed and tool lowering size affect hydrate generation rate under gas phase conditions by molecular dynamics.It is found that methane molecules are more affected by temperature and pressure in the range of temperature and pressure variation under the intervention operation conditions,and the decrease of temperature with the increase of pressure will make the diffusion rate of methane molecules accelerate,leading to the increase of dissolution rate of methane molecules in water to move rapidly to the hydrate-gas-water two-phase flow interface and accelerate the growth rate of methane hydrate.By analyzing the density of fluid in the wellbore under intervention operations in deepwater gas wells,it is found that when the fluid density in the gas well increases,it will promote hydrate generation in the wellbore.Based on the existing hydrate phase equilibrium equation,the hydrate phase equilibrium curve under intervention operation was modified to obtain the variation pattern of hydrate generation area under intervention operation in deepwater wellbore under different working conditions,and the identification of hydrate generation risk area under intervention operation was carried out for different working conditions to provide ideas for efficient hydrate control under intervention operation in deepwater gas wells.