Study On The Flowing Characteristics Of Gas-Liquid-solid In Annulus During High-Temperature And High-pressure Deep Well Drilling

Exploration and development of oil and gas resources in deep formations is an important strategic demand of national oil and gas development.Multiphase flow characteristics in annulus are complex and the bottomhole pressure is difficult to determine after gas kick during high-temperature and high-pressure deep well drilling.Besides,the operating accuracy is poor and processing efficiency is low when using conventional manual methods to handle gas kick in deep wells.Therefore,the aim of the present study is to investigate the gas-liquid-solid three-phase flow characteristics,the prediction model of the bottomhole pressure,and the automatic gas kick attenuation method.The numerical simulation and experimental study have been carried out and detailed results are as follows:Cuttings settling experiments in Newtonian and non-Newtonian fluids are conducted by using the high-speed camera system.Settling characteristics of sphere,cube,cylinder,and disc are investigated.Results indicate that the settling behaviors of cuttings are not only affected by the particle shape,but the projected area in its direction of motion.By introducing the projected area ratio and particle sphericity,a drag coefficient prediction model is developed.Based on the relationship between the dimensionless settling velocity and the dimensionless particle diameter,an explicit settling velocity prediction model is proposed that is suitable for non-spherical particles in Newtonian and non-Newtonian fluids.Based on the three-fluid model,heat transfer model for the wellbore-formation system,and the drag coefficient model for non-spherical cuttings,a transient nonisothermal gas-liquid-solid three-phase mechanistic model is developed.Based on the proposed model,the effects of gas solubility,initial bottomhole pressure difference,rate of penetration,cuttings diameter,geothermal gradient,and drilling fluids flow rate on the gas-liquid-solid three-phase flow characteristics are investigated.Results indicate that the cuttings existence and annulus fluids temperature variation affect annulus fluids hydrostatic pressure,and the effects of cuttings and heat transfer can not be ignored in the wellbore pressure prediction during deep well drilling.The bottomhole pressure increases as rate of penetration,cuttings diameter,and drilling fluids flow rate increase,while the bottomhole pressure decreases as initial bottomhole pressure difference and geothermal gradient increase.In order to meet the requirement of real-time bottomhole pressure prediction,an efficient computing model for the gas-liquid-solid three-phase is established,based on the gas slip model and cuttings settling velocity model.By combining the automatic adjustment model of choke opening and the efficient computing model for the gas-liquidsolid three-phase,an automatic gas kick attenuation model for deep well drilling is developed.Results indicate that compared with driller’s method and wait & weight method,the automatic gas kick attenuation method could effectively decrease the peak choke pressure due to its large frictional pressure drop and cuttings hydrostatic pressure.The automatic gas kick attenuation method is efficient,and the time required to remove all the invaded gas for the automatic gas kick attenuation method is one-tenth of driller’s method and one-seventh of wait & weight method.The peak choke pressure increases as gas influx size,formation permeability,and initial bottomhole pressure difference increase,while the peak choke pressure decreases as drilling fluids flow rate increases.The peak choke pressure increases as well depth increases in water-based drilling fluids,while the peak pressure decreases as well depth increases in oil-based drilling fluids.A gas-liquid-solid three-phase flow model in the annulus and an automatic gas kick attenuation model during deep well drilling are developed.And the results of this study could provide the basis for the bottomhole pressure prediction after gas kick and efficient gas kick handling during deep well drilling.