Investigate Of Wellbore Multiphase Fluid Flow During Well Killing Using Coiled Tubing In Deep-High-Pressure Gas Wells

Coiled tubing technology has been popularized and applied to the well intervention of deep-high-pressure gas reservoirs resulted from its advantages of high efficiency,low cost and reliable safety.However,caused by higher formation pressure,kick off or blowout is easy to happen during the coiled tubing operation process.Therefore,well killing during coiled tubing intervention is of great significance in the safe operation.In this work,based on the problems of complicated wellbore structure of a deep-high-pressure gas well,difficult to predict temperature and pressure distribution during coiled tubing well-killing and low efficiency of particles transport in the annulus during well-killing flowback,we conducted researches on temperature and pressure distribution prediction and particles flowback during coiled tubing well-killing.The major purpose of the work is to provide theoretical guidance to the well control method during coiled tubing intervention.First,based on the common wellbore structure and well completion methods of deep-high-pressure gas wells,we established a wellbore-formation transient heat transfer model and a wellbore multiphase flow model.Finite differential method was used to discretize and solve the models.Then,impacts of various factors including circulation time,flow rate of killing fluid,inlet temperature,killing fluid density,specific heat of killing fluid,etc.on the temperature distribution were systematically analyzed.Simultaneously,wellbore pressure distributions during kick-off,shut-in and well killing of coiled tubing intervention were predicted.Subsequently,lab studies of particles settling by considering different particle shapes and densities of spherical and non-spherical particles in the power-law fluid were conducted.Base on the experimental results,a correlation and prediction of spherical and non-spherical particle drag coefficient by considering the effects of particle sphericity and settlement direction were put forward.Then,an explicit settling velocity equation for predicting particles in power law fluid were put forward.The equation can directly predict the settling velocity of particles.Coupled particle settling velocity equation with annular fluid flow model,influences of circulation flow rate,particle size,particle density,fluid density and rheological characteristics on the particles flowback during coiled tubing flowback were investigated.The key findings of this thesis are expected to provide theoretical guidance and experimental basis for the prediction of temperature and pressure distribution and efficient particles flowback during coiled tubing well-killing.