Temperature And Pressure Distribution And Hydrate Prediction During Deepwater Gas Well Clean Up Stage

Deepwater gas well testing stage is the key node for deepwater drilling and completion operations to be put into production and development operations.At this stage,it is necessary to clean the well firstly to remove the remaining completion fluid and other fluids in the wellbore.In the meanwhile,the ambient temperature differs in seawater and formation,pressure response fastly with complex flow pattern change,the risk of hydrate formation is the high.It is necessary to accurately predict the temperature and pressure distribution during deepwater gas clear-up stage,and to determine the areas where hydrates may form then to provide accurate guidance of preventing the formation of hydrates.In view of above problems,this paper establishes an unsteady flow and heat transfer model through a combination of experiments and theoretical models.And data verification is based on a well data in the field.Through the visual unsteady-state flow experiment,the flow pattern change and pressure change law of well clean up process are determined.Based on this flow experiment,the mechanism of flow conversion is analyzed,the unsteady flow model is established and to solve this problem.Through heat transfer experiments,the expressions of convective heat transfer under different flow patterns during well clean up stage were obtained,and the unsteady temperature calculation models under different flow patterns were established.In this paper,the hydrate formation mechanism is analyzed,and the hydrate phase equilibrium conditions and temperature and pressure models are combined to establish a hydrate prediction model for deepwater gas well clean up.A software module is developed to analyze the relative factors affecting temperature,pressure and hydrate formation area.The accuracy of the established temperature and pressure distribution model for deepwater gas well cleaning tests is relatively good,and the error with field data is within 6%.The calculation results show that when the fixed choke is used to clean up gas well,the wellhead pressure rises firstly and then stabilizes.Different choke sizes have different wellhead pressure changes.The larger choke size is,the faster the growth trend of wellhead pressure and the smaller the peak value of wellhead pressure will reach.The height of the cushion has basically no effect on the peak wellhead pressure,however,the height of the cushion will affect the pressure growth rate after clean up gas well.During the deep water gas well clean up stage,the hydrate formation risk area also changes accordingly,and the hydrate formation is high at the initial condition.In this stage,as the clean-up time increases,the risk area for hydrate formation gradually decreases when the gas rate is constant.The smaller gas rate is,the longer the highrisk area for hydrate formation will exist.Moreover,hydrate formation is influenced by the size of choke,the size of testing string,the properties of working fluid in string and annulus,gas composition,gas rate and well clean-up time.The above factors should be considered comprehensively when formulating hydrate prevention measures.The above factors should be considered comprehensively when formulating hydrate prevention measures.The research in this paper can predict the temperature distribution and hydrate formate in the during deepwater gas well clean up stage,and save the working time and reduce the operating cost under the premise of ensuring safe operation.