Research And Application Of Fluid Friction Calculation Method For Coiled Tubing In Ultra-Deep Wells

The calculation of friction pressure drop of working fluids in the coiled tubing is an important part of hydraulic fracturing design,and its accuracy affects the success of construction directly.There are many models for calculating the pressure drop of the coiled tubing,and how to select the most appropriate model according to the actual working conditions is particularly important.The dissertation firstly conducts the in-pipe and annulus hydrodynamics theoretical study on the coiled tubing system,gives the continuous equation,momentum equation and energy equation that its flow should satisfy,and determines the conditions for fluid phase transition based on the change law of formation temperature and pressure with the well depth.Secondly,the commonly used friction pressure drop calculation models are sorted out,and the coiled tubing system is divided into spiral section,straight section,jetting section and annulus section.Combined with the type of common working fluids on construction site,the friction pressure drop calculation model of coiled tubing under different working conditions is determined.Thirdly,based on the actual coiled tubing parameters and on-site working fluid database,the coiled tubing friction pressure drop calculation software is developed using Delphi platform.The software is used to calculate three operating conditions:conventional fracturing,mixed gas fracturing and sand-containing fracturing.The OLGA software and field data are used to verify the newly developed software.The results show that the calculation results of the new software are in line with the field test data,and the maximum error does not exceed 10%,which is also in line with the OLGA calculation results,and the maximum error does not exceed 5%.Finally,the new software is used to analyze the frictional pressure drop of the coiled tubing system of an ultra-deep well with a depth of 6500 m.The result shows that under the same working conditions,the coiled tubing spiral section has the largest frictional pressure drop,and the jetting section and annulus section have smaller pressure drop.The diameter of coiled tubing has the greatest influence on frictional pressure drop,and the diameter of drum has the smallest influence.The working fluid flow,viscosity and fluidity index are positively correlated with the friction pressure drop of the coiled tubing.