Research On The Method Of Pressure Drop Calculation During Test String

The test string structure is complex,and the pipe diameter changes frequently.Especially the test well has a large output and a wide range of variation.In particular,the pressure in the wellbore of the offshore test well is higher and the fluid velocity is faster,causing flow patterns to change more frequently.The classical pressure drop calculation formula does not cover the entire flow interval.Based on the gas-liquid two phase flow theory for oil and gas well test conditions and the particularity of the test string,it is very important to propose a model that is suitable for the conditions of test wells and accurately calculating the pressure distribution of the test string.Therefore,based on the measured data of the test wells in the western part of the South China Sea,the pressure drop calculation methods for gas and oil test wells are studied.The main study contents completed are as follows:(1)This article coMPares the test string and production string from the structure and flow rate.Test string has many downhole tools,complex structure and frequent changes in internal diameter.In addition,the test wells have large output and a wide range of changes,resulting in abrupt changes in the flow rate,which in turn causing frequent flow pattern changes.Pipeline pressure drop in test wells is more complex than production wells.(2)For the single-phase test gas well average temperature and average deviation coefficient pressure drop calculation method,according to the characteristics of offshore oil and gas wells,the vertical temperature is divided into five parts from bottom to top.By IInalysing the influence of the tubing roughness and Reynolds number on friction coefficient,it is shown that Reynolds number is the main influencing factor of friction coefficient.According to Jain friction coefficient relationship,a modified model of friction coefficient is proposed.The temperature and pressure coupling model calculation program was written in C++.Based on the well data of 21 wells in the western South China Sea and eastern China,the correction coefficient was calculated and the optimal correction factor was determined.The corrected model was verified using the measured data of the LS-X well.The relative error of the calculation results was within 3%.(3)Selecting the multi-phase pipe flow pressure drop calculation model commonly used in five projects,using PIPESIM to simulate the pressure distribution of the test string at 25 wells in the western part of the South China Sea.Wellhead pressure error statistical analysis results show that the Hagedorn-Brown model is optimal.However,the calculation results cannot meet the requirements of engineering accuracy.The analysis shows that the gradient of pressure drop in the pressure drop gradient of the test pipe flow accounts for most of the gradient,the gradient of friction pressure drop accounts for a very small part,and the gradient of kinetic pressure drop is ignored.Therefore,this paper focuses on correcting the gravity term in the Hagedorn-Brown total pressure drop gradient equation.(4)Sensitivity analysis of the influencing factors of the Hagedorn-Brown pressure drop calculation model shows that the accuracy of wellhead pressure calculation results is affected by the ratio of gas to oil produced,and the relative percent error of the calculation result is linear with the ratio of gas to oil produced.Based on this,the modified model of Hagedorn-Brown was proposed.Using the modified model to recalculate 25 well test wells,the relative error of wellhead pressure calculations is within 3%.The WS-B well measured data was used for verification and the calculation results meet the engineering accuracy requirements.(5)Based on the correction model for the test string flow pressure drop calculation obtained in this study,a set of "Software of Pressure Drop Calculation during Test String"was successfully developed based on the Qt software development platform.The software comprehensively considers the characteristics of temperature distribution in deep-water oil and gas wells,and establishes a temperature-pressure coupling equation and a calculation module that are suitable for the calculation of flow-pressure drop in test string of offshore oil and gas wells.The software can output the calculation results of the pressure,temperature,and velocity distributions in the test string by both image and text.Through the research in this paper,the precision of the pressure drop of the tube flow in the test string is improved.This study provides a reliable basis for obtaining various parameters of formations and fluids under dynamic conditions,timely and accurate evaluation of production layers,and rapid and rational formulation of oil and gas well test programs,which also saves testing time.