Improvement Of Pressure Calculating Method For Offshore High Temperature And High Pressure Gas Wells

For offshore high temperature and high pressure(HTHP)gas wells,because of the wellbore structure of highly-deviated and horizontal wells,the pressure gauge is difficult to reach the bottomhole,and many test datas can only be obtained from wellhead.However,the test pressure of these gas wells decreases with time,which makes it difficult for conventional bottom hole pressure calculation methods to obtain correct results,and even the calculated bottom hole pressure decreases with time.And when the shut-in is fast,the water hammer phenomenon causes the wellhead pressure to fluctuate continuously.These problems bring great difficulties to productivity test and pressure build-up well test interpretation of gas wells.Based on the investigation of the calculation methods of wellbore temperature and pressure profiles at home and abroad,the causes of abnormal wellbore temperature and pressure field are analyzed by momentum equation.On the basis of accurately describing the vertical temperature profiles of seawater in mixing layer,thermocline layer and deepwater layer,a new transient heat transfer function suitable for seawater section is solved,and an unsteady heat transfer model of seawater section in the opening process of offshore gas wells is established.At the same time,the heat transfer model of formation section and the well bore heat transfer model when shutting down are derived and solved,and the multi-field coupling calculation method considering heat transfer,continuous flow,phase state and pressure is established.In order to accurately describe the phenomenon of water hammer in shut-in of gas wells,the continuity equation,motion equation and energy equation are improved and solved by using the characteristic line method,and the quantitative description of the loss of gas kinetic energy,the transmission velocity of water hammer wave,the continuation effect and friction loss in the fast shut-in wellbore of high temperature and high pressure gas wells is realized.It provides a theoretical basis for revealing early reservoir performance,advancing the radial flow section of pressure build-up curve and reasonably shortening shut-in time.At the same time,a software for calculating bottom hole pressure of offshore high temperature and high pressure gas wells considering various factors is developed.In the practical application of Dongfang Gas Field,the calculation results are compared with field test data,and the productivity calculation and well test interpretation of pressure recovery process are carried out.The results show that the coupling model established in this paper can well reflect the wellbore performance of offshore gas well,and continuation section the radial flow section in double logarithmic coincides well with the measured pressure.The accuracy of calculation is less than 0.5%.The problem of real-time monitoring of bottom hole pressure and analysis of production performance of high pressure gas wells such as DF1-1-F1 has been solved.