Feasibility Study On Downhole Throttle Depressurization Technology Of Testing String In Offshore High Pressure Gas Well

Compared with the ground gas well test ground flow,in the offshore gas well test ground flow,the test tree is connected to the ground flow using a hose connection.Due to the insufficient pressure rating of the hose,the development of offshore high-pressure gas well test technology has entered a bottleneck period,so that some of the currently discovered offshore high-pressure gas fields are still unable to be tested.So CNOOC Zhanjiang Branch put forward the idea of applying downhole throttling technology in test wells.For this reason,this paper has fully investigated the historical data of the site,and used theoretical analysis and software simulations to analyze the feasibility of downhole throttling technology in high-pressure gas wells string of offshore.By comparing and analyzing the differences between the testing process of offshore gas wells,the test procedures of gas wells in the land,and the test string of gas well production tubing and gas wells,the gas well test tubing columns were split into upper and lower parts.Therefore,in the test string structure,the maximum lower limit of the allowable depth of the downhole nozzle is determined.In combination with whether the hydrate is generated in the test string after throttling,the minimum limit of the depth of the downhole nozzle is analyzed.The reasonable depth range of the nozzle in the downhole throttling process was determined.According to the requirements of the flow state at the nozzle and the conditions generated by the cavitation phenomenon,the front and rear pressure ratio range of the nozzle that meets the test requirements was determined.Based on theoretical analysis of nozzle flow and test flow requirements,a set of methods for the selection and adjustable range analysis of downhole nozzles was established.Based on the gas well(M well)in a certain block in the South China Sea,the physical model was established using PIPESIM software,and the test flow and wellbore pressure distribution were analyzed.It was concluded that the wellbore with low flow needs to implement throttling and pressure reduction measures.At the same time,the analysis and detennination of the fixed downhole nozzle can not meet the requirements of large changes in the test flow range of offshore high-pressure gas wells,and proposed the solution to the application of adjustable downhole nozzles.Based on the parameters of the M and N wells,a gas well(X well)with a higher pressure than the currently tested gas well was designed.Based on the analysis method established before,the conclusions of the nozzle type selection and adjustable range analysis were verified.At the same time,a pressure disturbance analysis method was established between the downhole throttle nozzle and the ground throttle nozzle.According to this method,the pressure interference relationship between the downhole throttle nozzle and the ground throttle nozzle was studied.The analysis demonstrated that the high pressure gas well test tube was used at sea.Feasibility of Downhole Throttling and Pressure Reduction Technology in Column Wells.The analysis results show that it is completely feasible to apply the downhole throttle and pressure reduction technology to the offshore high pressure gas well test.