CASCADE-SHOCK-WAVE TECHNOLOGY FOR ELIMINATION OF COMPLETE HYDRATE BLOCKAGE OF AN UNDERWATER MARINE GAS PIPELINE

The article considers the issues of forecasting the conditions of hydrate formation during transportation of natural gas through subsea gas pipelines and methods for eliminating multi-stage complications. For the first time, a theoretical interpretation of the newly developped technology of cascade-shock-wave elimination of complete blockage of a gas pipeline by a hydrate plug is proposed and its practical implementation is described. The specificity of hydrate formation in offshore subsea gas pipelines and the unsuitability of methods developed for gas pipelines on land in marine conditions are noted. Additional factors influencing the processes of hydrate formation and methods for their elimination are indicated, a colder temperature at the depth of the gas pipeline, the impossibility of using, unlike on land, additional devices for measuring pressure and temperature along the pipeline. The author's systematization of the stages of hydrate formation in the main subsea gas pipeline, the corresponding methods for predicting the level of risk and eliminating emerging problems are given. The mathematical models and theoretical nuances of the proposed cascade-shock-wave technology, consisting of cyclic supply of high-pressure gas to a gas pipeline that was stopped due to hydrate blockage and then emptied, are considered. As a result of the analysis of the processes of high-pressure gas movement, it was revealed that each subsequent compression pulse, propa-gating with an ever-increasing speed of sound through the already heated gas, will catch up with the previous ones, forming a shock wave front. Natural constrictions of low sections of the pipeline due to accumulation of condensate perform the functions of nozzles, repeatedly passing through which gas flows acquire velocities exceeding the speed of sound. The procedure for carrying out an operation to eliminate a hydrate plug on a real gas pipeline is described, calculations of temperature conditions at the point of contact with the hydrate plug are carried out, the dependence of the temperature at the point of contact on the pressure of high-pressure gas supply to the gas pipeline is determined. In connection with the short-term (several seconds) although quite high heating of the plane of contact with the hydrate plug, it is justified to conduct several cycles of high-pressure gas supply to the emergency gas pipeline. The developed and tested cascade-shock-wave technology for eliminating the complete hydrate blockage of an underwater marine gas pipeline is based on the combined effect of thermal heating of the hydrate plug due to the increase in temperature in the plane of contact due to the formation of a supersonic flow and a dynamic wave gas flow. Bibl. 15, Tab. 1, Fig. 2.