Study On Hydrate Formation And Depressurization Production Simulation

The phenomenon that it is easier for dissociated water to synthesize hydrate after hydrate decomposition is called memory effect.Due to the memory effect,the natural gas and dissociated water released in the actual hydrate exploitation process are easy to form hydrate again in the deep water water water and gas production pipeline,causing pipeline blockage and reducing the exploitation efficiency.Therefore,it is of great benefit to solve the problem of hydrate pipeline blockage in deep-sea mining to evaluate the formation kinetics,memory effect mechanism and influencing factors in the process of multiple synthesis of hydrate.In addition,in most of the current numerical simulation studies on hydrate exploitation,the hydrate decomposition rate constant directly refers to the fixed value measured under ideal conditions.However,according to the research results of domestic and foreign scholars in recent years,many factors will affect the decomposition rate of hydrate,which means that the reliability of simulation results obtained by using fixed decomposition rate constant is limited.Three different experiments were carried out to study the above problems.The visualization of hydrate multiple synthesis was studied.The static hydrate growth morphology and growth law were explored.The differences of hydrate growth morphology between primary synthesis and multiple synthesis were compared and analyzed.A large number of experimental results of multiple hydrate synthesis were obtained by innovative experimental methods.From the perspective of statistics,the influencing factors and rules of memory effect of multiple hydrate synthesis were quantitatively evaluated.This paper attempts to put forward hypothesis and demonstration on the mechanism of memory effect.In addition,combined with physical experiments and numerical simulation,the hydrate decomposition rate constant in the process of numerical simulation was determined,and the numerical simulation results of different depressurization methods were analyzed.The experimental results show that:(1)the growth of hydrate can be divided into four stages,and the dissociated water will become more and more turbid,which is an important evidence of the existence of nano bubbles;(2)the main factors affecting the strength and stability of memory effect are decomposition temperature and time,while the decomposition pressure has little effect;(3)the root cause of memory effect It is very likely that it is nanobubbles,and the fundamental reason for the difference of memory effect is likely to depend on the number and activity of dipoles on the surface of nanobubbles;(4)it is feasible to determine the hydrate decomposition rate constant by physical experiments combined with numerical simulation fitting,which is helpful to improve the reliability of numerical simulation;(5)well shut in during depressurization mining will only affect the ground in a short time However,shut in operation will greatly prolong the time of complete decomposition of hydrate.