Study On The Flow-plugging Mechanism Of Natural Gas Hydrate In Oil-water System

During the exploitation of subsea oil and gas resources,the safe transportation of oil and gas resources is hindered seriously,due to hydrate blockage.The flow-plugging mechanism research of hydrate slurry in oil-water system is the theoretical basis of hydrate risk control work.The related experiment and numerical simulation have been done by many scholars,but the relevant experimental conclusion is not unified due to the difference from experimental medium and experimental device.In addition,the commercial software such as Fluent have been used to study the flow characteristics of hydrate slurry by most scholars,and the conclusion from the numerical simulation can accord with the experimental conclusions at some level,but it is difficult for numerical model to be implanted into the commercial software during the deep fitting of the actual process,due to the non-open nature of the code from the commercial software.Research on the above problem can be used to provide theoretical guidance for hydrate risk control work.In order to grasp the flow-plugging mechanism of hydrate slurry flow in oil-water system,the morphology of hydrate formation and aggregation in oil-water system and microscale sand system,the flow-plugging characteristics of hydrate slurry in oil-water system were respectively investigated using a high-pressure flow loop and a high-pressure autoclave.And,in terms of the numerical model of solid-liquid flow in pipeline with hydrate particle,the OpenFoam numerical simulation platform was built.Meanwhile,the characteristics of solid-liquid transient flow in pipeline with hydrate particles were investigated using OpenFoam.For the morphology of natural gas hydrate formation and aggregation,the result shows with the increase of the concentration of Span80,the emulsion is more stable,meanwhile,hydrate form is changed firstly from bulk to fractal aggregation and then particle,resulting in the formation of stable hydrate slurry.In microscale sand system,the morphology of hydrate particles with and without sand was observed experimentally,and that the wall-attached hydrate layer presented a sandwich structure;In microscale sand system,the manner in which the sand enters the hydrate layer contains the colliding implantations of hydrate particles with sand and particle-carry;In terms of the experimental results,a physical model of hydrate layer within sands and one-dimensional mathematical model of the growth of wall-attached hydrate layer are built.For the flow-plugging characteristics of gas hydrate slurry in oil-water system,the results shows: In the case of high initial pressure low,lower velocity and low moisture content,hydrate plugging is easy to occur in the pipeline.The presence of envelope structure of hydrate particle can lead to hydrate blockage with lower hydrate content(<2wt.%).Considering the presence of envelope structure of hydrate particle and the analysis of hydrate deposition process,the hydrate plugging mechanism in oil and water system was revised.For the numerical simulation about the characteristics of solid-liquid transient flow in pipeline with hydrate particles,the results show: the numerical model of solid-liquid flow in pipeline with hydrate particles is more reliable to investigate the problem of solid-liquid flow in pipeline with hydrate particles;Along the pipeline radial,the volume fraction of hydrate particle presents gradient distribution and the volume fraction of hydrate particle at the wall is the largest.Along the pipe axis,the volume fraction of hydrate particles decreases gradually in the upper area of pipeline,however,the volume fraction of hydrate particles increases gradually in the lower area of pipeline,which means that the risk of hydrate deposition plugging is highest in the end of pipeline;The larger the particle size of hydrate particles is,the more uneven the distribution of hydrate particles is in pipeline,and the larger the deposition tendency of hydrate particles is in the end of pipeline;The larger the inlet volume fraction of hydrate particles and the larger the inlet velocity,the more uniform the distribution of hydrate particles in pipeline,and the more difficult to deposit the hydrate particles.