Study On Hydrate Slurry Plugging Mechanisms And Flow Assurance

Gas hydrates pose the major deep water flow assurance problem in the production and transportation of oil and gas.As production moves to hasher environment,hydrate control strategies are shifting from hydrate avoidance to hydrate management.The study on natural gas hydrate slurry flow and plugging mechanisms,which is the fundamental basis for hydrate management strategies,is far from satisfaction.Little to no research has previously been performed to address gas hydrate particle adhering to pipe surfaces.Meanwhile,hydrate agglomeration and deposition mechanisms are not being incorporated simultaneously into the available hydrate plugging models;Industry still lacks practicable tools which enable the rapid assessment of gas hydrate slurry plugging risk.Research on the above aeras will make a further understanding of gas hydrate plugging mechanisms and promote the use of hydrate slurries in industrial applications.Hydrate deposition from particles adhering was investgated by analyzing forces applied on hydrate particles and particle removal mechanisms on pipe walls.The concept of the removal critical size and adhesion rate were introduced into the hydrate-pipe wall dynamic adhesion model.The proposed model presents a novel approach for quantitative description of the hydrate particle adhesion on pipe walls with or whitout the presence of free water.In order to study the flow and plugging mechanisms of natural gas hydrate slurry,initially,by considering the characteristic physical properties of hydrate slurry like inter-phase interactions,particle agglomeration,solids viscosity and the maximum packing fraction,a CFD-model based on Euler-Euler two-fluid model was built to describe the hydrate slurry isotherm flow in pipelines.The particle size and resistance characteristics of hydrate slurry were analyzed.The limitations of this method were also pointed out.In parallel with the CFD-model,a steady-state natural gas hydrate slurry flow model was developed based on the concentration distribution calculation model and the research on hydrate slurry flow patterns.This preliminary model has a coupling relationship with hydrate particle agglomeration and bedding.The model predictions were in a good agreement with the experiment data.Aggregate diameters,relative viscosity,pressure drop characteristics and flow patterns of natural gas hydrate slurry were analyzed using the steady-state flow model.Based on the work described above,a transient natural gas hydrate slurry flow model was established through the analysis of the Danielson hydrodynamic slug flow model and Zerpa model.The transient flow model includes a hydrate formation model to estimate the hydrate growth in oil-continuous systems.The water cut of liquid phase is tracked during the formation process.Camargo-Palermo model is also incorporated for the purpose of calculating the hydrate agglomerate diameter and the relative viscosity of hydrate slurry.The results predicted by the model agree well with the experimental results measured in a high-pressure flowloop facility at ExxonMobil.