Formation and Transportation of Methane Hydrate Slurries in a Flow Loop reactor : Influence of a Dispersant

6 pagesIn this paper, we present the experimental results obtained from a new flow loop reactor in which methane hydrate particles are crystallized in water droplets transported in a oil flow. The final goal of this apparatus is to couple the rheology with the Particle Size Distribution of water droplets and gas hydrate during crystallization and to observe the influence of dispersants and/or kinetics additives (PVP). In this paper, we describe the flow loop plant and we show preliminary results of the rheology of the emulsion before crystallization and suspension after methane hydrate appearance. The influence of a dispersant additive is observed at a water content of 9 % vol

Rheological characterization and modelling of hydrates slurries during crystallization under laminar flowing

10 pagesAn original experimental set-up was developed and used for studying crystallization and rheology of methane hydrate/water/dodecane system under laminar flowing. Dynamic viscosity and conversion of water and gas into gas hydrate crystals were measured during the process for various water contents. Experimental results were explained by means of a model including nucleation, growth and agglomeration. Due to the high value of crystal and drop concentrations, agglomeration takes place through three-bodies collisions between one water drop and two already formed agglomerates. Resulting agglomerates were considered as fractal-like ones. During crystallization and agglomeration, the effective volume fraction of drops and porous agglomerates is increased, then suspension viscosity increases. When all water drops are crystallized, agglomeration stops and viscosity do not change

Influence d'additifs anti-agglomérants sur les propriétés de transport des hydrates de méthane dans des émulsions eau/dodécane

National audienceNous présentons les résultats expérimentaux obtenus à partir d'un nouveau dispositif expérimental représentant une conduite pétrolière sous-marine dans laquelle des particules d'hydrate de méthane sont cristallisées à partir d'une émulsion eau dans huile. Le comportement rhéologique de l'émulsion puis de la dispersion a été étudié. Ce dispositif nous a permis aussi d'examiner l'influence de dispersants et/ou d'additifs cinétiques (PVP) permettant d'éviter l'agglomération puis le bouchage des conduites

Formation and Dissociation of Hydrate Plugs in a Water in Oil Emulsion

4 pagesIn this paper, we present experimental results of the formation and dissociation of methane hydrate plugs in a semi-batch reactor. The plugs are done from water in heptane emulsion (water content from 30 %). The experimental results shows that the formation rate and dissociation rate are controlled by the heat transfer at the wall of the reactor. An unexpected behaviour is observed as the temperature decreases under the 0°C temperature during dissociation and seems to form ice which slows down the dissociation rate

Influence d'additifs anti-agglomérants sur l'agrégation et les propriétés de transport des hydrates de méthane cristallisant dans des émulsions eau/dodécane

The gas hydrates are solid compounds of clathrate type which can be formed starting from cold water and hydrocarbon gas molecules under pressure. These conditions are met in certain oil conduits and can lead to a problem of production. Indeed, the oil effluent which leaves a well of production always contains light water and hydrocarbon molecules (methane, ethane, propane) suitable form a gas hydrate. The methane hydrates are not naturally present in the layers of production because the temperature is too high (until 200°C). On the other hand, the oil fluid cools at the time of its transport in a control, either because control is localized in a particularly cold zone, or because control is underwater, by the contact with cold water. It can then create hydrates being likely to block the conduits. To prevent their crystallization, the current tendency is to couple three types of approaches: insulation of the conduits, injection of additive at the time of the critical phases, reheating of control by hot water circulation at the time of accidental stopping. This thesis takes part in the modeling of the flows after formation of hydrates. It is not thus a question of preventing crystallization but of being interested in rheology of the flow after formation of crystals. The long-term objective is to identify the origin of the transportability of the purées of hydrates under the influence of additives known as "anti-binders". The mechanisms of crystallization indeed are very often coupled: germination, growth, agglomeration, attrition... The comprehension of the mechanism of action of an additive is thus a complex spot, more especially as crystallization is closely related to the physical system in which it develops. The studies seeking to identify the mechanisms of crystallization, for then including/understanding the effects of additives all (or practically) were carried out in closed engines and simple systems (eau/gas) (Herri (1996), Pic (2000)...). Conversely, tests of validation of additives were carried out on loops control representing a real flow, therefore complex. Our work is thus halfway of the two preceding approaches. It is a question of approaching the geometrical conditions of an oil flow (pilot buckles) while preserving a simple system (eau/dodécane) with for objective on the long term identifying the coupling: geometry/crystallization/influence of the additives. The experimental device (height 12m, width 3m, length 6m) carried out within the framework of this thesis is a pilot loop of circulation reproducing certain conditions of the flow of an oil fluid (emulsion water in oil) in a subsea pipe, i.e. under strong pressure [ 1-10 MPa ] and low temperature [ 0-10°C ]. The various parts of this instrument are:The serpentine being rolled up on 3 levelsThe tube going up is a riser. With the base of this tube is injected methane in order to reduce the column of fluid to create an effect elevator: gaslift.The separator located at the top of the riser separate by gravity the gas part, of the liquid part (water, oil) which goes down again in a tube parallel with the riser towards the loop of circulationThe system of recompression of gases recovers gases of the separator to reinject them with the bottom of the riser after increase in the pressure. This experimental system is composed in fine of two loops circulating on themselves: a loop liquidates and a loop gas. These two loops share a common section made up of the riser and separator. This device made it possible to make rheological studies on the phase only continues (dodecane) according to the pressure of methane and on emulsions containing various water contents and of additives. Studies concerning the crystallization of the methane hydrates within the emulsions were carried out by considering the influence of the water content then that of the content of additive on the apparent viscosity of dispersions thus formed. We finally propose a modeling connecting crystallization to the rheological behavior.Les hydrates de gaz sont des composés solides de type clathrate pouvant se former à partir de molécules de gaz hydrocarbonées sous pression et d'eau froide. Ces conditions sont réunies dans certaines conduites pétrolières et peuvent poser un problème de production. En effet, l'effluent pétrolier qui sort d'un puits de production contient toujours de l'eau et des molécules hydrocarbonées légères (méthane, éthane, propane) susceptibles de former un hydrate de gaz. Les hydrates de méthane ne sont pas naturellement présents dans les gisements de production car la température est beaucoup trop élevée (jusqu'à 200 °C). Par contre, le fluide pétrolier se refroidit lors de son transport dans une conduite, soit parce que la conduite est localisée dans une zone particulièrement froide, soit parce que la conduite est sous-marine, au contact avec de l'eau froide. Il peut alors se former des hydrates risquant d'obstruer les conduites. Pour prévenir leur cristallisation, la tendance actuelle est de coupler trois types d'approches: isolation des conduites, injection d'additif lors des phases critiques, réchauffement de la conduite par circulation d'eau chaude lors des bouchages accidentels. Cette thèse participe à la modélisation des écoulements après formation d'hydrates. Il ne s'agit donc pas d'empêcher la cristallisation mais de s'intéresser à la rhéologie de l'écoulement après formation de cristaux. L'objectif à long terme est d'identifier l'origine de la transportabilité des coulis d'hydrates sous l'influence d'additifs dits « anti-agglomérants ».Les mécanismes de cristallisation sont en effet très souvent couplés : germination, croissance, agglomération, attrition... La compréhension du mécanisme d'action d'un additif est donc une tache complexe, d'autant plus que la cristallisation est intimement liée au système physique dans lequel elle se développe. Les études cherchant à identifier les mécanismes de cristallisation, pour ensuite comprendre les effets d'additifs ont toutes (ou pratiquement) été effectuées dans des réacteurs fermés et systèmes simples (eau/gaz) (Herri (1996), Pic (2000)...). A l'inverse, des tests de validation d'additifs ont été effectués sur des boucles pilotes représentant un écoulement réel, donc complexe.Notre travail se situe donc à mi-chemin des deux approches précédentes. Il s'agit de se rapprocher des conditions géométriques d'un écoulement pétrolier (boucle pilote) tout en conservant un système simple (eau/dodécane) avec pour objectif sur le long terme d'identifier le couplage : géométrie/cristallisation/influence des additifs.Le dispositif expérimental (hauteur 12 m, largeur 3 m, longueur 6 m) réalisé dans le cadre de cette thèse est une boucle pilote de circulation reproduisant certaines conditions de l'écoulement d'un fluide pétrolier (émulsion eau dans huile) dans une conduite sous-marine, c'est-à-dire sous forte pression [1-10 MPa] et faible température [0-10 °C]. Les différentes parties de cet instrument sont :· Le serpentin s'enroulant sur 3 niveaux,· Le tube montant, plus souvent désigné dans sa terminologie anglosaxone par « riser ». A la base de ce tube est injecté du méthane de façon à alléger la colonne de fluide pour créer un effet ascenseur (terminologie anglosaxone « gaslift »). · Le séparateur situé au sommet du riser sépare par gravité la partie gaz, de la partie liquide (eau, huile) qui redescend dans un tube parallèle au riser vers la boucle de circulation.· Le système de recompression des gaz récupère les gaz du séparateur pour les réinjecter au bas du riser après augmentation de la pression.Ce système expérimental est composé in fine de deux boucles circulant sur elles-mêmes : une boucle liquide et une boucle gaz. Ces deux boucles partagent une section commune composée du riser et du séparateur.Ce dispositif a permis de réaliser des études rhéologiques sur la phase continue seule (dodécane) en fonction de la pression de méthane et sur des émulsions contenant diverses teneurs en eau et en additifs. Des études concernant la cristallisation des hydrates de méthane au sein des émulsions ont été réalisées en considérant l'influence de la teneur en eau puis celle de la teneur en additif sur la viscosité apparente des dispersions ainsi formées. Nous proposons enfin une modélisation reliant la cristallisation au comportement rhéologique

Rheological characterisation and modelling of hydrate slurries during cristallization under laminar flowing

International audienceAn original experimental set-up was developed and used for studying crystallization and rheology of methane hydrate/water/dodecane system under laminar flowing. Dynamic viscosity and conversion of water and gas into gas hydrate crystals were measured during the process for various water contents. Experimental results were explained by means of a model including nucleation, growth and agglomeration. Due to the high value of crystal and drop concentrations, agglomeration takes place through three-bodies collisions between one water drop and two already formed agglomerates. Resulting agglomerates were considered as fractal-like ones. During crystallization and agglomeration, the effective volume fraction of drops and porous agglomerates is increased, then suspension viscosity increases. When all water drops are crystallized, agglomeration stops and viscosity do not change

Rheology of methane hydrate slurries during their crystallization in a water in dodecane emulsion under flowing

International audienceAn original experimental set-up was developed and used for studying crystallization and rheology of methane hydrate/water/dodecane system. Methane is injected in a water in dodecane emulsion at low temperature and high pressure in order to form methane hydrate crystals and to move the suspension by gas lift. It behaves as a Newtonian fluid. Dynamic viscosity and conversion of water and gas into gas hydrate crystals were measured during the process for various water contents. Experimental results were explained by means of a model including nucleation, growth and agglomeration. Due to the high value of crystal and drop concentrations, agglomeration takes place through three-body collisions between one water drop and two already formed agglomerates. Resulting agglomerates were considered as fractal-like ones. During crystallization and agglomeration, the effective volume fraction of drops and porous agglomerates is increased, and then suspension viscosity increases. When all water drops are crystallized, agglomeration stops and viscosity does not change