Simulating Hydrate Growth and Transport Behavior in Gas-Dominant Flow

Abstract

The current hydrate kinetics model implemented in the multiphase flow simulator OLGA treats hydrate growth in oil-continuous systems by considering the solidification of emulsified water droplets to form a hydrate-in-oil slurry that is assumed to be stable. To date, the validity of this model has not been established for gas-dominant systems, where gas void fractions can exceed 90 vol %. Here, six experimental data sets, collected using a 40-m single-pass gas-dominant flowloop operating in the annular-flow regime, were compared with predictions made using the current hydrate kinetics model. The comparison identified discrepancies in the predicted flow regime and the gas–water interfacial area that significantly affect kinetic hydrate-growth-rate calculations; these discrepancies might be due, in part, to differences in dynamic similarity between flowloop experiments and industrial-scale simulations. By adjusting only the kinetic rate scaling factor, it was not possible to match the pressure drop observed experimentally, illustrating that the formation of a viscous hydrate slurry alone cannot account for the resistance to flow observed in gas-dominant systems. We demonstrate that it is possible to emulate deposition in the current model by adjusting the slip ratio between the hydrate particles and the condensed phases; this approach allowed stenosis-type restrictions to occur in the simulation, as well as pressure-drop behavior similar to that observed experimentally. Utilizing a simple in-house model with empirical correlations to predict the hydrodynamics, it is possible to match relatively closely the measured growth rate and pressure drop simultaneously. Such agreement could not be reached using the current hydrate implementation available in OLGA, highlighting the need for a gas-specific hydrate growth model that is capable of capturing both hydrate growth from suspended droplets in the gas phase and solid growth at the flowline wall, as well as the extent of hydrate deposition on the wall.

Changing the Hydrate Management Guidelines: From Benchtop Experiments to CSMHyK Field Simulations

“…In this paper, hydrate formation, agglomeration, and transportation in oil continuous systems are discussed. Hydrate bedding and deposition, as well as the transition from an oil-dominated system to a partially dispersed system at high water cuts, may also occur during oil/gas pipeline transportation, , however this is beyond the scope of this work and will not be discussed here. A subcooling of 2.8 °C is assumed for hydrate nucleation in all of the simulations to make a conservative estimation .…”

Molecular properties of interfaces relevant for clathrate hydrate agglomeration

“…1. Engineering design: it is possible to prevent the produced fluid from entering the hydrate-stability region during flow, via modelling the transport of multi-phase systems [13] and determining required insulation thickness, pipeline size and possible subsea pumping needs. Because the composition and rate of the produced hydrocarbons can change as wells age (i.e., lower flow overcoming the added specific heat of higher water content, with the higher water content raising the risk of plug formation), the fluid could still enter the hydrate stability region and form blockages during flow late in field life [14].…”

Reduction Clathrate Hydrates Growth Rates and Adhesion Forces on Surfaces of Inorganic or Polymer Coatings

“…Active methods have been developed to prevent the formation of hydrate inside oil and gas pipelines by applying heat to the pipelines, adding water-miscible alcohols such as methanol to shift the thermodynamic equilibrium away from hydrate formation, or using kinetic inhibitors to delay the crystallization and growth of hydrates. , However, these methods are expensive, require substantial power for operation, and may have detrimental environmental consequences . Since most of the active strategies are inefficient, energy consuming, high cost, or environmentally harmful, the development of passive antihydrate coatings is urgent …”

“…In general, the surface chemistry and morphology are the principal concerns for conceiving hydrate-phobic or antihydrate coatings. The particular properties of the coatings, such as low surface energy, low glass transition temperature, and low modulus, endow silicone-based or fluorine-based materials with remarkable hydrate phobicity.…”