High pressure micromechanical force measurements of the effects of surface corrosion and salinity on CH₄/C₂H₆ hydrate particle–surface interactions

Abstract

In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force (MMF) apparatus was applied to directly measure CH/CH hydrate adhesion/cohesion forces under low temperature and high pressure conditions. A CH/CH gas mixture was used as the hydrate former. Adhesion forces between hydrate particles and carbon steel (CS) surfaces were measured, and the effects of corrosion on adhesion forces were analyzed. The influences of NaCl concentration on the cohesion force between CH/CH hydrate particles were also studied for gas-dominated systems. It was observed that there was no measurable adhesion force for pristine (no corrosion) and corroded surfaces, when there was no condensed water or water droplet on these surfaces. With water on the surface (the estimated water amount was around 1.7 μg mm), a hydrate film growth process was observed during the measurement. CS samples were soaked in NaCl solution to obtain different extents of corrosion on surfaces, and adhesion measurements were performed on both pristine and corroded samples. The adhesion force was found to increase with increasing soak times in 5 wt% NaCl (resulting in more visual corrosion) by up to 500%. For the effect of salinity on cohesion forces, it was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model.

Structural Effects of Gas Hydrate Antiagglomerant Molecules on Interfacial Interparticle Force Interactions

“…The coatings were observed to reduce the interaction between hydrates and surfaces without any corrosion . The adhesive force of a hydrate particle to an uncoated carbon steel surface (in a gas phase) increased when the carbon steel surface was precorroded . In addition, the interparticle cohesive force was observed to decrease with the addition of NaCl.…”

“…Solid hydrate particles can agglomerate through collisions with other hydrates. , Insight into the properties and mechanisms of the agglomeration can be provided by the cohesive forces. , From previous studies, ,, the capillary liquid bridge (CLB) theory was shown to be the most appropriate model to explain the hydrate particle cohesive force phenomenon. This model describes the liquid bridge present between particles (as shown in Figure ), which is shown in eq : where F A is the cohesive force, γ is the interfacial tension between the liquid bridge and the bulk fluid, θ is the contact angle between the gas hydrate particle and the liquid bridge, α is the embracing angle, H is the particle separation distance, d is the liquid bridge immersion depth, and R* is the harmonic mean radius of two gas hydrate particles …”

“…The high-pressure interparticle force device, known as the HP-MMF, was initially described by Brown and Lee et al This HP-MMF instrument was used to measure the cohesive forces of ice particles and/or CH 4 /C 2 H 6 hydrate particles in a gas phase. Wang et al then performed adhesive force measurements with commercial coatings applied to carbon steel surfaces in a gas phase. The coatings were observed to reduce the interaction between hydrates and surfaces without any corrosion .…”

Correlating Antiagglomerant Performance with Gas Hydrate Cohesion

“…To probe realistic conditions, the high-pressure micromechanical force (HP-MMF) 44 apparatus was designed to quantify cohesive forces between ice particles and natural gas hydrate particles in both gas 44,45 and liquid hydrocarbons. 46−48 Recently, Koh and coworkers 48 employed the HP-MMF apparatus to measure CH 4 /C 2 H 6 hydrate cohesive forces in the presence of AAs.…”

“…Assuming that capillary cohesion governs hydrate interparticle forces, the results suggest that surfactants could disturb the liquid bridge formed between hydrate particles, potentially reducing the cohesive forces. , Most previous studies were conducted using hydrates that are stable at atmospheric pressure, for example, using hydrates of tetrahydrofuran (THF) and CyC5, ,,,,, although the conditions are different compared to those realistically experienced in typical flow assurance applications (high pressures and low temperatures). To probe realistic conditions, the high-pressure micromechanical force (HP-MMF) apparatus was designed to quantify cohesive forces between ice particles and natural gas hydrate particles in both gas , and liquid hydrocarbons. − Recently, Koh and coworkers employed the HP-MMF apparatus to measure CH 4 /C 2 H 6 hydrate cohesive forces in the presence of AAs. The flow assurance performance of those AAs was assessed using a rocking cell apparatus, as frequently done in industry.…”