Gas Hydrate Formation in High Water Content Systems Containing Anti-Agglomerat and Salt

Abstract

In this work, the effects of an anti-agglomerant (AA) and salt (sodium chloride, NaCl) on water-in-oil (w/o) emulsion stability with and without the presence of gas hydrates is presented. The characteristics of gas hydrate formation and the hydrate slurry transportability were determined using a high pressure autoclave cell, with continuous mixing. The stability of the emulsions was independently measured by performing bottle tests, where the stability of the emulsion was determined by observing any evidence phase coalescence for a period of one week after emulsification. In addition, the stability of the emulsion with hydrate formation and dissociation was tested using high pressure differential scanning calorimetry (DSC). From high pressure autoclave studies, it was observed that the formation of a stable emulsion was shown to with the subject oils led to transportable hydrate slurries. Note however, it was observed that for this specific oil at 75 vol.% water cut and the addition of both AA and salt, a highly viscous mousse with viscosity of ~100 000 cP formed when the emulsion was saturated with methane gas at 950 psia and 20 °C. Even without the presence of hydrate, the formation of a highly viscous mousse may not be desirable in the field production system since it could render the system inoperable (effectively plugged). Interestingly, it was observed that the highly viscous mousse produced dispersed slurry of hydrates upon hydrate formation. Based on the autoclave studies, the absolute motor current (which indicates the relative viscosity of the system) at maximum amount of hydrate is 2 times lower of its original viscosity.

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

“…It is known that salt can inhibit hydrate formation and shift the hydrate equilibrium conditions, ,− thereby affecting the performance of AAs. − To further investigate the effect of salt (NaCl in this study) on the gas hydrate surfaces and interparticle interactions, experiments were conducted at constant subcooling, which provides the same driving force to form hydrates with and without NaCl. Figure shows the cohesive force measurements in the systems with the AA-C8 and AA-C12 at 0, 3.5, 5, and 7.5 wt % of NaCl in DI water.…”

“…The results reported in this work can help in advancing new AA chemistry for flow assurance strategies of maintaining slurry flow. Future work could study the interaction intensity between salt and AA molecules by utilizing ion chromatography analysis, where the ions can be hydrated differently at various salinities . The presence of AAs may alter the capillary pressure and hydrate surface wettability .…”

“…Future work could study the interaction intensity between salt and AA molecules by utilizing ion chromatography analysis, where the ions can be hydrated differently at various salinities. 78 The presence of AAs may alter the capillary pressure and hydrate surface wettability. 86 Therefore, the direct relationship between the capillary pressure and the cohesive force would be also interesting for future studies in the presence of AAs.…”