Abstract
One of the main issues in the area of drilling and production in deep and ultra-deep water in the oil industry is the formation of natural gas hydrates. Hydrates are crystalline structures resembling ice, which are usually formed in conditions of high pressure and low temperature. Once these structures are formed, they can grow and agglomerate, forming plugs that can eventually completely or partially block the production lines, causing huge financial losses. To predict flow behavior of these fluids inside the production lines, it is necessary to understand their mechanical behavior. This work analyzes the rheological behavior of hydrates slurries formed by a mixture of water and Tetrahydrofuran (THF) under high pressure and low temperature conditions, close to the ones found in deep water oil exploration. The THF hydrates form similar structures as the hydrates originally formed in the water-in-oil emulsions in the presence of natural gas, at extreme conditions of high pressure and low temperature. The experiments revealed some important issues that need to be taken into account in the rheological measurements. The results obtained show that the hydrate slurry viscosity increases with pressure. Oscillatory tests showed that elasticity and yield stress also increase with pressure.
Highlights
Natural gas hydrates are solid, crystalline structures that looks like ice [1, 2], which are formed under extreme thermodynamic conditions of high pressure and low temperature [1,2,3,4]
Natural gas hydrates are a major concern of the oil industry, since their formation can deeply affect the flow during drilling and production [5, 6]
When the production lines or the wells are inside the hydrates formation envelope of high pressure and low temperature, it is imperative to know how all these variables will affect hydrates formation and agglomeration, in order to control and optimize the production and/or drilling operations [3, 17, 18]
Summary
Natural gas hydrates are solid, crystalline structures that looks like ice [1, 2], which are formed under extreme thermodynamic conditions of high pressure and low temperature [1,2,3,4]. This study analyzes the rheology of hydrate slurries formed from a model fluid composed of deionized water and Tetrahydrofuran (THF), in similar conditions to the ones obtained at deep water oil fields, i.e. high pressure and low temperature. This model fluid forms hydrates structure of type II, which are similar of that formed when a gas is present in water-in-oil emulsions. An abrupt increase of the viscosity of such systems was observed in an isochoric process as the gas was being consumed, leading to a decrease in pressure values. In the last two section the rheological results are presented and discussed, and some final remarks are presented
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