Abstract
The rapid increasing amount of produced water in the deep-water and ultra-deep-water fields, especially those at their later development stages, increases the risk of the occurrence of hydrates plugging. In order to prevent and remediate the hydrates risks, it is important to understand the hydrate formation, slurry flow, and plugging characteristics and mechanisms under high water cuts conditions. In this paper, experiments with high water cuts ranging from 60–100% were conducted using a high pressure flow loop with observation windows. The whole processes of the hydrate formation, slurry flow and plugging is visually seen and recorded, and has been discussed and explained in detail in this paper. Moreover, it is found that the increasing water cuts shorten the induction time, but increase the volume fraction of hydrates. As the water cuts increase, the flow time of the hydrate slurry decreases, which serves as a critical parameter for the safe operation of the pipeline. In addition, different hypothetical mechanisms have been proposed for the medium and high water cuts conditions. We believe that this research can provide theoretical support for the safe transportation of oil and gas development in the high water cut oilfield.
Highlights
Flow assurance problems such as hydrates [1,2], wax deposition [3,4,5,6,7], and asphaltenes are critical operating challenges to ensure the safe and efficient transportation of unprocessed well steams especially in offshore oil fields [8,9]
In order to explore the effect of water cuts on hydrate formation and plug, experiments with different water cuts (60%, 80%, 95%, 100%) were conducted under the condition of the initial pressure of 3 MPa, the temperature of 1.5 ◦ C and the liquid holding capacity of 90%
Asthe the water cuts increases, thecontact contactarea area the gas-water the driving force provided by water the gas space after the the formation ofofofthe gas-water increases, and the driving force provided by the gas space after the formation of the hydrate gas-water increases, the driving force provided by the gas hydrate space after the formation hydrate is large, whichand accelerates the continued formation of the particles, resulting of in the a is large, which accelerates the continued formation of the hydrate particles, resulting in a decrease in hydrate is large, which accelerates the continued formation of the hydrate particles, resulting in decrease in the fluidity of the slurry, and the flow time is shortened
Summary
Flow assurance problems such as hydrates [1,2], wax deposition [3,4,5,6,7], and asphaltenes are critical operating challenges to ensure the safe and efficient transportation of unprocessed well steams especially in offshore oil fields [8,9]. Understanding the hydrate plugging mechanism in high water cut systems is of great significance for the safe operation of offshore multiphase pipelines. It has been well-known that gas hydrates are ice-like solids, where the light hydrocarbon species (e.g., methane) get trapped in the hydrogen bonded molecular cage of water under high pressure and low temperature conditions [10]. The effect of water cuts on the time of hydrate slurry flows, friction change, and differential pressure change were reported as well. These results are believed to provide theoretical support for the safe transportation of oil and gas development in the high water cut oilfield
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