Natural Gas Industry B

Natural Gas Industry B

Volume 5, Issue 4, July 2018, Pages 344-350
Natural Gas Industry B

Research Article
Features and prevention of gas hydrate blockage in test strings of deep-water gas wells,☆☆,

https://doi.org/10.1016/j.ngib.2018.01.008Get rights and content
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Abstract

Due to the uncertainties in formation mechanism of gas hydrate blockages in strings during the test of deep-water gas wells, inhibitors are either excessively consumed or inefficiently used when conventional prevention techniques are used. In this paper, a study was conducted on multi-phase flows, in terms of hydrate formation kinetics and hydrate particle migration and settlement kinetics. In this process, a model for quantitative prediction of hydrate blockage was built to predict when and where the blockage occurs in the strings and evaluate the severity of such blockage, in order to define the high-risk zones. Eventually, an innovative hydrate blockage prevention technique based on hydrate blockage free window (HBFW) was proposed to determine the optimal concentration and the flow rate of inhibitors. The study results are in the following four aspects. First, gas hydrates generated in the wellbore may deposit on the internal walls of strings. With the increase in thicknesses of such gas hydrate layers, the diameter of a pipe string decreases. Accumulation of gas hydrates generated around liquid film on pipe walls is the key contributor to the blockage in strings. Second, as the water depth increases or the gas production reduces, the HBFW turns to be narrower for production safety, and the time to initiate blockage is shorter. Third, application of hydrate inhibitors can effectively delay the occurrence of blockage and expand the window of safe production. Fourth, the innovative prevention technique can effectively reduce the volume and the flow rate of inhibitors (by 50% in the case study). The innovative technique effectively eliminates the problems related to the excessive consumption of inhibitors in the conventional methods and provides a valuable reference for the prevention of gas hydrates formation in deep-water gas well tests.

Keywords

Deepwater
Gas well testing
Gas hydrate
Blockage
Prevention method
Hydrate blockage free window (HBFW)
Annular mist flow
Volume of inhibitor
Flow rate

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Project supported by the National Program on Key Basic Research Project (973 Program) "Basic research on safe and efficient drilling and completion of marine deepwater oil and gas wells" (No.:2015CB251204) and the National Science Foundation for Distinguished Young Scholars “Theory and application of multiphase flow of oil and gas wells” (No.: 51622405).

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This is the English version of the originally published article in Natural Gas Industry (in Chinese), which can be found at https://doi.org/10.3787/j.issn.1000-0976.2018.01.010.

Peer review under responsibility of Sichuan Petroleum Administration.