Experimental investigation and modelling of heat loss mechanism from offshore buried pipelines

Chakraborty, Suvra (2017) Experimental investigation and modelling of heat loss mechanism from offshore buried pipelines. Masters thesis, Memorial University of Newfoundland.

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Abstract

Modeling of heat loss from offshore buried pipelines is one of the major concerns for oil and gas industries. Offshore oil and gas production and thermal modeling of buried pipelines in Arctic regions are challenging tasks due to the harsh environmental conditions and hazards. Heavy components of crude oil start to precipitate as wax crystal when the fluid temperature drops. Gas hydrates also form when natural gas combines with free water at high pressure and low temperature. Significant heat loss may occur from offshore buried pipelines in the forms of heat conduction and natural convection through the seabed. The later can become more prominent where the backfill soil is loose or sandy. Theoretical shape factor model was widely utilized to estimate heat loss from buried pipelines. Several benchmark tests were performed to ensure the validity of the test using theoretical shape factor models which depend on the amount of heat flow, thermal conductivity and geometry of the surrounding medium. The degree of saturation of surrounding medium can play a significant role in the thermal behavior of fluid traveling through the backfill soil. This research presents several steady state and transient response analysis describing some influential geotechnical parameters along with test procedures for different parameters such as burial depth, backfill soil, trench geometries, etc. Several shutdown (cooldown) tests were performed to show the transient response in the dry and saturated sand medium. The outcomes of this research will provide valuable experimental data and numerical predictions for offshore pipeline design, heat loss from buried pipelines in offshore conditions, and efficient model to mitigate the flow assurance issues e.g. wax and hydrates.

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