Abstract
This paper presents experimental and modeling results of oil-dominated cold flow generation in a medium-scale test rig. The term “cold flow” is a flow assurance method suited for long tieback subsea oil and gas fields that are exposed to the risk of gas hydrate formation and wax precipitation. A cold-flow unit placed downstream of the subsea wellhead efficiently cooled the well fluids to ambient conditions and converted wax and gas hydrates into small and non-agglomerating particles suspended in the remaining liquid phase. The resulting slurry, in addition to any residual gas or water, can be transported in the pipeline at ambient seabed temperature, reducing the cost related to chemical injections, pipeline insulation, or pipeline heating techniques. A medium-scale testing facility produced cold flow slurry by seeding and local heat induction techniques in a 2-inch passive cooler of 300 m in length. The water cut in the experiments varied from 2% to 20%. The relative viscosity for a solid load of up to 22% was approximately 2. Shut-in and restart experiments indicate that relatively low pump pressure was required to initiate the flow. Downstream pigging indicated no agglomeration or settling of particles. A steady-state simplified heat and mass balance approach combines (1) solid deposition estimation on the basis of empirical data and (2) the crystallization and thermodynamic aspects of gas hydrate formation and dissociation to describe the bulk and outer temperature profiles during continuous cold flow generation with the recirculation of solids, achieving an absolute error within ± 1 ° C.