Advancing Laboratory Characterization and Qualification of Additives for Hydrate Slurry Flow in Multiphase Systems

Abstract

In the flowlines of oil/gas production systems, the formation of gas hydrates, icelike crystalline compounds of water and gas that form at low temperature and high pressure, can disrupt stable flow, often resulting in solid blockages that necessitate remediation and pose safety issues. Low dosage hydrate inhibitor antiagglomerants (LDHI-AAs) are chemical additives used to manage the hydrate slurry flow at relatively low dosage (∼1% of water content) by dispersing hydrates in the continuous liquid hydrocarbon phase. A reliable assessment of LDHI-AA performance is thus required for their optimal use under a given field condition. Rocking cells have been extensively used in the oil/gas industry for LDHI-AA qualifications as it is easy to build and allows full visualization of the cell interior. However, a solid rolling ball, which is put into the conventional rocking cell for mixing, brings significant disturbances to the flow and dispersion of the phases and, in particular, by breaking up the hydrates formed and pushing them to accumulate at the end of the cell, giving a very conservative (worst-case) evaluation of LDHI-AAs. There is a large gap between the testing conditions of rocking cells and the actual field conditions. The recently developed rock-flow cell can provide a much closer representation of the shear, phase dispersion and thus the flow regime in flowlines. Here, we demonstrate the capability of the rock-flow cell as a more robust testing tool for LDHI-AA qualification. The impact of the cooling mode, degree of subcooling, and salinity are well characterized in terms of hydrate aggregation, deposition, and bedding. The test results demonstrate the advantages of the rock-flow cell over the conventional rocking cell to characterize the hydrate slurry by visualization and quantification of the hydrate formation and accumulation. As such, the rock-flow cell can be used as an effective testing tool for LDHI-AA qualification, which can also be applied to many other phase precipitation problems encountered in flow assurance.