Omniphobic Surface Treatment Helps Mitigate Solids Deposition
Authors: Carpenter Chris 
Published: December 2022

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 32059, “Scaleup and Modeling Efforts Using an Omniphobic Surface Treatment for Mitigating Solids Deposition,” by Erika Brown, Oceanit, and Marshall Pickarts, SPE, and Jose Delgado-Linares, SPE, Colorado School of Mines, et al. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission.

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Gas hydrates, waxes, and asphaltenes represent significant flow-assurance challenges, especially in subsea lines where treatment options can be limited. As an alternative to constant chemical injection or thermodynamic controls such as insulation or heating, a robust omniphobic surface treatment (OST) material has been developed that has been shown in previous studies to reduce the adhesion of flow-assurance solids significantly, resulting in lower risk for deposition and plugging by gas hydrates, waxes, and asphaltenes.

Introduction
While laboratory-scale and mid-scale experiments have shown the OST to be effective for a range of solids-deposition scenarios, full-scale field trials require additional information to test new technologies and validate that small-scale data are applicable for deployment activities. In this work, simulations were performed that took parametric data from laboratory-scale results and applied them to a full-scale pipeline. Additionally, laboratory-scale survivability tests under a range of thermodynamic and chemical conditions were conducted, extending the range of conditions for which the surface treatment has been validated. Finally, application techniques were demonstrated on a 20-in. pipeline, showing that in-situ application, including surface preparation and material application, can be scaled up from laboratory scale without compromising coverage, adhesion, or surface-roughness characteristics.

Simulated Treated Pipeline
Modeling was conducted using part of a full-scale transient multiphase-flow simulator. The simulation was based on an existing field known to have hydrate-formation challenges that includes a 3.2-km-long, 4-in.-outer diameter, uninsulated horizontal pipe. The operating pressure in the flowline was approximately 1,200 psia. The reservoir produces a black oil with 10 vol% water cut and approximately 60 vol% liquid loading. The average liquid velocity in the pipeline was set to 0.8 m/s (3 kg/s) for this simulation. Both steady-state and transient (shut-in followed by a restart) simulations were performed because, historically, transient conditions represent a minority of operations but are the most high-risk scenarios from a hydrate-formation perspective. The transient-state simulations included a 1-day shut-in and 7 subsequent days of restart with 4 hours of ramp-up to return to the steady-state flow rate. The steady-state simulation was a 7-day constant-flowing simulation. The ambient temperature outside the pipe was 5°C. While the treatment can operate both by reducing the surface roughness and the surface energy of the pipe wall, for this simulation, the surface energy was the main parameter of focus. To model the treatment on the pipe, the wettability of the pipe surface was modified to match experimental data. This modification led to changes in the deposition behavior of hydrates in the simulation. Sloughing events were not considered in this model.