Paraffin Inhibitor Applications in Deepwater Offshore Developments

Abstract

Paraffin inhibitors can have a significant impact on crude oil production for some developments. Paraffin inhibitors are used for reducing wax deposition in flowlines and/or for improving the flow properties of waxy crude oils. The effectiveness of the paraffin treatment is dependent on the crude oil chemical composition, inhibitor chemistry, inhibitor dose rate, and the production conditions. The available choices of paraffin inhibitor formulations for a particular application are, however, often fixed by constraints related to delivery or injection of the product. For example, products for deepwater subsea umbilical injection must remain fluid and solids-free at all conditions of temperatures and pressures the products experience in their respective injection paths - from the storage tanks all the way through the umbilical and (if present) capillary injection lines. This paper details the challenges associated with the delivery of paraffin inhibitor chemicals for deepwater offshore developments. The stability of paraffin inhibitor formulations depends on both pressure and temperature. Umbilical and capillary line failure is a major concern in the oil industry. Best practices to qualify products for umbilical and capillary injection have been rapidly evolving over the last 10 years. Recently high-pressure viscometry has been found to be beneficial for product qualification. In particular, high pressure viscosity measurements have proven to be invaluable for determining whether pressure related stability concerns may exist in formulations at cold deepwater temperatures. Instability in the polymer solution phase behavior of paraffin inhibitor formulations at high pressures and cold temperatures may be the reason behind some industry umbilical line failures. Also discussed are contrasts between deepwater applications in subsea umbilical lines and in DVA dry-tree capillary lines as the constraints on the paraffin inhibitor can be very different. Four recent case histories of different types of deepwater paraffin inhibitor applications are presented: two subsea umbilical applications, one DVA capillary application, and one application for a well test. The case histories discuss how the paraffin inhibitor applications fit into the overall wax strategy for the projects, constraints placed on the products by the injection conditions, and performance of the products.

Recent advances on mitigating wax problem using polymeric wax crystal modifier

“…Due to close energies of interaction between different paraffin-like components, minor changes of experimental conditions may lead to dramatic effects. In terms of solvents, it is well known that wax inhibitors are usually formulated with active compounds (crystal modifiers) dissolved in organic (aromatic) solvents for oilfield use (Jennings and Newberry 2008). In other words, the performance of the wax crystal modifiers may be further improved if a synergistic effect exists between EVA and solvent(s).…”

Experimental Study of the Effect of Polyacrylate Polymer (C16-C22) on Wax Deposition

“…This inhibitor was reducing the wax deposition process by interfering with wax crystallization and growth process. However, this interfering mechanism has not yet been fully understood [14]. …”

“…Also, it reduced the wax thickness from 1.6 mm to 1.3 mm at flow rate 4.8 L/min and inlet coolant temperature 14 º C. Proposed mechanisms of waxing inhibition involve the possibility of wax inhibitor polymers, containing similar structure to the wax structure, are incorporated into the wax crystal growth. Sometimes the structural part of the polymer covers the wax site, thereby preventing further wax crystal growth and promoting the formation of smaller wax aggregates [14], [6].…”

Experimental study of wax deposition in pipeline – effect of inhibitor and spiral flow

“…This inhibitor was reducing the wax deposition process by interfering with wax crystallization and growth process. However, this interfering mechanism has not yet been fully understood [10].…”