A New Method for Evaluating Wax Inhibitors and Drag Reducers
Authors: Hsu J.J.C. , Brubaker J.P. 
Published: October 2008

Conventional wax inhibitor evaluation methods such as cold finger and laminar flow loop are not adequate and accurate for excluding wax inhibitors to be used in a wide operating temperature range and flow regimes such as North Sea subsea transport pipelines. A new method has been developed to simultaneously measure fluid theology change and wax inhibition and to evaluate wax inhibitors or drag reducers at the field operating conditions. Selection criteria have been defined to search for an effective wax inhibitor. The criteria ensure the chemical selected is the most effective one for the specific oil and flow conditions. The operation cost savings by this accurate method is significant.

Nine chemical companies joined the project of finding an effective wax inhibitor for a North Sea prospect. More than twenty wax inhibitors have been tested and evaluated with this new method for several waxy oil fields. The new method provides data of fluid theology, wax deposition rates and wax inhibition in the operating temperature range, overall average wax inhibition and degree of fluid /low improvement. These data are important to evaluale a wax inhibitor or drag reducer.

Most of the wax inhibitors tested have good wax inhibition at high temperatures, but not many chemicals work well al low temperatures. The chemical tested may improve fluid flow behavior at low temperature but not wax deposition. Drag reducers tested did not work well at North Sea seabed temperature.

INTRODUCTION

Either one or combination of chemical, mechanical, and thermal remediation methods are usually applied to prevent or reducewax deposition problems in a waxy crude production system. Wax problems become economic challenges to offshore waxy crude productions such as oil field in North Sea area.

Many oil companies still rely on chemicals to mitigate or prevent wax deposition problems in their waxy oil production lines. Selecting an effective wax inhibitor is a critical, but different task for either oil companies or chemical companies. The selection process significantly affects operating cost of the production lines. The screening methods and criteria for selecting wax inhibitors are apparently very critical to oil companies in savings of operating cost.

To assist our customers to evaluate and select the most effective wax inhibitor for a North Sea prospect, we sent an oil sample to eight chemical companies worldwide. We asked the chemical companies to use their own screening method(s) to select one or two best wax inhibitor for that oil. The ninth chemical company submitted their wax inhibitors to us for wax inhibition evaluation without screening procedure.

The screening methods used by the chemical companies are listed in Table 1. One chemical company withdrew from the project. Most of the screening methods used by the chemical companies were cold finger (or, plate) method under dynamic conditions. The temperature difference between oil sample and cold finger is usually fried for the screening. The oil sample is circulated or agitated. Therefore, the selected wax inhibitors (WI) work well at that oil temperature, but may not work well at other temperatures.