ABSTRACT

De-oiling processes and operations are crucial with regard to removing oil/condensates residuals from produced water prior reinjection or discharge. Offshore environments often increase the associated issues due to 1) the necessity to meet strict water specifications, 2) the operational criticalities and associated costs, 3) the necessity to improve the performance of existing facilities. This paper discusses the "unconventional" field application of a de-oiler based on coalescence technology usually applied for "civil" purposes (i.e. fuel service areas cleaning) to enhance the performance and capacity of the Produced Water Treatment in offshore gas production processes. The main goal of the application was to enhance the separation of residual hydrocarbons from produced waters in order to:

  1. Increase the lifetime of carbon filters;

  2. Reduce maintenance costs associated to the carbon filters replacement (work force, supply, re-generation, disposal of exhausted carbon);

  3. Recover the whole production of liquid hydrocarbon associated to water.

Key aspect is the easy operating principle based only on physics that exclude the need of electrically powered facilities.

Field test has been conducted in offshore Italy field following continuously both operational parameters and de-oiling performance. Laboratory and field activities, conducted in parallel, have been essential for the deep understanding of results and possible applicative constrains.

Results of the test as well as the main observations useful for a widespread application of the technology in existing offshore installations are extensively reported in the paper.

INTRODUCTION

Gas and oil production on mature fields is often associated to the production of huge quantities of formation water that, in some cases, can become a major operational, environmental and economic concern1,2.

The concern is even more severe in case of offshore platforms where the produced water has to be disposed overboard. Produced waters, in fact, must meet strict discharge regulations mainly related to the hydrocarbon content.

Thus, efficient separation and de-oiling treatments shall be implemented not only to meet the discharge specifications but also to reduce as much as possible the oil-in water content in order to:

  1. Increase the lifetime of carbon filters used to remove the remaining oil in water content;

  2. Reduce maintenance costs associated to the carbon filters replacement (work force, supply, re-generation, disposal of exhausted carbon);

  3. Recover the whole production of liquid hydrocarbon associated to water.

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