Abstract

More cost effective oil production is possible if process design engineers start treating use of production chemicals in a more systematic way when they design new production platforms. Typically it is not common to include the effect of foam breaker and emulsion breaker when sizing separators. Design criteria for separators like foaminess and size of water droplets have little value when sizing separators if it is used without evaluating the positive effect of the production chemicals. Testing on some of Norsk Hydro's offshore facilities have shown that water treatment plants are not able to operate according to design without using emulsion breaker and a polyelectrolyte at low water cuts. Testing also indicates that a small oil stream from an oil sump can "pollute" the oil-water separation system in the main separators because of its high content of surface active materials.

Injection systems for production chemicals are often added to the process on a "just in case" basis. Considering the importance of chemicals such as emulsion breaker and a polyelectrolyte, which are both vital to the quality of the water effluent, the process engineer should ensure that these chemicals work at optimum conditions. Parameters like temperature, concentration of active chemical component, and retention time in the pipe upstream of a processing vessel are important.

At the same time the oil companies requires that "green chemicals", combined with use of less chemicals in the effluent, to be used as part of their environmental policy. Unfortunately "green chemicals" are often less effective that other chemicals, making it difficult to reduce the amount of chemicals going overboard. The answer to the problems is to integrate the use of chemicals in the process design in order to achieve a synenergi effect.

Introduction

Use of production chemicals is essential for successful operation of the process plant on most production platforms. By integrating the application of the production chemicals with the production system it is possible to obtain a synenergy effect. A useful design approach is to compare the value of potential weight and cost reductions for the process equipment with the cost of injecting production chemicals over a platform's lifespan. The trend towards using more environmentally safe chemicals that have a tendency to imply higher operating cost due to higher cost pr. liter and lower efficiency, should also be kept in mind when designing new platforms.

Test methods for chemicals

For each production chemical that is expected to be applied on a platform, the process plant should have dedicated test points installed in order to perform screening tests. Easy to-use equipment for on-line screening of chemicals should be developed to allow simple testing of 20–30 different chemicals in a row. The common methods that are in use today, requires manual sampling and mixing with chemicals in the laboratory. But these methods can introduce large errors. Typically a demulsifier tested with this method would require 10 times higher concentration in the screening test than what is actually required when conducting a full-scale test.

Full scale testing offshore. Chemicals qualified in a screening test, should be tested in a full-scale test conducted offshore. The chemicals for such a test, are often supplied in barrels. Instead of pumping through the permanent system for injection of chemicals, a mobile pump-unit is normally used. Preferably the pump is hooked-up in parallel to the permanent injection point for the chemical to be replaced, in order to facilitate the evaluation of the test results. The test chemical is either pumped directly from the barrel, or from a small day tank mounted on the pump itself.

A full scale test of production chemicals requires stable production, otherwise it becomes difficult to find the optimum conditions defined as minimum injection rate and maximum effect.

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