Treatment of chemically emulsified produced water

Paul Boughton

Ruud Meinen and Paul Schouten look at a new field-tested process which treats chemically emulsified water to below 10ppm.

Operators are increasingly faced with production and frac water problems. The emulsified water does not easily separate under the influence of gravity and time (Stokes Law). In many cases this is caused by increased water cut from maturing wells and a growing use of corrosion inhibitors and methanol which contribute to the formation of chemically stable emulsions.

Another specific contributor is foam additions which are used to keep low pressure wells from choking. The emulsions contribute heavily to the total quantity of hydrocarbons discharged to the sea.

TwinZapp is a new field-tested process which treats emulsified water. A set-up to treat up to 2,400bwpd (about 15m3/h) consists of two skids with a total footprint of 70ft2 (6.5m2). The system is typically installed as an end-of-pipe retrofit after a (near) atmospheric skimmer tank. The only required input is around 0.5kW of electrical energy per treated cubic metre. It does not use any consumables (chemicals or absorption cartridges) and no specialist attention is required. The system uses turbidity (the presence of a haze in the output water) as a proxy for the presence of dispersed oil in the outlet.

The mobility of the system allows for use on specific work-over projects (foam jobs) or platforms and production sites with temporarily troublesome production water. On offshore well tests it ensures a quicker release of the drilling rig. Normally the drilling rig is used as (an expensive) method for storing water returns from the well test.

Instead of compressed air we have a new all-electric design. One of the advantages of local treatment of water on satellites is longer lasting interfield pipelines.

The system has been extensively tested on the North Sea. The tests included:

- Artificial set-ups such as a 20 per cent methanol loading;

- Corrosion inhibitor loading;

- Treatment of frac water;

- Well clean-up (returned from a recently drilled well where oil-based mud was used).

The platform crew was quickly able to start up and adjust the system as required. The turbidity control will largely remove the requirement for such involvement. As a back-up there is a lab test available which can be carried out by an operator.

Before installation it is considered good practice to test the production water in the lab. The test is then upsized to a trial on the shore base, using an IBC of production water (as fresh as possible).

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Ruud Meinen and Paul Schouten are with Parker Twin Filter Zaandam, The Netherlands. and

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