Plenty Tank Cleaning Report
Continued From Previous Page

After running for 6 hours the sample analysis showed no increase in B.S. & W.
only a small increase in Salt level.

See Graph.

In view of this the second mixer was started, also at 30E right. As shown on the above graph, this caused an immediate increase in both B.S. & W. and salt level.

Note: The test team reactions were governed by the time taken to take samples, transport to Laboratory, analyze samples (approximately 1½ to 2 hours) and return to Terminal South.

The two mixers were stopped after approximately 5 hours and further samples taken at 2 hour intervals to monitor the settling rate. After 14 hours settling the drain valve was opened to see if the mixers had cleaned the drain area and released an "free" water from the sludge. They had and water was drained for 2 hours through the 1" drain.

At this point the Royal Gauger came to sample and gauge the tank and we, therefore, had to stop. However, the Gauger samples showed the tank to be "off spec" and we were, therefore, able to drain more water the following morning. This time the 1" valve was removed and the water was drained off through the 4" diameter valve.

A sample of the water being drained off was taken and the analysis was as follows:

After all the possible water was drained off (approximately 560 Bbls. determined by drop in tank height) the oil samples being sent to the laboratory for B.S. & W. analysis were almost void of water. However, the oil was still not within the shipping 'spec' after two days of settling as the sediment content was still too high and, therefore, another solution was discussed.

It was agreed with all concerned that the best course of action would be to mix up the whole contents of the tank, let it settle, drain off the water which according to the sludge analysis would then leave the oil in 'spec.'.

Once agreed the two mixers were started and operated in the angle sequence recommended by PLENTY:-

The mixers were operated with both mixers always set at the same angle and 8 hours at each angle. The oil was sampled every 4 hours and the mixers were stopped after 48 hours.

Results: See graph

Four and a half days after the mixers were stopped, the B.S. & W. was 0.6% vol. and salt 20 PTB. During this period, repeated attempts were made to drain water from the tank, but only oil was found.

It became obvious that the water was not settling out as a separate layer and, therefore, other alternative solutions to the problem of removing the water and, hence, salt, were discussed.

It was felt that the water was suspended in the oil in the form of an emulsion which was delaying the settling and the formation of a separate water layer on the tank bottom.

Gauging the tank proved that the tank bottom was clean and the mixers had indeed dispersed the accumulated sludge, but there was no water on the bottom as expected.

The presence of water was gauged by using the Royal Gauger tape with colour cut compound.

The colour cut compound which is a golden colour is wiped on the tape.

The tape is then dropped to the bottom of the tank.

When it is removed, it is washed with Naphtha and it has been in contact with water will turn red. If not it will remain golden in colour.

After some discussion it was decided to introduce a Demulsifier into the tank in an attempt to break the emulsion and settle out the water. Aramco stock a demulsifier called TRETOLITE DEMULSIFIER RP-968.