The Situation

Processing problems at a crude oil terminal in Trinidad caused as much as 1,500 bbl/day of “slop oil” waste to be generated. Produced fluids from offshore platforms are piped to the onshore terminal where traditional techniques of chemical dehydration and settling time are employed. The slop is formed in the interface between the separated crude oil and the free water, and comprises a stable emulsion of oil, water and fine solids. The slop waste is partially recycled back into the upstream system creating separation problems in the crude dehydration process. Valuable tank space has to be used to store this slop which not only reduces the efficiency of the Production operations but also represents unrealized revenue for the operator.

The Solution

Production Waste Management experts from M-I SWACO used simulation and characterization techniques to design a mechanical-chemical separation system with two stages of centrifugation to split the slop oil emulsion. Initially the oil is heated and homogenized and then pumped to a decanter centrifuge which takes out any larger solid particles from the liquid. In the second stage a disk-stack centrifuge, utilizing in excess of 5,000 G force, is able to separate clean crude oil from the water and fine solids that make up the stubborn emulsion. Chemicals specifically designed by the Production Technologies specialists from M-I SWACO are used to enhance the separation performance and increase the treatment system throughput. Clean crude oil recovered from the slop waste is pumped to the client’s export tanks while the separated water is delivered to the onsite water treatment plant and the solids are sent for disposal.

The Results

Clean crude oil from the M-I SWACO system was recovered to <0.5%BS&W (basic sediment and water), i.e., direct export specification. In the first 8 months of operation over 50,000 bbl of clean crude oil has been recovered from the slop waste and returned to the client. The system is flexible enough to treat both fresh slop oil from the daily production and also the aged slop oil from the storage tanks without reconfiguration of the process. Crude dehydration in the upstream production system is now faster as a result of the elimination of the slop waste recycling. The system operates 24-hr per day 7 days per week, and with our policy of continuous improvement, an upgrading program is underway to further increase the system throughput.

No mixing or foaming problems were encountered during the mixing, pumping or flow back. At the end of the job, the operator observed that the actual CoF was 46% less than the coefficient of friction estimated initially.

The Details

In similar wells filled with seawater, wireline engineers normally used a CoF factor of 0.35 in their tool running simulations. Aware that the new lubricant would be bullheaded prior to the start of the wireline operation, they assumed the friction factor would be reduced to 0.25. Later this factor had to be decreased to 0.19 so the simulations would match the real time data of the seawater treated with 2% by volume Star-Lube lubricant. This value was a 46% reduction in the estimated friction coefficient.

The newly formulated Star-Lube lubricant:

• Minimized dramatically the expected impact of extreme metal-to-metal friction
• No foaming tendencies reduced operational time
• Allowed operator to successfully complete a wireline intervention and production liner inspection
• Delivered an actual friction factor that was 46% less than that anticipated
• Completed intervention with no damage to the production liner.

Questions? We’ll be glad to answer them

If you’d like to know more about STAR-LUBE defoamer and how it’s performing for our other customers worldwide contact the M-I SWACO office nearest you.