Friday is here, and with it returns the weekly column "A Taste of Science for the Weekend" — issue #54.
This week: hydrostatics, electrostatics, and their connection to giant sea monsters that produce oil.
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If the ungainly behemoth in the video strikes you as particularly polluting, you're right.
This is an FPSO — Floating Production Storage and Offloading vessel.
Like a conventional offshore platform, its job is to pump oil and natural gas — but unlike one, it also processes and stores those products on board, with no need for an onshore facility.
The FPSO makes a remarkably clever use of the forces of nature to produce its final outputs.
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When an FPSO moors above an oil field, it sends extremely long pipes down into the seabed — sometimes to depths of 2 kilometers or more.
At such depths, heat from Earth's core combined with the weight of the overlying seawater and rock keeps the oil and gas reservoirs under exceptionally high pressure and temperature.
The pressure exerted on fluids at rest is called hydrostatic pressure.
This pressure pushes a mixture of seawater, oil, and gas up through the pipes toward the surface, where the pressure is lower.
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The mixture that reaches the deck enters a separation system.
Separation relies on gravity: water sinks to the bottom, oil floats above it, and gas collects in the upper, empty portion of the vessel. The mixture is heated to reduce the oil's natural viscosity and accelerate the separation.
The second and third separation stages operate on the same principle, but the pressure inside the vessel decreases with each stage to allow more gas to escape into the headspace — with the ultimate goal of reaching a gas content of less than half a percent in the oil.
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At this point the oil is still considered crude, because it contains dissolved salts that reduce its efficiency as a fuel.
Processing the oil involves electrostatics — a static electric field.
First, the oil is thoroughly mixed with water, in which the salts dissolve.
The mixture is then introduced into a vessel and subjected to a very strong electric field.
The electric field polarizes the water droplets, causing them to attract and coalesce — much like magnets snapping together.
Gravity then causes the oil to float above the water, yielding a cleaner product. The process is sometimes repeated over several stages to achieve especially pure oil.
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An FPSO is capable of pumping, processing, and storing enormous quantities of oil and natural gas — and, unlike a fixed platform, it can move between oil fields.
It can also operate for decades at a time, which is why it is considered an efficient and profitable solution despite its steep price tag, which can exceed half a billion dollars per unit.
Shabbat Shalom ☺️
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