Geology And Geophysics

How do Oil Rigs Work



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The semisubmersible platform drilling rig discovered oil.  Once this occurs, the rig is replaced by a production platform considered a permanent platform. The assembly, completed on land, is brought to the oil site by a barge that has heavy lift cranes.

The platform is ready to drill.  At this stage, the drilling is called “spudding”.  The drill bit is lowered onto the sea floor.

There are two types of bits that can be used.  One is a “roller cone” that has three cones made of steel or tungsten carbide.  Another is “teeth” with embedded, small, industrial diamonds.

The derrickman helps the driller to center the drill on the rotary table on the platform floor.  As the drill digs deeper, the floorman begins to lengthen the drill by attaching the pipes with tongs.  The drill pipe is 30 feet long.

Drilling fluid is pumped down the drill pipe at high speeds and nozzles located in the drill bit.  The drilling fluid is to raise the drill cuttings to the surface for disposal.  The other purpose is to keep the underground pressure stable by weight and also, it cools the bit.  The drilling fluid consists of water, clay and barite (a weighting material).  The drilling fluid goes through a circulation system that separates the drill cuttings out of the fluid.  The filtered fluid is pumped back into the hole.

When drilling for oil in an offshore platform, water is brought up with the oil.  There is a device that is able to remove the water from the oil.  This is called “produced formation water” (PFW).  After purification, it is  returned to the ocean.

There are several ways that help prevent blow-outs.  One is the drilling fluid that stabilizes the pressure.  There is also a “blow-out prevention (BOP) system in place.  This is how it works.  If pressurized oil or gas rushes into the pipe, a set of hydraulically operated valves and rams (closure devices) seal off the well.  The pressurized fluids are sent to specialized pressure controlling equipment.

The newest development in offshore drilling is the “horizontal” pipe.  This tube allows directional drilling for several miles  to find more oil reserves.

To complete the well, after drilling it to its final depth, the  casing is set and cemented.  Tubing is placed in the hole with packers.  This seals the open space between the tubing and the casing.  The casing should have small holes at certain depths.  This is accomplished by small explosive charges that are set off remotely.  The small holes allow the oil under its own pressure to flow to the surface.

After extraction of all the oil, the hole is “plugged”.  This means that several cement plugs have been placed in the well. 

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