Drilling Rig, Drill String, Rotary Table, Kelly, Drill Collars, Drilling Mud, Blowout Preventers, Casing, Fracking and Sucker-Rod Pump

Posted by PITHOCRATES - September 19th, 2012

Technology 101

The Kelly is the Section of the Drill Pipe the Rotary Table Grips to Spin the Tool

There are places where oil oozes out of the ground.  All by itself.  Because of the great weight of that dirt and rock pressing down on it from above.  But there’s a lot more oil underground crushed by the weight of the earth.  That only needs a pathway up to the surface.  And because we like oil so much we provide that pathway.  By drilling deep holes into the ground.  And when we do that oil will come to the surface all by itself.  Making oil extraction rather simple and straight forward.  But getting to that point is a whole other story.

The drilling rig.  This is where it all starts.  The tall, tapered steel derrick that we see in the movies.  Even in Bugs Bunny cartoons.  This is a lot taller than your average drill because the drill bit is a lot longer.  Or, more accurately, the drill string.  A bunch of 30-foot sections, or joints, of hollow pipe screwed together.  As the drill makes its way underground they stop drilling, pull another joint up the derrick, screw it into the drill string and continue drilling.  Hence the tall height of the steel derrick.

At the end of the drill string is the bit, or tool, that does the actual drilling.  Which they spin with a rotary table back up on the rig platform.  Where the roughnecks work.  Manhandling together joints with giant pipe wrenches called tongs.  They break apart the drill pipe.  Hoist a joint up the derrick.  Screw it together to the drill string.  Then reattach the kelly to the drill string.  The kelly is the section of the drill pipe the rotary table grips to spin the tool.  As the table spins the kelly it slowly lowers through the hole in the rotary table.  Pulled down by a heavy section of pipe just above the tool.  Called drill collars.  That weighs about 10 times as much as a joint.

To get the Oil to Flow up through the Well and not into the Soil on the way up they Place a Casing in the Well

There’s a reason why the drill string is hollow.  Because something flows through it.  And, no, it’s not oil.  It’s mud.  A special kind of mud that they pump down from the rig to the drill bit.  Like oil used during drilling on a drill press this drilling mud provides lubrication for the cutting surface.  And being a thick fluid it does two other things.  Chunks of rock will stay suspended in the mud.  So it will rise up with the mud instead of settling at the bottom of the hole.  And it resists other fluids from seeping into the drill hole.  The pressure of the mud pumping down inside the drill pipe forces it back up the drill hole in the space around the drill pipe. As it exits the drill hole up top they examine the mud to see what’s happening at the bottom of the hole.

Below the rig platform are blowout preventers.  For unlike in the movies they want to prevent any gushers of oil (or anything else for that matter) out of the hole.  Because that would be dangerous.  And costly.  So to prevent a blowout they have a series of valves mounted to the wellhead that exits the ground.  At any sign of a back pressure that could blow out of the well they close these valves.  To continue drilling they make the drilling mud thicker.  Thick enough to hold back the back pressure from blowing out around the drill pipe.

To get the oil to flow up through the hole and not into the soil on the way up they place a casing in the hole.   Which is a steel pipe they line the hole with after they’re done drilling.  They pump cement down into the casing and mud behind it.  Forcing the cement out of the casing and up through the space between the casing and the wall of the earthen hole.  When the cement comes out at the top it fills the void between the casing and the hole.  Surrounding the casing in cement.  Which then sets and bonds the casing to the earthen walls of the well.  Providing a clean pathway down from the surface to the rock containing the oil.

Over Time the Pressure pushing the Oil up to the Surface dissipates as the Oil leaves Voids in the Rock

Yes, rock.  There isn’t a big underground lake of oil underground.  The oil is in the pours of rock.  Like a sponge holding a liquid.  One hole in the rock isn’t going to bring a lot of oil to the surface.  So they bust open some of that rock.  With explosions.  Chemicals.  Or high pressure water.  Once they crack open the rock they hold the cracks open by pumping in some porous material that can withstand the crushing weight of the earth above.  We call this fracking.  Short for fracturing.  Which allows the oil to accumulate around the well.  Where the weight of the earth above will push it up through the well casing to the surface.

This completes the drilling process.  They put a stack of valves on top of the wellhead.  Called the Christmas tree.  They close all the valves and break down the drilling derrick.  Pack everything up and leave the drilling site.  Leaving nothing behind but the wellhead with the Christmas tree on top.  Open a valve and the oil flows.  For awhile, at least.  Over time the pressure pushing the oil up to the surface dissipates as the pumped oil leaves voids in the rock.  Which eventually lowers the pressure to the point it no longer reaches the surface.  So to keep the well working they install a pump.

The pump they use has a rocking beam that is pushed up and down on one side.  The other end has cables draped over what looks like a horse’s head.  These cables attach to a string of sucker rods that enter the well and reach all the way to the bottom of the well.  Hence the name sucker-rod pump.  At the bottom of the well is a cylindrical chamber.  When the beam rocks down over the wellhead the sucker rods descend into the well.  At the same time a valve opens and the cylindrical chamber fills with oil.  When the beam pulls up one valve closes and another opens.  And pulls up the sucker rods.  Drawing up some oil into the well casing.   Forcing the oil further up the well with each pump cycle.  Until it reaches the surface.  Then it’s on to a refinery.  And into our car.



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