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OIL AND GAS WELL CASING
Casing
By the time the crew drills the well to final depth it usually has several strings and casing in it. These strings are called conductor casing, surface casing, intermediate casing and production casing.
Notice that the case well looks something like a telescope fold out to full length that is as the crew drills the well deeper, the size of the hole and the size of the casing get smaller in diameter. Almost all ways the drilling gun tractor cannot begin drilling at the surface and go all the way to total depth in one step.
For one thing formations near the surface tend to crumble and cave-in endlessly. So conductor casing prevents cave-ins. For another thing formations near the surface also hold fresh water that the well cannot contaminate.
So surface casing protects freshwater zone. For still another thing deep formations are sometimes so called troublesome formations. That is they can be drilled by adjusting the properties of the drilling mud but once drilled need to be sealed of to prevent problems in drilling the deeper portions of the well.
Intermediate Casing
So, intermediate casing seals of troublesome zones. Sometimes deep wells require more than one intermediate casings string. Finally once the producing zone is drilled it n
So, production casing isolates the producing zone. The first string of casing is the conductor casing.
Size of the hole
The hole drilled forward is pretty big, often as much as 36 inches or more, almost a meter in diameter.
The conductor hole
The conductor hole has to start up pretty big because as drilling goes on, the holes diameter decreases. In some cases the rig will hammer the conductor casing in place if the ground near the surface is really soft.
If the conductor hole is drilled the casing is cemented in it. Using a bit who’s diameter is small enough to easily go inside the conductor casing, the rig drills the hole below the conductor to a prescribe depth.
Surface Diameter
The diameter of the surface hole can still be large, says 17 inches over 400 millimeters or even more.
Surface Holes
The surface holes dept is usually set by regulatory agencies. They require that the surface hole be drilled for all fresh waters alone and that surface casing be set and cemented to protect the zones from damage by additional drilling operations.
This depth could be from hundreds to thousands of feet or meters. Normally crew member’s nipple up or connect the BOP to the surface casing at the well head.
So, this casing must be strong enough to support the BOP stack. In addition it has the wistam, the gas are fluid pressures the well may encounter.
Surface casing also has to be strong enough to support the additional casing strings hung inside of it.
How to drill the hole
To drill the intermediate hole, the operator chooses a steal smaller in diameter bit which easily fits inside the surface casing. A bean of a bound 12 inches or 300 mm in diameter is one example of the size. Intermediate casing is also cemented in the place to see of troublesome formations like moss circulation zones or abnormally pressured zones.
BOP Stack
It is often the longest section of casing in the well. Also the crew connects or nipples up to the BOP to the top of the intermediate casing by using an adaptor and casing head or a drilling spool which is stunt on or connected to the top of the surface casing well head. It therefore anchors the BOP where the drilling that comes later. Remember that the cross has to nipple up a stack of BOP to each string of casing that is run into the well.
First, by nipple up on the surface casing then on the intermediate casing and finally on the production casing. The drill to final depth below the intermediate casing the rig owners selects a bit whose diameter is small to fit inside the intermediate casing say from 8 to 10 inches or 200-250 mm.
This part of a whole penetrates theproducing zone. When cemented in place, production casing seals of the producing zone and ready set for production. Production casing also houses and protects the tubing another equipment used to produce the well.
The operator usually perforates, puts holes in this casing when the well is completed or ready for work to begin.
Well completion is the term to scrapping the activities and methods of preparing the well for production of oil and gas.
Oil and gas flow into well through the perforations. Sometimes well owners run liners instead of casing into casing into the well.
Liner
A liner is a shorten string of casing used to case the smaller open hole section below an existing casing string in the hole. It skills like casing except that a liner does not run all the way to the surface instead the casing crew hangs it from the bottom of our previously run casing or liner string using a special of equipment called liner hanger.
In this case, there's an intermediate liner and the production liner. Using liner saves money since they do not extend to the surface.
