Casing and Cementing (Part 1 )
Virtually every well-drilled requires casing and cement. What is the relationship casing and cementing. Or how to understand casing and cementing?
Casing is steel pipe that the crew puts into the wellbore. The casing prevents the hole from caving in and seals off formations. To do its Job, the casing has to be submitted in place. A cement crew pumps cement down inside the casing and up the Annulus. The cement hardens or sets to hold the casing in place.
Casing Pipe / OCTG
Casing is steel pipe that comes to the rig and individual joints. A casing crew couples the joints together to run them into the Wellbore. To run the casing, the crew joins the joints with threaded connections called couplings or collars.
Do not confuse casing collars with drill Collars.
Casing collars are couplings. They use special heavy-duty elevators and large casing slips call spiders. They make up the casing joints with multi speed power casing tongs.
Our casing tongs not only screw the threaded connections together,but also torque them to the correct amount.
By the time, the crew drills the well to final depth. It usually has several strings of casing in it. These strings are called conductor casing, surface casing, Init casing and production casing.
Notice that the cased well looks something like a telescope pulled out two full-length. That is as the crew drills the well deeper, the size of the hole and the size of the casing gets smaller in diameter.
Almost always the drilling contractor cannot begin drilling at the surface and go all the way to total depth in one step.
1–For one thing,formations near the surface tend to crumble and cave in easily. So conductor casing prevents cave-ins.
2–For another thing,Formations near the surface may also hold fresh water. That the well cannot contaminate.So surface casing protects fresh water zones.
3–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 off to prevent problems in drilling the deeper portions of the well. So intermediate casing seals off troublesome zones. Sometimes deep wells require more than one intermediate casing string.
4–Finally once the producing zone is drilled. It needs to be protected and sealed. So production casing isolates the producing zone.
The first string of casing is the conductor casing.The hole drill for it is pretty big.Often as much as 36 inches or more. Almost a meter in diameter. The conductor hole has to start out pretty big.Because as drilling goes on,the holes diameter decreases. In some case is 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 submitted in it. Using a bit whose diameter is small enough to easily go inside the conductor casing. The rig drills the hole below the conductor to a prescribed depth .The diameter of the surface hole can still be relatively large say 17 inches over 400 millimeters or even more.
The surface holes depth
The surface holes depth is usually set by regulatory agencies. They require that the surface hole be drilled through all freshwater zones. 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 crew members nipple up or connect the VOpie’s to the surface casing at the Wellhead. So this casing must be strong enough to support the BoP stack.
In addition it has to withstand the gas or fluid pressures the well may encounter. Surface casing also has to be strong enough to support the additional casing strings hung inside of it. To drill the intermediate hole, the operator chooses a still smaller in diameter bit .Which easily fits inside the surface casing.
A bit of about 12 inches or 300 millimeters in diameter is one example of the size intermediate. Casing is also submitted into place to seal off troublesome formations, like lost circulation zones or abnormally pressured zones. It is often the longest section of casing in the well.
Also the crew connects or nipples up the Bop eas to the top of the intermediate Casing. By using an adapter and casing head or a drilling spool. which is stacked on or connected to the top of the surface casing well head. If they’re four anchors that Bop were the drilling that comes later remember that the crew has to nipple up a stack of vo peas to each string of casing that is run into the well.
First,they nipple up on the surface casing. Then on the intermediate casing and finally on the production casing to drill to final depth.
Below the intermediate casing, the rich owner selects a bit whose diameter is small enough to fit inside the intermediate casing, say from 8 to 10 inches or 200 to 250 millimeters. This part of the hole penetrates the producing zone.
When cemented in place. Production casing seals off the producing zone and readies it for Production.
Production also houses and protects the tubing and other 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 describing the activities and methods of preparing the well for production of oil and gas. Oil and gas flow into the well through the perforations. Sometimes well owners run liners instead of casing into the Well. A liner is a shortened string of casing used to case the smaller open hole section.
Below an existing casing string in the hole.It’s just 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 a previously run casing or liner string.
Using a special piece of equipment called a liner hanger. In this case there’s an intermediate liner and a production liner. Using liners saves money since they do not extend to the surface.
Because the crew will cement the casing string in place.They also have to install some special devices on the String. Which come into play during the cementing operation.