Casing comes in odd assortment of diameters ranging from 4.-in. to 20-in. that may seem quite puzzling at first encounter, such as 5.-in., 7-in., 7⅝-in., 9⅝-in., 10.-in. Why such odd sizes? All we can really say about that is that they stem from historical sizes from so far back that no one knows the reasons for the particular sizes any longer. Some sizes became standard and some vanished. Within the different sizes, there are also different wall thicknesses. These different diameters and wall thicknesses were eventually standardized by the API (and now ISO). The standard sizes as well as dimensional tolerances are set outin API Specification 5CT (2001) and ISO 11960 (2004).
Outside Diameter
The size of casing is expressed as a nominal diameter, meaning that is the designated or theoretical diameter of the pipe. API and ISO allow for some tolerance in that measurement, and the specific tolerance differs for different size pipe. The tolerance for the pipe being under sized is typically less than for the pipe being oversized. This is to ensure that the threads cut in the pipe are full threads. The tolerances for non-upset casing 4. in. and larger are given as fractions of the outside diameter, +0.01do, –0.005do. For upset casing, Table 1–1 shows the current API and ISO tolerances measured 5 in. or 127 mm behind the upset.
2015 Casing Reference Tables World Oil®/JANUARY 2015 C–109 Dimension nomenclature D = Casing nominal OD of tube, in. W = Casing weight, lb/ft d = ID (drift), in. Remington 0.22' long rifle ammunition, the company logo, a ' U', gives an indication of the date and country of manufacture as follows (Figure 2.17). Browning ammunition was made by Amron up until January 1973, and had the word ' Browning' stamped at the 12 o ' clock position. 1.4.2 Inside Diameter and Wall Thickness 7 1.4.3 Joint Length 7 1.4.4 Weights of Casing 8 1.5 Casing Grades 9. 2.2.1 Weight and Mass in Oil-Field Context 22 2.2.2 Standard Gravity 24 2.2.3 Fluid Density 25. Casing design without need of an instructor to “explain” it to you. API Casing Data Tables sizes 5.00 - 5.50. Specification 5C3 of the American Petroleum Institute standardizes 14 casing sizes from 4.5 inches (11.43 cm) to 20 inches (50.80 cm) outside diameter ('OD'). First of all, I'm pretty sure the 'O' headstamp on case #1 does indeed stand for Olin which is synonymous with Western Cartridge Company. Made brass casings for their WCC ammunition. I seem to recall seeing.22 cases in all sizes from WCC with the 'O' as the headstamp. Even so, double check to be sure the 'O' isn't actually a 'C'.
Table 1–1 API/ISO Tolerances for Upset Casing Outside Diameter (API 5CT, ISO 11960)
Inside Diameter and Wall Thickness
The inside diameter of the casing determines the wall thickness or vice versa. Rather than a specific tolerance for the amount at which the internal diameter might exceed a nominal value, the tolerance specified by API and ISO is given in terms of minimum wall thickness. The minimum wall thickness is 87.5% of the nominal wall thickness. The maximum wall thickness is given in terms of the nominal internal diameter, however. It specifies the smallest diameter and length of a cylindrical drift mandrel that must pass through the casing (see Table 1–2).
The internal diameter of casing is a critical dimension. It determines what tools and so forth may be run through the casing. It is not uncommon to have to select a casing for a particular application such that the drift diameter is less than the diameter of the bit normally used with that size casing, even though the bit diameter is less than the nominal internal diameter of the pipe. In cases like this, it is a practice to drift the casing for the actual bit size rather than the standard drift mandrel. This may be done with existing pipe in inventory, and those joints that will not pass the bit are culled from the proposed string. Or it may be done at special request at the steel mill, in which case there will be an extra cost. This procedure applies only to casing where the desired bit diameter falls between the nominal internal diameter and the drift diameter of the casing.
Casing is the major structural component of a well. It is a tubular steel product used to line the wellbore (maintain borehole stability), prevent contamination of water sands, isolate water from producing formations, and control well pressures during drilling, production, and workover operations. Casing provides locations for the installation of blowout preventers, wellhead equipment, production packers, and production tubing.
The cost of casing is a major part of the overall well cost, so the selection of casing size, grade, connectors, and setting depth is a primary engineering and economic consideration.
Casing Strings:
Since the well is normally drilled in segments, multiple concentric casing strings are usually installed in the well. There are six basic types of casing strings:
Conductor Casing:
The first casing installed in the well is called the conductor casing, as shown in the figure below. Onshore this is a short segment usually around 60 ft (20 m) long. The conductor isolates unconsolidated formations and water sands and protects against shallow gas. This is usually the string onto which the casing head is installed. Conductor casing is always cemented to surface.
Surface Casing:
Surface casing must be set deep enough to protect freshwater aquifers from contamination, and prevent lost circulation. Because of this, the surface casing is always cemented to surface. Surface casing depths typically vary between 1000 and 3000 ft (300-900 m).
Intermediate Casing:
Intermediate casing is set to isolate unstable hole sections, lost-circulation zones, low-pressure zones, and production zones. It is often set in the transition zone from normal to abnormal pressure. The casing cement top must isolate any hydrocarbon zones.
Some wells require multiple intermediate strings and some other wells do not have intermediate casing string.
Production Casing:
Production casing is used to isolate production zones and contain formation pressures. It may also be exposed to injection pressures from fracture jobs, gas lift, or water injection support. A good primary cement job is very critical for this string.
Liner:
Liner is a casing string that does not extend back to the wellhead but instead is hung from another casing string. Liners are used instead of full casing strings to reduce cost, improve hydraulic performance when drilling deeper, allow the use of larger tubing above the liner top, and not represent a tension limitation for a rig. Liners can be either an intermediate or a production string. Liners are typically cemented over their entire length.
Tieback String:
Tieback string is a casing string that provides additional pressure integrity from the liner top to the wellhead. An intermediate tieback is used to isolate a casing string that cannot withstand possible pressure loads if drilling is continued (usually because of excessive wear or higher than anticipated pressures). Similarly, a production tieback isolates an intermediate string from production loads. Tiebacks can be uncemented or partially cemented.
An example of a typical casing program that illustrates each of the specified casing string types is shown in the following figure.
Typical Casing Combination Strings:
A typical casing combination casing strings for a mature water-flooded field might be:
- 13-3/8″ (340 mm) Conductor
- 9-5/8″ (244 mm) Surface Casing
- 7″ (178 mm) Production Casing
For a deeper, higher pressured well a typical casing string might be:
- 16″ (406 mm) Conductor
- 13-3/8″ (340 mm) Surface Casing
- 9-5/8″ (244 mm) Intermediate Casing
- 7″ (178 mm) Production Casing
- 4-1/2″ (114 mm) Production Liner
Casing Specifications:
Casing is specified by grade, outer diameter (in or mm), nominal weight (lb/ft or kg/m) and connection type.
Steel Grade:
The grade reflects the material composition and yield strength of the casing material. API casing grades are listed in the table below:
Nominal Weight:
Nominal weight is the average linear weight of the tubing, connection included. It is expressed in lb/ft or kg/m and it determines the tubing wall thickness that in turn determines the nominal inner diameter.
Length:
Casing usually comes in lengths between 40 and 46 ft (12-14 m).
Inner Diameter:
Because the inner diameter is nominal, a guaranteed inner diameter called the drift diameteris also specified. The drift diameter is typically 1/8″ (3.2 mm) less than the nominal inner diameter. Equipment with a larger diameter than the drift diameter should not be run into a well.
Connection Type:
The connection is the type of thread used to connect the joints of casing. API thread types are short thread (STC), long thread (LTC), buttress and extreme line. A number of proprietary premium casing threads are also available.
22 Inch Casing Id
Standards for Tubulars:
C 22 Casing Hanger
- API Bull 5C2, Performance Properties of Casing, Tubing, and Drill Pipe.
- API TR 5C3, Technical Report on Equations and Calculations for Casing, Tubing, and Line Pipe Used as Casing or Tubing; and Performance Properties Tables for Casing and Tubing.
- API Spec 5CT, Specification for Casing and Tubing.
- ISO 11960, Petroleum and natural gas industries –Steel pipes for use as casing or tubing for wells.
- ISO 11961, Petroleum and natural gas industries –Steel drill pipe.
- ISO 13679, Petroleum and natural gas industries –Procedures for testing casing and tubing connections.