Casing\Tubing
NoDoC model for estimation of casing and tubing are based on the following criterias and fundamentals that are used in many years for drilling engineering and operation.
In the past few years, man is forced to dig a well and aqueduct for exploiting the underground waters. but caving of well, during and after digging was one of major problems in operating of this process the first solution was overlaying of wells. due to lack of waterproof overlays and mortars, the possibility of well caving wasn’t diminished but it postponed for a short period. next solution was reverting the wall of well and using brick revetments are entire from many years ago.
In drilling process of oil and gas well, running of casing to protect the wall of well against caving and penetrating of the fluids which are under pressure in ground structure is essential. initially iron has been used as a casing but today , because of its corrosion and related problems , casings are made of various steel alloys .
Casing running methods of oil and gas wells have been developed and complicated in recent years . In seeking for more oil and gas, deep wells have been drilled and also methods of casing running developed to overcome many hard conditions ., in the depths of ground .
1. Casing
Casing is very resistant steel pipe and made of alloy steel , which is used in oil and gas wells with three length ranges (16-25,25-34 and 34-38 ft) casing is a part of oil and gas industry (OCTG-Oil country tubular goods)
Generally the casing performs six important functions, as follows:
According to usage various casing strings consist of :
1.1.1. Surface Casting String
Surface casing prevents the weak formations that are encountered at shallow depth . It is also very important to isolate the fresh water and prevent its contamination by drilling fluid and fluids of lower layers .The length of surface casing string may be just 200 ft but in some cases and according to local conditions, the length may be increased to thousands of feet .
1.1.2. Intermediate Casing String
The most important purpose of using this string is protection of well and so it is called protection casing string several intermediate casing strings usually used for one well . this string may extend from surface to depth of 7,000 ft .
Figure 1
In the past few years, man is forced to dig a well and aqueduct for exploiting the underground waters. but caving of well, during and after digging was one of major problems in operating of this process the first solution was overlaying of wells. due to lack of waterproof overlays and mortars, the possibility of well caving wasn’t diminished but it postponed for a short period. next solution was reverting the wall of well and using brick revetments are entire from many years ago.
In drilling process of oil and gas well, running of casing to protect the wall of well against caving and penetrating of the fluids which are under pressure in ground structure is essential. initially iron has been used as a casing but today , because of its corrosion and related problems , casings are made of various steel alloys .
Casing running methods of oil and gas wells have been developed and complicated in recent years . In seeking for more oil and gas, deep wells have been drilled and also methods of casing running developed to overcome many hard conditions ., in the depths of ground .
1. Casing
Casing is very resistant steel pipe and made of alloy steel , which is used in oil and gas wells with three length ranges (16-25,25-34 and 34-38 ft) casing is a part of oil and gas industry (OCTG-Oil country tubular goods)
Generally the casing performs six important functions, as follows:
- Prevent caving and eroding of the well
- Prevent contamination of fresh water by the fluids of lower layers and drilling fluid
- Prting of formations from each other
- Confine production to one formation
- Provide required information for controlling the pressure of well
- Establishing of a path for produced fluids
According to usage various casing strings consist of :
1.1.1. Surface Casting String
Surface casing prevents the weak formations that are encountered at shallow depth . It is also very important to isolate the fresh water and prevent its contamination by drilling fluid and fluids of lower layers .The length of surface casing string may be just 200 ft but in some cases and according to local conditions, the length may be increased to thousands of feet .
1.1.2. Intermediate Casing String
The most important purpose of using this string is protection of well and so it is called protection casing string several intermediate casing strings usually used for one well . this string may extend from surface to depth of 7,000 ft .
Figure 1
1.1.3. Production Casing String
Production casing string isolates producing zones, provides reservoir control , and permits selective production in multi zone production , also this string protects tubing . this string usually is the longest, heaviest and the last string, so it shall be made of resistant alloy steel pipes. on the other hand, a little leak may cause the blowout of well . so threaded joints of production casting shall be resistant against probable pressures.
1.2. Exerted Stresses To Casing
When casing is running in a well, it is subjected to three significant forces. these forces resulted from below stresses .
1.2.1. Tensile Tension
This tension results from weight of casing string and causes tensile of pipe , also collapse strength of pipe will be decreased for tensile tension .
1.2.2. Collapse Pressure
Collapse pressure is defined as external pressure that tends to collapse the casing and results from hydrostatic pressure . collapse of casing string often occurs in cement injection process .
1.2.3. Burst Pressure
Burst pressure is defined as internal pressure that tends to burst the casing . generally, burst pressure is high in upper casing (near the surface)
2. Technical Specification Of Casing
Casing is classified according to these 5 characteristics :
1. The outside diameter
2. The wall thickness
3. Materials
4. The type of joint
5. The length range
Unit weight of pipe length is another characteristic which is determined according to wall thickness and outside diameter. technical specifications of casing are selected in accordance with API SPEC 5CT.
Figure 2
Production casing string isolates producing zones, provides reservoir control , and permits selective production in multi zone production , also this string protects tubing . this string usually is the longest, heaviest and the last string, so it shall be made of resistant alloy steel pipes. on the other hand, a little leak may cause the blowout of well . so threaded joints of production casting shall be resistant against probable pressures.
1.2. Exerted Stresses To Casing
When casing is running in a well, it is subjected to three significant forces. these forces resulted from below stresses .
1.2.1. Tensile Tension
This tension results from weight of casing string and causes tensile of pipe , also collapse strength of pipe will be decreased for tensile tension .
1.2.2. Collapse Pressure
Collapse pressure is defined as external pressure that tends to collapse the casing and results from hydrostatic pressure . collapse of casing string often occurs in cement injection process .
1.2.3. Burst Pressure
Burst pressure is defined as internal pressure that tends to burst the casing . generally, burst pressure is high in upper casing (near the surface)
2. Technical Specification Of Casing
Casing is classified according to these 5 characteristics :
1. The outside diameter
2. The wall thickness
3. Materials
4. The type of joint
5. The length range
Unit weight of pipe length is another characteristic which is determined according to wall thickness and outside diameter. technical specifications of casing are selected in accordance with API SPEC 5CT.
Figure 2
Table 2
| group | Casing grade | type | Yield Suength(psi) | Minimum tensile streng(psi) | Maximum hardness | ||
| minimum | maximum | ?????? | ?????? | ||||
| 1 | H-40 | _ | 40,000 | 80,000 | 602,000 | _ | _ |
| J-55 | _ | 55,000 | 80,000 | 75,000 | _ | _ | |
| K-55 | _ | 55,000 | 80,000 | 95,000 | _ | _ | |
| N-80 | _ | 80,000 | 110,000 | 105,000 | _ | _ | |
| 2 | L-80 | 1 | 80,000 | 95,000 | 95,000 | 23 | 241 |
| L-80 | 9cr | 80,000 | 95,000 | 95,000 | 23 | 241 | |
| L-80 | 13cr | 80,000 | 95,000 | 95,000 | 23 | 241 | |
| C-90 | 1.2 | 90,000 | 105,000 | 100,000 | 25.4 | 255 | |
| C-95 | _ | 95,000 | 110,000 | 105,000 | _ | _ | |
| T-95 | 1.2 | 95,000 | 110,000 | 105,000 | 25.4 | 255 | |
| 3 | P-110 | 110,000 | 140,000 | 125,000 | _ | _ | |
| 4 | Q-125 | 1-4 | 125,000 | 150,000 | 135,000 | _ | _ |
1.HRC : Rockwell hardness c scale
2.BHN: Brinell hardness
Table 2
| Grade | Total extension of gage Length, perrent |
| H40 | 0.5 |
| J55 | 0.5 |
| K55 | 0.5 |
| L80 | 0.5 |
| N80 | 0.5 |
| C90 | 0.5 |
| C95,t95 | 0.5 |
| P110 | 0.6 |
| Q125 | 0.65 |
2.1. Grades of Casing
API SPEC 5CT recognizes ten grades of casing .
2.1.1. Mechanical Specifications
Grade of casing is specified according to its yield strength . in table 1 . group, grade , yield strength and mechanical specifications have been presented the yield strength shall be the tensile stress to produce a total elongation of the gauge length , as determined by an extensometer .
Sometimes , defined grades do not meet the requirements (for example : well with high corrosion) to solve this problem , manufactures of casing furnish pipes with special specification which are called non-API casing grades . some samples of
2.1.2. Chemical Composition
Pipes and couplings which are produced according to API SPEC 5CT, shall be met the chemical requirements , mentioned in table , numbers are based on percentage of weight.
2.1.3. Casing Dimensions And Weight Specifications
According to API SPEC 5CT , there are two types of joints for casing which their dimensions and specifications are selected in accordance with API SPEC 5CT.
API SPEC 5CT recognizes ten grades of casing .
2.1.1. Mechanical Specifications
Grade of casing is specified according to its yield strength . in table 1 . group, grade , yield strength and mechanical specifications have been presented the yield strength shall be the tensile stress to produce a total elongation of the gauge length , as determined by an extensometer .
Sometimes , defined grades do not meet the requirements (for example : well with high corrosion) to solve this problem , manufactures of casing furnish pipes with special specification which are called non-API casing grades . some samples of
2.1.2. Chemical Composition
Pipes and couplings which are produced according to API SPEC 5CT, shall be met the chemical requirements , mentioned in table , numbers are based on percentage of weight.
2.1.3. Casing Dimensions And Weight Specifications
According to API SPEC 5CT , there are two types of joints for casing which their dimensions and specifications are selected in accordance with API SPEC 5CT.
