What is the difference between casing and liner

Tubing that is too large, however, may have an economic impact beyond the cost of the tubing string itself, because the tubing size will influence the overall casing design of the well. The American Petroleum Inst. Casing is classified according to five properties:.

Almost without exception, casing is manufactured of mild 0. Strength can also be increased with quenching and tempering. API has adopted a casing "grade" designation to define the strength of casing steels. This designation consists of a grade letter followed by a number, which designates the minimum yield strength of the steel in ksi 10 3 psi.

Table 1 summarizes the standard API grades. The yield strength , for these purposes, is defined as the tensile stress required to produce a total elongation of 0. However, the case of P— casing is an exception where yield is defined as the tensile stress required to produce a total elongation of 0.

There are also proprietary steel grades widely used in the industry, which do not conform to API specifications. These steel grades are often used in special applications requiring high strength or resistance to hydrogen sulfide cracking. Table 2 gives a list of commonly used non-API grades. To design a reliable casing string, it is necessary to know the strength of pipe under different load conditions. The most important mechanical properties of casing and tubing are:.

Threads are used as mechanical means to hold the neighboring joints together during axial tension or compression. For all casing sizes, the threads are not intended to be leak resistant when made up. API Spec. The internal yield pressure is the pressure that initiates yield at the root of the coupling thread. This dimension is based on data given in API Spec. The coupling internal yield pressure is typically greater than the pipe body internal yield pressure.

The internal pressure leak resistance is based on the interface pressure between the pipe and coupling threads because of makeup. This equation accounts only for the contact pressure on the thread flanks as a sealing mechanism and ignores the long helical leak paths filled with thread compound that exist in all API connections. In round threads, two small leak paths exist at the crest and root of each thread. Buttress threads have a much larger leak path along the stabbing flank and at the root of the coupling thread.

API connections rely on thread compound to fill these gaps and provide leak resistance. The leak resistance provided by the thread compound is typically less than the API internal leak resistance value, particularly for buttress connections.

The leak resistance can be improved by using API connections with smaller thread tolerances and, hence, smaller gaps , but it typically will not exceed 5, psi with any long-term reliability.

Applying tin or zinc plating to the coupling also results in smaller gaps and improves leak resistance. The round-thread casing-joint strength is given as the lesser of the fracture strength of the pin and the jump-out strength. The fracture strength is given by. These equations are based on tension tests to failure on round-thread test specimens. Both are theoretically derived and adjusted using statistical methods to match the test data. For standard coupling dimensions, round threads are pin weak i.

The buttress thread casing joint strength is given as the lesser of the fracture strength of the pipe body the pin and the coupling the box. Pipe thread strength is given by. These equations are based on tension tests to failure on buttress-thread test specimens. They are theoretically derived and adjusted using statistical methods to match test data. When performing casing design, it is very important to note that the API joint-strength values are a function of the ultimate tensile strength.

This is a different criterion from that used to define the axial strength of the pipe body, which is based on the yield strength. In the case of the driven casing, a vibratory hammer is almost always used for temporary casing; an impact hammer may be used to install permanent casing, but temporary casing will require a vibratory hammer for extraction since casing installed with an impact hammer may be impossible to remove.

In principal, jetting could be utilized as an aid to installation, but jetting around the casing would not be advised during extraction due to the potential for jet water to adversely affect the fluid concrete.

In planning the construction of drilled shafts in congested areas, it should be noted that the use of vibratory installation of casing can cause significant vibrations that can affect nearby structures, or cause settlement in loose sands which can affect nearby structures.

The attenuation of vibrations with distance away from the source is affected by the size of the hammer and casing, the operating frequency of the hammer, the soil and rock properties, the localized stratigraphy, groundwater, and other factors that are likely site-specific. In most cases, vibrations from casing installation are extremely small at distances of 50 to 70 ft from the source. In cases where sensitive structures may be present nearby, a program of vibration monitoring should be included in the installation plan.

Vibration monitoring can help avoid potential damage and can also provide documentation as protection against lawsuits or claims of damage caused by vibratory installation of casing. Monitoring during construction of the technique and test shaft installations can provide valuable measurements of vibrations at various radial distances from the source before moving the work into production locations.

Installation of the casing using a vibratory hammer is most effective in sandy soil deposits, and to penetrate through sandy soils into a clay or marl stratum below. The hammer clamps to the top of the casing Figure , which is often reinforced at the end with an extra thickness to aid in resisting the transmitted forces. The vibration of the casing often causes temporary liquefaction of a thin zone of soil immediately adjacent to the casing wall so that penetration is achieved only with the weight of the casing plus the hammer.

This technique is particularly effective in sandy soils with shallow groundwater. Penetration of an underlying hard layer such as hard rock may be difficult or impossible with a vibro- driven casing. Attempts to twist the casing with the drill rig to seat into rock are likely to be ineffective because of the side resistance of the soil against the casing after removal of the vibration.

In general, a vibratory hammer is used to place the entire length of temporary casing into the soil before excavation of soil inside the casing. However, to facilitate penetration through particularly dense soils, the casing can be installed by an alternating sequence of driving the casing and drilling to remove the soil plug within the casing.

In this case, it would typically be necessary to install the casing in sections, with the sections joined by welding. Removal of the casing with the vibratory hammer must be accomplished while the concrete is still fluid. During extraction, the hammer is attached and powered, and then typically used to drive the casing downward a few inches using the weight of the casing and hammer to break the casing free of the soil.

Once the casing is moved, the crane pulls the casing upward to remove it and leave the fluid concrete filled hole behind. Installation of temporary casing ahead of the excavation may be accomplished with a drill using the special casing and tools illustrated previously in Figures and The oscillator or rotator clamps onto the casing with powerful hydraulic jaws and uses hydraulic pistons to twist the casing and push it downward, reacting against a large drilling machine or temporary frame.

The casing is therefore used in the same manner as a coring tool to advance into the soil or rock. In order to advance the casing and overcome the soil side shearing resistance to twisting, it is necessary that the casing have cutting teeth slightly larger than the outside dimension of the casing.

The bottom section of casing is fitted with a cutting shoe to promote penetration Figure by cutting a slightly oversized hole and relieving the stress against the sides of the casing. The soil on the interior of the casing is excavated simultaneously as the casing is installed to remove the resistance of this portion of the soil.

During installation of the casing, it is essential that a plug of soil remain inside the casing typically about one shaft diameter in thickness so that the bottom of the excavation does not become unstable during installation.

In water-bearing soils, the head of water inside of the casing must also be maintained so that bottom heave does not occur.

It is possible to use slurry inside the casing to maintain stability, but the need for slurry is usually avoided by maintaining a soil plug. It is necessary to maintain stability during installation because heave of soil into the casing would cause loosening of the ground around the excavation with adverse effects on side shear and possible subsidence around the shaft.

At completion of the excavation, the soil plug may be removed to the base of the casing or below if the casing is extended into a rock or stable formation or if a slurry head is used to maintain stability. If the hole terminates in water-bearing soil with only a water head for stability, it may be necessary that the casing extend below the base of the final excavation to avoid instability at the base.

However, this procedure may result in an annular zone of loosened soil at the base of the drilled shaft excavation. The thicker casing typically about 2 to 2. If a single wall pipe is used with the casing joints as shown in Figure , the joints will protrude inside the casing because the joint is typically thicker than the pipe. To avoid potential torsional deformation of reinforcement, the casing is typically oscillated back and forth during extraction, even if a continuous rotation was used during installation.

The casing is typically extracted simultaneously as concrete is placed into the excavation, and concrete head above the tip of the casing must be maintained so that a positive concrete pressure is provided against the hole.

If exterior groundwater pressure is present, the head of concrete and water inside the casing must exceed the exterior water pressure in order to prevent inflow of water and contamination of the concrete. It is also essential that the concrete remain fluid so that the oscillation of the casing does not transfer twisting forces into the reinforcing cage and cause distortion.

Drilled shafts installed through a body of water typically use a permanent casing that serves as a form until the concrete sets, and then is left permanently in place. It is often specified to remove portions of otherwise permanent casing that is exposed above the ground surface or above the surface of a body of water following completion of the drilled shaft installation and after the concrete has reached sufficient strength. In such cases, typically only a short section of casing would need to be removed.

The removal would typically be accomplished by torch cutting the steel into sections, taking care to avoid damaging the underlying concrete surface, and detaching the individual sections from the surface of the concrete. However, temporary casings have occasionally been used for such applications, including various types of removable forms attached to the top of the permanent casing.

There have been numerous reports of difficulties with the use of temporary casing over water. An example of a removable casing is shown in Figure ; this photo is taken from the I Fuller Warren Bridge over the St. Tubings are usually run inside casing cased hole and serves as a conduit through which oil and gas is produced. It is basically a tube inside casing which is used to produce reservoir fluids.

Casing pipes are used to protect the well from the rubble either tubing used for the purposes of many of us pumping nitrogen. Casing is very necessary for smooth drilling operations in deep and ERD wells so that hole collapsing may be got rid of. Tubings are run after drilling.

Thru tubing we safely and efficiently produce wells according to reservoir volume and nature. Products By Bayt.