Changes

* Provide a conduit to measure the changes in flow rate and pressure needed to run a well test

* Provide a conduit to measure the changes in flow rate and pressure needed to run a well test

The wellbore provides the only path from the surface to the reservoir. To a large extent, the successful production and depletion of a reservoir depends upon the successful completion and workover operations applied to a well. In most companies, the production engineer designs and supervises all completion and workover operations.

The wellbore provides the only path from the surface to the reservoir. To a large extent, the successful production and depletion of a reservoir depends upon the successful completion and [[workover]] operations applied to a well. In most companies, the production engineer designs and supervises all completion and workover operations.

==Types of completions==

==Types of completions==

===Open hole completions===

===Open hole completions===

Open hole completions were originally used in the early days of the petroleum industry when most wells were drilled with cable tools. Normally, casing was run as the hole was drilled. When the formation was penetrated and oil and gas began to flow, drilling ceased and the well was produced as an open hole completion. As rotary rigs began to drill a majority of the wells, it was still common to complete a well using an open hole completion. If the well needed to be stimulated, nitroglycerine was used to rubbleize the formation near the wellbore. [[:file:well-completions_fig1.png|Figure 1(a)]] illustrates a typical wellbore diagram for an open hole completion. Although not common in most areas, open hole completions are still used today in certain situations, such as the horizontal well completions in the Austin Chalk and in the Devonian shales in Appalachia. In a typical open hole completion, casing is set prior to drilling into the producing interval. A nondamaging fluid can then be used to drill into the pay section.

Open hole completions were originally used in the early days of the [[petroleum]] industry when most wells were drilled with cable tools. Normally, casing was run as the hole was drilled. When the formation was penetrated and oil and gas began to flow, drilling ceased and the well was produced as an open hole completion. As rotary rigs began to drill a majority of the wells, it was still common to complete a well using an open hole completion. If the well needed to be stimulated, nitroglycerine was used to rubbleize the formation near the wellbore. [[:file:well-completions_fig1.png|Figure 1(a)]] illustrates a typical wellbore diagram for an open hole completion. Although not common in most areas, open hole completions are still used today in certain situations, such as the [[Well types#Horizontal wells|horizontal well]] completions in the Austin Chalk and in the Devonian shales in Appalachia. In a typical open hole completion, casing is set prior to drilling into the producing interval. A nondamaging fluid can then be used to drill into the pay section.

One important disadvantage of an openhole completion is that production casing must be set prior to drilling and logging the reservoir. If for some geological or engineering reason the target formation is not productive, then money has been spent to set casing in a well that may be plugged as a dry hole. Another disadvantage is the lack of control that occurs when an open hole completion is made. One cannot control the flow of fluids from the reservoir into the wellbore nor the injection profile in an open hole completion. In addition, if the formation is not competent, sloughing zones can cave into the wellbore and restrict flow to the surface.

One important disadvantage of an openhole completion is that production casing must be set prior to drilling and logging the reservoir. If for some geological or engineering reason the target formation is not productive, then money has been spent to set casing in a well that may be plugged as a [[dry hole]]. Another disadvantage is the lack of control that occurs when an open hole completion is made. One cannot control the flow of fluids from the reservoir into the wellbore nor the injection profile in an open hole completion. In addition, if the formation is not competent, sloughing zones can cave into the wellbore and restrict flow to the surface.

===Liner completions===

===Liner completions===

The slotted liner completion is similar to an open hole completion and has all the major advantages and disadvantages discussed for open hole completions. The only difference is that a slotted liner is hung in the open hole interval to minimize sloughing of the formation into the well bore ([[:file:well-completions_fig1.png|Figure 1b]]). A screen and liner completion is similar to the slotted liner completion in that a screen and liner is set in the open hole section of the wellbore. The difference is that gravel is sometimes placed behind the screen ([[:file:well-completions_fig2.png|Figure 2a]]). The advantages and disadvantages are the same as for open hole completions. The screen and liner completion is used primarily in unconsolidated formations to prevent the movement of formation materials into the wellbore, restricting the flow of reservoir fluids.

The slotted liner completion is similar to an open hole completion and has all the major advantages and disadvantages discussed for open hole completions. The only difference is that a slotted liner is hung in the open hole interval to minimize sloughing of the formation into the well bore ([[:file:well-completions_fig1.png|Figure 1b]]). A screen and liner completion is similar to the slotted liner completion in that a screen and liner is set in the open hole section of the wellbore. The difference is that gravel is sometimes placed behind the screen ([[:file:well-completions_fig2.png|Figure 2a]]). The advantages and disadvantages are the same as for open hole completions. The screen and liner completion is used primarily in unconsolidated formations to prevent the movement of formation materials into the wellbore, restricting the flow of reservoir fluids.

The cemented liner completion is used when intermediate casing is set in a well prior to reaching total depth ([[:file:well-completions_fig2.png|Figure 2b]]). Many times intermediate casing is used to isolate zones behind pipe such as low pressured intervals that tend to cause lost circulation problems or to isolate zones such as sloughing shales or salt layers. Intermediate casing is also set in transition zones between normally pressured intervals and geopressured intervals. After the casing is set, the weight or chemistry of the drilling fluid can be changed to continue drilling the well. The cemented liner completion is advantageous because the particular intervals behind the liner can be selectively perforated. This selection will allow one to control both the production and injection of fluids in those intervals. The main disadvantage of a cemented liner is the difficulty encountered in obtaining a good primary cement job across the liner. If a good cement job is obtained, then a cemented liner completion is very similar to a perforated casing completion.

The cemented liner completion is used when intermediate casing is set in a well prior to reaching total depth ([[:file:well-completions_fig2.png|Figure 2b]]). Many times intermediate casing is used to isolate zones behind pipe such as low pressured intervals that tend to cause lost circulation problems or to isolate zones such as sloughing shales or salt layers. Intermediate casing is also set in transition zones between normally pressured intervals and [http://www.glossary.oilfield.slb.com/en/Terms/g/geopressure.aspx geopressured] intervals. After the casing is set, the weight or chemistry of the drilling fluid can be changed to continue drilling the well. The cemented liner completion is advantageous because the particular intervals behind the liner can be selectively perforated. This selection will allow one to control both the production and injection of fluids in those intervals. The main disadvantage of a cemented liner is the difficulty encountered in obtaining a good primary cement job across the liner. If a good cement job is obtained, then a cemented liner completion is very similar to a perforated casing completion.

===Perforated casing completions===

===Perforated casing completions===

===Multiple completions===

===Multiple completions===

In certain cases, multiple completions may provide the best control of reservoir operations. Multiple completions include the tubing-casing dual, dual tubing strings, and the typical triple completion consisting of three tubing strings. [[:file:well-completions_fig4.png|Figures 4]] and [[:file:well-completions_fig5.png|5]] illustrate these multiple completions.

In certain cases, multiple completions may provide the best control of reservoir operations. Multiple completions include the tubing-casing dual, dual tubing strings, and the typical triple completion consisting of three tubing strings. [[:file:well-completions_fig4.png|Figures 4]] and [[:file:well-completions_fig5.png|5]] illustrate these multiple completions.

[[file:well-completions_fig5.png|left|thumb|{{figure number|5}}Wellbore diagram of a conventional triple completion.]]

The more complex the completion, the more trouble one can expect in both completion operations and in subsequent [[workover]] operations. Multiple completions should be considered only in special situations. These situations include areas where drilling costs are very high or where the area allocated for drilling wells is at a premium. Such areas include offshore areas, highly populated areas, and remote land locations.

The more complex the completion, the more trouble one can expect in both completion operations and in subsequent workover operations. Multiple completions should be considered only in special situations. These situations include areas where drilling costs are very high or where the area allocated for drilling wells is at a premium. Such areas include offshore areas, highly populated areas, and remote land locations.

The main advantage of multiple completions is that two or more reservoirs can be simultaneously produced from a single wellbore. If all goes properly, the [[economics]] of using multiple completions can be attractive; however, operating and workover costs can be quite high. These operational factors must be considered when considering multiple completions.

The main advantage of multiple completions is that two or more reservoirs can be simultaneously produced from a single wellbore. If all goes properly, the economics of using multiple completions can be attractive; however, operating and workover costs can be quite high. These operational factors must be considered when considering multiple completions.

===Alternate completions===

 

Alternate completions are used to allow inexpensive recompletions. Normally, a single interval is completed and produced to abandonment and then, using wireline tools, the lower interval is isolated and the upper interval opened to production ([[:file:well-completions_fig6.png|Figure 6]]). Alternate completions eliminate the need for costly [[workovers]] using rigs. It is possible to have a dual well with two alternate completions; however, as the completion gets more complex, more problems will occur. Alternate completions are used in areas where workover costs by conventional methods can be quite high. The most common use of alternate completions is offshore.

Alternate completions are used to allow inexpensive recompletions. Normally, a single interval is completed and produced to abandonment and then, using wireline tools, the lower interval is isolated and the upper interval opened to production ([[:file:well-completions_fig6.png|Figure 6]]). Alternate completions eliminate the need for costly [[workovers]] using rigs. It is possible to have a dual well with two alternate completions; however, as the completion gets more complex, more problems will occur. Alternate completions are used in areas where workover costs by conventional methods can be quite high. The most common use of alternate completions is offshore.

==Perforating==

==Perforating==

 

[[file:well-completions_fig7.png|thumb|300px|{{figure number|7}}Construction of a typical shaped charge.]]

[[file:well-completions_fig7.png|thumb|{{figure number|7}}Construction of a typical shaped charge.]]

[[file:well-completions_fig8.png|thumb|300px|{{figure number|8}}Jet stream generated by shaped charge.]]

The major purpose of perforations is to provide effective flow communication between the wellbore and the reservoir. To create a perforation, a perforating gun is used to “shoot” a hole through the casing and cement. The hole is called a ''perforation tunnel'' and provides a pathway for fluid flow from the reservoir to the wellbore.

The major purpose of perforations is to provide effective flow communication between the wellbore and the reservoir. To create a perforation, a perforating gun is used to “shoot” a hole through the casing and cement. The hole is called a ''perforation tunnel'' and provides a pathway for fluid flow from the reservoir to the wellbore.

Over 90% of wells are perforated using a ''shaped charge'' perforating system. The shaped charge, or jet charge, came into use in the oil field shortly after World War II. The perforating shaped charge is a derivative of the charge used to construct a bazooka. The shaped charge has essentially replaced the bullet gun, which was the main perforating tool prior to World War II.

Over 90% of wells are perforated using a ''shaped charge'' perforating system. The shaped charge, or jet charge, came into use in the oil field shortly after World War II. The perforating shaped charge is a derivative of the charge used to construct a bazooka. The shaped charge has essentially replaced the bullet gun, which was the main perforating tool prior to World War II.

[[:file:well-completions_fig7.png|Figure 7]] illustrates the components of the shaped charge. The main characteristic of the shaped charge is the cone-shaped cavity. To fire the shaped charge, the primer cord ignites the primer charge, which in turn ignites the main explosive charge. As the powder burns, it reaches the apex of the cone. The cone collapses and creates a jet stream that is capable of penetrating the steel casing, cement, and formation. [[:file:well-completions_fig8.png|Figure 8]] illustrates the formation of the jet stream from a shaped charge.

[[:file:well-completions_fig7.png|Figure 7]] illustrates the components of the shaped charge. The main characteristic of the shaped charge is the cone-shaped cavity. To fire the shaped charge, the primer cord ignites the primer charge, which in turn ignites the main explosive charge. As the powder burns, it reaches the apex of the cone. The cone collapses and creates a jet stream that is capable of penetrating the steel casing, cement, and formation. [[:file:well-completions_fig8.png|Figure 8]] illustrates the formation of the jet stream from a shaped charge.

====Thru-tubing gun====

====Thru-tubing gun====

The guns that are run inside the tubing to perforate the casing are called thru-tubing guns. Typical thru-tubing guns range in diameter from 1–3/8 to 2–3/8 in. Because thru-tubing guns are much smaller than casing guns, smaller jet charges must be used; therefore, the resulting perforations are smaller in diameter and length, compared to a casing gun.

The guns that are run inside the tubing to perforate the casing are called thru-tubing guns. Typical thru-tubing guns range in diameter from 1–3/8 to 2–3/8 in. Because thru-tubing guns are much smaller than casing guns, smaller jet charges must be used; therefore, the resulting perforations are smaller in diameter and length, compared to a casing gun.

===Perforating methods===

===Perforating methods===

 

[[file:well-completions_fig10.png|thumb|{{figure number|10}}Qualitative description of perforations using (a) a casing gun and (b) a thru-tubing gun.]]

well-completions_fig9.png|{{figure number|9}}Two perforating methods: (a) Perforating overbalanced with a casing gun and (b) perforating underbalanced with a thrutubing gun.

well-completions_fig10.png|{{figure number|10}}Qualitative description of perforations using (a) a casing gun and (b) a thru-tubing gun.

A well can be perforated three different ways:

A well can be perforated three different ways:

[[Category:Production engineering methods]]

[[Category:Production engineering methods]]