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===

<gallery mode=packed heights=300px widths=300px>

<gallery mode=packed heights=300px widths=300px>

well-completions_fig5.png|{{figure number|5}}Wellbore diagram of a conventional triple completion.

well-completions_fig5.png|{{figure number|5}}Wellbore diagram of a conventional triple completion.

</gallery>

</gallery>

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.

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===

==Perforating==

==Perforating==

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

well-completions_fig7.png|{{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.]]

well-completions_fig8.png|{{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.

===Perforating methods===

===Perforating methods===

<gallery mode=packed heights=200px widths=200px>

<gallery mode=packed heights=300px widths=300px>

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_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.

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

[[Category:Production engineering methods]]

[[Category:Production engineering methods]]