Changes

Completions can be divided into three categories: ''open hole completions, liner completions'', and ''perforated casing completions''. In most wells, conventional single perforated casing completions are used; however, multiple, alternate, or slim hole completions may be used under certain conditions. The choice of completion type should be closely coordinated with the development of the reservoir management plan. For example, the size, weight, and grade of the tubular goods will be determined based upon the ultimate use of a wellbore. An injection well may require stronger casing than a production well.

Completions can be divided into three categories: ''open hole completions, liner completions'', and ''perforated casing completions''. In most wells, conventional single perforated casing completions are used; however, multiple, alternate, or slim hole completions may be used under certain conditions. The choice of completion type should be closely coordinated with the development of the reservoir management plan. For example, the size, weight, and grade of the tubular goods will be determined based upon the ultimate use of a wellbore. An injection well may require stronger casing than a production well.

===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. 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 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.

[[file:well-completions_fig1.png|thumb|{{figure number|1}}Wellbore diagram of (a) an open hole completion and (b) a slotted liner completion.]]

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.

[[file:well-completions_fig2.png|thumb|{{figure number|2}}Wellbore diagram of (a) a screen and liner completion and (b) a cement liner completion.]]

===Liner completions===

===Liner completions===

* Cemented liner

* Cemented liner

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 wellbore (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 (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.

[[file:well-completions_fig3.png|thumb|left|{{figure number|3}}Wellbore diagram of (a) a perforated completion and (b) a single completion inside perforated casing.]]

[[file:well-completions_fig2.png|thumb|{{figure number|2}}Wellbore diagram of (a) a screen and liner completion and (b) a cement liner completion.]]

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 (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 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===

A perforated casing completion, illustrated in Figure 3a, is the most commonly used completion technique today. The main advantage of this type of completion is that the well can be drilled and logged to total depth prior to running and cementing production casing. By obtaining cores and logs of the potential producing interval, one can estimate the economic value of that wellbore prior to committing funds to complete the well. Another advantage of a perforated casing completion is that it is easier to obtain a good cement job, compared to a liner completion. If the primary cementing job is properly performed, one can selectively produce from and inject into the reservoir and isolate intervals as required. The production of an unconsolidated formation can be accomplished by performing an inside gravel pack. Finally, the perforated casing completion is quite adaptable to multiple completions and alternate completions.

A perforated casing completion, illustrated in [[:file:well-completions_fig3.png|Figure 3a]], is the most commonly used completion technique today. The main advantage of this type of completion is that the well can be drilled and logged to total depth prior to running and cementing production casing. By obtaining cores and logs of the potential producing interval, one can estimate the economic value of that wellbore prior to committing funds to complete the well. Another advantage of a perforated casing completion is that it is easier to obtain a good cement job, compared to a liner completion. If the primary cementing job is properly performed, one can selectively produce from and inject into the reservoir and isolate intervals as required. The production of an unconsolidated formation can be accomplished by performing an inside gravel pack. Finally, the perforated casing completion is quite adaptable to multiple completions and alternate completions.

 

===Single completions===

===Single completions===

Once the decision has been made to either complete a well using an open hole completion, liner completion or perforated casing completion, a decision must be made on how many different intervals will be produced. The most common method is the single completion in which only one interval is produced at a time (Figure 3b). A single completion is simple and results in fewer operating problems and less cost than multiple completions. Single completions are common on land where the reservoirs are either shallow or very deep. If the formation is very shallow, then drilling costs are minimal and single completions are usually best. In very deep wells, single completions are preferred because of the complexity and expense involved with a dual or triple completion in reservoirs deeper than [[depth::10,000 ft]].

Once the decision has been made to either complete a well using an open hole completion, liner completion or perforated casing completion, a decision must be made on how many different intervals will be produced. The most common method is the single completion in which only one interval is produced at a time (Figure 3b). A single completion is simple and results in fewer operating problems and less cost than multiple completions. Single completions are common on land where the reservoirs are either shallow or very deep. If the formation is very shallow, then drilling costs are minimal and single completions are usually best. In very deep wells, single completions are preferred because of the complexity and expense involved with a dual or triple completion in reservoirs deeper than [[depth::10,000 ft]].

===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. Figures 4 and 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_fig4.png|thumb|{{figure number|4}}Wellbore diagram of (a) a casing-tubing dual completion and (b) a completion with dual packers and dual tubing strings.]]

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

[[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===

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 (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.

 

===Slim hole completions===

===Slim hole completions===