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===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.