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Drilling problems include any difficulties encountered while drilling a well. The most common drilling problems are the creation of doglegs and key seats, hole instability, lost circulation, and excessive bottom hole temperatures.

Drilling problems include any difficulties encountered while [[drilling a well]]. The most common drilling problems are the creation of doglegs and key seats, hole instability, lost circulation, and excessive bottom hole temperatures.

==Doglegs==

==Doglegs==

A ''dogleg'' is usually defined as any deviation greater than 3° per [[length::100 ft]], and it occurs when a sharp change of direction is taken in the wellbore. Typically, a dogleg is caused by a change in the [[dip]] of the formation or by a change in the weight applied to the bit. Severe doglegs can result in stuck casing, drill pipe failure, and inability to run [http://www.glossary.oilfield.slb.com/en/Terms/c/casing.aspx casing] to total depth. If casing is successfully run through the dogleg, excessive wear on production equipment can occur. The use of properly placed stabilizers, large diameter drill collars, and the proper weight applied to the bit will minimize the formation of doglegs.

A ''dogleg'' is usually defined as any deviation greater than 3° per [[length::100 ft]], and it occurs when a sharp change of direction is taken in the wellbore. Typically, a dogleg is caused by a change in the [[dip]] of the formation or by a change in the weight applied to the bit. Severe doglegs can result in stuck casing, drill pipe failure, and inability to run [http://www.glossary.oilfield.slb.com/en/Terms/c/casing.aspx casing] to total depth. If casing is successfully run through the dogleg, excessive wear on production equipment can occur. The use of properly placed stabilizers, large diameter drill collars, and the proper weight applied to the bit will minimize the formation of doglegs. (See [[Wellbore trajectory]].)

==Key seats==

==Key seats==

* Overburden pressure

* Overburden pressure

* Earth movement forces

* Earth movement forces

* Pore pressure

* [http://www.glossary.oilfield.slb.com/en/Terms/p/pore_pressure.aspx Pore pressure]

* Water absorption, swelling, or dispersion

* Water absorption, swelling, or dispersion

* Ineffective hole cleaning

* Ineffective hole cleaning

* Stuck pipe

* Stuck pipe

* Bridges and fill-up

* [http://www.glossary.oilfield.slb.com/en/Terms/b/bridge.aspx Bridges] and fill-up

* Wellbore enlargement

* Wellbore enlargement

* Increased mud volume

* Increased mud volume

==Bottom hole temperatures==

==Bottom hole temperatures==

Extremely high bottom hole temperatures can occur in deep wellbores or in areas of abnormally high [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=geothermal%20gradient geothermal gradient]. These excessively high bottom hole temperatures (greater than [[temperature::250°C]]) can cause drilling problems because of the accelerated thickening of water-based drilling fluids. The increase in viscosity and density of the drilling can may result in the following:

Extremely high bottom hole temperatures can occur in deep wellbores or in areas of abnormally high [[geothermal gradient]]. These excessively high bottom hole temperatures (greater than [[temperature::250°C]]) can cause drilling problems because of the accelerated thickening of [[Drilling_fluid#Water-based_muds|water-based drilling fluids]]. The increase in [[viscosity]] and density of the drilling can may result in the following:

* Reduction in penetration rates

* Reduction in penetration rates

* Lost circulation

* Lost circulation

* The well being swabbed when drill pipe is pulled

* The well being [http://www.glossary.oilfield.slb.com/en/Terms/s/swab.aspx swabbed] when drill pipe is pulled

* Stuck tools

* Stuck tools

This problem can be mitigated by using oil-based muds.

This problem can be mitigated by using [[Drilling_fluid#Oil-based_muds|oil-based muds]].

==See also==

==See also==

[[Category:Engineering]]

[[Category:Engineering]]

[[Category:Engineering – Development and Operations]]

[[Category:Engineering – Development and Operations]]