Casing Design Principles• Definition; – Casing design involves the determination of factors which influence the failure and the selection of the most suitable casing grades and weights
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Casing Design Principles
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• Lecture Contents;
– Lecture Objectives, – Definitions,
– Casing Design Criteria,
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• Lecture Objectives
– At the end of this lecture YOU will be able to:
consideration when a casing string is to be designed with respect to:
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• Definition;
– Casing design involves the determination of factors
which influence the failure and the selection of the most suitable casing grades and weights for specific
operations,
– The casing program should also reflect the completion
and production requirements,
– A good knowledge of the stress analysis and the ability to
apply it are necessary for the design of casing strings.
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• Definition;
– The end product of such design is a pressure vessel capable of withstanding the expected internal and external pressures and axial loading,
– Hole irregularities further subject the casing to bending forces which must be considered during the selection of casing grades,
– In general, the cost of a given casing grade is proportional to its weight, the heaviest weight being the most expensive,
– And hence the designer must ensure the cheapest and the best quality
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• Design Criteria;
– Collapse Pressure:
• This pressure originates from the column of mud used to drill the hole and acts on the outside of the empty casing,
• Since the hydrostatic pressure of a column of mud increases with depth collapse pressure is highest at the bottom and zero
at top
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• Design Criteria;
– Basic Collapse Assumptions:
at shoe or at TD,
which casing was run in,
CSD
TD
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• Design Criteria;
– Burst:
formation pressure resulting from a kick during the drilling of the next hole section.
Pressure
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• Design Criteria;
– Burst:
influx fluid (gas) displaces the entire drilling mud,
bursting effects of formation pressure
CSD
TD
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• Design Criteria;
– Burst:
• Gas to Surface:
head of mud is zero and the internal pressure must be supported entirely by the casing body,
the casing shoe where internal pressure is resisted by the external pressure originated from fluids outside the casing
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• Design Criteria;
– Burst:
• Gas to Surface:
kick, thereby anticipating the worst possible type of a kick,
causes a small decrease in formation pressure as gas rises up the well,
shoe is less than the formation breakdown at the shoe,
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• Design Criteria;
– Burst:
maximum formation pressure at next hole TD, assuming the hole is full of gas:
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• Mud for 9 5/8” casing = 10 ppg
• Collapse at shoe = 10 * 0.052 * 5000 = 2600 psi,
• Burst at surface = 5000 - ( 0.1 * 10000 ) = 4000 psi,
• Burst at shoe = { 5000 - ( 0.1* [ 10000 - 5000] ) } - { 0.465 * 5000}
= 4500 - 2325 = 2175 psi,
• Selection L80 40lb/ft, B = 5750 psi, C = 3090 psi.
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considered the weakest in tension as it has to carry the total
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• Design Criteria;
– Tension:
vertical depth,
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Pi
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• Design Criteria;
– Tension:
Wn = wt of casing (lb/ft) positive force,
has been designed
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• Now You should be able to:
– Be familiar with the design criteria that is taken into
consideration when a casing string is to be designed with respect to:
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Casing Design Principles
End of Lecture