2 1 casing seat selection

Casing Point Selection • Lecture Objectives; – At the end of this lecture YOU will be able to: • State the two Drilling related reasons for running casing, • State the difference in sel

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Casing Point Selection

Casing Point Selection

– Lecture Objectives,

– Exploration Well Casing Setting Depths,

– Restrictions on Casing Shoe Depth,– Special Criteria,

Casing Point Selection

• Lecture Objectives;

– At the end of this lecture YOU will be able to:

• State the two Drilling related reasons for running casing,

• State the difference in selecting casing points for

exploration and development wells,

• Describe functions of different type of casings

• State restrictions that govern shoe depth selection,

• Calculate the minimum conductor setting depth offshore to

enable returns to be taken to the flowline

Casing Point Selection

– Casing is set for two Drilling reasons;

• Consolidate the hole already drilled (protect sensitive

formations, water sources etc),

• Provide pressure control integrity to drill ahead (be able to

safely handle a kick)

Casing Point Selection

– Exploration wells are planned with little offset data, – Each casing should be set as deep as it is safe This is to:

• Allow maximum contingency in case extra casings are

needed lower down,

• Minimize the number of casing strings run to minimize

well cost,

– Each casing string is run as deep as possible based on

kick tolerance, unless other reasons dictate it be run higher.

Casing Point Selection

– Casings are run as minimum as possible This to:

• Reduce the cost of the well (less time running casings; less

casing)

• Run smaller casings to reach the reservoir at a particular

hole size which will also lead to large cost savings (smaller casings cheaper than larger; same for drillbits etc.)

– Each casing string is only set deep enough to enable the

next casing point to be reached,

– Contingency is less critical.

Casing Point Selection

20”

13-3/8”

9-5/8”

Intermediate

Casing Point Selection

– Kick tolerance:

• The hole section should not be

drilled deeper than is possible to safely circulate out a kick, based on formation pressures, fracture

gradients and kick tolerance policies

Casing Point Selection

Casing Point Selection

• Restrictions on Casing Shoe Depth;

– Wellbore Stability:

• We may be restricted by

deterioration of the wellbore with time,

• If a formation is stabilized by our

mud system for up to 10 days, then drilling ahead for 12 days might prevent us logging the hole or running casing

Casing Point Selection

• Restrictions on Casing Shoe Depth;

• We may have formations which

have mutually exclusive requirements for the mud,

• For instance if we have very

reactive shale requiring ideally OBM at a higher density to drill, but the mud will cause emulsion blocking in the reservoir, then we need to separate the two with casing.

Casing Point Selection

• Restrictions on Casing Shoe Depth;

– Directional Requirements:

• We may anticipate problems

related to torque and drag, or differential sticking due to stationary string while using downhole motors,

• The build up section may

need protection before drilling ahead

Casing Point Selection

• Restrictions on Casing Shoe Depth;

– Fracture gradient at the shoe:

• We need to set our casing in a competent formation for

drilling ahead,

• We could drill to the limit for kick tolerance on a hole

section; but if the place where we set the casing is fractured

or underpressured then the shoe will be too weak to drill ahead

Casing Point Selection

Casing Point Selection

– Conductor Pipe (offshore):

• The Conductor needs to be set deep enough in a formation

which allows returns to the flowline,

• The minimum depth for the conductor shoe to allow

returns to the flowline can be calculated:

 

ρReturns ρFormation

ρSea y

ρReturns y

x n

Penetration = depth of shoe from seabed, feet

x = Height of flowline above sea, feet

y = Water depth, feet

 Sea = Sea water density, psi/ft

 Returns = Returns density, psi/ft

 Formation = Formation density, psi/ft.

Casing Point Selection

– Calculate the minimum setting depth BRT, on a

development offshore Well:

• Height of flowline = 80' MSL,

• Height of drill floor = 90' MSL,

• Water depth = 100'

• Formation density gradient = 0.85 psi/ft,

• Seawater in the area = 0.45 psi/ft ,

• Expected returns gradient = 0.5 psi/ft.

'

129 5

0 85 0

45 0 100 5

0 180 n

Casing Point Selection

• Surface Casing:

• The Surface Casing is usually set in the first competent

formation which is strong enough to close in on a kick,

• The setting depth is selected to allow a BOP to be nippled up

for drilling ahead

• Other considerations:

– Support subsequent casing strings,– Isolate of surface fresh water formation,– Case-off unconsolidated or lost circulation areas,– On a multi well platform, well may be kicked off in surface hole

and surface casing will also protect the build up section Common sizes and depth: 20” - 9 5/8” threaded,

» 100’ - 3000’ (or more).

Casing Point Selection

• Intermediate Casings:

• The Intermediate Casing is set as deep as possible to allow sufficient shoe strength for drilling ahead,

• It is often planned to be set in a pressure transition zone, where

pore pressures and fracture gradients are increasing Care must

be taken to not drill into transition zone-well kicks,

• Other considerations:

– Directional (reduce torque and drags in an extended reach hole) or

wellbore stability reasons - Case off troublesome zones (Lost Circulation, Salt Section, Over-pressured Zones, Heaving Shales) prior to drilling ahead Separates hole into workable sections

• Common sizes and depths:

Casing Point Selection

• The Production Casing is set through or just above the

reservoir, depending on the type of completion to be used,

• The completion type will dictate the production casing

setting depth:

– If a production liner is run, then generally the production

casing will be set somewhere above the reservoir,

– If the completion calls for the production casing or liner to be

perforated, it will be set through the reservoir,

– In a non-cemented completion (such as a prepacked screen in a

horizontal well) then the casing may be set just inside the reservoir.

Casing Point Selection

• Production;

• Purpose:

– Isolates the pay zone from other formations and the fluids in them,

– Protective housing for production equipment,

» Subsurface artificial lift,

» Multiple zone completion,

» Screens for sand control,– Covers worn or damaged intermediate string

• Common sizes:

– 4 1/2”, 5”, 7”, & 9 5/8”.

– Lost circulation zones,

– Shales or plastic formations,

Liner Hanger

Liner Wiper Plug

Running Tool Shear Pin

Casing Point Selection

• Liners;

• Tie-Back (Liner Complement);

– The integration of the liner with casing from top of existing liner to surface,

– To further up casing to cover

corroded or damaged zone,

– This is often done if

production is commercially viable or there is damage to casing above the liner.

TIE BACK

STINGER WITH SEALS

LINER

Casing Point Selection

– State the two Drilling related reasons for running casing,

– State the difference in selecting casing points for

exploration and development wells,

– Describe functions of different type of casings – State restrictions that govern shoe depth selection, – Calculate the minimum conductor setting depth offshore

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Casing Point Selection

End of Lecture