Casing Setting Depth Selection

Casing Setting Depth Selection

Prof. Dr. Eissa Mohamed Shokir

Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

Casing Setting Depth Selection Casing Setting Depth Selection

• Intermediate Casing Depth Selection

• Liner Depth Selection

• Surface Casing Depth Selection

• Conductor Pipe Depth Selection


Prof

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Intermediate Casing and Liner


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Prof

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Prof

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Prof

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Prof

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Prof

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Prof

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Surface Casing Setting Depth

Selection


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

Surface Casing Depth Selection Surface Casing Depth Selection

• Shallow casing strings such as surface casing are often imposed to pressures that are more severe than the considerations used to select the setting depths for intermediate casing and liner. These pressures usually result from kicks inadvertently taken when drilling deeper sections.

• As a result, surface setting depths are selected to contain kick pressures rather than the previously described procedures for intermediate casing.

• Kick-imposed equivalent mud weights are the cause for most underground blowouts. When a kick occurs, the shutin casing pressure added to the drilling mud hydrostatic pressure exceeds the formation fracture pressure and results in an induced fracture.

• Therefore, the objective of a seat selection procedure that avoids underground blowouts would be to choose a depth that can competently withstand the pressures of reasonable kick conditions.


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

• A precise determination of kick-imposed pressures can be difficult. However, a procedure that estimates the values has been proven in field applications to be quick and effective. Fig. 5-4 represents a well whose pumps and blowout preventers have simulated a kick. Eq. 5.3 describes the pressure relationships:

Surface Casing Depth Selection Surface Casing Depth Selection

Where:

EMWkick = equivalent mud weight at the depth of interest, lb/gal Total depth = deepest interval, ft Depth of interest = ft M = incremental kick mud weight increase, lb/gal OMW = original mud weight, lb/gal

5.3


Prof

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Kick pressure-equivalent mud weight relationships Prof. Dr. Eissa Mohamed Shokir

Prof

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Prof

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Prof

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Prof

. Dr.

Eis

sa M

oham

ed S

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Kick Tolerance

• Maximum Casing Pressure - MCP

• Maximum Allowable Annular Surface Pressure - MAASP, MASP

• Maximum Casing pressure that the formation can withstand prior to fracture

= (EMW-MW)*0.052*TVDcasing seat


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

Kick Tolerance

• Maximum ppg kick - Maximum mud weight increase on a kick prior to formation fracture

= (EMW-MW)*TVDshoe/TVDwell

• Assumes zero pit gain


Prof

. Dr.

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Kick Tolerance

• Maximum Kick Volume

MKV = Maximum kick volume, bbl rs = frac gradient at the casing seat, psi/ft rm= mud gradient, psi/ft rK= formation pressure gradient, psi/ft ann cap = annular capacity at depth of influx, bbl/ft Hs = vertical depth of casing seat, ft Hv = Vertical depth of the well, ft


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

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Kick Types

• Gas Kicks

– Rapid expansion as gas circulated through choke

– Mud gas separators and flare lines used

– Gas migration problems

– Higher SICP than others


Prof

. Dr.

Eis

sa M

oham

ed S

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Kick Types

• Gas Kicks, cont.

– Barite settling in OB mud

– Solubility of gas masks kick indicators

– Flammability of gas

– Slugging of gas at choke


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

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Kick Types

• Water kicks

– not flammable

– very little expansion

– lower SICP than gas or oil

– But, there is still usually some gas present.


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

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Kick Types

• Water kicks

– not flammable

– very little expansion

– lower SICP than gas or oil

– But, there is still usually some gas present.


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

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Kick Types

• Prediction kick types

– Density of gas =1-2 ppg

– Density of oil = 6-8 ppg

– Density of salt water =8.6-9.0 ppg

ftbblCapAnn

bblPitGainheight

height

SIDPPSICPMWyKickDensit

/,.

,

052.0


Prof

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Casing Size Selection Casing Size Selection

What size casing and what size bit do we required?


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

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Once the setting depths have been determined the next step is obviously to select the sizes of the casing strings to be set. The sizes will depend on a number of things, Two important things to know about selection of casing size: Hole size determines casing size, the recommended clearance For cementing should be taken into consideration.

Hole size at any point in the well except the surface is determined by the previous string of casing This means one thing to us.


In selecting casing size usually have to start at the bottom of the hole. Prof. Dr. Eissa Mohamed Shokir

Prof

. Dr.

Eis

sa M

oham

ed S

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• The size of the last string of casing run in a well is determined by the type of completion that will be employed. • That decision is usually the function of an interdisciplinary team of reservoir, production, and drilling personnel. • There are numerous criteria on which this decision is based, so we will assume for our purposes that the size of the last string is predetermined and we will proceed from that point.



Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

Once we know the diameter of the final liner or string of casing the procedure proceeds like this: • Determine the hole size (bit size) for the final string of casing.

• Determine what diameter casing will allow that size bit to pass through it That is the size of the next string of casing.

• Repeat the procedure until all of the hole sizes and casing sizes have been determined. Precaution: After the casing string have been designed be sure to check the drift diameter to be certain that the bit will pass



Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r


Casing Size Selection

Prof

. Dr.

Eis

sa M

oham

ed S

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Typical bit and casing size for hard rock formations.

Casing Size Selection

Solid lines indicate commonly used bits for that size pipe and can be considered to have adequate clearance to run and cement the casing or liner.

The broken lines indicate

less commonly used hole

sizes. The selection of one

of these broken paths

requires that special

attention be given to the

connection, mud weight,

cementing, and doglegs.

Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

typical bit and casing sizes for unconsolidated formations.

Casing Size Selection Solid lines indicate commonly used bits for that size pipe and can be considered to have adequate clearance to run and cement the casing or liner.

The broken lines indicate

less commonly used hole

sizes. The selection of one

of these broken paths

requires that special

attention be given to the

connection, mud weight,

cementing, and doglegs.


Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

The previous chart starts with the last string of casing or liner and works downwards to the first casing string of the well. You can see on this chart there are many options even for those situations where the same size liner or casing is to be run. In general, hard rock offers us more choices and clearance between the casing and borehole wall can be less than for unconsolidated wells.



Prof

. Dr.

Eis

sa M

oham

ed S

hoki

r

Documents

Casing Setting Depth Selection