23533669 bo 019 drilling engeneering

8/3/2019 23533669 BO 019 Drilling Engeneering

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Agip KCO Training Special Project SP 2Basic Oil and Gas in Exploration

and Production Activities

Drilling engineering

BO-019-GIA-001-E

Drilling Engineering


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and Production ActivitiesBO-019-GIA-002-E



a)Objectives of drilling engineering

b)Evaluation of pressure gradients

c) The design of the drilling programme: selection

of bits, casings & muds

d)Monitoring & logging while drilling

e)Cutting disposal: problems and solutions


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Drilling an oil well involves two main actions:

Overcoming the resistance of rock material

Transportation of rock material to the surface


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Objectives Of Drilling Engineering

a) To drill a well safely and economically

b) Drilling cost equations

c) Drilling fluid treatmentd) Pump operation

e) Bit selection


5/77Agip KCO Training Special Project SP 2

Basic Oil and Gas in Exploration



BO-019-GIA-005-E

Pressure Gradient


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Well Planning:

Casing Point Selection

Casing Design

Mud Density

Fracturing Gradient

Drilling Rig Selection

Importance of Formation Pressure Gradients


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While Drilling:

To use adequate mud density:

> to avoid kicks o blow-outs

> To avoid mud absorption and/or mud loss circulation

> to avoid sticking of drilling string for differential

pressure

> to avoid sticking of drilling string due to caving hole

> to reduce drilling times

To change, in case of need, the casing point depth while

drilling.

To reduce the drilling problems and reach the planned welldepth.

To cut drilling costs.

Importance Formation Pressure Gradients


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Hydrostatic pressure at a certain depth is defined as the pressure exerted by theweight of the fluid column with a given density.

P = hydrostatic pressure expressed in kg/cm2

H = examined depth expressed in meters

f

= fluid density expressed in kg/dm3, usually for water assumed to be equal to 1.03 kg/dm3

P

Hf=

10where

Hydrostatic Pressure


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where:

Ghyd = hydrostatic gradient expressed in kg/cm2/10m

P = pressure expressed in kg/cm2

H = examined depth in m

Pressure Gradient is defined as a ratio of pressure value and depth:

GP

Hhyd

= 10

Hydrostatic Pressure Gradient


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ABNORMAL Pore Pressure

The Formation Pressure can be :

OVERPRESSURE. Its value is > than the hydrostatic Pressure

UNDERPRESSURE. Its value is < than the hydrostatic Pressure

Formation Pressure (Ppore)


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Gradient > 1.03-1.07 kg/cm2/10m OVERPRESSURED:

UNDERPRESSURED: Gradient < 1.03-1.07 kg/cm2/10m

NORMALPore Gradient is considered normal when its value isbetween 1.03 and 1.07 kg/cm2/10m.

Pore Gradient is considered

abnormal when its value isdifferent from the ones mentioned above.

Hence there might be:

ABNORMAL

FORMATION GRADIENT

Formation Gradient


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OVERPRESSURESOVERPRESSURES

TectonicsTectonics

Sedimentation Speed

Reservoir GeometryReservoir Geometry

Artesian PressureArtesian Pressure

DiapirismDiapirism

OsmosisOsmosis

Clay DiagenesisClay Diagenesis

Sulfate DiagenesisSulfate Diagenesis

Reservoir RepressurizedReservoir Repressurized

Volcanic Ash DiagenesisVolcanic Ash Diagenesis

UNDERPRESSURESUNDERPRESSURES

Drop of Water TableDrop of Water Table

Depleted ReservoirsDepleted Reservoirs

Dilatation due toTectonic Phenomena

Dilatation due toTectonic Phenomena

ABNORMAL PRESSURESABNORMAL PRESSURES

Abnormal Pressures


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GpGp >>

kg/cmkg/cm22/10/10mm

Overpressure Index


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Sedimentation Velocity

Tectonics

Reservoir Geometry

Artesian Pressures

Diapirism

Diagenesis

Osmosis

Sedimentation Velocity

Tectonics

Reservoir Geometry

Artesian Pressures

Diapirism

Diagenesis

Osmosis

Origin Of Overpressures


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A

BB

C

A - C = Normal PressureBB = OverpressureA - C = Normal PressureBB = Overpressure

Tectonics Uplift


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A - C = Normal PressureBB = Overpressure

A - C = Normal PressureBB =Overpressure

BB

C

A

Tectonics Uplift


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2000 m PPORE = (2000 * 1.03)/10 = 206 kg/cm2 ; GPORE = (206/2000) * 10 = 1.03 kg/cm

2/10 m

1500 m PPORE = 206 - (1.03 * 500/10) = 154.5 kg/cm2; GPORE = (154.5/1500) * 10 =1.03 kg/cm

2/10m

1000m PPORE =154.5 kg/cm2 -(0.7 * 500/10) = 119.5 kg/cm2 - GPORE = (119.5/1000) * 10 =

= 1.195 kg/cm2/10 m

1.195 > 1.031.195 > 1.031.195 > 1.031.195 > 1.03

OilOild = 0.7d = 0.7

Water d = 1.03Water d = 1.03

OverpressureOverpressure

1500

2000

1000

Reservoir Geometry


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2000 m PPORE = (2000 * 1.03)/10 = 206 kg/cm2 ; GPORE = (206/2000) * 10 = 1.03 kg/cm

2/10 m

1500 m PPORE = 206 - (1.03 * 500/10) = 154.5 kg/cm2; GPORE = (154.5/1500) * 10 =1.03 kg/cm

2/10m

1000m PPORE =154.5 kg/cm2 -(0.1 * 500/10) = 149.5 kg/cm2 - GPORE = (149.5/1000) * 10 =

= 1.495 kg/cm2/10 m

Water d = 1.03Water d = 1.03

OverpressureOverpressure

1500

2000

1000

Gasd. = 0.1

1.495 > 1.031.495 > 1.031.495 > 1.031.495 > 1.03

Reservoir Geometry


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+ 300 m

San

ds

San

ds

RKB 0 m

- 250 m

Piezometric Level


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221

3

Diapiritic Structures - Creation Of A Saline Dome

Di i i


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Overpressure

Salt

Diapirism


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BO-019-GIA-0022-E

Underpressures

U d I d


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kg/cmkg/cm22/ 10 m/ 10 m

(in depleted wells, for instance )(in depleted wells, for instance )

Gp


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BO-019-GIA-0024-E

Overpressure Analysis

O A l i


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Analysis methods are based on the following concepts:Sediment compaction grows with depth

(a higher sediment compaction corresponds to a higher depth.)

Overpressure analysis is performed taking

SHALES ONLY (possibly pure) into consideration.

Shales are overpressured when, not having been able to

expel their pore water, are more porous and therefore

NOT COMPLETELYCOMPACTED.



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BO-019-GIA-0026-E


While Drilling

Overpressure Analysis While Drilling


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THE EMPIRICAL METHODS OF OVERPRESSURE CONTROL WHILE DRILLING ARE:

dc Exponentdc Exponent

Sigma LogSigma Log (developed by AGIP)

FEATURES:

BOTH METHODS ARE INDICATORS OF SHALE FORMATIONS DRILLABILITY.

THEY ARE BASED ON THE CONCEPT THAT ROP (Rate of Penetration) DECREASES

FROM THE SURFACE DOWNWARD AS DEPTH INCREASES, ON ACCOUNT OF HIGHER

SEDIMENT COMPACTION.

WHEN OVERPRESSURED, FORMATIONS ARE ALSO UNDERCOMPACTED.

Overpressure Analysis While Drilling

Overpressure Analysis Well Indications


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GAS PRESENCE

Pipe connection gas

Trip gas

BOREHOLE SHRINKAGE

Torque while drilling

Overpulls while trippingBit reaming

Cavings

Borehole collapse

MUD PUMPING PRESSURE

Overpressure Analysis - Well Indications



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The parameters that this tool can measure at bottomhole and make available to thesurface in real time are:

Wellbore inclination Wellbore direction

Drilled formation resistivity Neutron log Temperature Bit Torque Weight on bit


Measurement while Drilling (MWD)


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Fracturing Gradient

Fracturing Gradient


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Pressure Gradients (referred to RKB), expressed in Kg/cm2/10m, are:

Pore Gradient or Pore Pressure Gradient.

Sediment Gradient or Overburden Gradient (GOV).

Fracturing Gradient - Knowledge of the fracturing gradient curve along the well

profile is of fundamental importance, together with pore gradient:

>To plan the well. It allows to determine the best casing points in function of two

parameters:

choke margin

differential pressure

>To drill the well. It allows to operate safely while drilling the well, and in case of kick

or blow-out control.

Fracturing Gradient


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BO-019-GIA-0032-E

Leak - Off Test (Lot)

Formation Integrity Test (Fit)

Leak-Off Test


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PURPOSE OF LOT

To check the real Fracturing value, after a casing string has been run.

To check the real Fracturing value, after drilling through a layer with highporosity and/or permeability.

Leak Off Test

Formation Integrity Test


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It consists in a check of a formations resistance to a predetermined pressure. This pressure

value corresponds to the highest mud density that is going to be employed during drillingoperations.

The procedure is similar to that of LOT, the only difference being that an engineer wont look forthe leak point, but will stop pumping once the predetermined pressure value has been reached.

Mill cement and shoe, and drill maximum 10m of new hole.

Circulate mud in the well, and uniform mud density.

Close the BOPs.

Pump with a low flow rate (1/4 - 1/2 bbl/min), and plot pumped volume and pressure values.

Stop pumping when the predetermined pressure value has been reached (pumping pressureplus mud pressure).

Formation Integrity Test

Rotary Drilling Bits


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y g

Bit Selection



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Bit Selection

Theoretically, bit selection is a simple procedure. Select the proper bit based

on:

Type of formation to be drilled

Type of drilling fluid being used

Strength and characteristics of BHA

Capability of surface equipment (pumps, rotary, drawworks, etc) to

supply the power needed

Unfortunately, downhole conditions are too unpredictable and changeable for

this to happen.




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The most important consideration affecting bit design is the type of rock that the

bit will be drilling:

Is the formation hard or soft?

Is it composed of abrasive sand?

Is it a sticky, heavy shale?

Is is porous chalk?

One bit to drill all these formations would be ideal. However, no single bit can do

this with equal efficiency.

Bit Selection




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The hardness of a rock depends upon its strength of cementation. Sand can

range from a tightly fused matrix to an unconsolidated matrix.

Bit Selection: Formation Hardness

Soft Soft shales, clays, weak sandstones, salt, gypsum, anhydrite

Medium Hard limestones, sandstones, dolomite, hard shales

Hard Chert, dolomite, sandy shales

Extremely Hard Quatzite, chert, basalt




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The abrasiveness of a rock can range from low abrasiveness to very abrasive for

each formation hardness.

Bit Selection: Formation Abrasiveness

Low abrasion Clays, shales, limestones, basalt

High abrasion Mixtures of clay and limestone with sand

y g



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Optimizing Drilling Parameters

y g



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As the bit drills, it eventually starts to wear out.

The teeth that crush the formation begin to wear down. The bearings that allow

the cones to turn start to wear out and fail.

The more weight put on the bit and the faster it turns - the greater the wear, yetthe faster it drills.

As the bit wears out, it will not drill as efficiently, and the ROP decreases.

Eventually the bit slows down so much that it is not economical to leave it in the

hole any longer, so it is pulled from the hole and replaced with another.


y g



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Drill bit optimization can be viewed as having 3 distinct phases:

Selecting the proper bit for the drilling conditions

Monitoring the drilling conditions on the well so that the drilling

performance is at least equal to the best well in the area

Implementing a bit weight/rotary speed program from theoretical

calculations that will improve drilling performance above the best wells

in the area


y g



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There is a known relationship between drilling rate and rotary speed:

Soft formations: drilling rate is directly proportional to rotary speed

Hard formations: ROP decreases with increased RPM

In hard formations, the cutting action of the bit requires that the teeth first

penetrate the formation and then scrape or gouge out the formation. If the RPM

is too fast, the teeth will not have enough time to fully penetrate the formation

before they get pulled out again as the bit rotates.

Optimizing Drilling Parameters: Rotary Speed



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Drilling rates increase in close proportion to rotary speed, providing -

Bottom hole cleaning is adequate.

Unless the cuttings already produced are cleaned out of the path of the bit assoon as possible, the bit will end up cutting the cuttings, when it could be used

to cut virgin rock.

Optimizing Drilling Parameters: Hole Cleaning



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Low solids content mud will give a better rate of penetration in a similar fashion

to low mud overbalance.

It is not clear exactly why, but it is speculated that the mud solids may slow

down the equalization of pressure under the chip.

With a solids-free system, the drilling fluid can more easily penetrate past the

chip to reduce the hold down effect.

Optimizing Drilling Parameters: Mud Solids and ROP



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The ROP of any drill bit is limited by the ability of the mud to clean the bottom of

the hole.

The goal of the hydraulics program is to remove the cuttings from the face of the

bit as soon as they are dislodged.

If the cuttings are not quickly removed, the bit will end up cutting them again,

needlessly.

Using the proper nozzles to increase the flow rate and increase the speed at

which the mud flow hits the bottom will increase ROP.

HOWEVER

Optimizing Drilling Parameters: Hydraulics


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BO-019-GIA-0047-E

Casing Design

Casing Profile


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30" CP

20" csg

9 5/8" csg

8 1/2 hole

13 3/8"csg

standard" profile

Casing Design - Casing Profile


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Role Of The Casing - Conductor Pipe

The depth at which the conductor pipe (C.P.) will be fixed must allow the mud to circulate to

the surface.

Isolate surface unconsolidated formation.

Shallow gas.



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Role Of The Intermediate Casing

Allow a greater choke margin ( 40 kg/cm

2

).

One or more intermediate casing string may be required to isolate different targets.

Isolate formations with different pressure gradients.

Etc.



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Role Of The Production Casing

The production casing string will serve to isolate the productive intervals, to facilitate properreservoir maintenance and/or prevent the influx of undesired fluids.

This is the string through which the well will be completed, produced and controlled

throughout its life.

Diameter.

Thickness (or weight in lb/ft).



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Role Of The Liner

CASING DESIGN (CASING PROFILE)

Role of the LINER

INTERMEDIATE LINER

PRODUCTION LINER

Casing Point


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P3

P2

P1

P4

De

pthm

Depth 2

Depth 1

Depth 3

Depth 4

PORE PRESSURE

FRACTURING

PRESSURE

Pressure

Casing Profile


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30" CP

20" csg

9 5/8" csg

8 1/2" Hole

13 3/8" csg

Slim"

Casing Profile

133/8" CP

95/8" csg

7" csg

5" csg

4 1/2 Hole

Standard

Casing Profile

Casing Profile


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Standard"Profile

(5 casingstrings)

Lean"Profile

(5 casingstrings)18 5/8

30 CP

24 1/2

133/8

9 5/8

8 1/2

Hole

24 1/2 CP

16

18 5/8

133/8

9 5/8

8 1/2Hole

Casing Design


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Casing Threads

NON API

ANTARES DALMINE BIG OMEGA MANNESMAN FJWP HYDRIL VAM VALLOREC

etc..

API Standard

SHORT THREAD COUPLING

LONG THREAD COUPLING

BUTTRESS THREAD

EXTREME LINE THREAD

Casing Design


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Safety Factor

COLLAPSE 1.1 ALL

BURST 1.05 H40 - J/K55

1.1 C75 - P110

1.2 Q125

TENSION 1.7 C95

1.8 > C95

Casing Design

M i St


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Main Stresses

BURSTBURST

COLLAPSECOLLAPSE

TENSIONTENSION

Casing Cementing

T Of C t


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Top Of Cement

1. Surface Casing

a) Offshore wells

b) Offshore wells

> From Jack-up / Fixed Platform

- Exploration wells - Development wells

> From Floating Rig

Casing Cementing


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2. INTERMEDIATE CASING

The main aim of the rise of the cement in the annuls is to restore the hydraulic conditions in

the well after the borehole has been drilled (avoid communication between formations withdifferent pressure gradient and containing different hydrocarbons), isolate overpressure

zones; temperature problems.

a) Onshore wells

b) Offshore wells

> From Jack-up / Fixed Platform

> From Floating Rig

Well Heads


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The well heads available on the market have working pressure of :

- 2.000 psi

- 3.000 psi

- 5.000 psi

- 10.000 psi

- 15.000 psi

- Theselected WORKING PRESSURE of the well head is according to the

maximum formation pressure predicted at bottom hole.

- In thepresence of CO2 or H2S special steels will have to be used in

accordance with corrosion Standards.

Well Heads


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Well heads for:

Onshore andJack-up Rigs

Semisubs or Drilling Ships (subsea well heads)

Onshore and Jack-up Rigs

A. Conventional well head.

B. UNITIZED well head (compact well head).

Christmas Tree


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Bop Selection


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The pressure rating of the BOPs must be higher than the maximum pressurepredicted at the well head (with the exception of the annular preventer).

- BOP for DRILLING

- BOP for PRODUCTION TEST

Wellhead


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Blow-out

Preventers


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BO-019-GIA-0066-E

Cement Job

Cementing Jobs


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Primary cementing

Cement plug

Cement squeeze

Primary Cementing


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Primary Cementing


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Primary cementing means the cementing of the casings or liners of a well.

All the casings and liners of a well must be cemented except for some liners,

normally those with slots for the passage of the produced fluids and which, once

positioned in the well, are simply left anchored to and suspended from the casing

above.

So surface, intermediate and production casings are all cemented with slurries of

different properties and formulas to take into account the different well parameters at

the depth at which they are positioned.

Calculating a Primary Cementing


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previous

csg shoe

csg shoe

csg collartail cement

lead cement

excess (..%) in

open hole

mud

Two-stage Primary Cementing


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Casing can be cemented in one or two stages.

Cementing is one-stage when the work is completed in one step; that is, when all the

cement is placed where needed in a single job.

Instead, cementing is two-stage when the annulus is filled with cement in two steps; during

the first step the cement is placed in the lower part of the annulus followed by a second

step when the cement is placed in the top part of the annulus.

Cement Plug


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These are operations which may be necessary at any point during the construction or life

of the well.

During drilling, to solve serious lost circulation problems (lost circulation plug), or when

the bit has to be deviated from vertical drilling (kick-off plug).

During production, when levels which are no longer economically viable or levels which

produce water or gas have to be shut-in.

At the end of the wells producing life when, in accordance with mining laws, a well has to

be shut-in with a given number of cement plugs (abandon plugs).

Cement Squeeze


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Cement squeeze means the forced pumping of slurry inside the rock to create a solidsleeve which acts as a barrier so that fluids do not flow into or out of the rock.

A squeeze is often a remedial job and takes place during a wells producing life.

A squeeze is a difficult operation to plan because many variables are involved:

appropriate formula of the slurry

squeeze pressure

pumping rate

type of formation and its permeability

Cement Squeeze


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BOP or

Hydrill(closed)

the pressure applied

during the squeeze

acts along the entirelength of the casing

P of the

squeeze

Cement Squeeze


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lower packer which isolates the

squeeze zone

squeeze packer

tubing string

or drill pipe

casing

shot interval

to be closed stinger

slurry

Examples Of Problematic Cement Jobs


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Figure 1

Figure 1 shows a typical case of cement

channelling where the casing rests on the

wall of the well.

The result will be the formation of an

excess of filtration deposit and a film which

adheres to the casing . Even if the slurry

had completely filled the annulus, its

adherence to the casing would not beperfect.

Examples Of Problematic Cement Jobs


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Figure 2

The eccentricity of the casing inside the

borehole favours the settling of the cement

through the mud. Moreover, the cavities of

the borehole will have collected viscous mud

and cuttings.

Figure 2 shows an excessive formation of

cake at the two permeable zones.

23533669 bo 019 drilling engeneering

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