Cementing & cement evaluation.pdf

Cementing & cement evaluation

P R E P A R E D B Y : A . N A C E F D R I L L I N G I N S T R U C T O R

School of Boumerdes

UFR: Drilling and Production

لورتبلل يرئازجلا دھعملا

INSTITUT ALGERIEN DU PETROLE

Contents

Introduction

Types of cementing

Primary cementing

Methods of primary cementing

Primary cementing-casing

Designing a cement job

Casing & cementing accessories

Cementing additives

Remedial cementing

Plug cementing

Squeeze cementing

Introduction

A critical Well Construction process used worldwide

Cementing is an important steps in the well’s finishing

process.

Cementing is done by pumping a slurry of cement and

water at a strategic point around the casing to bind these up

to the formation

3

Types of cementing

When drilling oil and gas wells, several different cementing methods can be needed:

Primary Cementing : is the introduction of cementacious material

into the annulus between casing and open hole

Remedial jobs : to repair primary cementing jobs (Squeeze

cementing, Cement plug)

Other cementing: plugs for abandonment, sidetracking, loss zones

Primary cementing

The placement of a cement slurry into the annulus between the casing and the formation exposed to the wellbore (open hole) or previous casing.

The most important objective of primary cementing is to provide zonal

isolation (that is, to prevent communications between the different

zones in a well). In addition, the cement provides support for the several casing strings run in a well.

5

Zonal Isolation

Poor Zonal Isolation:

improper reservoir evaluation

crossflow of unwanted fluids

corrosion of pipe and scale production

annular pressure and environmental hazards

more than $45 Billion/year spent on unwanted produced water management

Purpose of primary cementing

Fasten the casing to the formation

Reduce the possibility of blowout from high pressure zones
Protect all Production zones

Prevent fluid movement between different formations, or between formation and the surface

Strengthen and protect casing/tubing against corrosion

Support the borehole

7

Methods of primary cementing

Thru-Drill Pipe Cementing (Stab-in)

Outside Cementing (Top Job)

Single stage cementing ( two plugs cementing)

Two Stage Cementing

Primary Cementing - Casing

Conductor

Surface

Intermediate

Production

Liners

9

Conductor Casing (stove pipe)

Confines circulating fluids

Prevents washing out under rig

Provides elevation for flow nipple and bell nipple

BOP are usually not attached to conductor casings.

Set from 40 to 100 feet

Casing is large; 36/42 inches inches

diameter

Hole may be eroded severely.

Casing can be pumped out easily and must

be tied down.

Large excess

Stab-in cementing common

Accelerated neat cement

Conductor Casing (stove pipe)

11

Surface casing

Protect water sands.

Case unconsolidated formations.

Provides primary pressure control.

(BOP usually nippled up on surface

casing)

Supports subsequent casings.

Case off loss circulation zones.

Surface casing

Characteristics:

(Set from 100 to 3000 feet)

Casing may stick easily in unconsolidated

formations.

Loss of circulation may be a problem.

Most areas require that cement be circulated.

Guide shoe, or float shoe, and stab-in shoe

commonly used.

Light weight lead and neat tail slurries

Large excess ( 50 - 150 %)

18 5/8 ‘’ casing in 26 ‘’ hole or 13 3/8” casing in 17 ½” hole @ 100 ft – 3000 ft 13

Surface casing

Characteristics:

Often cemented through drill pipe with

stinger.

Top plug should be prepared for any

failure to seal with stinger.

Shoe Bottom joints should be centralized

and thread locked to prevent loss down

hole.

Cemented to surface /top job

18 5/8 ‘’ casing in 26 ‘’ hole or

13 3/8” casing in 17 ½” hole @

Itermediate casing

Cases off loss circulation zones, water flows, etc.

Isolates salt sections

Protects open hole from increase in mud weight

Prevents flow from high-pressure zones if mud weight must be reduced

Basic pressure control casing BOP always installed

Supports subsequent casings 15

Intermediate casing

3000 to 10,000 ft (vertical or deviated)

13 3/8” casing in 16” or 17 ½” hole

9 5/8” casing in 12 ¼” hole

Guide shoe, or float shoe, and float collar commonly used.

Cement volumes usually largest in well

Intermediate casing

Potential problems: over-pressured, loss zones, salt formations

or heaving shales

Narrow pressure window, between pore @ bottom & frac @ top

Long casing string may need a two-stage job

Best cementing practices are required

Cemented to surface or to previous casing shoe

Typically filler slurries followed by high compressive tail

Specialized slurries (light, heavy, salt etc)

17

Production casing

Conduit for Completion String

Provides pressure control

Cover worn or damaged intermediate casing

Setting depth through producing zone

Common sizes 4 1/2 ”and 7 " casing

Generally cemented back to intermediate casing

Good cement job is vital to successful completion.

Can be a liner

Production Liner

Isolates the pay zone from other

formations and the fluids in them.

Protective housing for production

equipment.

usually cemented and perforated

Can be blanked or slotted

Common sizes: 3 ½ ,4 ½”, 7’’,

19

Liners

•

Key Points:

•

Requires less casing

•

Deeper wells

•

Small annular clearance

•

Specialized equipment

Liner Wiper Plug Pump Down Plug

“Dart” Liner Hanger

Previous Shoe Liner Over Lap 20

Methodes of primary cementing

Thru-Drill Pipe Cementing (inner string cementing)

Outside Cementing (Top Job)

Single stage cementing ( two plugs cementing)

Two Stage Cementing

21

Thru-Drill Pipe Cementing (Stab-in)

Key Points:

Less cement contamination

Less channelling

Small displacement volume

Pump until cement to

surface

Less job time (rig time)

Less cement

Inner string cementing

Operational Sequence for running & cementing 18 5/8”

Prepare and measure the 18 5/8” string (prepare the landing joint according to section TD).

Remove the 30" conductor pipe raiser, respecting all the time the safety procedures.

Run 18 5/8” casing in the hole circulating from the cellar with a jet pump.

Connect last casing joint with the minimum torque.

Center the 18 5/8” string (see figure 1) with metal rig-made slips.

Install the IPN in the top of the cellar, perpendicular to the 18 5/8” casing.

Install the 18 5/8” casing elevator between the IPN and the next joint couple. The side door elevator needs to be landing on top of the IPN.

Land casing.

23

Inner string cementing

24

Disconnect landing joint.

Check the condition of the “O” rings of the cementing stinger nipple.

Use 18 5/8'' X 5 1/2'' DP Centralizer
Run in hole stinger string.

Set stinger in casing shoe. circulate through the cement stinger, and ensure the stinger seal is not leaking.

R/U CMT head, R/U cementing lines. Well Service flush lines with water and test lines to 3000 psi

Have enough cement and additives on location for 100% excess over required volume

Conduct a pump efficiency test and report the results on the daily

drilling report

Inner string cementing

25

Stinger

26

Inner string cementing

27

Cement 18 5/8” casing, pump cement slurries (lead then tail)

While cementing closely monitor any return from DP X Csg annulus.

Observe returns from the well for any indication of hole losses or instability

Displace cement, check for mud return

Disconnect stinger from float shoe, flush & POOH the stinger string,
Proceed to weld the centralizing slips.

Cut 18 5/8” casing as detailed in the procedures to install casing head housing.

Install casing head housing.

Inner string cementing

28

Outside Cementing (Top Job)

Key points:

Bring cement to surface

Macaroni tubing used

Max. depth 250-300 ft

High friction pressures

Non-standard connections

Tubing moved during job 29

Single stage cementing ( two plugs cementing)

It is conventional method

The most method used in drilling

Long pumping times

High pump pressures

Run 13 3/8" to TD w/Circulation. Adjust column

R/D WFT running gear & LA Fleur

Offline Verify the cement top & bottom plugs type and load it on the

plug holder

perform pump efficiency tests and record it in the daily drilling report

R/U CMT head and lines

Pressure test lines to 4000 psi

Circulate prior cementing: Circulate to cool down, hole clean and break gelled up mud. Reciprocate casing gently and continuously at 3m up and 3m down. Meanwhile mix cement.

Mud conditioning (low viscosity = good mobility) is the most important

variable in achieving good cement placement behind the casing.

Single stage cementing ( two plugs cementing)

31

Pump spacer ahead

Release bottom plug
Pump cement

Release top plug

Pump spacer

With rig pump displace cement, wait for bottom plug bump

Record final displacement pressure, bump top plug and continue

pressure up to 3000 psi

If the plug does not bump after finished theoretical displacement

volume do not over displace at all (max half shoe track volume)

In case of float equipment not holding back press keep the CMT head

valve closed till CMT set

Single stage cementing ( two plugs cementing)

Two Stage Cementing

The cementing of a string of casing in 02

Stages, using a stage collar

1st Stage Stage Collar

33

Why?

Potential Casing Collapse due to Hydrostatic Pressure of a full column of Cement

Lost circulation zone or low Frac gradient

Cement very long intervalle (time/volume limitations)

Reduce use of expensive slurries due to special well problems (salt zone, gas zone)

Incomplet fill up (Can leave zone in the annulus uncemented)

Two Stage Cementing

Hardware

Stage collar

Plugs

•

First stage wiper plug (bottom

plug is optional)

•

Opening plug/bomp

•

Closing plug

Two Stage Cementing

35

Stage collar

SHEAR PINS OPENING BOMB OPENING BOMB CLOSING PLUG 36

Where to place stage collar?

Problematic formations (lost circulation, salt zone …etc)

Inside previous casing to:

•

Avoid jetting effect on the formation while circulating

cement

•

To ensure that if the collar fails to open, at least the open

hole section is cemented

Two Stage Cementing

37

Some other points

The stage collar is eventually drilled out leaving the same

drift as the rest of the casing

3 stages cementing is the same as 2 stages, but with 2 stage

collars

A stage collar is considered to be a weak point in the casing

by many clients and so avoid using them.

Alternatives: use of lightweight slurries (foam cement)

Two Stage Cementing

Pressure test lines

Pump wash/spacer

Pump slurry

Drop first stage plug

Slowdown when the first stage plug passes the stage collar

Displace, bump plug, check returns

Drop bomb, wait allocated time (rule of Thumb 200ft/min)

Pressure up to open stage collar
Circulate (W.O.C if required)

Pump wash/spacer then pump slurry

Drop closing plug

Displace close stage collar

Check for returns

Two Stage Cementing job procedure

39

Two Stage Cementing examples

13 3

13 3//88” ” 68 68 lb/ft Casinglb/ft Casing

Top of cement at Top of cement at 2461 2461 feetfeet 13 3

13 3//88” shoe at ” shoe at 2789 2789 feetfeet 9 5

9 5//88” Stage collar at ” Stage collar at 42654265..3 3 feetfeet 12 1 12 1//44” O.H.” O.H. 9 5 9 5//88” ” 5353..50 50 lb/ft Casinglb/ft Casing 4 4 3 3 Calculate

First stage cement and displacement volume
Second stage cement and displaced volume 40

1. Would you recommend a 2-stage ? Why ?

2. What depth would the Collar be?

3. What is the maximum density of

slurry possible during the first stage (assume cmt to stage collar)?

4. Where would the TOC be for the first stage

Two Stage Cementing examples

Frac Gradient: 0.8 psi/ft MW = 12 ppg

salt zone salt zone

2400’

5500’

5850’

TD:8400’

41

Frac Gradient: 0.8 psi/ft MW = 11.2 ppg

Two Stage Cementing examples

weak formation weak formation 4100’ 7100 -7250 FG: 0.6 psi/ft TD:10200’ 8400 - 8450 FG:0.68 psi/ft 42

Liners

Any string of casing whose top is located below the

surface, hung inside the previous casing and is run to

its setting depth by drill pipe.

LINER HANGER CASING SHOE OVERLAP 50 - 500 FT 43

Liners

Way liners?
Prime reason:

Save money (Cost of 1 Joint of Casing can be $3,000!)

Cover Corroded/Damaged Casing

Cover:

• Lost Circulation Zones.

• Shale or Plastic Formations

• Salt Zones

Deep Wells: Rig Unable to Lift Long String of Casing 44

Types of liners

Production: • Most common • Save$$ • Slotted liner • Blanked liner
Intermediate/drilling:

• Cover problem zone in order to be able to continue drilling

Tie-back/liner complement:

• From top of existing liner to surface, or further up casing to cover corroded or damaged zone.

45

Types of liners

Tie-Back (Liner Complement)

This is often done if production is commercially viable or there is damage to casing above the liner

TIE BACK STINGER WITH SEALS

LINER

Liners

47

Procedure for Setting Liner

RIH hole with drill pipe

At liner hanger depth, condition mud (Reciprocation / Rotation)

Release slips (liner hanger) (Rotation mechanical pressure -hydraulic)

Set slips, release liner weight, check to see if running tool is free

Pump mud - to ensure free circulation

Cement/ Displace/ Bump plug/ Bleed off

Release setting tool

POOH above TOC and circulate 48

Liner cement job procedure

Pressure test lines.

Pump wash/spacer.

Pump slurry.

Drop "Pump Down" plug (or drill pipe wiper dart).

Displace

• To running tool and slow down the rate

• Shear "Wiper Plug“

• Displace to Float Collar. Slow down while approaching end of

displacement

Bump plug/checkf or returns.

Release tool.

Pull up to T.O.C. and reverse circulate / circulate

Liner.exe

49

Liner overlap

Cementing the liner "lap" is critical.

Too much cement above the liner hanger is not recommended

So make sure that "uncontaminated" cement is present at the liner lap -washes and spacers / WELLCLEAN

If not, there is communication from the annulus to the formation 50

Recommendations for Liner Cementing

Ensure rheology of cement System is adequate for 100% mud removal

Turbulent flow, if possible

Consider 5 -10 min. "contact time" at liner lap

Batch mix cement

Minimize U-tubing effect

Adequate mud conditioning prior to cementing 51

Liner example: well data

1) Well Information:

• 9-5/8" 47 Ib/ft intermediate casing surface to 6500‘

• 7" 29 Ib/ft intermediate liner 6200 ft to 10,500‘

• 6“OH to TD at 14,500‘ • DP 3-1/2" 13.30 Ib/ft G105

• 4-1/2" 16.90 Ib/ft liner required 14,400' to 400' inside 7" liner.

• FC 80' above shoe.

2) Cement required to TOL with 20% excess in OH 3) Calculate Slurry and displacement volumes 4) Give Job Procedure

Liner exemple: well schematic

3 1/2” drill pipe 13.3 lb/ft 9 5/8” casing shoe at 6,500 ft 9 5/8” casing 47 lb/ft 7” liner 29 lb/ft Top at 6,200 ft 7” liner shoe at 10,500 ft 4 1/2” liner 16.6 lb/ft top @ 10,100ft ; collar @ 14,320 ft 4 1/2” liner shoe at 14,400 ft

6” Open hole + 20% Excess

53

Designing a Cement Job

Compute fluid volumes

Slurry

Wash, Spacer,

displacement volumes

based on :

Hole capacity

Casing capacity

Annular length

54

Designing a Cement Job



Check that well security is respected:

Simulate cement pumping process to compute hydrostatic and

dynamic pressures and compare them to :

• pore pressure

• Fracture pressure

• Tubular burst pressure



Ensure well security when Running In Hole



Check Temperature and thickening time

55

Designing a Cement Job



Check for an efficient mud removal to prevent

mud channeling and to ensure good zonal

isolation

•

Optimize fluid properties

•

Optimize the pumping rate

•

Optimize casing centralization



Ensure good wall cleaning

•

Optimize pre-flushes volume, and flow rate

Parameters required

WELL PARAMETERS FLUID PARAMETERS

Hole size and depth

Casing tally

PP and FP

Temperature

Centralization

Densities

Rheology, PV and Ty

Cement additives

57

Cement calculations

Prior to a cement job, the following calculations are made

1.

Cement volume requirements

2.

Cement displacement volume

3.

Cement slurry composition calculations

The following categories are involved:

Cement volume (annular volume)

Amount of water to make the cement

Cement density and yield

Displacement for landing top plug

Pumping pressure for landing top plug

Hydrostatic pressure on the formation

Pressure for casing axial force during pressure test after the top cement plug is bumped

Cement calculations

59

Cement slurry volume

Before a cementing job can be carried out, volume calculations are needed.

Depending on the drilling fluid program and types of formation, the hole diameter will be somewhat larger than the drill bit diameter.

Annular volume is calculated to determine the amount of cement to be mixed.

The amount is decided by making calculations based on the drill bit diameter, plus an extra amount based on experience or what is known about the formations in that particular area or caliper log.

Cement calculations

60

Cement slurry volume

After the casing is put into place, this calculated amount will normally be adjusted, based on data collected via the caliper log.

The caliper log does not give completely reliable results, and is usually used to find out whether the calculated cement volume, based on the drill bit diameter, is satisfactory.

We normally use between 1.25 and 2 times the cement volume which was calculated by using drill bit diameter, this to compensate for wash-out in the well

Cement calculations

61

Cement slurry volume

This is especially important with regard to deviation drilling, as these wells have a tendency to become oval, and so excess cement is needed.

This can often vary up to as much as 50% of the calculated hole volume.

The ratio of fullness in the annulus will vary somewhat, depending on practice in the different companies, and the demands from the authorities.

The two upper casings are always cemented back to the surface.

Normal cement volume is 100-200% more than calculated volume, based on ideal diameters.

12 1/4" and 8 1/2" sections often have 30-50 % excess.

Cement calculations

62

Cement slurry volume

The required volume of cement slurry is based on the following factors:

Length of open hole

Diameter of the open hole (drill bit diameter and degree of washout)

External and internal diameter in the particular casing

Top of cement in the well

Cement calculations

63

Cement slurry composition calculations are based on kilos or liters per 100 kg cement powder.

Slurry composition is characterized by:

1. Slurry Density

2. Thickening time

3. Ultimate cement strength

4. Slurry permeability

5. Slurry viscosity (Pressure loss)

6. Fluid loss

Cement calculations

64

A 7" liner cementation require 43 m3 cement slurry volume.

From cementing company laboratory

• The slurry density is 1,90 kg/liter

• Slurry yield is 96,88 LHK

Additives

• Micro Block: (Gas Block Additive) 18 LHK

• CFR3L: (Thinner) 1,15 LHK

• SCR-100L (Retarder) 2,0 LHK

• HALAD (Fluid loss reducer) 6,5 LHK

• NF-5 ( De-foamer) 0,1 LHK

• Fresh Water 37,38 LHK

Cement calculations

65

Step 1 : Calculate cement requirements:

Cernent Requirement = CementVolume.x.100/slurry yield (LHK) = 43000 x 100/96.88

= 44.39 ton

LHK = Litre per Hundred Kilo Cement

Cement calculations

66

Additive calculations

67

A 9 5/8" casing cement job require 123 m3 cement slurry volume. Calculate cement and mix water and liquid additives per measuring tank.

From cementing company laboratory

• The slurry density is 1,92 kg/litre

• Slurry yield is 95,88 LHK

Additives

• CFR3L: (Thinner) 1,27 LHK

• SCR-100L (Retarder) 1,40 LHK

• HALAD (Fluid loss reducer) 5,70 LHK

• NF-5 (De-foamer) 0,15 LHK

Additive calculations exercise

68

Displacement Volume

After the cement is mixed and pumped into the well it is

displaced down the casing and up the annulus

The displacement volume is the volume needed to send the top

plug from the cement head to the float collar.

This is normally done by multiplying the length with the capacity

for the string.

A pump efficiency is used for these calculations

This capacity varies normally between 96% - 99%

Cement calculations

69

Pumping Pressure to Charge Top Plug

When the cement leaves the casing shoe and start to move up in the

annulus we will notice the u -tube effect by the heavier slurry in the annulus.

Example

A casing is cemented with 1,90 sg slurry and displaced with 1, 35 sg. Top Of Cement, TOC, is at 1000 m. Cement shoe is at 2000 m and the float collar is at 1976 m. What is the differential pressure just before the top plug lands (ignore friction)

AP = (1976 -1000) x 0,0981 x (1,90 - 1,35) = 52,7 bar 70

Hydrostatic Pressure

To ensure we are not fracturing the formation during the cement job, it

is necessary to calculate the hydrostatic pressure in the cement slurry to be used.

Get an idea of whether there is a risk of the well fracturing when we are cementing.

We must calculate pressure at different levels in the well, based on the geological conditions.

In very weak zones, we must take extra care with regard to friction pressure, in addition to the hydrostatic pressure.

71

Casing & cementing Accessories

72

Guide Shoe

Attached to first length of casing to be lowered into hole

Guides casing into borehole and around obstructions

Can be drilled out with the bit 73

• Float Collar:

– This is set about two-three joints above the casing shoe, and act as a one way valve,

– When it is used, the cement plugs land on top of it.

Ball Type

Float collar

74

Wiper Plugs

To Separate Fluids, (cement/wash/spacer/mud)

Wiping the casing clean,

Surface indication of placement

Bottom Plug (pump through) Top Plug (Solid)

75

Others

Centralizer: to centre

casing in bore hole to promote even distribution of cement around casing

Cementing Basket: to

minimize losses in weak zones.

Scratchers; to scratch off

the mud cake to improve cement bond

Cement Heads

Conventional cement head

77

Bulk Plant

Silos, WBB, Compressor, Dust Collector

Equipment On-Shore

78

LAS

Liquid Addtive System

Slurry Chief

Mixing System

CPS

Cement Pump Skid

Batch Mixer

Cement Head

(Sub Sea System)

Equipment Off-Shore

79

Mixing & Surface equipment

Mixing & Surface equipment

81

Casing String Components from bottom up

Float shoe

Float shoe

–

– guide and check valve to prevent guide and check valve to prevent

cement back flow cement back flow

2

2 Casing joints

Casing joints

–

– to capture any contaminated cementto capture any contaminated cement

Float collar

Float collar

Centralizers

Centralizers

Scratchers

Scratchers

Cement Head Drilling Fluid Cement Casing Float

Collar Float Shoe

Centralizer Ground Level

Rig Floor

REMEDIAL CEMENTING

What is remedial cementing?

Why do we do it?

Plugs

Lost circulation

Kick off

Abandonment

Squeeze

Primary cement job repair

Unwanted Water Production

High Gas-Oil Ratio (GOR)

Casing Splits or Leaks

Nonproductive or Depleted Zones

PLUG CEMENTING

Plug Cementing

Purposes

•

To side track above a fish or to initiate directional

drilling.

•

To plug back a zone

•

To plug back a well (abandonment or later re-entry)

•

To solve a lost-circulation problem during the drilling

phase

•

To provide an anchor for OH tests.

Side Track and Directional Drilling

Kick Off Point

NEW HOLE CEMENT PLUG

Design considerations

• High compressive

strength, typically with

high density

• Length should be enough

to kick off

87

Plug Back a Depleted Zone

Depleted Zone

Cement Plug

Design considerations

• Sufficient length to provide

a long term barrier

• Legal requirements

dictated by authorities

• Reservoir zones may

require additional

additives

Lost Circulation

ThiefZone CEMENT PLUG CEMENT PLUG

Design considerations

• Sufficient length to cover

the thief zone

• Successive treatments may

be required, depending on

losses

• Lower density to minimise

hydrostatic pressure

89

Abandonment

CEMENT PLUG CEMENT PLUG CEMEN T PLUG

Design considerations

• Sufficient length to provide

a long term barrier

• Legal requirements

dictated by authorities

• Reservoir zones may

require additional

additives

Test Anchor

Test String Zone to be Tested Weak Formation CEMENT PLUG

Design considerations

•

Sufficient compressive

strength to withstand

pressure testing

•

Reservoir zones may

require additional additives

91

Cement Plugs - design

Design criteria
1. Quality • Cement hardness • Cement weight • Cement permeability
2. Time

Cement setting time (Pumping time): The minimum thickening time should be the job time plus a safety factor

2. Cement hardening time (ultimate strength) For kick off plugs the ultimate setting time should be achieved prior kick off operation

Cement testing should be carried out using samples of the

actual materials to be used during the job (samples of mix

water and lead/tail slurries)

Calculate the hydrostatic pressures throughout the job and

check that the formation is never under balanced. Weighted

spacers or mud must be used to maintain primary well

control at all times.

Cement Plugs - design

93

Wherever possible run a slim tubing stinger below the main

pipe. The minimum stinger length should be the plug

length plus 30m.

The natural tendency for cement slurry is to travel

downwards when it leaves the string, since the slurry will

generally be heavier than the drilling fluid.

This can be avoided by spotting a viscous pill below the

plug setting interval.

Cement Plugs – string design

94

Slurry Properties

Density

lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batch

mixing

Rheology

higher for Lost Circulation
Optimum (mud removal)

for Sidetracking

lower for placement with

Coiled Tubing

Compressive Strength
higher for Sidetracking
less important for Lost

Circulation

minimum 500 psi for drill

out

Thickening Time

enough for placement,

POOH & circulating clean 95

Optimising Cement Plugs - Slurry mixing/placement

1.

Pump a spacer ahead of the slurry to give a separation between

the drilling mud and the cement slurry.

2.

Cement slurry should be batch mixed.

3.

A slight under-displacement is required in order to pull a dry

string

4.

Pump a spacer behind the slurry to give a separation between

the drilling mud and the cement slurry.

5.

Displace at maximum rates

6.

If possible rotate the string during the slurry placement and

displacement.

7.

Pull back slowly above the plug and circulate out excess cement.

At the same time the inside of the drill pipe will be cleaned for

cement.

Reasons for Cement Plug Failures

Lack of hardness (sidetracking).

Poor isolation (plug back, abandonment).
Wrong Depth.

Not in place due to sinking to the bottom .
Not in place due to loss to thief zone.

97

Balanced Plug Placement

•

Most commonly used

method.

•

Set using drill pipe and

stinger

Balanced Plug Placement

99

Water or other fluid of different density from that hole is run ahead and behind cement slurry. The volume of fluid ahead and behind slurry is calculated so that height in casing is same as height inside the string.

mud water

cement hW Height of

Balanced Plug Placement

100

Procedure:

1.

Pump required spacer volume

2.

Mix and pup required cement volume

3.

Pump spacer behind cernent inside stinger

4.

Displace with mud

5.

POOH above cement plug

6.

Circulate

7.

POOH

Balanced Plug Placement

101

Example

When the cement stinger is pulled above the plug, The last "drop" of cement is leaving the stinger,

Then the displacement volume is: V = Stinger capacity X distance to top

plug.

5"DP19,5# -> 9,15lpm

V= 9,15 x 1450 = 13267 Litre mud +

50 m Spacer = 457 litre

Total displacement volume: 13724 litre

Balanced Plug Placement

102

Exercise:

Set 200m balanced cement plug inside 12 14" hole.

Use 3 ½” 13,3 Ibs/ft DP, cap. 3,86 lpm.

50 m spacer between DP and open hole

Bottom of plug at 3000 m

Calculate

1.

Required plug cement volume,

2.

Spacer volumes ahead and behind

3.

Displacement volume.

Balanced Plug Placement

103

Question

If the mud density is greater than the cement density

should you over displace or under displace?

Balanced Plug Placement

104

SQUEEZE CEMENTING

Squeeze Cementing - Definition

• Injection of Cement Slurry into the voids behind the casing

• Dehydration of cement requires: fluid-loss, porous (permeable) matrix, differential pressure, time.

• Injection below or above

fracture pressure cementnodes casing FORMATION DEHYDRATED CEMENT cement slurry tubing packer CHANNEL BEHIND CASING PRIMARY CEMENT 106

Squeeze Cementing - Applications

•

Primary cement job repair

•

Unwanted Water Production

•

High Gas-Oil Ratio (GOR)

•

Casing Splits or Leaks

•

Non-productive or Depleted Zones

107

Squeeze Cementing - Methods



Squeeze techniques:

High pressure - above formation frac pressure

Low pressure - below formation frac pressure



Pumping techniques:

Hesitation Running



Placement techniques:

Packer/Cement Retainer Bradenhead

Coiled tubing

108

Low Pressure Squeeze

Squeeze pressure below fracture pressure

Best way to squeeze the pay zone

Use small volume of slurry

Applicable for :

Multiple zones
Long intervals

Low BHP wells

Naturally fractured formations 109

High Pressure Squeeze

Fracturing is necessary to place cement in the void

Requires placement of large volumes of slurry

Wash or acid ahead to minimize pump rates required to

initiate fracture

Running Squeeze

Continuous pumping until final squeeze pressure is attained

Clean fluid in the hole

Large slurry volumes without fluid loss control

Low or high pressure squeeze

Applications

Water flow

Abandon perforations

Increase cement top

Casing shoes

Liner tops

Block squeeze

Lost circulation zones

111

Hesitation Squeeze

Intermittent pumping

Low pump rates

Small slurry volumes

Long job times

Applications

Channel repair

Long perforated interval

Long splits in casing

Lost circulation

Bradenhead Squeeze

Done through tubing or drill

pipe without packer

Advantages

No tools are used (simplicity)

Cost

Disadvantages

Casing and wellhead are

exposed to pressure

BRIDGE PLUG Sand CEMEN T BO P 113

Packer with Tailpipe Squeeze

•

Downhole Isolation tool

•

Casing and wellhead

protection

•

Tailpipe for placement

or setting a bridge plug

•

Long intervals

Packer

CEMENT Tail Pipe

Cement Retainer Squeeze

Drillable Isolation Tool

Similar to packer without

tailpipe

Applications

Squeeze pressure trapped

BRIDGE PLUG Sand CEMENT CEMENT RETAINER 115

Coiled Tubing Squeeze

Applications

Producing wells

Through tubing

Advantages

Cost

Accurate placement

116

Cement Chemistry & Additives

Cement is made of Limestone and clay or shale mixed in

the right proportions

Each run may be slightly different due to impurities

Cement is heated in a rotary kiln from 2600 to 2800

degrees F

What comes out of the kiln is called clinker

The Clinker and Its Components

The Clinker and Its Components

The clinker is the mixture formed by the clinkering process.

The clinker has four components: C3S, C2S, C3A, and C4AF

The letters in the clinker names are not chemical formulas.

Instead, the letters represent abbreviations of chemical

formulas:

C – CaO

S – SiO2

A – Al2O3

F – Fe2O3

119

Clinker Scientific Name Chemical Formula

Properties in Cement C3S Tricalcium silicate 3CaO . SiO2 Major component (50 to

60%)

Strength development C2S Dicalcium silicate 2CaO . SiO2 Final compressive

strength C3A Tricalcium

aluminate

3CaO. AlO3 Sets rapidly

Controlled by gypsum Early strength development C4AF Tetracalcium 4CaO . Al2O3. Fe2O3 Little influence

The Clinker and Its Components

Portland Cement

After the clinker is formed and cooled, it is moved to a second grinding mill where it is combined with 1.5% to 5% gypsum (CaSO4. 2H2O), by weight of clinker. When added in this amount (generally +/- 3%), gypsum prevents "flash set" by controlling the hydration of C3A.

If more than 5% gypsum is added to the clinker, the cement undergoes a "false set." Excess gypsum causes false set because it tends to hydrate quicker than the cement. The clinker and gypsum mixture is ground and blended to form Portland cement.

Cement reactivity to water depends a lot on surface area, which is related to the size of the cement grains. Cement grain size ranges from 1 to 100 microns (average size around 30 microns).

121

API Cement Classes

122

API Cement Classes

123

Cement must be placed in wells ranging from shallow to

very deep

Additives are used to adjust cement properties and tailor

the cement to specific needs

Cement Additives

124

Extenders

Lightweight additives or extenders are used to decrease

the density of cement

Excess mix water can be used to decrease the density to

a limited extent

Excess water increases thickening time, increases free

water and reduces compressive strength

Cement Additives

125

Extenders

•

Bentonite is the most common light weight additive

•

Bentonite will tie up extra mix water reducing density

•

Light weight cements have as much as 12% bentonite

•

Adding bentonite thickens the cement slurry and it must

be thinned by adding a thinner or friction reducer

Cement Additives

Perlite is volcanic glass bubbles that has some times been

used in geothermal wells because of its insulating

properties

Perlite is considerably more expensive

Gilsonite and kolite are used to reduce density; however,

their primary function is as a lost circulation material

Gilsonite is a black asphalt

Kolite is crushed coal

Extenders

Cement Additives

127

Foamed cements are also used to reduce the density of the

slurry

In a foamed cement, nitrogen is added to the cement

mixture

Very low densities can be obtained with foamed cement but

they are more expensive

Extenders

Cement Additives

128

Weighting Agents

Hematite is one of the more common additive for high

density cement due to its high specific gravity

For smaller increases in density, barite can be used

Barite is ground fine and requires more mix water to keep

the slurry pumpable

Sand can be added to increase the density due to low mix

water requirements

Cement Additives

129

Densified slurries can be used up to 17.5 ppg

A densified slurry is produced by reducing the mix water

and adding a dispersant to make it thin enough to pump

Salt can be used to increase the density of a slurry

Salt increases the density of the liquid phase

Cement Additives

130

At low temperatures, it would

take too long for the cement

to set up so accelerators

are added to the cement

Decrease the thickening time

of cement for shallow, low

temperature applications

Cement Additives

131

As a rule of thumb,

accelerators are

inorganic

compounds

Cement Additives

132

A little salt will

accelerate

A lot of salt will

retard the

cement

Cement Additives

133

Retarders

Increase the thickening time of cement for deeper, hotter

applications

Typically retarders are organic compounds

Cement Additives

Retarders

One of the most common retarders is calcium

lignosufonate

Sodium Chloride is a retarder at high concentrations

As bottomhole temperatures change, the type of

retarder will change

Cement Additives

135

Friction loss additives (

Dispersants)

: are used to

thin the cement slurry

•

Organic acids

•

Lignosulfonate

•

Alky aryl sulfonate

•

Phosphate

Cement Additives

136

Lost circulation material

•

Granular material such as gilsonite, kolite, perlite and

walnut hulls

•

Organic compounds can

retard the cement

Cement Additives

137

Other Additives

Antifoam/ defoamer agents

Bonding agents

Gas migration control additives, etc.

Fluid Loss Control

Cement Evaluation

139

Cement evaluation

Cement bond logs are used to:

•

Determine hydraulic isolation between zones of

interest

•

Locate cement top

•

Determine feasibility of a cement squeeze

•

Evaluate the quality of the cement

Pipe to Cement Bond

Directly related to surface finish of the pipe.

A clean surface greatly enhances the bond potential.ie, no

grease, oil spots or paint on the pipe exterior.

The pipe to cement bond was formerly the top priority. Today

the cement to formation is now considered more critical.

Cement evaluation

141

Cement to Formation Bond

Generally determines whether there will be gas or liquid

communication in the annulus.

Hydraulic bond across permeable zones is largely influenced by

the presence or absence of mud filter cake.

Permeable formations will leach fluids so cement with water

loss additives must be used in these conditions.

Cement evaluation

142

Two types of cement evaluation tools

:



The Sonic Tools



The Cement Bond Log



The Radial Bond Tool



The Ultrasonic Tools



The Circumferential Acoustic Scanning

Tools

Cement evaluation

143

Acoustic Bond Logs

Acoustic cement bond logs do not directly measure hydraulic seal.

Instead they measure the loss of acoustic energy as it propagates through casing.

This loss of acoustic energy can be related to the fraction of the casing perimeter covered with cement.

Travel Time (Transit Time)

For free-pipe, the travel time should match the expected time for that casing size.

For bonded pipe the travel time should increase as it triggers later arrivals.

If the travel time decreases below casing arrival time and the amplitude drops then suspect eccentralization.

If the travel time decreases below casing arrival time and the amplitude increases suspect fast formations.

The travel time difference between the 3ft and 5ft receivers should be 114 µs. If it less than this suspect fast formations.

145

Amplitude

For bonded pipe the amplitude should be low.

For free-pipe the amplitude will be high.

If the amplitude is intermediate cross check with the cement

map to see if it’s due to cement channeling or low

compressive strength cement.

Decentralized Tools String

Centring of the Tool is critical for valid measurements.

If the tool is eccentered there are 2 paths for the sonic

signal to take

the travel time will be less than the expected travel time

and the amplitude will be low which will falsely indicate

good bonding.

147

CBL Tool

Advantage:

Widely Used Method to Evaluate the Cement Job.

Used to Evaluate the Zonal Isolation, Bonding to Casing, Bonding to Formation, and Cement Compressive Strength.

Tool Response Characterized and Well Documented. 148

CBL Tool

Cement Formation Casing TRANS-MITTER 3 FT RECEIVER 5 FT RECEIVER A B C D E F G 149

CBL Log

Free Pipe Partial Bond 150

CBL Tool

Disadvantage:

Affected by tool centralization, fluid attenuation, pressure and temperature.

Affected by fast formations, thin cement sheath.

Gives only qualitative cement-formation bonding information.

Omni-directional signal- Assumes uniform distribution of cement in the annulus.

Cannot evaluate the radial placement of cement materials in the casing formation annulus.

Does not provide positive channel identification. 151

Sector Tool

(Radial Bond Tool)

Measures the quality of the cement bond laterally around the circumference of the casing.

It has a single omni-directional transmitter

The 3 foot near spaced receiver is divided into 8 radial segments measure 45° increments to produce cement map for channel identification.

The receiver located at 5 feet is the traditional omni-directional sensing.

The amplitude of the received acoustic signal in each of the segments represents radial

variations in material in the casing-formation

GR

Electronics

Transmitter

3 Ft. Receiver

Advantages

Less affected by heavy drill fluids. Can log in #18 ppg mud

Not affected by oil based mud.

Identifies channels.

Not affected by casing thickness. Good in wells with corrosion.

Centralized very easily in deviated wells up to 60°

Sector Tool

(Radial Bond Tool)

153

Disadvantages

Three foot spacing will be affected by fast formation arrivals.

Reads incorrect amplitudes in presence of micro annulus( unless run under pressure)

The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels.

Sector Tool

(Radial Bond Tool)

Ultrasonic Tools

Use a single rotating transducer combined transmitter and receiver.

Acquire ultrasonic waveform data for both cement

evaluation and casing evaluation in the same logging run or pass.

The sampling rate of the rotating transducer can provide 100% azimuthal coverage of the casing.

Allows to distinguish cement, liquid, and gas in the casing-formation annular space, based on the acoustic properties of the received waves

155

Ultrasonic transducer is located 1.25” to 2.5” from the casing wall

Sends a beam of ultrasonic energy in the 500 kHz band.

Ultrasonic energy causes the casing to vibrate or “ring”

Frequency and decay rate of return signal is measured

Casing thickness and impedance of cement sheath is calculated

By measuring the energy of the vibration

Ultrasonic Tools

Ultrasonic Theory of Measurement

Ultrasonic transducer acts as transmitter & receiver

• Transmits short pulse of acoustic energy

• Receives multiple echoes from the casing, cement & formation

Casing Resonates

Casing resonance dampened in the presence of cement

Mud Casing Cement Formation Transducer

157

Acoustic Impedance

The Impedance of a material defines the sound properties for that material. It is a product of the density of the medium and the velocity of sound of the medium.

Z= p x c

• Where Z = Impedance in MRayls • P = the density in kg/m3

• C = speed of sound in m/s

• Example: Z_water= 1000 kg/m3* 1500 m/sec = 1.5 MRayls • At any bed boundary (Z₁ / Z₂) with different Impedances, sound

energy will be reflected and refracted.

• Acoustic impedance of steel: Z_steel= 45 MRayls

Ultrasonic Technique

The amplitude of the signal is proportional to the acoustic impedance of the material behind pipe

Color Acoustic Impedance Material Behind Casing White 0.00-0.38 Gas

Light Blue - Dark Blue 0.39-2.30 Liquid Gas - Fresh Water

Yellow - Light Brown 2.31-2.70 Heavy Drilling Fluid – Light Cement

Light Brown - Dark Brown 2.71-3.85 Low Impedance Cement

Dark Brown 3.86-5.00 Medium Impedance Cement

Black > 5.00 High Impedance Cement

159

White color = Z < 1.4 Mrayls Blue color = 1.4<Z<1.8 Mrayls Yellow color = Z>1.8 Mrayls

Acoustic Impedance Map

160

Advantages

Identifies Presence of Channels, Large and Small

Not sensitive to Micro-annulus

Not Sensitive to Fast Formations

Can be used to Evaluate Light Cements and Foam Cements

Indicates Casing Geometry and Thickness

Disadvantages

The ultrasonic measurement is of the casing-cement interface only, cannot provide cement-formation interface information.

Cement Evaluation Affected by Casing Corrosion

Scanner head difficult to rotate in heavier mud.

Signal Affected by Heavy Drill Fluids or Oil Based Drilling Fluids (14-16 ppg mud weight limit)

Affected by Thin Cement Sheath

Ultrasonic Technique

161

The amplitude and travel time of the reflected pulse received by the transducer depends upon:

• Centralization

• Geometry of the borehole • corrosive condition of casing

• The acoustic impedance contrast between the borehole fluid and

the borehole wall, i.e. the relative hardness of the rock

• Mud attenuation, i.e. in heavy weight or oil-based mud, the

reflections are lost, especially those with high solids content

Ultrasonic Technique

162

Channel in the cement

Micro-annulus

Fast formations

Cement Evaluation-Difficulties

163

Cement channels are longitudinal pockets with no cement.

May happen when the mud is not adequately flushed from the wellbore during the cementing process (accentuated when the casing is not centralized).

Channeling could be caused by gas or water migration during the time that the cement is curing and or in high angle wells where heavy cement sinks to the low side of the wellbore leaving little or no cement on the high side.

Channel in the cement

A micro annulus is a microscopic gap between the cement and the casing which causes poor acoustic coupling.

The gap has been estimated in the range of 0.005-0.01” (0.12 to 0.25 mm).

A micro annulus does not compromise hydraulic isolation

Log indicates moderate casing amplitude and formation arrivals.

Indicates poor bond when good hydraulic isolation is present

If a micro annulus is suspected re-run the log with the casing under pressure (500 to 1000 psi).

Micro-annulus

165

Pressure differential placed on casing

• Pressure on a cement plug • Pressure testing casing

• Stimulation (acidizing, fracturing, etc.)

Different hydrostatic pressures on casing

• Change of wellbore fluids while cement is curing

Mechanical

• Moving pipe after cementing, etc.

Thermal Micro-annulus

Heat generated by curing cement

Micro-annulus

Fast formations

•A Fast formation is a formation where the sonic velocity is higher or faster than the sonic velocity in casing.

•Formation signals can arrive at the 3ft receiver before the casing signal.

•Formation signal arrives in the amplitude gate resulting in interpretation as poor bond.

•As a check the travel time to the first arrival should be examined;

•Indications on the log are increased amplitude and decreased Travel Time

167