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Primary Cementing Results –Evaluation, Special Cases and Pitfalls

Primary and Remedial Cementing Core

Learning Objectives

By the end of this lesson, you will be able to:

Evaluate cement bond laboratory testing to assess the strengthand extent of cement-to-formation and cement-to-casing bond

Describe the concept of the cement “micro-annulus” effect and howto prevent this problem from occurring

Evaluate case study data for improving primary cement job quality

Identify other cementing problems and challenges such ascementing through gaseous zones and salt formations

Describe cement fluid properties and how those properties affectthe flow of cement; this is referred to as “cement rheology”

Calculate the cement volume required for a casing cementing job

Evaluate a cement bond log (CBL) and make recommendations

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© PetroSkills, LLC., 2016. All rights reserved._____________________________________________________________________________________________

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• This thinking is inaccurate

Achieving Isolation

The term “isolation” is often used interchangeably with the term “bond”

Conventional thought in primary cementing is that: what is really needed is good cement “bond”

What is actually needed is good zonal “isolation”

Shear Bond and Hydraulic Bond lab tests evaluate the potential to achieve zonal isolation

Hydraulic Bond Test Cell

Pressure

Mud Cake

Formation Core

Cement Slurry

How good is the cement bond?- to the formation and to the pipeHow good is the cement bond?- to the formation and to the pipe

What are the forces required to break the bond?

What are the forces required to break the bond?

Has mud cake been removed?Has mud cake been removed?

Can gas flow in formation / pipe cemented annulus?

Can gas flow in formation / pipe cemented annulus?

Pressure

Primary Cementing Results - Evaluation, Special Cases and Pitfalls ═════════════════════════════════════════════════════════════════════════

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© PetroSkills, LLC., 2016. All rights reserved.

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Casing

Cement

Pressure:Water or Gas

Hydraulic Bond Test Cell

Formation

Quantitative measurement is made to determine cement bond to the formation and to the pipe

Heating oil is circulated to establish temperature

FiltrateReturnsFluid In

Casing

Halliburton Cement Test Cell

MudCement

H2O

Formation

Cement



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Shear Bond (psi)

Water Bond (psi)

Gas Bond (psi)

2400(16,547.42)

1200(8,273.71)

400+(2,757.9+)

141(972.161)

500-700(3,447.38-4,826.33)

150-250(1,034.21-1,723.69)

123(848.06)

500-700(3,447.38-4,826.33)

150-250(1,034.21-1,723.69)

79(544.69)

200(1,378.95)

10-20(68.95-137.90)

Shear Bond (psi)

Water Bond (psi)

Gas Bond (psi)

Mill Varnish

Sand-Blasted

Rusty

External Pipe Surface Affects Bond

141(972.161)

500-700(3,447.38-4,826.33)

150-250(1,034.21-1,723.69)

123(848.06)

500-700(3,447.38-4,826.33)

150-250(1,034.21-1,723.69)

Resin-Sand Coat

2400(16,547.42)

1200(8,273.71)

400+(2,757.9+)

79(544.69)

200(1,378.95)

10-20(68.95-137.90)

Pipe / Cement Bond and the Micro-Annulus Effect

Avoid pressure on casing during Waiting On Cement (WOC) (if float valves holding pressure)

• If pressure is released, pipe returns to smaller outside diameter• Micro-annulus forms between pipe and cement

Displace (pump down) cement with light, clean salt water

Heat of hydration will: • Increase fluids temperatures, and,• Increase casing pressure

– Could cause casing expansion

Circulation while WOC is helpful

Increased pressure after WOC helpful


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• Cement plus additives based upon total volume

Cost of Primary Cementing

Cost of cement slurry

Cost of Pumping Equipment

Cost of Rig Time and Waiting On Cement (WOC)

Cost of Evaluation

Cost of Remedial Operations (initial + future)

Primary Cement Study: Katy Field

25 casing strings cemented

22 Failures (88%)

Causes:• 2 due to lost circulation• 20 due to:

– Excess filter cake

– Lost returns

– Inefficient mud displacement

Cockfield

Wilcox

14-3/4"Hole

9-7/8"Hole

6-3/4"Hole

(0.375 m)

(0.251 m)

(0.171 m)

10-3/4"Csg

7-5/8"Csg

5" Liner

(0.273 m)

(0.127 m)

(0.194 m)



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Depth

6100'

6500'

7000'

7500'

7700'

Gas &WaterZones

SP

Spontaneous Potential (SP) Log of Katy Cockfield Sands

Pressure (psi)600 (4,136.9)

840 (3,923.1)

1600 (5,791.6)

2000 (13,789.5)

700 (4,826.3)

569 (3,923.1)

700 (4,826.3)

530 (3,654.2)

640 (4,412.6)

2500 (17,236.9)

(kPa)

(1,859.3 m)

(1,981.2 m)

(2,133.6 m)

(2,286 m)

(2,346.96 m)

Evaluation of Cement Jobs

9 Wells / 8 Failures / Average 8 squeezes per well

7-5/8"(0.1937 m) Casing Through Cockfield Zone

Well # Squeezes Well # Squeezes

1 0 6 7

2 6 7 9

3 11 8 4

4 8 9 4

5 10

Conclusion: Must improve primary cementing practices


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Changes After Study

Improved drilling mud system fluid loss

Casing rotations and reciprocation • Requires power swivel

Added centralizers and scratchers to help mud displacement

Results: • Drilled 13 new wells• Only 2 primary cement job failures

– Each of these 2 failures required 3 squeezes

Bottom Line:• Saved enough money to drill 3 additional wells

Special Cementing Problems

Deep Wells• Depths greater than 15,000' (4,572 m)

• Temperatures greater than 250°F (121°C)

Liners• High temperatures, small hole, no movement

Gas communication

Highly deviated wells

Thermal wells strength retrogression:• For > 230°F (110°C), add 30% to 40% silica flour

Frozen formations:• Use gypsum / cement blend

Multi-Stage Cementing



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Cementing Through Gas Zones

Gas communication between zones and migration to surface is a common problem

First, understand problem and set objectives

Next, correct problem with careful slurry design, pipe movement, additives, proper displacement pressure program, etc.

ChannelGas

Leakage

Gas Zone

Cementing Thru Salt Sections

• Use salt saturated water while drilling

Control hole washouts

Use salt-saturated cement through salt and shale zones

Caliper hole to assure correct cement volumes

Use ample cement to cover zone

Design casing to withstand 1.0 psi/ft (22.621 kPa/m) collapse loads


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SaltSection

Casing Failure Patterns

SaltSection

InitialInitial

Tubing

CasingSalt

CollapsedCollapsed

DeformedDeformed

Effect of Salt Zones

Salt zones can create cavities or washouts

If a salt water slurry is used, check salt for pumpability

Salt may act as either an accelerator or retarder

Sal

t W

ater

Slu

rry

Fre

sh W

ater

Slu

rry



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Cement Rheology

Shear stress and shear rate determination Shear stress and shear rate determination Shear stress and shear rate determination

Field measurement of cement slurry properties Field measurement of cement slurry properties Field measurement of cement slurry properties

Shear Rate

She

ar S

tres

s Herschel-Buckley

Rheological Models


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Tru-WateBalanceTru-WateBalance

Pressured Mud Balance

Pressurized Mud Scale for Field Measurement of Cement Slurry Density

Pressured Mud Balance



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Radioactive Densometer

Useful Cementing Data

Volume: (hole diameter)2 x 0.97 = Bbls/1000 ft (304.8 m)

Mix Water: ~5 gal (18.9 L) per sack

Volume Conversion:

Hydrostatic Pressure:

• 5.614 ft3 / bbl and 6.29 bbls/m3

• 10 lb / gal = 0.52 psi/ft or 11.76 kPa/m


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Not doing the calculations needed and not keeping good records

Relying too much upon chemical additives to solve all cementing problems

Failing to recognize and handle mud gel problems and failure to condition the mud

Using “hole problems” as an excuse not to implement correct, known procedures

Primary Cementing Pitfalls

PIT

FAL

LS

Company thought processes that say: “It’s the Service Company responsibility to provide a good primary cement job”

Compressive Strength versus Bond Index

Bond Index = Attenuation / Attenuation Max

Where:

Attenuation = Attenuation at any point on thelog (db/ft or db/meter)

Attenuation Max = Maximum attenuation(db/ft or db/meter)

Example for this 7" (0.1778 m) casing:Max log reading 3.5 mV eq 8.8 dB/ft (28.9 dB/m)

Min log reading 2 mV eq 10.5 dB/ft (34.4 dB/m)

> B.I. = 84%



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Interval Isolation Evaluation

Graph from experimental work, courtesy Schlumberger

A Bond Index of 0.80 suggests that only about 80% of the annulus is filled with good cement.

Casing size, in

5 6 7 8 9 10

15

10

5

0

ft

9 5/8 "

Cem

ente

d in

terv

al,

ft

FOR 80% CEMENT

Isolation can reasonably be ensured by a Bond Index higher than 0.80 over a minimum cemented interval, the interval length depending on casing size.

(m)

(0.127) (0.152) (0.178) (0.203) (0.229) (0.244) (0.254)

(1.524)

(3.048)

(4.572)

Example Log: CBL / VDL with "Bond Index"

Cement bond log should show > 10 millivolts over an interval of 7 meters to

be interpreted as providing isolation

Cement bond log should show > 10 millivolts over an interval of 7 meters to

be interpreted as providing isolation


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Primary Cementing Planning Strategy Summary

and

Work to achieve successful primary cement job execution and results looking at both the drilling and the production operations perspectives

Work to achieve successful primary cement job execution and results looking at both the drilling and the production operations perspectives

Work with the drilling organization and cement services companies to strive to achieve a properly designed primary cement job

Work with the drilling organization and cement services companies to strive to achieve a properly designed primary cement job

Learning Objectives

Evaluate cement bond laboratory testing to assess the strength and extent of cement-to-formation and cement-to-casing bond

Describe the concept of the cement “micro-annulus” effect and how to prevent this problem from occurring

Evaluate case study data for improving primary cement job quality

Identify other cementing problems and challenges such as cementing through gaseous zones and salt formations

Describe cement fluid properties and how those properties affect the flow of cement; this is referred to as “cement rheology”

Calculate the cement volume required for a casing cementing job

Evaluate a cement bond log (CBL) and make recommendations



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