Applying welllife slurry for cementing HPHT wells at y field, nam con son basin

- Study how WellLife Cement System works from collecting data to cement slurry design; Applying WellLife Slurry for cementing HPHT wells at Y field, Nam Con Son Basin.. ABSTRACT This is

VIETNAM NATIONAL UNIVERSITY, HO CHIMINH CITY

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

-oOo -

STUDENT’S NAME: LƯƠNG THỊ HỒNG SƠN

APPLYING WELLLIFE SLURRY FOR CEMENTING HPHT WELLS AT Y FIELD, NAM CON SON BASIN

SPECIALITY: PETROLEUM ENGINEERING (60520604)

STUDENT ID: 7140880

MASTER THESIS

HO CHI MINH CITY, 08/2018

Auxiliary pages

We, the undersigned, recommend that the thesis is completed by student listed above,

in partial fulfilment of the degree requirements, be accepted by the Ho Chi Minh City

University of Technology for deposit

Professor/Advisor: Dr ĐỖ QUANG KHÁNH

Reviewer 1: Dr NGUYỄN HỮU CHINH

The Master Thesis is defended at the Committee of Master Thesis Examiners at Ho

Chi Minh City University of Technology on 04th August 2018

The Committee members include:

(Name of Advisor and Thesis committee members)

1 MAI CAO LÂN – Chairman of Committee

2 NGUYỄN HỮU NHÂN - Secretary

3 NGUYỄN HỮU CHINH – Member/Examiner

4 HOÀNG QUỐC KHÁNH – Member/Examiner

5 TRƯƠNG HOÀI NAM - Member

The Master thesis is evaluated and approved by Committee Chair

COMMITTEE CHAIR HEAD OF DEPARTMENT

DEAN OF FACULTY

VIETNAM NATIONAL UNIVERSITY, HO CHIMINH CITY

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

MASTER THESIS TASK

Student’s name: LƯƠNG THỊ HỒNG SƠN STUDENT ID: 7140880 Date of birth: 24/12/1978 Place of birth: Rach Gia, KG SPECIALITY: PETROLEUM ENGINEERING

I THESIS’S NAME

APPLYING WELLLIFE SLURRY FOR CEMENTING HPHT WELLS AT Y FIELD, NAM CON SON BASIN

II TASK AND CONTENT

- Overview about petroleum geology, temperature and pressure of Nam

Con Son Basin Information about cementing for HPHT wells in Nam

Con Son Basin Explore challenges and solution applied in HPHT wells

- Study Cement components in Conventional and HPHT environment

- Study how WellLife Cement System works from collecting data to cement slurry design; Applying WellLife Slurry for cementing HPHT wells at Y field, Nam Con Son Basin

- Evaluate cement quality of WellLife cement in HPHT wells of Y field

III THESIS DATE RECEIVED: 11/01/2018

IV THESIS DATE COMPLETED: 25/06/2018

V ADVISOR: Dr Do Quang Khanh

DEAN OF FACUTY (Name and Signature)

ABSTRACT

This is a comprehensive study of applying WellLife slurry for cementing high temperature high pressure wells at Y field, Nam Con Son Basin In this research, I explore basic information about petroleum geology, temperature and pressure at Nam Con Son Basin, information about cementing technology application history with failure or success, the effects of temperature and pressure to cement’s property Then

to study cement components for HPHT not only cement itself but scan through types

of additives used in HPHT cementing slurries Also research challenges and solutions

of cementing HPHT wells, research WellLife components and WellLife cementing design for 5 ½ casing of a HPHT well in Y field which includes WellLife design for special cement G applied WellLife Slurry for cementing HPHT wells at Y field, study the process from well information, well schematic with all strings to Pore Pressure and Fracture Gradient windows to see the challenges and come up with solution applied for cement design for the last section, also the highest temperature and pressure section of the well Come up with components for blending Get assistance from WellLife software and lab test to evaluate how WellLife slurry modify YM &

PR & trend of modifying YM & PR with elastomer and recommended %bwoc Finally, find out cement evaluation methodology and evaluate WellLife cement quality in a well via cement bond log result The last conclusion and suggestion part, this thesis highlight what not yet been done and suggest development topic

DEDICATION

This is my own dedication The data in the thesis is honest and experimental

ACKNOWLEDGMENTS

This project would not have been possible without the support of many people Many thanks to my advisers, Dr Khanh & Dr Nam for the invaluable assistance and insights leading to the writing of this paper as well as their patience and enduring this long process with me for the production of this paper Thanks to my colleagues at Halliburton company for their assistance and dedication to support me to witness all the tests in lab on the requirement of the paper as well as real experience over learning curve of the project to come up with the best solution as well as to review and provide many examples used in this sample research paper have been quoted

And finally, thanks to my customer who supports me with the actual data to complete this project accurately

LIST OF FIGURES

Figure 1.1: Y field at Nam Con Son Basin

Figure 1.2 Play types of Nam Con Son Basin [20]

Figure 1.3 Matrix of High Pressure High Temperature Operation [1]

Figure 1.4 Matrix of High Pressure High Temperature Operation [1]

Figure 1.5 HPHT Tiers, Courtesy of Baker Hughes 2005 [1]

Figure 1.6 HPHT Tiers, Courtesy of Schlumberger, 2008 [1]

Figure 1.7 HPHT Tiers, Courtesy of Halliburton, 2012 [1]

Figure 1.8 Pressure profile at block 04, 05 Nam Con Son Basin [19]

Figure 1.9 Pressure profile at block 04, 05 Nam Con Son Basin [19]

Figure 1.10 Temperature profile at block 04, 05 Nam Con Son Basin [19] Figure 3.1 Maintaining Overbalance pressure

Figure 3.2 Gas channel forms under the following conditions

Figure 3.3 Example of long-term gas migration problems

Figure 3.4a General trend for modification of Young’s modulus with elastomers

Figure 3.4b General trend for modification of Poisson’s ratio with elastomers

Figure 3.5a General trend for modification of Young’s modulus with elastomers

Figure 3.5b General trend for modification of Poisson’s ratio with elastomers

Figure 3.6: Model 6265 Mechanical Properties Analyzer

Figure 3.7: Report of 6265 Mechanical Properties Analyzer

Figure 3.8: Highly permeable sections require good fluid-loss

Figure 3.9 Uncontrolled fluid loss can result in a rapid cement

Figure 3.10 Cement node buildup

Figure 3.11 Thermal thinning effect

Figure 3.12: Well schematic contains 8 strings to reach to multiple reservoirs

Figure 3.13: Pore Pressure – Fracture Gradient contains very narrow window 0.8ppg

Figure 3.14 Temperature profile in Y field [18]

Figure 3.15 Conventional cement sheath with catastrophic failure

Figure 3.16 WellLife cement resiliently withstands load

Figure 3.17 Remaining capacity between conventional and WellLife cement

Figure 3.18 UCA chart at BHST 160Deg C

Figure 3.19 TT chart at Baseline 135Deg C – cement sample from Silo3

Figure 3.20 SGS chart at BHST 160Deg C

Figure 3.21 UCA chart at BHST 160Deg C

Figure 3.22 TT chart at Baseline 160Deg C-Silo1

Figure 3.23 SGS chart-Silo#1

Figure 3.24 UCA chart at BHST 185deg C-Silo1

Figure 3.25 UCA chart at TOL 155deg C - Silo1

Figure 3.26 TT chart at Baseline 160deg C-Silo 3

Figure 3.27 UCA at BHST-Silo3

Figure 3.28 SGSA chart –silo#3

Figure 4.1 Relationship between Received Amplitude (E1) and Casing Size

Figure 4.2 Correction Factor (Amplitude Ratio) for different wellbore fluids

Figure 4.3 Cement Bond Log Interpretation Chart

Figure 4.4: Acoustic Impedance of typical materials present behind pipe

Figure 4.5 SBT Pad arrangement and Attenuation rate computation methodology

Figure 4.6 Baker Atlas SBT Interpretation Chart

Figure 4.7 Examples of TT and Amplitude data

Figure 4.8 Casing Collar Locator Radial CBL of 5-1/2 tubing of well Y after cementing with WellLife Slurry

LIST OF TABLES

Table 1.1 Wells at Nam Con Son Basin with water depth of HPHT

Table 1.2 Technical design and technology of cementing wells in block 04 & 05 Nam Con Son Basin

Table 1.3 Cementing design from service providers for wells at Nam Con Son Basin

Table 1.4 Slurry Design applied for HPHT wells in Nam Con Son Basin

Table 2.1 Water Requirements for Different Classes of Cement

Table 2.2 Maximum allowable limits for Ions in mixing water

Table 3.1 Comparison of Compressive Strength, Young’s Modulus and Poisson’s Ratio between WellLife 665 Additive and FDP-987-10 Material

Table 3.2 Special WellLife Cement component

LIST OF SYMBOLS AND ABBREVIATION

API American Petroleum Institute

CBL Cement Bond Log

CSR-100L Cement Retarder

CFR-3L Cement Friction Reducer

Ex-HPHT Extreme High Pressure High Temperature

HPHT High Pressure High Temperature

MPRO Mechanical Properties Analyzer

ppg Pounds per gallon

SG Specific gravity

SSA-1 Strength-Stabilizing Agent

UCA Ultrasonic Cement Analyzer

Ultra HPHT Ultra High Pressure High Temperature VDL Variable density log

BWOC By weight of cement

TABLE OF CONTENTS

Pages

ABSTRACT i

DEDICATION ii

ACKNOWLEDGMENTS iii

List of Figures iv

List of Tables vii

List of Symbols and Abbreviation viii

TABLE OF CONTENTS ix

PRELIMINARY 1

Target, tactics and objectives of the thesis: 2

Reseach Methodology 2

Literature Review 3

Contents 7

New contribution of Thesis 7

Supporting Documents 8

Findings/Results/Data Analysis 8

CHAPTER 1 OVERVIEW OF CEMENTING HPHT WELLS IN Y FIELD, NAM CON SON BASIN 9

1.1 Petroleum geology and temperature of Y field, Nam Con Son Basin 9

1.1.1.Petroleum Geology 9

1.1.2.Temperature & Pressure 11

1.2 Information about cementing for HPHT wells in Nam Con Son Basin [19] 15

CHAPTER 2: CEMENT IN HIGH TEMPERATURE HIGH PRESSURE ENVIRONMENT 20

2.1 Basic Cements 20

2.2 High Temperature Cements 25

CHAPTER 3: CHALLENGES AND SOLUTIONS OF CEMENTING

HPHT WELLS, CEMENT SYSTEM DESIGN PROCESS AND

APPLYING SAME WELLLIFE SLURRY FOR 10” LINNER AND 5-1/2

TUBING OF HPHT WELL IN Y FIELD 34

3.1 Challenges and Solutions of Cementing HPHT wells: 34

3.1.1.Challenges 34

3.1.2.Solution 41

3.2 HPHT WellLife Cement System Design Process 46

3.2.1 Data to collect to design cement for HPHT wells: 46

3.2.2WellLife/Elastic cement slurry design 48

3.3Applying WellLife slurry for cementing HPHT wells at Y field 62

3.3.1 Well information and requirement of designing cement for 5-1/2 casing in HPHT well of Y field 62

3.3.2Solutions applied in cement design for 5-1/2 casing of well in Y field 66 3.3.3 10” Liner Cement Job Summary 69

CHAPTER 4: EVALUATE CEMENT QUALITY IN 5-1/2 CASING OF HPHT WELLS IN Y FIELD NAM CON SON BASIN 79

4.1 Running and Interpreting Bond Logs with WellLife Cement 79

4.1.1 Cement Bond Logs 79

4.1.2 Ultra-Sonic Logs 84

4.1.3 Segmented Bond Tool 85

4.1.4 Derivative Analysis 87

4.1.5 Combination Logs 87

4.2 Evaluation result of WellLife cement quality for HPHT of well in Y field 87

CONCLUSION & SUGGESSION 97

REFERENCES 98

CURRICULUM VITAE 102

PRELIMINARY

Oil and gas is the leading industry in the national economy, it makes a great contribution to country GDP and accelerate industrialization and modernization Producing oil requires a complex process from exploration, drilling, production in upstream and processing in downstream During drilling operation, cementing plays

an important role in securing well operation quality, especially the high temperature high pressure wells in Nam Con Son basin The failures and non-productive time in cementing operation in this basin are varies such as unable to displace cement to annulus or cement harden in the casing or production liner or cement didn’t set in the annulus due to high temperature and/or high pressure in the wellbore change cement’s properties The above failures cause non-productive time and extra cost of operation, moreover it implies a gas kick, one of the serious problem of cement quality causes the well to be plugged and abandoned One of the cause of those cement problem due

to we don’t have fit cement slurry design, lack of suitable chemical fit to HPHT environment

In Vietnam, one of HPHT basin is Nam Con Son, this basin is 2nd largest oil and gas basin in Vietnam mainly gas and condensate This basin has complicated geology, with sea water depth from 70m-more than 1000m from East to West In the past 40 years, there are about 100 drilling wells from exploration, appraisal to production well and the above failure used to happen in this basin

In upcoming years, there are some new development projects executed in this area or other high temperature area for gas production therefore the fact that an application, solution for HPHT cementing which successfully proven by the wells drilled in same basin at the same temperature and pressure as this field is a great experience and highly contribute to the success of upcoming HPHT projects

Therefore, in this thesis, I would like to understand challenges and solution of cementing in HPHT wells From that to research on how WellLife cement contributes

to enhance the success of cementing HPHT environment that has been proven in wells

at Nam Con Son Basin The thesis outline is as follows:

TARGET, TACTICS AND OBJECTIVES OF THE THESIS:

 Target & aims: finding and applying suitable slurry in cementing for HPHT well of

Y field

 Tactics: the thesis are to:

- Analyze temperature and pressure of Y field at Nam Con Son basin, research about state and property of cement in high temperature, the effects of temperature and pressure to cement’s property, cement hydration

- Research challenges and solutions of cementing HPHT wells

- Research WellLife components and WellLife cementing design for 5 ½ casing of a HPHT well in Y field which includes WellLife design to change Poisson’s ratio and Young’s modulus of cement property to get the best result

- Evaluate WellLife cement quality in a well via cement bond log result

 Zonal Evaluation: Apply cement bond log to analyze and evaluate cement quality

LITERATURE REVIEW

 Research in the world

Successful Applications of Conventional Elastomers in HPHT Environments [24] of Steve Streich, Earl Webb, and Hank Rogers find out the appropriate

conventional elastomers for HPHT cementing which consist of various compound mixtures of the base polymer Nitrile rubber (NBR) in which the main compounds include Hydrogenated Nitrile (HNBR), Fluorocarbon (FKM), and Perfluorocarbon (FFKM) However ASTM data does not tell the final story of how a compound will perform in a given product under given conditions and design parameters therefore the paper do not take into consideration other field-based factors, such as time of exposure, differential pressure, seal volume/cross-sectional thickness, or fluid concentration It also does not consider whether the temperature is static or circulating, whether the pressure is static or dynamic, or whether backup mechanisms are part of the product design All of these factors are important and should be considered when deciding on which sealing material to use

The Application of High-Density Elastic Cements to solve HPHT Challenges in South Texas: The success Story [25] of Barry Wray, Cimarex Energy; David

Bedford, Lennox Leotaud, and Bill Hunter shows the successful cases of 2 representative examples using high-density elastic cements (HDEC) which have been placed in more than 40 wells with bottomhole static temperature from 300degF – 448degF and performed well on the set cement sheath during the life of the well The paper show the pilot results test for thickening time, UCA Comp Strength or Stirring fluid loss and the best practice of the pumping rate but not yet show the elastic cement component as well as percentage of cement component to make the success of the well

Successful Cementing Case Study in Tuscaloosa HPHT Well [10] of Barry Wray,

Cimarex Energy; David Bedford, Lennox Leotaud, and Bill Hunter shows the experience of failures using conventional cementing technique in Tuscaloosa, South Louisiana wells and success after investigating and identifying the possible problem and underlying causes which are the difference between actual temperature and API methods (195degF vs 230degF), the effect of wells events on cement sheath, slurry design, field implementation…cross check with actual log data and simulation data The cement system was modified based on simulation data to prevent such failure and the new cement system was designed and tested The modified cement system was deployed in the field since Apr 2006 and the well was put on production in a few months later and since then until the published of the paper in Oct 2008 (over 2 years) has been online and producing without annular pressure problems

Applied Technologies for successful cementing in high temperature and highly depleted fields in Southern Mexico [13] of Roberto Hernandez-Enriquez, Edgar

Cerrillo-Caro; Halliburton; Roberto Solano-de la Cruz; Pemex shows the case study

of applying technical and commercial contribution for “Delta del Grijalva” project Commercial example is 27.4MWell cost + 9.5M impairment cost of poor zonal isolation vs no remedial work due to poor zonal isolation during production life up to present-7 years Technical is to correctly determine for cementing operation, centralize and apply cementing technologies including Slurry design with proper additives, Rheology and displacement modeling

Strength Retrogression in Cements under High Temperature Conditions [22]of

Benjamin Iverson and Joe Maxson, Halliburton; and Daniel Bour, AltaRock Energy, Inc though all record of mechanical properties and permeability of studied samples has proved that the strength retrogression in a Class G Portland cement containing silica additions ranging from 40 to 80% when subjected to elevated temperature ranging from 500 to 650degF and the previous information for including 35-40% additional crystalline silica to help prevent loss of compressive strength and an increase in permeability for all HPHT is now limited at temperature up to 230degF Above that, additional silica was required to provide a high-strength stable crystalline structure

What Petroleumm Engineers and Geoscientists Should Know HPHT Wells Environment [1] is the article of Arash Shadravan; Mahmood Amani to discuss

about the HPHT theory, explains the technological challenges in developing HPHT fields, deepwater drilling, completions and production considering the reports from the Bureau of Ocean Energy Management, Regulation and Enforcement also provides formation information of some fields in North Sea and Middle East to support the explanation

Considered factors in designing HPHT development wells is the article from

BDPOC team sharing their experience of designing wells in Hai Thach & Moc Tinh field of Nam Con Son Basin not limit to casing design, completion design, small gap

between pore pressure and fracture gradient material selection, ECD managmenet and

fluid and cement selection

Research and select cement slurry for HPHT wells in Nam Con Son Basin [4] is

the Doctorate Dissertation of Dr Truong Hoai Nam for HPHT cement for Nam Con Son Basin has listed very detail all components of cement slurry including cement physical property and available chemicals including the strength stabilizing additives used to mix with cement for HPHT environment and also the practical chemicals in detail such as different types of silica flour with recommended bwoc (by weight of cement) and its effect to cement’s permeability, stress, durability… as well as heavyweight additives to increase slurry density, restrain high formation pressures and improve mud displacement or retarders, suspension additives, dispersants to reduce cement friction…

After studying the work from article or journal of different authors about different HPHT cement in related research, I found different methodologies of applying cement for HT wells as well as its effect to cementing a HPHT well including successful cement case studies for HPHT wells or cement system design or selection

of foamed cement for HPHT gas well or a review of HPHT drilling campaign in which cementing is part of it

I not yet can find many thesis and articles, journals about applying WellLife slurry for HPHT wells and its effect Therefore, I decided to select this topic

Referencing the above research, further experimental test result done by my colleague

in Halliburton lab in Pune, India, the thesis is to pursue on how WellLife can contribute to the elastomer property of cement by modifying Poisson’s ratio and Young’s modulus which is tested and applied to HPHT wells at Y field of Nam Con Son Basin

Due to the proprietary of WellLife product, this thesis didn’t analyze the detail ingredient inside WellLife but considered it as one type of cement chemical of the slurry which made effect on Young’s modulus and Poisson’s ratio in order to fit to the HPHT environment

Chapter 1 Overviewing some information about cementing HPHT wells Study petroleum geology, pressure and temperature, information about cementing process for HPHT wells in Nam Con Son basin

Chapter 2: Cement components in HPHT environment including basic cement and HPHT cements

Chapter 3: Challenges and solutions of cementing HPHT wells, cement system design process and applying same WellLife slurry for 10” Liner and 5-1/2 tubing of HPHT well in Y field

Chapter 4: evaluate cement quality in 5-1/2 casing of HPHT wells in y field Nam Con Son basin

Conclusion and Suggestion

NEW CONTRIBUTION OF THESIS

To prove WellLife can affect the Young’s modulus and Poisson’s ratio of Cement and prove that WellLife slurry can successfully applied in HPHT well of Y field in Nam Con Son Basin

SUPPORTING DOCUMENTS

 SPE, AAPG articles, Master Thesis, Doctorate Thesis

 Oil & Gas Magazines and articles

 Cementing for HPHT wells

The proven result of applying WellLife slurry brought a great confidence of pumping cement in HPHT wells in Nam Con Basin which helps to enhance the life of the wells and reduces failure/ incident as well as non production time caused by cement in this basin

CHAPTER 1 OVERVIEW OF CEMENTING HPHT WELLS IN Y FIELD, NAM CON SON BASIN

1.1 Petroleum geology and temperature of Y field, Nam Con Son Basin

1.1.1 Petroleum Geology

The Nam Con Son Basin is situated within 6deg6’- 9deg45’ and 106deg0’ – 109deg30’E Its southern and southeastern boundaries are in the Vietnamese waters which border the neighboring countries, and its eastern, northern and western boundaries are on the Vietnamese continental shelf All geological formations in Nam Con Son Basin can be divided into two complexes of major structural elements, the basement composed of Pre-Cenozoic strata and the cover composed of Cenozoic sediments Good source rock sequences are developed in Oligocene lacustrine claystone and in Miocene fine grained clastic

Figure 1.1: Y field at Nam Con Son Basin

Figure 1.2 Play types of Nam Con Son Basin [20]

1.1.2 Temperature & Pressure

The fact that high temperature and high pressure appeared at well X, true vertical depth is 3,740 meters, bottom hole pressure (BHT) is 172degreeC and Reservoir pressure is 74MPa; and at another well X1, true vertical depth is 4,548 meters, BHT

is 210degreeC and Reservoir pressure is 91MPa [8,9] are research target of this thesis

Figure 1.3 Temperature and Pressure vs True Vertical Depth in NSC Basin [7]

Figure 1.4 Matrix of High Pressure High Temperature Operation [1]

Figure 1.5 HPHT Tiers, Courtesy of Baker Hughes 2005 [1]

Figure 1.6 HPHT Tiers, Courtesy of Schlumberger, 2008 [1]

Figure 1.7 HPHT Tiers, Courtesy of Halliburton, 2012 [1]

Figure 1.8 Temperature and Pressure map at Nam Con Son Basin [19]

Figure 1.9 Pressure profile at block 04, 05 Nam Con Son Basin [19]

Figure 1.10 Temperature profile at block 04, 05 Nam Con Son Basin [19]

1.2 Information about cementing for HPHT wells in Nam Con Son Basin [19]

According to consolidated information from drilling programs and/or well information including cementing programs and cementing evaluation reports

Below is the results of the cementing process for high pressure, high temperature (HPHT) wells in the Nam Con Son basin, for the purpose of evaluating the success rate, geological and operation challenges and lessons learnt in order to propose solutions and techniques to improve the quality of future drilling and cementing for high pressure, high temperature wells in the Nam Con Son basin A number of oil companies have drilled in this area over the periods such as ONGC, BP, Shell, BG, Petrocanada and BHP…

No Well name Water depth (HPHT) (m)

Table 1.1 Wells at Nam Con Son Basin with water depth of HPHT

Nowsco, Dowell/Schlumberger, BJ Halliburton are the 4 cement service providers for the wells in Nam Con Son Basin Class G cement and some additives were used such as silicate, retarder, fluid loss additive, weighting agent… Cement density is 1.75 – 2.22s.g, bottom hole temperature is 130-155degC and apply one or two stages cementing

Block Casing TOC (m) Cement density

Lead (ppg)

Cement density Tail (ppg)

20” 167 m –

Seabed

12,5 - 12,9 15,74 - 15,9

Extended + R- 15LS + FL9LS

7” 29450 -

4155 m

14,5 - 16 16 – 17

Halad, SCR- 110L, HR- 25L…

Table 1.2 Technical design and technology of cementing wells in block 04 & 05 Nam Con Son Basin

Well name Service

Well name Casing Cement Slurry design

35 GPS+D080/0,5GPS+D109/0.16GPS+ 25r/0.23gps

HL-Table 1.4 Slurry Design applied for HPHT wells in Nam Con Son Basin

Complex geology in Nam Con Son basin, especially Miocene area with abnormal temperature and pressure has incurred serious failure during cementing operation Some failures such as Cementing stuck in 13 3/8” casing, loss circulation, cement set in casing 2.097 – 2.882 m due to pressure affects cement slurry, reduce its

thickening time The cement set quicker than expected and causes loss circulation or Cement failure in 7 5/8” casing, unable to displace cement to annulus so it’s set in casing at 1.743 – 4.510 m due to unable to mill out the plug and the valve was stuck [19]

CHAPTER 2: CEMENT IN CONVENTIONAL AND HIGH TEMPERATURE HIGH PRESSURE ENVIRONMENT

2.1 Basic Cements

Portland cements are used for well cementing throughout the world They are manufactured by combining limestone (calcium carbonate) and clay (silicon oxides + aluminum oxides + iron oxides) in about a 2:1 ratio then heating to a temperature

of 2,600degF to 3,000degF The mixture is heated to initiate chemical reactions between the limestone and clay Several products from as a result of these reactions and the combined mixture of these products is called cement clinker The cement typically encountered is in power form It is made by pulverizing and grinding the clinker

The limestone/clay reactions lead to the formation of four different products that comprise four distinct crystalline phases: alite, belite, aluminate, and ferrite The alite phase is composed primarily of tricalcium silicate (C3S) and it makes up 50-70% of typical cement clinker Belite consists of primarily of tricalcium aluminate and tetracalcium aluminoferite and typically constitute 5 to 10% and 1-15% of a clinder, respectively In addition to the four major clinker produces, gypsum can be ground with the clinker to control the rate of setting, and CaSO4, MgO, Na2O, K2O, and other oxide impurities can be present in varying quantities, depending on the composition of the raw materials (limestone and gray) Used for clinder manufacture Each of the cement constituents participate in dry ration reactions in the present of water, but the rate of hydration can differ for each constituent For example, C3A hydrates much more rapidly than other cement components, and C2S hydrates at a much slower rate than C3S In general the relative hydration rate follows the sequence: C3A>C3S>C4AF>C2S The overall hydration rate for a cement depends

on the relative quantities of each of the cement constituents The development of compressive strength is primarily dictated by the two major cement components, C3S and C2S C3S is the constituent primarily responsible for the development of early (1-28days) compressive strength, while C2S is responsible for the development of

later (28+days) compressive strength The diffraction rate for a cement is also highly dependent on the cement particle size (controlled during the process of grinding the clinder) and the temperature experienced by slurry during setting It is possible to control the hydration rate, to some degree, by using accelerating and retarding additives

The hydration of cement is an exothermic process (i.e.: heat is liverated during the reactions) and each of the cement components has a characteristic heat of hydration that contributes to the overall heat of hydration depends on the relative quantities of each of the constituents in the cement The relative heat of hydration follows the sequence: C3A>C4AF>C3S>C2S Therefore, a cement with high proportion of the aluminate and ferrite phases is expected to generate a great deal of heat on hydration

In practice, however, it is more important to know the expected temperature increase within cement slurry rather than the total amount of heat liberated on hydration In general, the rise in temperature with the cement slurry with increase with increasing section thickness and increasing quantities of hydration accelerators Therefore, cementing narrow sections (e.g., slim holes) with retarded slurries should minimize the temperature increase caused by hydration Cementing wide sections with accelated slurries can require additional steps (e.g., adding pozzolaniz materials to the slurry) to prevent excessive heat up of the slurry during setting

The different classes of cement used in well cementing are as below:

Class A Cement

The product is obtained by grading Portland cement clinker, consisting essentially of hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an interground addition At the option of the manufacture, processing additions can be sued to manufacture the cement if such materials in the amounts used meet the requirements of ASTM C 465 This product can be used when special properties are not required It is only available in ordinary (O) grade (similar to ASTM C 150, Type I)

Class B Cement

The product is obtained by grinding Portland cement clinder, consisting essentially

of hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an interground addition At the option of the manufacture, processing additions can be used to manufacture the cement of such materials in the amounts used meet the requirements of ASTM C 465 This product can be used with conditions require moderate or high sulfate resistance It is available in both moderate (MSR) and high sulfate-resistant (HSR) grades (similar to ASTM C 150, Type II)

Class C Cement

The product is obtained by grading Portland cement clinder, consisting of hydraulic calcium sulfate as an interground addition At the option of the manufacture, processing additions can be used to manufacture the cement if such materials in the amounts used meet the requirement of ASTM C 465 This product can be used when conditions require high, early strength It is available in ordinary (O), moderate sulfate-resistant (MSR) and high sulfate-resistant (HSR) grades (similar to ASTM C

150, Type III)

Class D Cement

The product is obtained by grading Portland cement clinder, consisting essentially of hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an inter ground addition At the option of the manufacture the cement if such materials in the amounts used meet the requirement of ASTM C 465 Further at the option of the manufacturer, suitable set-modifying agents can be interground or blended during manufacture This product can be used in conditions of moderately high temperatures and pressures It is available in moderate sulfate-resistant (MSR) and high sulfate-resistant (HSR) grades

Class E Cement

The product is obtained by grinding Portland cement clinker, consisting essentially

of hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an interground addition At the option of the manufacturer, processing additions can be used to manufacture the cement if such materials in the amounts used meet the requirements of ASTM C465 Further, at the option of the manufacturer suitable set-modifying agents can be interground or blended during manufacture This product can be used in conditions of high temperatures and pressures It is available

in moderate sulfate-resistant (MSR) and high sulfate-resistant (HSR) grades

Class F Cement

The product is obtained by grinding Portland cement clinker, consisting essentially

of hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an interground addition At the option of the manufacturer, processing additions can be used to manufacture the cement if such materials in the amounts used meet the requirements of ASTM C 465 Further, at the option of the manufacturer, suitable set-modifying agents can be interground or blended during manufacture This product can be used in conditions of extremely high temperatures and pressures It is available in moderate sulfate-resistant and high sulfate-resistant grade

Class G Cement

The product is obtained by grinding Portland cement clinker, consisting essentially

of hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an interground addition Only calcium sulfate, water, or both can be interground or blended with clinker during the manufacture of Class G well cement This product can be used as a basic well cement It is available in moderate sulfate-resistant and high sulfate-resistant grades

Class H Cement

The product is obtained by gridding Portland cement clinder, consisting essentially

of Hydraulic calcium silicates which usually contain one or more forms of calcium sulfate as an interground addition Only calcium silicates which usually contain one

or more forms of calcium sulfate as an interground addition Only calcium sulfate, water, or both can be interground or blended with the clinder during the manufacture

of Class H well cement This product can be used as a basic well cement It is available in moderate sulfate-resistant and high sulfate-resistant grades

In the United States, the primary cements used for well cementing are Class A, B, C,

G and H In other countries, the primary cement used in the well cementing is Class

A or G

In most other countries of the world outside US, service company use the API nomenclature for well cement descriptions as customer normally wants a cement that meets all API specifications, the cement manufacturer will furnish a quality control sheet providing the testing information for that batch of cement For the specification testing purposes, the water requirements for the different classes of cement primarily used in well cementing are detailed in Table 2.1

Water requirements for Different Classes of Cement

Cement Classes Water % of Weight of

Cement

Calculated water (gal/sk)

For basic cementing, the high yield (in terms of cubic meter of slurry per sack of cement) makes cement the lowest cost slurry we can mize at typical density required for riserless cementing

If circulating cement is the only concern for a specific well, the slurry design does not need to be < 11.5 lb/gal, and delayed initial set is not an issue, then a basic cement

is a good solution for the casing string

However, the extra water makes it less capable of withstanding high stresses and other complications as it may not be able to prevent cement sheath damage or address other specialty issues

2.2 High Temperature Cements [20]

Cements for high-pressure/high-temperature applications should be good quality API Class G or H cements These cements are obtained by grinding Portland cement clinker, consisting essentially of hydraulic calcium silicates that usually contain one

or more forms of calcium sulfate as an interground addition Only calcium sulfate, water, or both can be interground or blended with clinker during the manufacture of Class G or H well cement This product can be used as a basic well cement It is available in moderate sulfate-resistant (MSR) and high sulfate-resistant (HSR) grades Portland cement is manufactured by combining limestone (calcium carbonate) and clay (silicon oxides + aluminum oxides + iron oxides) in a 2:1 ratio and then heating the mixture to a temperature of 2,600°F to 3,000°F The mixture is heated to initiate chemical reactions, and the combined mixture of these products is called cement clinker Cement is made by pulverizing and grinding the clinker Elevated temperatures and pressures can greatly accelerate the hydration rates or thickening and setting times of the cement Certain chemical parameters become critical in the performance of the cement at elevated temperatures The levels of aluminate (C3A) should be fairly low (generally below API requirements) since C3A hydrates rapidly The free lime should be kept below 0.5% (0.3% or less is even better

in most cases) Free lime or calcium oxide is the most rapidly hydrating component

in cement and can be responsible for premature gelation and ineffective retarder responses Gypsum levels normally should be around 3to 4%, and bass onite (plaster

of paris form of CaSO4) should be less than 1%because it may cause gelation Tricalcium silicate (C3S) should be in the medium range as recommended by API Specification 10A Hydration of the C3S is the main reason for early thickening and strength development of the hydrating cement Dicalcium silicate (C2S) is responsible for the final stage of cement hydration and gives the cement its final

“kick” in high strength development API does not require C2S, but good strength cements should have 15 to20% C2S for optimum strength development The grind or fineness of the cement is important and can become a critical factor in the performance of the cement as it hydrates under elevated temperatures and pressures General data for fineness usually is given as a measurement of specific surface or surface area These numbers are good guidelines but do not always reveal the true nature of the cement grind A particle size distribution analysis or a sieve analysis can determine the actual amount of fines and coarse particles in the cement Excessive fines may cause premature thickening, water requirement changes, etc Excessive coarse particles may cause the opposite effect Sometimes these two parameters may “average out,” and the fineness data may look normal Blaine fineness values normally fall around 2,700 to 3,300cm2/g Sieve analysis of suitable Class G or H are generally 78 to 85% passing through a 325 mesh sieve Slurry consistency from batch to batch can minimize lab time, physical testing, and design changes Cement suppliers should be encouraged to develop and produce good quality cement and to maintain consistent quality

high-Temperature in the range of 400degF to 500degF for deep oil and gas wells are not uncommon Geothermal wells with bottom hole temperatures ranging from 400degF

to 750degF producing flashing brine are frequently encountered Cement slurries used in these operations should remain competent at high temperatures and pressures for extended periods of time Set cement exposed to temperatures higher than 230degF gradually increase in permeability and decrease in strength Strength

retrogression can eventually produce inadequate pipe support, and increased permeability can result in the loss of zonal isolation

When Portland cement is mixed with water, tricalcium silicate (C3S) and dicalcium silicate (C2S) hydrate to form calcium silicate hydrate (C-S-H) gel and hydrated lime (Ca(OH)2)2 At temperatures higher than 230degF, C-S-H gel converts to α-dicalcium silicate hydrate (α-C2SH) Conversion to the α-C2SH phase results in the loss of compressive strength and an increase in permeability Conversion of C-S-H gel to α-C2SH at 230degF and higher can be prevented by adding crystalline silica (fine sand, SSA-1, or coarse sand, SSA-2) The concentration of crystalline silica varies from 35 to 70%, depending on bottom hole static temperature and water content of the slurry Recent work has shown silica flour (SSA-1) provides maximum benefit for temperatures ranging from 230° to 440°F For conditions where density is critical, coarse grade sand (SSA-2) is preferred for a densified slurry The reaction between SSA-2 and cement takes place slower than the reaction between SSA-1 and cement.4The conversion to a-CaSH at 230°F can be pre-vented by adding either SSA-

1 or SSA-2 AddingSSA-1 or SSA-2 increases the molar ratio of CaO/SiO2 to one or less, resulting in crystalline to bermorite formation Formation of the to bermorite phase prevents strength retrogression and permeability increase At temperatures higher than 300°F, to bermorite converts primarily to xonolite At 480°F, truscotlite begins to appear Above 750°F, xonolite and truscotlite reach the limit of their stability At higher temperatures, crystalline phase’s xonolite and truscotlite dehydrate, resulting in the breakdown of the set cement To achieve maximum strength and minimum permeability at high temperatures, a CaO/SiO2 ratio of one or less should be maintained

Other components of cement - Cement Additives

Cement additives have been developed to allow the use of Portland cement in many different oil and gas well applications Cement additive development has been ongoing for decades These additives make obtaining required performance properties relatively easy