industrial training experience(well cementing)

7/30/2019 Industrial Training Experience(Well Cementing)

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CHAPTER ONE

1.0IntroductionIn our society today, there is an obvious gap between the academia and the industry and this

leads to Universities producing what employers refer to as half-baked graduates. There is no

bridge between the theory that a student learns in the classroom and the industry which he

aspires to belong to, as a result he has no hands on skill, no practical knowledge on how to apply

what he has learnt and no true knowledge of how the industry works. This leads to a reduced

efficiency and productivity from him which is the exact opposite of what an employer expects to

get from an employee. As a result, the Federal Government deemed it fit to create theIndustrial

Training Fund (ITF), an agency charged with the responsibility of bridging that gap.

The ITF in turn introduced the Students Industrial Work Experience Scheme (SIWES)

commonly referred to as the Industrial Training program. A program that not only exposes

students to the industry so as to gain some practical experience before graduation but also serves

as an opportunity to learn about workplace ethics, safety standards of the industry, interpersonal

relationship between colleagues, team work but to mention a few. It also gives the student an

opportunity to create a link/network with professionals to further ease his search when he

graduates. The program was introduced in 1973 with its primary focus being technical

disciplines such as engineering, agriculture, some science courses, fine arts and so on with the

duration of the training program ranging from six months to one year depending on the

institution i.e. polytechnic or university.

Though the scheme has undergone some challenges such as funding, supervising, lack of

cooperation from some companies, its primary aim still remains to harmonize the theoretical

knowledge gained from the University with the actual industrial practice thereby creating better

prepared graduates. Also since the training exposes the student to the challenges faced in the

industries he is in a better position to apply all that knowledge to create solutions to the problems

leading to more practicable innovations and in the long run more technological advances in the

nation.


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1.1 History of Baker Hughes Incorporated

Baker Hughes Incorporated is the product of the 1987 merger of two oilfield-services companies

with surprisingly similar histories, Baker Oil Tools and Hughes Tool Company. Both were

founded shortly before World War I by aggressive entrepreneurs who won valuable patents. Both

embarked on massive worldwide expansion and diversification projects. Baker and Hughes

became public companies within ten years of each other. The two rivals experienced the

fluctuations of an unpredictable world oil market jarred by political and economic events.

Finally, the companies suffered financial slumps in the lean years of the 1980s, leading to their

turbulent but successful consolidation and the name Baker Hughes Incorporated. Since then, BHI

has acquired and assimilated numerous oilfield pioneers that have developed and introduced

technology to serve the petroleum service industry. They include Brown oil tools; Elder and

Elder oil tools (completions); Milchem and Newpark (drilling fluids); Exlog (well logging);

Eastman, Christensen and Drilex (directional drilling diamond drillbits); Teleco (measurement

while drilling); Tri-state and Wilson (fishing tools and services); Aquaness, Chemlink and

Petrolite(specialty chemicals), Western Atlas (seismic exploration, well logging); BJ Services

Company (pressure pumping). Some acquisitions date back to the early nineteenth century and

some are relatively more recent though most of the companies have a combined history dating

back to the 1900s.

Baker Hughes is one of the world's largest oilfield services companies. It operates in over 80

countries and employs over 58,000-plus employees, in fact it was one of the first oil servicing

companies to take residence in Ghana after its discovery of oil in 2008. Baker Hughes Inc. has its

headquarters in the America Tower in the America General, Neartown. Houston. It operates

world-wide with major offices in Liverpool, United Kingdom, Singapore and Dubai, research

and maintenance facilities in Celle, Germany, Lafayette, Louisiana, Houston, Texas, Pescara,

Kuala lumpur, and Malaysia. The company is administered in two hemispheres, the eastern

hemisphere with five Regions (Europe, Africa, Middle East, Asia, Pacific and Russia) and the

Western hemisphere with four Regions (Canada, US Land, US Gulf, and Latin America. These

regions are further divided into about nineteen geo-markets to help understand and cater for

location specific needs and further increase efficiency and productivity.


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Baker Hughes offers a wide variety of oilfield services including drilling and evaluation,

completions and production, pressure pumping, reservoir development, drilling fluids, integrated

operations, tubular services, process and pipeline services, mud logging, chemical and industrial

services, specialty chemicals and so on. BHI is one of the world leaders in the field of oilfield

servicing. This is not unconnected to the fact that they work to lower costs, reduce HS&E and

economic risk, improve productivity, and increase ultimate recovery for their clients. Major

competitors are Schlumberger Limited, Halliburton Company, Smith International, Inc.,

Weatherford International Ltd., Precision Drilling Corporation, Veritas DGC Inc. etc. Of course

the indigenous companies are not lagging behind especially with the increased demand for local

content; companies such as Geoplex, Greatwall Nig Ltd.

BJ Services is a subsidiary of Baker Hughes that provides pressure pumping services for the

petroleum industry; it is one of the more recent acquisitions of Baker Hughes. Pressure pumping

services consist of cementing and stimulation services used in the completion of new oil and

natural gas wells and in remedial work on existing wells, both onshore and offshore. Oilfield

services include casing and tubular services, coiled tubing services, sand control services, water

management, production chemical services, and pre commissioning, maintenance and turnaround

services in the pipeline and process business, including pipeline inspection. It is no doubt an

invaluable addition to the Baker Hughes family.


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1.2 Companys Organizational Chart

VICE

PRESIDENT:

TAX

VICE

PRESIDENT&

TREASURER

VICE

PRESIDENT&

CONTROLLER

VP: CORPORATE

DEVELOPMENT

VP: INTERNAL

AUDIT

VP: INVESTOR

RELATIONS

VICE

PRESIDENT:

SALES AND

MARKETING,

AMERICAS

VICE

PRESIDENT:

CENTRILIFT

VP: BAKER

PETROLITE

PRESIDENT:

BAKER ATLAS

PRESIDENT:

HUGHES

CHRISTENSEN

PRESIDENT:BAKER HUGHES

DRILLING

FLUIDS

CHIEF

INFORMATION

OFFICER

PRESIDENT:

GLOBALPRODUCTS AND

SERVICES

VP: GROUPPRESIDENT D&E

SVP&CHIEFFINANCIAL OFFICER

PRESIDENT ANDCEO

BOARD OF DIRECTORS

13 DIRECTORS INCLUDING COB

CHAIRMAN OF THE

BOARD

SVP&GENERALCOUNSEL

CORPORATE

SECETARY

VP: CHIEF

COMPLIANCE

OFFICEER

PRESIDENT:

BAKER OIL

TOOLS

VICE

PRESIDENT:

HUMAN

RESOURCES

VICE

PRESIDENT: BJ

SERVICES

(PRESSURE

PUMPING)

CEMENTINGLABORATORY

CEMENTINGCOILEDTUBING


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1.3 Various Departments and their functions

Baker Hughes Inc. is a very large company that cuts across nations, provides employment for

millions and provides basically all the oilfield products and services ranging from drilling to

completions and production. As a result, it requires a lot of departments in order to run

efficiently and keep its standards of service; these departments include

1. Administration Department

The role of this department is to process and properly file all documents for the rest of the

company for future purposes. They are also responsible for looking after the internal

communications.

2. Legal Department

They handle legal issues which may come up in the course of business and offer legal advice on

issues pertaining to the company. They also organize trainings and provide employee manuals so

as to reduce the risk of potential suits. It consists of qualified lawyers and their legal assistants.

3. Human Resource Department

This department deals with the management of people within the company. It is responsible for

hiring staff, monitoring them and in necessary cases, firing staff. It is also responsible for

enforcing company policies. It consists of the human resource manager and his assistants

4. Accounting Department

This department is charged with the responsibility of looking after the finances of the company.

They control money inflow and outflow. They also recommend budgets and estimates to the

company. It consists of a team of qualified accountants.

5. Health, Safety and Environmental (HS&E) Department

Their job is to ensure and enforce safety compliance in all activities performed in the company.

This includes safety to human life, company property and the environment. They organize

monthly meetings& trainings. It consists of the safety manager and his assistants.


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6. Quality Assurance/ Quality Control Department

This department is in charge of ensuring that products and practices meet up with the accepted

industry standards. They organize trainings for employees from time to time. It consists of the

quality control officer.

7. Engineering Department

This department consists of the field engineers and the technical support engineers. Their

responsibilities include preparing the design of jobs and going to the field to implement them.

They are engaged in onshore and offshore rig work. Vital to this department is the laboratory as

they run tests prior to the actual job to ensure accurate results on the field. In the pressure

pumping base, the engineering department consists of the cementing engineers, coiled tubing

engineers, engineering trainees and the laboratory technicians.

8. Operations Department

Members of this department are mostly involved in actual operations of the tools on the field and

in warehouse activities. They are most times at the field running jobs awarded to the company. It

consists of field specialists, operators and trainee engineers.

9. Maintenance Department

They are responsible for maintenance of tools and equipment on and off the base. They are also

charged with the maintenance of every asset of the company. It consists of the maintenance

manager and his team.

10. Research and development Department

Members of this department are charged with innovation of new ideas practicable in the oil and

gas industry. The industry is a very dynamic one and as such companies that hope to stay in the

game must continually research to develop new technology. It consists of the RDD technologists.

11. Security Department

As the name implies, they are in charge of securing all company staff and property.


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CHAPTER TWO

2.0Introduction to CementingThe process of drilling a well in order to produce oil and gas is a very delicate one that involves

many different operations; each vital in its own unique way, each key to the overall process,

every one of them coming together like a jigsaw puzzle to form a perfect picture. Cementing is

one of such processes; it involves pumping liquid cement slurry into the annulus between the

casing and the wellbore using surface and subsurface equipment and allowing it some time to

harden and attain sufficient compressive strength. This operation is vital to the overall well

completion because it effectively seals the annulus between the casing string and the drilled hole

thereby providing zonal isolation i.e. to exclude fluids (say oil, gas or water) in one zone from

fluids in another zone. It also aids in corrosion control and stabilizes the formation and

improves pipe strength, as a result if a good cement bond is not attained, further drilling is not

possible until the error has been rectified. This operation is done after running in the casing and

afterwards, a Cement Bond Log (CBL) is run to evaluate the job and check for channeling;

drilling commences immediately or in the case of production casing, completion begins.

After drilling the well to its desired depth, the drill pipe is pulled out and a bigger pipe called

casing is run into the well. This poses a challenge of how to hold the casing string to the

wellbore; then comes the cement. Since there is still drilling mud in the well, a spacer i.e. a fluid

compatible with both cement and mud is circulated into the hole after which the cement is then

pumped in, a displacement fluid typically follows the cement. The spacer serves to prevent

contamination of the cement by the mud or vice versa as they are incompatible. Once there is an

indication at the surface that all the cement slurry has entered the annulus, the well is shut in for

some time to allow the cement to harden. A number of equipment are used in this process such

as the top and bottom plugs, float collar, guide shoe, centralizer ,pumps, jet mixers, batch mixers

and so on. The cement slurry used is a mixture of cement, water and additives and its properties

and behavior depends on the additives used. Most cement used in the industry are a type of

Portland cement and though they are of different classes, class G is most commonly used. The

process of cementing is largely dependent on time as wrong timing could lead to flash setting

and NPT or recirculating out of hole in cases of cement not setting and NPT.


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2.1 Types of Cementing

There are two major types of cementing. They are:

1. Primary CementingPrimary Cementing is the introduction or placement of a cement sheath in the annulus between a

casing and an open hole or between a casing and a previous casing. It is done on the different

casing typessurface, intermediate, production, liner for slightly varying reasons but generally,

it is done to provide zonal isolation, protect and support the casing and serve as a support for the

borehole.

Typically a single slurry designed to specification is used for primary cementing but at times, as

a cost saving technique the lead and tail cement slurry is used.

Lead Cementing

A Lead cement slurry is so called because it is the initial slurry pumped through the casing. It

falls at the top of the annulus. It is usually a low quality and low density slurry. Also it has a low

cement to water ratio. Extenders are added to lead cement to aid in gelling and increase their

yield i.e. increasing the depth of casing with which a limited amount of slurry can be used. It is

most times used to decrease cost while still achieving the intended objective.

Tail Cementing

A tail slurry is the slurry pumped after the lead, thus it ends up cementing the bottom part of the

annulus around the casing shoe. This part of the casing requires a firm bonding with the

formation, and thus the quality of slurry used is usually high. The tail slurry is usually of higher

quality and higher density than the lead slurry and has a high cement to water ratio. Extenders

are rarely used with tail slurries as there is really no use.

The truth is every cementing engineer hopes to do the primary cementing once and get it right

because if not he has to spend more money and incur more downtime or Non Productive Time

(NPT) trying to solve the problem. This brings about the second type of cementing.


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2. Secondary CementingThis includes

i. Remedial/Squeeze Cementing

As the name implies, the remedial cementing commonly is done to rectify errors from the

primary cementing. After primary cementing, a Cement Bond Log (CBL) is usually done to

evaluate cement bonding and to check for channels in the cement. If it is found that a section of

the well is not well cemented, a squeeze cementing job is carried out. This is done by squeezing

cement slurry under pressure through perforations made in the casing at the exact problem

spot/hollow section.

ii.

Plug Cementing

Plug cementing is the general term for all the cementing processes that require sealing/ plugging

the actual wellbore. Plug cementing is of various types depending on the reason for plugging;

Plug and Abandon

This is done for two main reasons. Either because a new well is found to be unproductive or

because a producing well has been depleted sufficiently and is now deemed unproductive. Either

ways, the specified length of slurry is pumped in at different intervals to effectively block the

well.

Plug Kick-off / Side-track

This is also done for two main reasons. Either in directional wells to serve as kick off point for

deviation or in a case where the original well path of a vertical well can no longer be accessed

due to certain problems in the hole like stuck pipe, salt dome and so on and the obstruction must

be bypassed, it serves as a kick off point for the sidetrack.

iii. Top up cementing

This is done when the slurry pumped into well stops a few feet short of the desired depth due to

unforeseen circumstances. In this case, more cement is mixed and poured directly into the

annulus to top up the cementing.


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2.3 Cement testing

Prior to the actual cementing job, laboratory pilot tests are carried out with representative

samples of the actual field productscement, water, additives and under simulated conditions of

temperature and pressure. This is to predict accurately the performance and behavior of the

slurry to be used on the field since cementing is not an exact science; it serves as a quality

assurance, assuring clients that the job will be done accurately barring any complications. Actual

field samples are used because cementing is a very delicate process and any slight change in

composition of say cement, water or additive could drastically affect the expected results leading

to downtime or in extreme cases total loss of casing due to flash setting. Laboratory tests are run

according to API specifications.

2.3.1 Cement Additives

In the course of drilling, different types of formations are encountered, these formations come

with their unique set of conditions; some may be a gas zone prone to gas migration or a lost

circulation zone or an over pressured zone or a number of other different conditions that could

exist particular to a well. Whatever the case, the cement slurry needs to be designed to

accommodate the wide range of conditions that occur in the wellbore. Cement additives are

added to the Portland cement to modify or enhance the behavior of the cement system. They

ideally allow successful slurry placement between the casing and the formation, rapid

compressive strength development and adequate zonal isolation during the lifetime of the well.

They are available in both liquid and solid forms though most times, liquid additives are

preferred. Though each additive has a primary effect on the slurry i.e. it modifies one aspect of

the cement slurry, it hasother effects called secondary effect which could either be helpful

orvery unhelpful to the overall picture. At any rate, they must be taken into account when

designing the slurry. Another phenomenon which can and does further complicate the picture is

that ofsynergistic effects which is a change in the slurry which results when two additives are in

the slurry together, but which will not result from either additive being in the slurry by itself.

Other synergisms also occur with more than two additives. There a great number of cement

additives typically used in cement slurry design, they include:

i. Accelerators


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ii. Retarders

iii. Foam Preventers

iv. Extenders

v. Weighing agents

vi. Dispersants

vii. Fluid Loss control agents

viii. Bonding Agents

ix. Lost Circulation Materials

x. Strength Retrogression Materials

xi. Multipurpose Additives

Others include additives used in specialty cement systems like thixotropicsystems, retarded

liquid cement, freeze protected cement etc.

i. AcceleratorsAccelerators are added to cement slurries to shorten the setting time and increase early

compressive strength development so as to decrease the waiting on cement (WOC) time.

Typically inorganic salts are used; these include chlorides, carbonates, silicates, sulphates, etc.

however, chlorides are especially preferred because they produce the highest accelerating power.

Chlorides used include CaCl2, KCl, NaCl etc. All chlorides are added to the cement slurry by

weight of cement (BWOC) with the exception of Sodium and Potassium Chloride which are

added by weight of water (BWOW).

Calcium chloride is undoubtedly the most efficient andeconomical of all accelerators;

regardless of concentration, it always acts as an accelerator. It is normally added at

concentrations of1% to 4%BWOC. Its secondary effect is that it causes excess heat and could

increase slurry viscosity. Also, results are unpredictable at concentrations exceeding 6% BWOC

and premature setting may occur. Its effectiveness reduces in the presence of fluid loss additives.

It is compatible with all cement additives.

Sodium chloride affects cement slurry in different ways depending upon its concentration. It

acts as an accelerator at concentrations up to 10% BWOW, remains neutral at 10% to 18%

BWOW, and at concentrations above 18% BWOW causes retardation. Its side effects are that it


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causes foaming and reduces slurry viscosity. Also it acts as a mild dispersant at all

concentrations. It is used for cementing across salt zones or salt domes. Sodium chloride is not a

very efficient accelerator, and is used only when calcium chloride is not available at the well site.

Potassium chloride acts similar to NaCl but stabilizes shale or clay containing formations. Its

effective concentration is 5% BWOW. Though an acceptable accelerator especially in fresh

water zones, it is quite expensive and as such is rarely used.

ii. RetardersRetarders are cement additives used to extend/increase the setting time of cement. There are

many materials that could serve this purpose but due to their limitations, they are rarely used. As

a result there are only a relatively few chemicals which are actually used as retarders. These

include:

Lignosulfonates: These are polymers derived from wood pulp. They contain varying amounts of

saccharine compound (sucrose). They are the most commonly used retarders in oil well

cementing. Typically, the sodium and calcium salts are used. They are effective with all Portland

cements and are generally added in concentrations ranging from 0.1% to 1.5% BWOC.

Depending on a number of conditions, they are effective to about 250F (122C) BHCT. Their

effective temperature is increased when they are blended with sodium borate (borax). Their most

common side effect is the thinning or dispersing effect which they have on cement slurries.

Other retarders include sugars, organophosphates, inorganic compounds (NaCl, ZnO etc.), and

cellulosederivatives. It is important to note that each retarder is generally either a low

temperature or a high temperature retarder and this must be put into consideration in cement

slurry design to achieve good results.

iii. Foam preventersMany cement additives can cause slurry to foam during mixing coupled with the high rate of

shearing. Excessive slurry foaming can have several undesirable consequences one of which is

entrainment of air. Entrained air could result in higher than desired slurry density and on

hardening of cement, could lead to channeling. Foam preventers are used to prevent all these;

they work by lowering the surface and interfacial tension between the cement particles. In well

cementing two classes of antifoam agents are commonly used: polyglycol ethers and silicones.


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Very small concentrations are necessary to achieve adequate foam prevention, usually less than

0.1% BWOW.Poly (propylene glycol) is most frequently used because of its lower cost, and is

effective in most situations; however, it must be present in the system before mixing. Silicones

on the other hand will defeat a foam regardless of when they are added to the system. Foam

preventers are added to all cement slurries and do not affect the chemical behavior of the slurry.

iv. ExtendersCement extenders are used to accomplish two purposesto reduce slurry density and to increase

slurry yield while still maintaining slurry integrity. A reduction of slurry density reduces the

hydrostatic pressure during cementing; this helps to prevent induced lost circulation in case of

weak formations with low fracture gradient. They increase yield by reducing the amount of

cement required to produce a given volume of set product. This results in greater economy.

Different extenders use different mechanisms to achieve their purpose, these include water

extending and use of low density aggregates. Commonly used extenders include

Clays

This refers to materials composed chiefly of clay minerals. Two types of clays are majorly used

in oil well cementing: attapulgite (also known as salt gel) and bentonite. Bentonite, commonly

referred to as gel is the most frequently used clay-based extender in the industry. It contains 85%

of the clay mineral smectite (also called montmorillonite). It works using the water extending

mechanism where excess water is added to the cement. When placed in water, it absorbs the

water and expands several times its original volume resulting in higher fluid viscosity, gel

strength, and solids suspending ability. It tends to improve fluid loss but at high concentrations

may slightly reduce the compressive strength development. Free water or settling is rarely

experienced when bentonite is in use. It can be added in concentrations up to 20% but is most

effective at concentrations ranging from 2-8%. It is majorly used with fresh water slurries as its

effectiveness reduces in the presence of salts; this is because salt inhibits its hydration and as

such reduces slurry yield. It remains very effective at elevated temperature. It can be dry blended

with dry cement but it is generally preferred that it be pre-hydrated in water prior to usage. A

slurry containing 2% pre-hydrated bentonite is equivalent to one containing 8% dry-blended

bentonite. Complete hydration of a good quality bentonite (no beneficiating agents added) occurs

in about 30mins but when rheology is to be carried out, it is pre-hydrated for 2 hours. Bentonite

is majorly used in lead slurries where the cement to water ratio is low.


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Sodium Silicates

Silicates work using a different mechanism from that of clay extenders. They absorb the lime in

the cement forming a calcium silicate gel which provides sufficient viscosity to allow the

addition of excess water. They are available in both solid and liquid forms but in solid forms are

known as sodium metasilicate Na2SiO3, the liquid form is also known as water glass. Though

they are very effective extenders, they tend to slightly accelerate the setting time of the cement.

They lower compressive strengths somewhat, provide some thixotropic properties and aid in free

water control. They are majorly used in salt water slurries but in case of use with fresh water,

CaCl2 is added as an activator prior to use. Sodium silicate has a temperature limitation of

150 F.

Other extenders used include pozzolans (diatomaceous earth, fly ash), silica, commercial light

weight cements, light weight particles etc.

v. Weighing agentsThese are materials that are used to increase the density of cement slurries so as to maintain high

hydrostatic pressures. They are used in cases of high formation pressure, unstable wellbores and

deformable/plasticformations.They have little or no effect on thickening time and compressive

strength development. One method of increasing density is to reduce the amount of water used

but due to its limitations, is rarely used. Alternatively, materials with high specific gravities are

used to increase the slurry density. To be acceptable as a weighting agent, such materials must

meet the following criteria.

The particle-size distribution must be compatible with the cement.

The water requirement must be low.

The material must be inert with respect to cement hydration, and compatible with other

cement additives.

Materials used include Barite, Hematite, Ilmenite, Manganese Oxide, and sand among others.

The most widely used weighing agent worldwide is Hematite; this is probably due to its

effectiveness with all classes of cement, its fine sized particle distribution and its economic

value. Barite on the other hand, though commonly used due to its availability from mud jobs is

not as effective as the others; this is due to its additional water requirement.


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vi. DispersantsThey are added to cement slurry to reduce the viscosity of the slurry or to thin the slurry thereby

making it easier to pump (pumpable). The most common dispersants used are Sulfonates. Also

used are lignosulfonates though they cannot be used at low temperatures since they retard cement

systems. The side effect of dispersants is that they could cause free water, sedimentation and

segregation.

vii. Fluid loss control agentsFluid loss is a process whereby the aqueous phase (filtrate) of the slurry escapes into a permeable

formation. If fluid loss is not controlled, premature hydration or formation damage could occur

leading to job failure. As the volume of the aqueous phase decreases, the slurry density increases

and its properties i.e. rheology, thickening time, etc. deviate from that of the original design. If

sufficient fluid is lost to the formation, the slurry becomes unpumpable. To control the fluid loss,

fluid loss control agents are added to the slurry to obtain fluid loss rate less than 50mL/30min

required to maintain adequate slurry performance. Two principal classes of fluid loss additives

exist; the particulate materials and water soluble polymers such as HEC and CMHEC, liquid

latex is also used.

viii. Bonding agentsBonding agents are additives added to the cement slurry to increase the bonding of the cement

slurry to prevent gas intrusion. They also improve fluid loss. One of the materials used is

Styrene-Butadiene which is latex based.

ix. Lost Circulation Materials (LCM)Lost circulation is the loss of whole fluid to the formation; this is mostly due to problematic

formations like vuggy or cavernous formations and highly fractured incompetent formations.

Most times, these zones are noticed during drilling so the cementer is better prepared for it and

puts this into consideration in his design, hence he adds LCM to his design. Most materials used

are bridging materials (granules like gilsonites) which physically bridge over fractures and block

weak zones. Also used are the cellophane flakes which form a mat across the face of the fracture.

Another LCM commonly used is fibre which tends to block the fractures. Thixotropic cements


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which are cements that remain liquid while pumping but when no longer subjected to shear, gel

and become self-supporting are used in extreme cases.

x. Strength Retrogression materialsStrength retrogression is the term used to describe the breakdown of cements compressive

strength when the cement is exposed to excessive temperatures. At BHST of 230 degF or higher,

cement will over a period of time lose its compressive strength, become permeable and generally

be unable to support the casing, provide pressure back-up, or keep corrosive well fluids from

boring holes in the casing. This starts eight hours after the cement sets. While there is no way to

stop the process, or reverse it (other than by multiple remedial squeeze jobs), strength

retrogression can be prevented; this is done by adding strength retrogression materials to the

slurry. Materials used include Silica Flour or Coarse Silica. They are added to cement at

concentrations ranging from 40to 45% BWOC.

xi. Multipurpose additivesAs the name implies, these additives serve many purposes in the cement system; they do not only

perform one function. They could serve purposes ranging from accelerating to anti settling. They

are quite useful in cementing operations.

2.3.2 Cement testing equipment and methodology

To aid in the effective laboratory testing of cement prior to the actual cementing operation so as

to approach exactness and accuracy, API has approved a list of equipment and methodology

required to carry out these tests. This is in a bid to ensure reproducibility of results anywhere in

the world and to standardize the whole process of cement testing. The approved equipment

includes:

i.

Electronic balance

This equipment is used in accurately weighing samples used in the laboratory. According to API

standard, electronic balances should be accurate to 0.1% of indicated load.


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Methodology

1. The Container or syringe to be used in measuring is weighed and tarred/zeroed toeliminate its weight.

2. The sample is then measured and weighed as accurately as possible.Calibration Interval: at least annually.

ii. Constant Speed MixerThe Constant speed mixer is designed for precise mixing of cement slurry so as to attain a

homogenous mixture. It is capable of maintaining two known constant speeds.It has a variable

speed, mixingfrom 100 to 21,000 rpm with two preset constant speeds of 4,000 and 12,000 rpm,

as established by theAPI. It eliminates slurry property irregularities associated with shear; rate of

shear affects thickening time, fluid loss and free fluid of a cement slurry design. The instrument

features a digital tachometer that continuously indicates the mixing speed, a speed control for

setting the desired speed, and an electronic timer. It works with a 1 litre (I quart) blender cup

which is large enough to accommodate the API recommended 600ml laboratory sample.

Methodology:

1. After slurry design and accurate measurement of samples, the additives and cement are added

to the water with the blender maintaining a constant speed of 4000200rpm. The cement must be

added in not greater than 15secs.2. The slurry is then allowed to mix properly for 35 seconds using a constant speed of

12000500rpm.This is done to eliminate slurry irregularities associated with shear.

Fig 1: Constant Speed Mixer


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Note: The slurry is expected to be used within one minute of mixing according to API standards.

Calibration Interval: 6Months.

Precaution: The blade for the mixing cup should be weighed prior to use and replaced with an

unused blade when 10% weight loss has occurred. If leakage occurs during mixing, the slurry

should be discarded and the entire blender blade assembly should be replaced. The right

electrical rating should be used as directed by manufacturer.

iii. Atmospheric ConsistometerThe Atmospheric Consistometer is used to condition cement slurries to test temperature to enable

further testing. It uses its water bath in conditioning of slurries to any temperature from ambient

to 200F by rotating the slurry containers at 150 rpm while continuously shearing the slurry by

means of a paddle.

Methodology:

1. 470ml of the cement slurry is poured into the slurry cup and the paddle and potentiometerare fixed.

2. The slurry cup is placed in the water bath of the Consistometer. 3. The temperature panel is programmed to the required temperature and the heater is

switched on.

4. The motor is switched ONand left for 20 minutes.

Fig 2: Atmospheric Consistometer


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Calibration Interval:

Rotational speed 3 Months

Thermocouple 1 Month

iv. Rotational ViscometerThe Viscometeris used to determine the rheological properties of cement slurry. It is a rotational

direct reading viscometer. It consists of concentric cylinders; a rotational sleeve and bob. The

sleeve rotates at a constant velocity for each RPM setting. The slurry creates a frictional drag

between the sleeve and the bob which is connected to a torsion spring and a dial. The dial will

read out proportional to the drag experienced by the bob. The viscometer is capable of rotating at

speeds of 600, 300, 200, 100, 6 and 3 rpm though the 600rpm is not used in cement testing

because the high speed causes segregation in cement slurries.

Fig 3: Rotational Viscometer

Calibration interval: 3 Months for the springs and Rotational speed.

Precaution: The bob and sleeve must be checked for centralization before use. The rotor and

bob should be thoroughly cleaned after each test. Care should be taken to ensure that the bob

shaft does not become bent and that the rotor shaft assembly is not submerged in water. Water

may contaminate the bearings, causing excessive friction.

v. HPHT Filter PressThis device is designed to measure the rate at which water will be forced out of a static cement

slurry when it contacts a permeable formation. The test incorporates high pressure and specified


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filters to simulate the pressure drop caused by such a permeable formation. The cell consists of a

stainless steel cylinder with removable end caps, which are fitted with O-rings and pressure

valve stems. The cell has an opening at the top and bottom; the top opening is used to introduce

nitrogen while the filtrate passes through the bottom opening. A 60-mesh screen rests on the

bottom cap backing up the 325 mesh screen. The temperature is controlled by a thermostat in the

heating jacket, the temperature of the cement slurry is measured using a type J thermocouple

mounted in the wall of the Cell and this thermocouple mounted in the heating jacket measures

the temperature of the jacket. The test is run at 1000psi as specified by API.

Fig4: HPHT Filter Press Fig5: Double ended fluid loss cell

Calibration intervals:

Thermometer 1 month

Gauges 12 months.

Precaution: Nitrogen must be supplied in an approved nitrogen gas cylinder and secured to meet

safety standards. Due to the high temperature and pressures involved in this test, extreme care

must be exercised at all times. All safety precautions must be met, especially in the cell

breakdown procedure after the filtration procedure has been completed.

vi. HPHT ConsistometerThe Pressurized Consistometer is used to determine the thickening time of cement slurries in

strict compliance with API 10A and API RP-10B specifications. In addition, the unit can be used

to condition slurries for free water content, rheology, fluid loss, and various other tests. It


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consists of a rotating cylindrical slurry cup equipped with a stationary paddle assembly, all

enclosed in a pressure chamber. They are operated either by magnetic drive or by packings. Most

are capable of exposing cement slurries to a maximum temperature and pressure of 400Fand

25,000 psi (204C and 17.5 MPa); however, special units capable of 600F and 40,000 psi (3

15C and 280 MPa) are available for deep-well applications. Thermocouples are provided for

determining the temperature of the oil bath and the cement slurry. The slurry cup is rotated at a

constant speed of 150rpm. The consistency of the cement slurry is indicated and recorded as a

DC voltage obtained from a potentiometer mechanism mounted on the paddle shaft, which

contains a standardized torsion spring to resist the rotating tendency of the paddle. Operation of

the pressurized Consistometer is simple with all the operational controls conveniently located on

the front panel.

Calibration interval:

Rotational Speed: 3 months

Potentiometers: 1 month

Timer: 6 months

Thermocouples: 1 month

Fig6: Pressurized Consistometer

Precaution:Since high temperatures and pressures are used, one must ensure that all safety rules

are complied to avoid accidents.


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vii. Ultrasonic Cement AnalyzerThe Ultrasonic Cement Analyzer (UCA) is used to determine the compressive strength of cement

slurries under simulated well conditions. This instrument is designed to measure and record the

velocity of sonic waves through cement slurry as a function of time and to convert the

measurement via an algorithm to compressive strength. The UCA provides a continuous reading

from beginning to end of test and produces a graph to show the transition time from liquid to

hard set. It also plots out the transition time. It has a thermocouple to determine and record the

temperature and transducer to monitor the sound waves velocity. It is a nondestructive method of

testing the compressive strength of the slurry.

Fig7: Ultrasonic Cement Analyzer

Calibration interval: 12 months

vii. Pressurized balanceThe pressurized balance is used to measure the absolute density of a fluid sample. It consists of a

cup mounted on a ruler, a pressuring plunger, and a fulcrum or balance. Although the unit is

similar in operation to a conventional mud balance, pressure is introduced to the system so as to

eliminate entrained air. The standard scale density may be read directly in units of: lbs/gal,

lbs/cuft,sg, psi/1000ft.

Fig 8: Pressurized Mud Balance


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Methodology

1. Fill the sample cup to a level slightly below the upper edge of the cup (approx. inch).

2. Place the lid on the cup with the check valve in the down (open) position; push the lid

downward into the mouth of the cup until surface contact is made between the outer skirt

of the lid and the upper edge of the cup. Ensure that excess slurry is expelled through the

check valve.

3. Pull the check valve up in the closed position, rinse off the cup and threads with water,

and screw the threaded cap on the cup.

4. Fill the pressurizing plunger by submersing the nose of the assembly in the slurry with

the piston rod in the completely inward position. Draw the piston rod upward in order to

fill the plunger cylinder with slurry.

5. Push the nose of the plunger onto the mating O-ring surface of the check valve and apply

force to pressurize. Ensure that the check valve is in closed position.

6. Rinse the exterior of the cup and wipe properly.

7. Place the instrument on the knife-edge and move the sliding weight right or left until the

beam is balanced i.e. when the attached bubble is centered between the two scribed

marks.

8. Record the density of the slurry.

9.

Use the plunger to release the pressure when testing is complete.; ensure that the check

valve is open.

10. Empty the cup and plunger, and then clean thoroughly.

Calibration interval: 12 months

viii. Free Fluid Test ApparatusThe free water test is performed in a 250 ml glass graduated cylinder. A foam rubber pad is used

to minimize vibration of the cylinder. For horizontal or highlydeviated wells, the graduatedcylinder is mounted at a 45-degree angle by means of a free water standand clamp. To prevent

any evaporation, the cylinders are sealed by plastic and elastic bands.


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Fig 9: Free water stand

ix. Low Temperature CirculatorThis instrument is used to lower the temperature of other equipment such as the pressurized

Consistometer or the UCA when running low temperature tests. It enables the simulation of low

temperature conditions in the well; temperatures as low as32deg.F (0deg.C). It is also used to

cool the machines after a very high temperature test.

2.3.3 General Cement tests

There are a number of tests carried out on cement slurries under simulated conditions prior to

actual field use; each is done to measure a certain property of the cement so as to serve as a

quality assurance for the cementer and ensure good results on the field. As such these tests must

be carried out according to API specifications. The tests carried out include:

2.3.3.1Rheology and gel strength testRheology is the study of the flow behavior and deformation of a fluid under applied stress. The

viscosity and yield points are calculated from rheological values. The rheology values help to

evaluate the slurry mixability and pumpability.

Aim

To determine the rheological properties and behavior of cement slurries.

Material

Freshly prepared cement slurry.


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Apparatus

6 speed Viscometer, a viscometer cup, Atmospheric Consistometer.

Procedure

1. Fill the viscometer cup with the slurry to the 350ml scribed line and place it on the

sample cup table; ensure that freshly prepared slurry is used.

2. Raise the viscometer cup and cup table until the slurry level meets the inscribed line on

the sleeve and tighten the locking nut ensuring that it covers the two holes below the line.

3. Use the red knob at the top of the viscometer to select gears, and the black switch to opt

between low and high speeds.

4. Take the dial readings after duration of 10seconds for the different gears starting from the

lowest to the highest and then take the reading again this time starting from the highest to

the lowest. At gear 1, obtain the 10seconds Gel and 10minutes Gel at 3 rpm respectively.

5. Condition a freshly prepared slurry using the Atmospheric Consistometer then repeat

steps 1-4.

6. Take an average of the two readings gotten then do all necessary calculations at both

ambient and test temperature.

Plastic Viscosity, PV = (300rpm-100rpm) x 1.5cp

Yield Point, YP = PV- 100rpm, lbs/100ft2

Interpretation of result

When the ratio at all the speeds is approximately 1, this is an indication that the slurry is a non-

settling, time independent fluid at the average temperature.

Ratio values mostly higher than 1 may suggest settling of the slurry at the average temperature.

Ratio values mostly lower than 1 may suggest gelling of the slurry. And when significant

difference in the readings indicates that the cement slurry is not stable i.e. prone to settling of

excessive gelation, adjustments in the slurry design should be considered


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2.3.3.2Fluid loss testFluid loss is a process whereby the aqueous phase (filtrate) of the slurry escapes into a permeable

formation. It could lead to several serious problems like shale swelling, flash setting of cement

etc. Regardless of whether the slurry is conditioned in a Consistometer or in a stirred fluid loss

cell, the fluid loss value is determined under static conditions.

Aim

The test is carried out to estimate the volume of filtrate lost to the formation.

Material

Freshly prepared cement slurry, Nitrogen.

Apparatus

HPHT Filter press, Fluid loss cell, 325-60 mesh screen, Atmospheric Consistometer.

Procedure

1. Condition freshly prepared slurry to test temperature using the atmospheric

Consistometer for 20mins.

2.

Assemble the fluid loss cell ensuring that the mesh, the o rings and the valves are placed

correctly.

3. Pour in the conditioned slurry into the fluid loss cell and secure the end cap in the cell.

4. Place the cell in the heating jacket ensuring that the screen is on the bottom and that the

pin engages.

5. Connect the nitrogen line, secure it with the retaining pin and apply a differential pressure

of 1000, 50 psig.

6.

Open the top fluid loss cell valve to apply and maintain 100050psi pressure to the cell.7. Open the bottom valve (which starts the test) and start the timer.

8. Collect the filtrate using a calibrated measuring cylinder and record the volume to 1 mL

at 30 minutes; if the nitrogen blows through at less than 30 minutes, record the volume

and time at which the blowout occurs and do the necessary calculations.


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9. Shut down the pressure supply and ensure that you bleed off the pressure totally before

dismantling the cell.

10.Calculate the fluid loss and record in cc/30mins.

Calculated API Fluid loss = 2xvol cc/30mins.

In case of a blowout,

Calculated API Fluid loss =2xVtt

477.5cc/30mins.

Where

t is the time of the blowout, expressed in minutes.

2.3.3.3Thickening time testThe thickening time of a cement slurryprovides an indication of the length of time that a cement

slurry will remain pumpable in a well. It is the time elapsed from the initial application of

pressure and temperature to the time at which the slurry reaches a consistency deemed sufficient

to make it unpumpable. Two related terms are also used; the pump time the time at which

ideally all pumping operations should be done with and the set time the time at which the

cement slurry is expected to have hardened enough to start building some if negligible

compressive strength. Of course the thickening time is the most important parameter in this test.

The laboratory test conditions should represent the heating time, temperature and pressure to

which cement slurry will be exposed during pumping operations.

Aim

To determine the thickening time of cement slurries under simulated wellbore conditions.

Material

Freshly prepared cement slurry, Hydrocarbon oil as specified by API.

Apparatus

Pressurized Consistometer


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Procedure

1. Grease and assemble the slurry cup and paddle assembly ensuring that the diaphragms

used are really tight and that the collar is holding the paddle stationary.

2.

Invert and fill the slurry cup to within 6 mm (1/4 in) of the top, pour out your surface

sample.

3. Strike the cup to remove entrained air.

4. Screw in the base plate and make sure slurry is comes out through the centre hole,

thenscrew the centre plug (pivot bearing) into the container.

5. Wash off excess cement from the slurry cup.

6. Place the filled slurry container on the drive table in the pressure vessel ensuring that the

pins engage in the cup table then switch on the motor.

7. Secure the potentiometer mechanism so that it engages the paddle shaft drive bar

properly.

8. Close all pressure valves and open the air supply so as to start filling the vessel with oil.

9. Close the head assembly of the pressure vessel and put in the thermocouple; do not

tighten the screw totally so as to remove entrained air in the system.

10.When all air bubbles have escaped, tighten the thermocouple screw.

11.Program the Consistometer to test temperature using the BHCT and heating time and

ramp to 500psi.

12.Start the test and switch on the heater, recorder and timer.

13.After the Consistometer has reached the test temperature, ramp to the test pressure.

14.Closely monitor the test and record the pump time, thickening time and setting time;

these correspond to 40BC,70BC and 100BC.

15.Shut down the test ensuring all necessary parts are switched off and that all pressure

release valves are opened so as to bleed off pressure in the system.

16.

Open the slurry cup, discard the slurry and dismantle and clean the cupthoroughly.Special care should be taken to ensure no cement is trapped in any of the

threads.

17.If the result gotten is as expected, then the slurry can now be pumped in the field or

reconfirmed by the clients, if not, the slurry is redesigned and tested again till adequate

results are obtained.


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2.3.3.4Compressive strength testCompressive strength is the ability of the cement sheath to withstand differentialpressures in the

well.A minimum compressive strength of 500psi is required before further operations can

commence. There are two methods of testing for compressive strength; the destructive and the

non-destructive testing. For the destructive testing, the cement slurry is poured into a cubical

mould and cured in a Curing Chamber for 24hrs, and then it is crushed using a Carver Press.

In this case, the compressive strength is the pressure it takes to crush the set cement. In the non-

destructive testing, sonic speed is measured through the cement as it sets. This is done using an

Ultrasonic Cement Analyzer. In present times, the non-destructive testing is rarely used as the

NDT is preferred.

Aim

The test is carried out to determine the compressive strength that can be attained by the set

cement under simulated wellbore conditions.

Material

Freshly prepared cement slurry, water

Apparatus

Ultrasonic Cement Analyzer (UCA), Slurry cup.

Procedure

1. Grease and assemble the slurry cup generously ensuring that you take note of the top and

bottom.

2. Place the slurry level gauge at the top of the cup and pour in freshly prepared slurry to the

slurry level, then pour in fresh water carefully to the water level.3. Place the top lid and properly screw it in.

4. Place the slurry cupin the Pressure Curing Chamber and secure it properly; connect the

transducer and the thermocouple.

5. Close all pressure valves and open the water supply, allow excess water to flow out

through the vent then tighten the thermocouple.


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6. Program the UCA to test temperature using the BHST and heating time and ramp the

pressure slightly,program the software taking note of slurry density.

7. Start the test and switch on the heater. After the test temperature is attained ramp the

pressure to 3000psi as recommended by API.

8. Closely monitor the test and record the compressive strength at 8hrs, 12hrs and 24hrs.

9. Shut down the test ensuring all necessary parts are switched off and that all pressure

release valves are opened so as to bleed off pressure in the system.

10.Open the slurry cup, discard the slurry and dismantle and clean the cup

thoroughly.Special care should be taken to ensure no cement is trapped in any of the

threads.

Fig 10: A typical UCA plot

2.3.3.5Free fluid and sedimentation testFree fluid is caused by the segregation of water from the cement slurry after placement in the

annulus. It can lead to channel formation, gas migration and non-uniform compressive strength

of the cement sheath. It is a measure of the slurry stability. It normally occurs hand in hand with

0:00 5:00 10:00 15:00 20:00 25:00 30:00Time (HH:MM)

0

40

80

120

160

200

240

280

320

360

400

tempuca2(F)

0

2

4

6

8

10

12

14

16

18

20

Timeuca2(microsec/in)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

CompressiveStrength(psi)


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solids settling. Since free fluid and sedimentation occurs after placement in the wellbore, the test

is done under static conditions and at well conditions.

Aim

The test is done to determine the stability of cement slurry under static conditions.

Material

Freshly prepared cement slurry

Apparatus

250ml graduated cylinder, Atmospheric Consistometer, syringe

Procedure

1. Condition freshly prepared slurryto test temperature using the Atmospheric

Consistometer for 20mins.

2. Pourthe conditioned slurry into a 250ml graduated cylinder. Stir the slurry with a spatula

while pouring to ensure a uniform sample of the slurry.

3. Place the cylinder on a foam pad for vertical wells but in the case of deviated wells place

it in the 45deg inclined free water stand .

4. Seal the cylinder to prevent evaporation and leave the test to stand for 2 hours

5. When the time is elapsed use a syringe to remove all the free fluid and record the amount

gotten.

6. Discard the slurry and carefully wash the cylinder

7. Express the volume of free fluid as a percentage of the slurry volume used.

2.4 Special Cement Systems

Aside from the conventional cement system used in oil well cementing operations, some special

cement systems have been developed to combat certain problems encountered in the well bore;

problems such as slurry fallback, lost circulation, micro annuli, cementing across salt formations,

and corrosive well environments. Some of these systems are discussed briefly below.


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Thixotropic Cements

Thixotropy is a term used to describe the property exhibited by a system that is fluid under shear,

but develops a gel structure and becomes self-supporting when at rest. Thixotropic cement

slurries are relatively thin and fluid during mixing and displacement, but rapidly thicken and

become self-supportingwhen pumping ceases. Upon reagitation, they become fluid and are once

again pumpable but immediately thicken upon cessation of shear. This type of rheological

behavior is continuously reversible with truly thixotropic cements. They are mostly used for

setting plugs in lost circulation zones since they set up quickly. Harder cement plugs can then be

added asneeded. Thixotropic cements are very viscous and have very high strength, this could

cause some problems when pumping is temporarily stopped before the cement reaches its target.

Common additives include class G cement, Sodium metasilicate, gypsum, dispersant etc.

Retarded Liquid Cements

These arestorable, premixed cement slurries that can be kept in a liquid state for an extended

period, then activated to function as a zonal isolation material. Additives used include class G

Portland cement, a set-retarding agent, a dispersant/ plasticizer to provide long term fluidity, and

a suspending agent to prevent settling. Upon activation, they yield a finished slurry with

properties suitable for well cementing in a wide range of temperature and density conditions. To

maintain them, they must be sheared for 5- 10 minutes every 1- 2 days.

Ultra-Light Weight Cement

These arevery low density cements with very good compressive strength. They are formulated to

cement across weak formations where low hydrostatic pressures are required and can be used in

wells as deep as 12000ft. They provide superior strength compared to slurries with conventional

extenders at the same density and have excellent insulating properties. Additives include class G

Portland cement, lightweight silica microspheres and other cement additives.

Freeze Protected Cements

These are cements that can set at temperatures as low as 20degF (-3degC). They can set in

permafrost zones without freezing while attaining high early compressive strength and effective

insulation (low thermal conductivity). Permafrost is defined as any permanently frozen


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subsurface formation; the depths may range from a few feet to 2,000 ft. Below the permafrost,

the geothermalgradients are normal.This cement system is a blend of class G Portland cement

and gypsumwith Calcium Chloride as a freezing point depressant.

Foamed Cements

These are used to cement across weak formations where normally extended slurries cannot

produce the desired cement density and compressive strengths. They can be formulated and used

where adequate compressive strengths are still required in very low density cements. They can

minimize slurry loses in cases where activelost circulation is being experienced. Slurry stability

is maintained by the foamer or additional stabilizers. Foam cement is produced from cement

which has been blended to meet downhole conditions, a foaming agent usually a surfactant and

nitrogen as the foam density control agent. The cement is slurried to its designed weight in a

mixer, then the foaming agent is added from an additive injection system and then the slurry is

foamed by mixing with nitrogen. It is a very economic and effective way of cementing lost

circulation zones as opposed to light weight cements which can be quite expensive.

Magnesium/Calcium System

These are unique acid soluble cements used to seal off and protect producing formation and to

stop lost circulation where conventional bridging materials fail. It is a Mixture of magnesium and

calcium compounds and other acid soluble inorganic materials. It is a free flowing powder that

can be easily mixed to form a smooth pumpable slurry. Unlike normal cement, it hardens by

chemical reaction rather than hydration. It requires special additives especially tailored for it to

modify its properties. It can be pumped through drill bits nozzles and is compatible with most

drilling fluids thus eliminating the need for spacers and washes.

2.5 Compatibility test

Before any cementing operation commences, the well must be adequately prepared; this involves

conditioning the mud and circulating it out of hole while cleaning the well so as to remove any

mud filter cake on the walls of the well.This is to ensure good cement bonding and effective

annular seal because the mud could contaminate the cement and vice versa. The mud is displaced

with a spacer or chemical wash or flush depending on the design, after which the cement slurry is


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pumped into the well. Bonding and cement seal durability is directly related to the efficiency of

the displacement process. Because of the importance of this displacement process, tests are

carried out in the laboratory to determine the most effective spacer system to be used in the well;

the spacer must be compatible with both the mud and the cement. This test is called a

Compatibility test. It includes examination of rheology, static gel strength, and wettability.

2.5.1 Spacer preparation

This is a fluid used to separate drilling fluids and cement slurries; the spacer displaces the mud

and the cement displaces the spacer. It is usually compatible with both the mud and the cement.

It can be used alone or with chemical wash or a pre-flush. It can be designed for water based

mud, oil based mud or both. It prepares both the pipe and the formation for the cementing

operation. Because of the displacement order, the density of the spacer is expected to be slightly

higher than that of the mud but lower than that of the cement.

Additives

For water based mud: foam preventer, surfactant, gel, water and weighing agent.

For oil based mud: foam preventer, surfactant, solvent, gel and weighing agent.

Note: The basic difference between the spacer for water based mud and that for oil based mud is

the use of a solvent in the latter.

The concentration of the additives to be used is set as a standard but it varies depending on the

density of the spacer to be prepared.The concentration of everything remains constant but that of

water and the weighing agent varies with varying density. A typical example is shown below.

Spacer Density,

ppg

Foam

Preventer

Surfactan

t, gal

Gel, lb Solvent,

gal

Water,

gal

Weighing

agent, lb

ForWaterBased

Mud

10 0.084 1.000 0.50 39.90 36.00

10.2 0.084 1.000 0.50 39.10 64.00


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For Oil

Based

Mud

9 0.084 2.000 0.50 3.00 35.90 36.00

9.5 0.084 2.000 0.50 3.00 35.10 64.00

This design is specifically to prepare a spacer of 1bbl using fresh water. If salt water is used or a

different volume is required, concentrations will vary.

Apparatus

Syringe, Electronic Balance, Constant Speed Mixer, Atmospheric Consistometer, Viscometer.

Procedures

1.

Accurately measure the additives; for the liquid additives measure in mls using a syringewhile for the solid ones measure in grams using an electronic balance.

2. Prehydrate the gel for 30mins maintaining a low speed for the duration.

3. After the 30 minutes, add the other additives ensuring that the mixing order is

maintained.

4. Slightly increase the speed and leave for 5 minutes.

5. Check the density using a pressurized Mud Balance and record.

2.5.2 Procedure for compatibility testThe rheology of mixtures of cement/mud, cement/spacer and mud/spacer in different ratios is

determined. The API recommended ratios are 95/5, 75/25, 50/50, 25/75 and 5/95. The test is

done at both ambient and test temperatures. The rheology values gotten are interpreted to

determine whether the systems are compatible or not. Usually, cement/spacer and mud/spacer are

compatible but mud/cement is not.

A wettability test is also done. This is to test the water wetting capability of the spacer. There

are different methods and apparatus available but the simplest one is the use of the viscometer

sleeve. This is done by shearing 100%mud at 600rpm for 10mins, then shearing 100%spacer

with the same parameters and afterwards sprinkling water on the sleeve. If a clean sleeve is


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obtained, then the spacer is capable of adequately cleaning the mud from the pipe and well, if

not, a different design might have to be recommended.

2.6 Introduction to Stimulation

Stimulation is the general term used to describe a variety of operations performed on a well to

improve its productivity and maximize hydrocarbon recovery. Stimulation operations can be

focused solely on the wellbore or on the reservoir; it can be conducted on old wells and new

wells alike; and it can be designed for remedial purposes or for enhanced production. It is a very

vital operation in oil and gas production.

2.6.1 Types of stimulation

Oil well stimulation is of two types; matrix acidizing and hydraulic fracturing though most times,

matrix acidizing is preferred because of its relatively low cost.

In matrix acidizing, acid is squeezed into the matrix of the formation (including the network of

pores and pore throats within the rock) at pressures below those that would initiate fracturing.

The primary function of matrix acidizing is to remove near-wellbore damage, and return the well

to its original productivity. In matrix acidizing, acid penetrates into the formation, radially

around the wellbore, enlarging flow channels and dissolving pore-space plugging

particles.Typically, hydrofluoric acid is used for sandstone/silica-based problems, and

hydrochloric acid or acetic acid is used for limestone/carbonate-based problems. Most matrix

stimulation operations target up to a ten foot radius in the reservoir surrounding the wellbore.

Hydraulic fracturing is a process of creating a fracture by the injection of fluids into a

formation at a pressure higher than the parting pressure of the formation. Injection rate has to be

high enough and formation permeability to the injected fluid has to be low enough that fluid loss

is not excessive so that pressure canbuild up sufficient to fracture the formation or to open

existing natural fractures. The variety of materials used includes amongst others: water, acid,

special polymer gels, and sand. These cracks are held open by proppants which are basically

specialized sands.The creation of acid channels allows for an enhanced conduit to the wellbore

from distances in excess of a hundred feet.


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2.6.2 General Stimulation tests

A number of stimulation tests are carried out in the lab to effectively predict the correct acid

system to be used for a specific treatment. They include

Dissolution test

This test is done to determine the treatment fluid that will effectively dissolve a solid sample

from the well bore. The different treatment acid systems are prepared and mixed with the

formation sample are desired ratios. The mixture is thenheated to the test temperature using a

water bath, after which it is filtered and weighed. The treatment system that gives the most

noticeable change is the most effective.

Shake out test/ Blend Compatibility test

This test is used to determine the most effective combination of additives and the concentration

of those additives needed to prevent stable induced emulsions. The treatment fluid and formation

fluids are mixed in ratio 1:1 in a test bottle, agitated thoroughly and allowed to stand for 10mins

at ambient and test temperatures. If complete separation occurs within10mins time frame, the test

is successful.

Scale Analysis

The test is used to identify scales that are formed in wells, tubings and pipelines. This is done by

dissolving the scale in different solvents such as water, diesel and xylene and acid solutions.

Emulsion Break test

Emulsions sometimes form in producing oil wells and increase the viscosity so much that they

stop or restrict production. Recommendations for removal of an emulsion block are based on

determinations made of the emulsion this is where laboratory testing comes in. They testtodetermine the type emulsion - whether it is oil-in-water, water-in-oil or complex,the percentage

of oil, water and solids, and the best treating fluid that can be used to break the emulsions. The

treatment fluid and the formation fluid are mixed in ratio 1:1, vigorously shaken and allowed to

stand in a glass jar at ambient and test temperatures, The emulsion break time is recorded at time


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intervals of 1, 5 , and 10mins. If 100% separation occurs then the test is successful; if not, the

treatment fluid has to be redesigned or an alternate one is used.

Acid Sludge test

This test is used to determine if an acid system will cause the formation of a sludge when used to

treat a specific crude oil.

2.6.3 Stimulation additives

Additives used in the design of acid system include

Iron Control Agents

These are used in reducing the effects of dissolved iron.The intermixing of iron-contaminated

acid containing inappropriate additives and formation crude oils can to result in many problems

in the well bore such assludge precipitation, formation of scale productsetc.

Surfactants

Surfactants (surface-active agents) are chemicals that are added to an acid blend to alter the

surface and/or interfacial tension properties of the acid. This alteration can affect the flow of

fluids in the wellbore region in either favorable or unfavorable ways. Where used, surfactants

can promote different changes in reservoir rocks and fluids. They can act to create, break,

weaken, or strengthen emulsions, reduce acid-induced sludging, create or break foams etc.

Corrosion Inhibitors

Inhibitors serve to control the rate of dissolution of steel in a well. Corrosion acts on base metals

to change them into other types of materials. When a corrosive fluid is in contact with a metal, at

any point on that metal surface corrosion is occurring. This is totally undesirable because if the

pipes downhole are corroded, it could lead to serious problems during production.

Solvents


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Solvents are often chosen as the additive to accomplish a number of purposes: to decrease

interfacial tension, provide detergency, convert or restore the rock surface to a water-wet

condition among others.

Scale Inhibitors

They are used to inhibit the growth of scale as it precipitates as scale formation could lead to a

lot of problems in the well.

Friction Reducers and Acid Gellants

Friction reducers are those chemicals that, when dissolved in the fluid, reduce the fluids

frictional pressure drop through well tubing, particularly where high injection rates are required

in acid fracturing treatments.

2.6.4 Types of Acid systems

The types of acids that can be used are grouped into: Mineral acids, Organic Acids and Acid

Mixtures. Mineral acids include HCL, HCL-HF. Organic acids include Acetic Acid and Formic

Acid. We also use one shot acid systems and Paravan D can also be used. Though not an acid

system, diesel-xylene mixtures are also used as treatment fluids. Aside from the conventional

acid systems, we also have the retarded acid system. Stimulation additives can be used to

enhance the properties of the acid systems. Different acid systems are compatible with different

formations and this must be taken into consideration when designing an acid stimulation job.

2.7 Laboratory safety policies

The oil industry is very particular about HS&E standards. It maintains that in every action, safety

must be put into consideration; safety to human life, environment and property. Because of the

high exposure to chemicals, high temperature and pressures in the laboratory, special care must

be taken in carrying out. Some of these safety precautions are:

1. Ensure that a JSA and HRA is done before any job.

2. Necessary PPE must be worn before handling chemicals.

3. Proper housekeeping must be maintained at all times,everything must be in its place and

there should be no crowding of space with materials.


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4. All laboratory wares and materials should be kept clean.

5. If skin is contacted with chemicals/additives and cement, wash off thoroughly with fresh

water.

6. All chemical containers should be properly labeled and sealed.

7. On inhalation of acid, immediately drink water.


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CHAPTER THREE

3.1 Problems encountered during SIWES period

There is no doubt that the Industrial training experience was very beneficial in more ways than

one however, some problems were encountered during the training that could cause a setback to

the program. They include:

1. Placement

It was very difficult to secure a space for the training; this of course was largely due to the

number of students searching for IT placement. Despite the fact that I started the search quite

early, it was a grueling experience nonetheless and I almost had to resort to settling to for an

unrelated industry. This is a trap that a lot of students fall into.

2. Finance

The monthly stipend I received from my company was barely enough to cater for my needs

during the training period; these needs include transportation, feeding, accommodation etc. As a

result, the duration of the training was very stressful with me trying to make ends meet. In fact in

some companies where I tendered my application, they refused to pay any salary and instead

demanded that I pay them.

Possible solutions

i. The students should be encouraged to purchase log books and IT letters on time so that

they can resume the search for a suitable industry for his/her IT placement.

ii. The ITF should assist students in securing IT placement so that they can start and finish

on time.

iii. The ITF (Industrial Training Fund) as well as the government should make provision for

the payment of the specified amount to the industrial training students on a monthly basis

during the training period.


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3.2 Relevance of the SIWES program

The relevance of the SIWES program to the student and industry alike cannot be

overemphasized; they include

1. It serves to bridge the gap between the theory learnt in class and actual practice in the

industry.

2. It gives students an opportunity to gain some hands on skills useful in the industry while

still in the University. This enhances their understanding and performance in their

respective courses of study.

3. It exposes students to a workplace environment, most for the first time in their lives

where they can learn about workplace ethics, safety standards etc.

4.

It exposes students to the professional method of work and good practices, including use

of industrial tools, equipment and machines.

5. It enables students create a network with professionals in his/her field of study. This

gives him an edge on graduation.

6. It motivates students to work harder in school so as to secure such a job on graduation.

7. It exposes students to current challenges in the industry that they could work on either as

a school or personal project so as to proffer a solution.

8.

For some it renews their interest in their course of study; as the popular saying goesseeing is believing.

9. It broadens students perspective on their field and the jobs available therein.

10.It exposes students to what to expect on graduation thereby making the transition from

school to industry easier

11.It enlists and strengthens employers involvement in the entire educational process of

preparing universities and other tertiary graduates for employment into industries

12.It is important to note that these only come to play if the student is able to secure an IT

placement in an industry relevant to his/her field.


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CHAPTER FOUR

4.1 Conclusion

The industrial training experience was indispensable to me. It gave me what to look forward to

and reason to strive harder to learn in school. It opened up a world of opportunities for me and

afforded me an opportunity to learn new things such as workplace ethics, HS&E, QA/QC. It

gave me reason to appreciate my lecturers more cause everything I saw, I had been taught one

way or the other by them. It exposed me to the world of cementing and how it is used to aid in

oil and gas production. It exposed me to the oil and gas industry; its working standards, practices

and terms. It was great and I can safely say that the training is the one pillar of academic learning

that must be held strong.

4.2 Ways of improving the programme

The program is key to the attainment of a degree from a higher institution and is quite beneficial

to students that undergo it, however I am of the opinion that some changes must be made for it to

achieve its full potential; these being

1. The ITF should take the time to properly orientate and sensitize the students prior to the

commencement of the training; they should discuss expectations and brainstorm on how

to solve these recurring problems. This would also reduce the issue of students

misbehaving in the workplace.

2. The ITF and the government should assist students in securing IT placement in their

relevant industries because for all the good the training does, it makes no difference if the

student has no work.

3. The ITF should ensure that students undergo the training in an industry relevant to their

field of study; this can only be achieved by proper supervision.

4.

The industry based supervisors should ensure that they take the time to teach the students

properly and equally assess them from time to time.

5. In spite of the large number of students assigned to them, the supervisors should ensure

that they have one on one talks with their students and ensure proper follow up.


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6. The ITF should ensure that companies allow students to actively participate in the work,

of course under supervision and not to become the handymen in the office thereby not

gaining anything from the experience.

4.3 Advice for the future participants

Prospective IT students should start searching for a place of attachment in a relevant industry as

early as possible, so that they can resume training on time and finish up before the next academic

session commences.

They should focus on whats important; money is important but they should make sure they learn

as much as they can take and then more.

They should also make sure they follow all company rules and are on their best behavior

throughout the training.

IT students should use the opportunity to create a network with professionals in their field that

they come across and leave them with a wonderful and lasting impression.

Finally, they should make sure that they are a 100% dedicated to their work; its just IT but its

work all the same and everything counts.

4.4 Advice for the SIWES managers

I would firstly thank the SIWES mangers for such an opportunity and give kudos to them. My

advice is that they should ensure that they properly sensitize industries and companies on the

importance of accepting IT students and the role it plays in the development of the student and if

possible with government support, enforce it.

They should also ensure that they pay regular visits to the IT students, discuss extensively with

them and know their problem areas.

Finally, they should actually make an effort to look into the recurring problems faced by IT

students and find a solution to them.


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industrial training experience(well cementing)

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