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    Subsurface Safety Valves

    Minor Project Report

    Submitted By:

    Akhilesh Kumar Maury

    Under Guidance of:

    Dr. Surya Prakash Rao

    HOD, Earth Sciences

    College of engineering Studies

    University of Petroleum & Energy Studies,

    Bidholi, via Prem Nagar, Dehradun

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    CERTIFICATE

    This is to certify that the project work on SUBSURFACE SAFETY VALVE submitted to the

    University of Petroleum and Energy Studies, Dehradun, by AKHILESH KUMAR MAURY

    (R040307003), BHAWUK LUTHRA (R040307007) and RESHMA RAMAN (R040307043) in

    partial fulfillment of the requirement for the award of degree of B.Tech in Applied Petroleum

    Engg. (2007-2011) is a bonafide work carried out by them under my supervision and guidance.

    Place: DEHRADUN Signature of Mentor

    Date: 15-12-2009 (Dr.Surya Prakash Rao)

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    ACKNOWLEDGEMENT

    With completion of minor project on Subsurface safety valves we would like to

    express my gratitude to all of people who helped me and guided.

    Firstly I would like to express my thanks to Dr. S.P. Rao sir, HOD, Earth sciences,

    University of Petroleum and Energy studies, Dehradun, forbeing mentor for our

    minor project.

    We would like to extend my gratitude to Mr. A. Arvind Kumar Sir, for providing

    such opportunity to work as team in one direction for submission of minor project.

    We would also like to extend my thanks to all those friends who helped us

    throughout.

    We would like to thank all once again.

    Akhilesh Kr. Maury (R040307003)

    Bhawuk Luthra (R040307007)

    Reshma Raman (R040307043)

    Btech (Applied Petroleum Engg-II)

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    CONTENTS

    Abstract

    Objective

    Methodology

    Introduction

    History of the safety valve

    Safety valve operation

    Types of subsurface safety valve

    List of components

    Conclusions

    Bibliography

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    ABSTRACT

    Subsurface safety valves is an integral part of well completions, that provides the ultimate

    protection against uncontrolled flow from producing oil and gas wells in case of catastrophic

    damage to wellhead equipment. It is incorporated in the tubing and comprises of a tubular body

    adapted for placement within a wellbore and defining a fluid passageway. Their use offshore is

    legislated in many parts of the world to protect people and the environment. Safety valves have

    evolved from the relatively simple downhole devices of the 1940s to complex systems that are

    integral components in offshore well completions worldwide.

    Closing mechanism is either by Ball type valve or Flapper type valve. Safety valves are of two

    types: surface operated and subsurface operated safety valves. Surface operated valves are

    further classified into pressure differential and pressure operated safety valves while surface

    operated safety valves are classified into wireline retrievable and tubing mounted safety valves.

    An SCSSV is operated remotely through a control line that hydraulically connects the safety

    valve, up and through the wellhead, to an emergency shutdown system with hydraulic-pressure

    supply. The design is fail-safe: through the control line, hydraulic pressure is applied to keep the

    valve open during production. Aspects of the safety valve are employed by a related method and

    system.

    Date:

    Signature

    Dr. Surya Prakash Rao

    (Mentor)

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    Objective

    The objective of this project is to develop a clear understanding of the working and applications

    of one of the most widely used artificial lift methods in the industry, the subsurface safety valve.

    The project involves studying the various parameters that affect both in terms of enhancing and

    reducing the performance, efficiency of subsurface safety valve.

    However, apart from above, the main intent of this project has been to push our technical skills

    to the extreme so that we can come up with an innovative design which would help demonstrate

    future research and development into more efficient models for subsurface safety valve.

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    Methodology

    To complete the present study the following methodology will be adopted:-

    Collection of literature

    Explore the available theoretical data

    Generate mathematical expression over its working principle

    Compilation the published data.

    All above methods have been scheduled within time framework given bellow table:

    WORKING SCHEDULE TIME

    (DAYS)

    Literature Review 3

    Preparation for synopsis 2

    Data collection & Work done 4

    Presentation 2

    Completion of Project Report 5

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    Introduction

    A term subsurface safety valve has very clear meaning: a safety valve installed beneath the

    surface. It is completion tool installed in well to shut in oil/gas production in case of acatastrophic surface or at subsurface level and to control the fluid flow producing formation tosurface of the well. Fluids like water, brine, oil & gas which are readily available are used in

    control line to control the safety valve. It is incorporated in the tubing and is located approx 30 to

    50 m below the ground level (onshore) or below seabed (offshore). It provides emergency, fail-

    safe closure to stop fluid flow from a well- bore if surface valves or the wellhead valves are

    damaged or inoperable (not being operated).

    Safety valves are essential in offshore wells and in many land wells located in sensitive

    environments, or in wells that produce hazardous gases. They are installed to protect people, the

    environment petroleum reserves and surface facilities. Successful installation, dependable

    operation and reliability of safety-valve systems are crucial to efficient and safe wellperformance.

    Manufacturers have to apply for a level of diligence and testing beyond of related well

    completion and flow control equipment, it shows the crucial role of subsurface safety valves.

    These valves meet the specification of American petroleum Institue (API) and ISO standards. Aspart of the safety system subsurface safety valves serve a relatively unglamorous but critical role.

    By working properly when other systems fail, these valves are a final defense against the disaster

    of uncontrolled flow from a well.

    In principle, a safety valve is a simple device. Most of the time it is open to allow flow of

    produced fluids, but in an emergency situation it automatically closes and stops that flow. Toaffect this task, sophisticated engineering designs and state-of-the-art materials have been

    developed. The valves closure mechanism must close and seal after months of sitting in the

    open position and years after its installation. Special procedures and technologies applied to

    reopening the valve after closure ensure its continued reliability.

    Wells are drilled and completed under diverse conditions, so before an appropriate subsurfacesafety valve is selected and installed, a thorough review of the reservoir, wellbore and

    environmental conditions must be conducted.

    In September and October 2002, Hurricane Lili impacted about 800 offshore facilities, including

    platforms and drilling rigs, Category 4 storm passed through the oil-producing region (offshore)

    in Louisiana, USA. Despite sustained winds of 145 miles/hr (233 km/hr), the US MineralsManagement Service (MMS) reported that the storm caused no fatalities or injuries to offshore

    workers, no tires and no major pollution. Six platforms and four exploration rigs were damaged

    by the storm. There were nine reported leaks of oil; only two exceeded one barrel. None of these

    spills was associated with the six severely damaged platforms.

    Subsurface safety valves are integral part of well completion and a no of oil and gas companies

    have come up with their innovative idea to develop the technology and to reduce the

    complexities in operational mechanism. Big players like Schlumberger, Halliburton, Otis

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    Engineering, and Baker Hugs are leaders in safety valve technology. They are manufacturing

    safety valves for around 40 years from now. Schlumberger surface-controlled subsurface safety

    valves use the innovative rod piston hydraulic actuation system. It offers six main safety valvestyles, ranging from basic to the most high-tech design available in the industry.

    History of safety valves

    The first safety device to control subsurface flow was used in US inland waters during the mid

    1940s. Otis Engineering valve was dropped into the wellbore when a storm was imminent and

    acted as a check valve to shut off flow if the rate exceeded a predetermined value. A slick line

    unit had to be deployed to retrieve the valve.

    Those first valves were deployed only as needed, when a storm was expected. The use of

    subsurface safety valves was minimal until the state of Louisiana passed a law in 1949 requiring

    an automatic shutoff device below the wellhead in every producing well in its inland waters.

    Safety valve operation

    Key features of ball

    and flapper valves

    A ball valve has a sphere

    with a hole through it,

    allowing flow through

    the valve when the hole

    is aligned with the

    tubing. Rotating the boll

    900

    places the solid part

    of the ball in the flow

    stream, stopping flow.

    The more common

    flapper valve works like a

    hinge with a spring.When the flow tube is

    down, the flapper is open,

    and when it is pulled up

    the flapper closes

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    Early subsurface safety valves

    were actuated by change in

    production flow rate. A flow

    tube in such valves is equipped

    with a choke bean, which is a

    short, hard tube that restricts

    flow, creating a differential

    pressure between the top and

    bottom of the tube. Productionfluid flowing through this choke

    creates a differential pressure

    across the beanthe pressure

    on the lower face of the choke

    bean is higher than the pressure

    on the upper face. When the

    force on the lower face exceeds

    the combination of pressure on

    the upper face and the force of

    the power spring holding the

    valve open, the flow tube

    moves up and allows the

    flapper to hinge into the flow

    stream and close against a seat,

    sealing off flow. The flow rate

    to close the valve can be set

    during manufacture by spring

    and spring-spacerselection and

    by adjusting the hole size

    through the bean.

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    Typical subsurface-

    controlled safety valve

    Early safety valves were

    relatively simple in

    operation and created a

    significant restriction to

    production. The force of

    the valve spring F5, actson the flow tube to keep

    the flapper valve in a

    normally open position.

    The pressure below the

    restriction is P1 and that

    above is P2. These

    pressures act on the

    exposed faces of the

    piston, creating a force F1

    F2 to close the valve.

    When fluid flows upward,

    the constriction creates a

    pressure differential that

    increases closure force.

    The spring force is preset

    for a specific flow rate, so

    when the flow rate reaches

    that critical rate, the piston

    moves up, releasing theflapper to close and shut

    off fluid flow

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    Surface-controlled

    subsurface safety valve

    (SCSSV)

    The more recent SCSSV

    design is a normally closed

    valve, with the spring

    force, F5, acting to push

    thepiston upward and

    release the flapper to close

    the valve. Control pressure

    transmitted from surface

    through hydraulic-control

    line acts against the spring

    to keep the flapper valve

    open during production.

    This concentric-piston

    design, which has been

    replaced in many modem

    valves by a rod-piston

    design, has a ring-shapedarea between the piston

    and the valve body that the

    hydraulic pressure acts

    upon to generate the

    opening force F The small

    difference in the piston-

    wall cross sections

    between the upper (U) and

    lower (Ii faces of the

    piston adds a small

    additional upward force,

    FLFu.

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    Types of Subsurface safety valves

    1. Subsurface controlled subsurface safety valves.2. Surface controlled subsurface safety valves.

    Subsurface controlled subsurface safety valves (SSCSV)

    Those valves which are installed beneath the surface are called SSCSV. They are also termed as

    storm choke. They are set and retrieved by wire line. They closes the well whenever there is

    change in flow conditions like either when there is increase in ambient flow rate i.e. (There is apressure loss across the valves) or when there is pressure drop opposite the valve. SSCSVs

    constitute:

    (i) Pressure differential safety valve and(ii) Pressure operated safety valves.

    Pressure differential safety valves are designated as pressure differential valves or velocity

    safety valves. Pressure loss in valve leads to close the valve. A return spring is fitted to keepvalve open, but if flow rate increases excessively, pressure loss occur creating a closing force

    greater than that of return spring thus the valve closes.

    The spring compression is set in such order that it can work at predetermined conditions, ie. it

    shuts the well when there is any increase in velocity or flow rate beyond a suitable condition.

    Closing and sealing mechanism is either a ball valve, a check valve or a poppet valve.

    It cant tolerate a high variation in flow rate. It suits to well being produced at relatively low flow

    rate and thus it is confined to wells with high potential or wells whose reduced flow rate is

    economically justified.

    Pressure operated safety valves are also known as ambient safety valves. The closing

    mechanism is controlled by a return spring and a gas chamber. It is normally closed and pressure

    in the well keeps it open.

    Pressure equal or greater than the specified operating pressure is exerted from above to open thevalve. As long as pressure remains greater than the value of set point, valves remain opened.

    Moment the ambient pressure drops, valve is no longer open now and it closes abruptly.

    The closing and sealing mechanism is either a ball valve, a check valve or a poppet valve and

    these valves suits to well whose flow rate is very much sensitive to pressure variation.

    Schlumberger has developed pressure differential valves naming A-series velocity valves. Itsa flapper type valve and it can work with 10,000 psi (69,850 kPa). It is sweet to moderately

    corrosive environment and in a temperature range of 40

    F to 3000

    F (40

    C to 1490

    C). It has so

    many added advantages over other safety valves

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    Surface controlled subsurface safety valve (SCSSV)

    These valves are controlled by hydraulic pressure in control line from surface. Valves are

    normally closed. Control pressure applied on jack attacked to valve pushes the sleeve whichcompresses the spring attached to it causing the valve to open. As long as control pressure equals

    the set pressure the valve remains open. Failure of pressure leads to closing of valve.

    SCSSV were developed around 40 years back taking well safety into consideration. It adhere toAmerican institute of Petroleums specification (API 14-A) and ISO 10432:1999. It depends on

    parameters measured at wellhead rather depending on ambient flow condition. It allows

    interference of surface facilities in controlling mechanism. The greatest advantage is that wells

    safety can be achieved manually and automatically in both the conditions whether the problemoccurred is directly related to well or not. In case of fire, explosion, process problems etc we can

    directly access the valves. Depending on complexities of problem occurred we can take suitable

    decisions to close the valves installed on wellhead or to close the valve installed subsurface.

    Due to limited value of return spring force, depth at which valve need not be much. The spring

    must be sufficiently compressed to overcome the opposing force (acting on jack directly) due to

    weight of hydrostatic column of the fluid in the control line.

    The valve cant be opened when pressure difference between above and below exceeds 100psi

    (0.7MPa). So in order to open the valve either we need to increase the pressure in control line or

    to recompress the tubing above the vale by means of pump.

    The surface controlled subsurface safety valve closing and sealing mechanism is either a flapper

    valve or a ball valve. Earlier the ball valve was in fashion due to its sealing quality but nowadays

    check valves are preferred over the ball valve because of its simplicity, roughness and robustproperty. Lots of changes have been made in reliability and tightness of flappers and its in its

    eleventh edition.

    There are two types of surface controlled subsurface safety valves:

    (i) Wire Line retrievable valve(WLR)(ii) Tubing retrievable valve(TR) or Tubing mounted(iii) Combination safety valves.

    Wire Line retrievable valve (WLR)

    It is set in a special landing nipple and retrieved by wire line. The valve is attached to a mandrelthat has been modified in order o transmit the control fluid pressure to valves jack. Some special

    tools are like control shear pin, locking dogs are set in, in order to enhance the safety. In spite of

    all these facts most oil wells are equipped with WLR valve because it makes well maintenance

    easier.

    Tubing retrievable safety valve (TR)

    Generally gas wells are preferably equipped with tubing retrievable safety valve that provide an

    inside diameter same as the tubing diameter. The production string must be pulled out to change

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    the valve. It is usually associated with tubing anchor and a disconnection system and thus it canbe pulled out by pulling the upper part of tubing. Gulf of Mexico wells are primarily equipped

    with Tubing Retrievable and followed by Wire Line retrievable as secondary valve to avoid

    hazardous conditions in malfunctioning of primary valves.

    Combination safety valves

    A sleeve, a flapper and a return spring are installed, integrated in tubing. Approximately it has

    same advantages as both of wire line retrievable and tubing retrievable valve.

    Comparison of slick line- and tubing-retrievable safety valve systems

    The slick line-retrievable system typically locks into a landing nipple in the

    completion string and seals on either side of the control-line port to isolate the

    control fluid from wellbore fluids. The tubing-retrievable system is an integral

    part of the completion string. The inside diameter of the valve is similar to the

    inside diameter of the production tubing.

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    Conclusion

    The trend toward more complex reservoir development continues to present challenges for

    designers of safety-valve systems. Petroleum reserves today are exploited from deeper water and

    in harsher producing and operating conditions than ever before.

    An essentially unlimited setting depth could be achieved by developing subsurface safety valves

    that incorporate solenoids to activate the valve. This would alleviate the problem of pressure

    contributions from the weight of fluid in the control line or leaks in that line.

    The success and reliability of features developed in the past are keys to the development of

    innovative safety valves for the future.

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    Bibliography

    http://www.slb.com/media/services/completion/safetyvalves/subsurface_

    sv.pdf

    http://www.halliburton.com/ps/Default.aspx?navid=114&pageid=201&f

    olderid=MSE%3A%3A1045229747050391

    http://www.glossary.oilfield.slb.com/Display.cfm?Term=subsurface%20

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    http://www.bakerhughesdirect.com/cgi/bot/resources/ExternalFileHand

    ler.jsp?bookmarkable=Yes&channelId=-

    546906667&programId=546999579&path=/private/BOT/public/complet

    ions/subsurface/cementsafe.html

    Well completion and servicing By Dennis Perin

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