Subsurface Safety Valves
Minor Project Report
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
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)
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, for being mentor for our
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
We would like to thank all once again.
Akhilesh Kr. Maury (R040307003)
Bhawuk Luthra (R040307007)
Reshma Raman (R040307043)
Btech (Applied Petroleum Engg-II)
History of the safety valve
Safety valve operation
Types of subsurface safety valve
List of components
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
Dr. Surya Prakash Rao
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.
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
Literature Review 3
Preparation for synopsis 2
Data collection & Work done 4
Completion of Project Report 5
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 a
catastrophic surface or at subsurface level and to control the fluid flow producing formation to
surface 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 well
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. As
part 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. To
affect this task, sophisticated engineering designs and state-of-the-art materials have been
developed. The valve’s 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 subsurface
safety 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 Minerals
Management 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
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 valve
styles, 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
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. Production
fluid flowing through this choke
creates a differential pressure
across the bean—the 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-spacer selection and
by adjusting the hole size
through the bean.
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, acts
on 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 the
flapper to close and shut
off fluid flow
subsurface safety valve
The more recent SCSSV
design is a normally closed
valve, with the spring
force, F5, acting to push
the piston upward and
release the flapper to close
the valve. Control pressure
transmitted from surface
line acts against the spring
to keep the flapper valve
open during production.
design, which has been
replaced in many modem
valves by a rod-piston
design, has a ring-shaped
area 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,
FL — Fu.
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 a
pressure loss across the valves) or when there is pressure drop opposite the valve. SSCSV’s
(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 keep
valve 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 can’t 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
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 the
valve. 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”. It’s
a 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
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 which
compresses 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 to
American institute of Petroleum’s 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 well’s
safety can be achieved manually and automatically in both the conditions whether the problem
occurred 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 can’t 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 robust
property. Lots of changes have been made in reliability and tightness of flappers and it’s in its
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 mandrel
that has been modified in order o transmit the control fluid pressure to valve’s 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
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
the valve. It is usually associated with tubing anchor and a disconnection system and thus it can
be 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.
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.
Well completion and servicing By Dennis Perin