Subsurface safety valves
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Subsurface safety valves Subsurface safety valves Document Transcript

  • 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
  • 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)
  • 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, for being 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) View slide
  • CONTENTS Abstract Objective Methodology Introduction History of the safety valve Safety valve operation Types of subsurface safety valve List of components Conclusions Bibliography View slide
  • 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)
  • 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.
  • 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
  • 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 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 performance. 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.
  • 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, 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
  • Surface-controlled subsurface safety valve (SCSSV) 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 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-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 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 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 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 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 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 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 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
  • 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.
  • 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.
  • 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 safety%20valve%20(SSSV) 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