X-Mas Tree & Wellhead [PDF]

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X-MAS TREE & WELLHEAD OPERATIONS, MAINTENANCE AND TESTING By Engineer: Jamal Amer



Course Introduction • Wellhead and Xmas tree is the main equipment for oil production, water injection and down hole operation. • It is installed on the casing head to seal the annular space between casing and tubing, control wellhead pressure, adjust well flow rate and transport oil to pipeline. • This course is designed to provide an up-to date overview of x-mas tree, wellhead equipment, mechanical barriers, safety valves and wellhead operating control system. • Participants will develop a better understanding of wellhead operating procedures and working under safe conditions.



Course Objectives: Upon successful completion of this course, the delegates will be able to: ➢ Apply and gain an in-depth knowledge on x-mas tree & wellhead operations, maintenance and testing ➢Discuss the various wellhead equipment as well as x-mas tree, tubing hanger, production packers & landing nipples Practice barriers principles & well safety on hydraulic barriers and mechanical barriers as well as subsurface control valve packer setting and testing ➢Demonstrate flanging of the wellhead, wellhead safety valves and control system ➢Apply the proper procedures of x-mas tree and wellhead operations to work under safe conditions



Xmas Tree General



➢ The Xmas tree is an item of safety equipment that is placed on top of the wellhead. It consists of a system of valves



which may be either open or closed according to the state of the well (ordinary operation, well-tool intervention, pumping, testing, repairs). ➢ The purpose of the Xmas tree is to control the flow of hydrocarbons from the well and to allow access to the well



during the operational phase. We call the Xmas tree a safety barrier.



Xmas Tree Components Upper Master Valve (UMV) • The Upper Master Valve is used on moderate to high pressure wells as an emergency shut-in system • Valve should be capable of cutting braided wireline and slick line • Valve can be actuated pneumatically or hydraulically. • The UMV valve is normally connected to an emergency shutdown (ESD) system. • The UMV can be considered as a primary barrier



Normally used



Not normally used: always fully open. Close in emergency



All above valves are gate valves



Xmas Tree Components Crown Or Swab Valve ▪ Topmost valve on a Christmas tree ▪ Swab valve is used to a. control access to, and b. isolation of the wellbore when performing well-intervention operations such as slickline, electric wireline or coiled tubing. ▪ Valve is usually a manual valve. Wing Valve ▪ Used for production. ▪ Usually a hydraulic valve



▪ Tree cap: it allow entry of tools into the well



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Summary of Well Construction Hole Size



Casing Size



Casing Name



30”



26”



Conductor



23”



20” or 18 5/8”



Surface



17 ½”



13 3/8



Intermediate



12 ¼”



9 5/8”



Production



8 ½”



7”



Production Liner



wel d



Wellh ead



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Summary of Well Construction ▪ Well construction based on a repeated set of processes. ▪ Drill a hole, run and cement steel casing ▪ Install a wellhead section and nipple up BOPS. ▪ Drill a hole, run and cement steel casing and run another wellhead section ▪ Process is repeated several times until the hole total depth ( TD) is reached. ▪ The table belwo showss the sequence of hole and casing sizes in common use



wel d



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Well Head Assembly • A wellhead is part of an oil/gas well that terminates at



the surface, whether on land or offshore. • The primary role of the wellhead is pressure containment and to hold the casings and the production tubing. • Every oil or gas well has some type of wellhead. • Conventional wellhead assemblies include the casing head Housing , casing hangers, spool sections, tubing head, tubing hanger, valves and fittings. • The assembly of valves and fittings that sit on top of the wellhead are also known as the Christmas tree.



Conventional Wellhead and Christmas Tree Assembly 200 0 100 0 0



3000



4000 500 0



Section D Production Tree Section C Tubing Spool



Section B Casing Section A Spool Casing Head with Landing Base



Conductor Pipe Surface Casing Intermediate Casing Production Casing Production Tubing



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Wellhead Main Functions • Casing/Tubing suspension. • Pressure sealing and isolation between casing at surface



when many casing strings are used. • Provides a means of attaching a blowout preventer during drilling. • Provides a means of attaching a Christmas tree for production operations. • Provides a reliable means of well access. (Tubing Head) • Provides a mean of attaching a well pump. (Artificial Lift) • Provides pressure monitoring and pumping access to annuli between the different casing/tubing strings.



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Casing Head (Housing)



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Casing Head Components



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Casing Head (Housing) • Casing head is the primary interface for the surface pressure control equipment, for example blowout preventers (for well drilling) or the Christmas tree (for well production). • Casing Head has a straight bore bowl with 45°landing shoulder design which avoids damage to sealing areas by drilling tools and prevents test plug and bowl protector. • Most casing heads allow for the pressure readings to be taken on the annulus and provide the means to pump out or into if necessary. The top of the casing string and annulus is usually sealed. • Casing Head provided are normally furnished with threaded outlets and studded outlets and also can be manufactured by request. • Bottom connections can be furnished threaded or slip-on for welding.



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Casing Head (Housing)



Pressure testing: • A pressure test must be carried out using hydraulic oil after cooling of the base flange. • Do not exceed 70% of API casing collapse pressure rating. • During this test, no sweating should occur. Upon completion of the test, install a wellhead protection cap to prevent objects accidentally falling into the wellbore. • Re-install the 3/4” NPT plug in the test port.



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Casing Hangers



▪ A casing hanger is a retainer / packer mechanism which supports, centers, and seals a string of casing in a casing head ,casing spool or tubing head bowl.



Casin g Hang er



Slips



Casing head Bowl



20” casing



Casing hanger Elastomer Seal element



Landing profile



13 3/8” casing



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Casing Hanger Types There are two types of casing hanger in common use. Wellheads can be designed to accept both types of hanger.



Mandrel (boll weevil) Type Casing Hangers: • This type of hanger is screwed onto the top of the casing string so that it lands in the casing housing when the casing shoe reaches the required depth. • Short lengths of casing, known as pup joints may have to be added to the string so that the casing shoe is at the correct depth when the hanger lands in the wellhead. • The calculation which determines the length of pup joints required to achieve this positioning is known as spacing out the string. • Although this is the most common type of hanger it cannot be used if there is a risk that the casing will not reach bottom and therefore that the hanger will not land in the



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Casing Hanger Types Slip Type Casing Hangers:



• This type of hanger is wrapped around the casing and then lowered until it sits inside the casing spool. • The slips are automatically set when the casing is lowered (in a similar fashion to drillpipe slips) • This type of hanger can be used if the casing stands up on a ledge and cannot reach its required setting depth. • These types of hanger are also used when tension has to be applied in order to avoid casing buckling when the well is brought into production.



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Casing Hanger



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Casing Hanger



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Casing Spools The casing spool in a conventional wellhead system is the component that allows for an additional string of casing to be set in the well. Depending on the casing program for the well, there can be one or more casing spools and they perform the following functions: •Allows for suspending the next casing string in the well •Provides outlets for fluid returns •Provides a means to test the blowout preventers while drilling •Has flanges on both the top and bottom of the assembly •Has a seal area in the bottom flange for a secondary seal between the casing annulus and the flanged connection •Utilize a test port in the bottom flange that allows for seal and the flanged connection to be pressure teste



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Casing Spool Components



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Casing Head Housing - Description



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Types of Casing Head Housing (CHH): Threaded Although safer, threaded CHH requires to have • the uppermost casing thread at precise depth. • If the surface casing has to be set off depth (fill on bottom, stuck casing), slipon CHH has to used.



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Christmas Tree Type Composite Trees • This type of tree should only be used for low pressure and low risk applications.



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Normal (Convention)Wellhead & Christmas Tree Electric submersible pumps • Used in oil production to provide a relatively efficient form of "artificial lift“. • Able to operate across a broad range of flow rates and depths. • By decreasing the pressure at the bottom of the well (by lowering bottom hole flowing pressure, or increasing drawdown), significantly more oil can be produced from the well when compared with natural production. • The pumps are typically electrically powered.



Tubing Hanger



Function Of Sub- Surface Safety Valves



Control Line Flow Coupling SCSSV Landing Nipple



▪ DHSV: are used to close the well in an emergency ▪ Potential situations include: ▪ serious damage to the wellhead ▪ failure of surface equipment, and ▪ fire at surface.



▪ Set below the depth where they can be damaged by surface impact explosion



Top No-Go Nipple



SPM Top No-Go Nipple SSD Top Packer



SSD Producing Zone 2



Blast Joint



Btm Packer Bottom No-Go Nipple Perforated Joint WL Entry Guide Producing Zone 1



PRODUCER COMPLETION SCHEMATIC



Function Of Sub- Surface Safety Valves Downhole safety valves (DHSVs) are installed in the well in order to prevent blowouts if: ➢ ➢ ➢ ➢



The topside Xmas tree becomes damaged (e.g. by collision with a crane lift) surface equipment is sabotaged A neighboring well suffers a blow-out (in order to prevent a domino effect) drilling collision from nabouring well (the valve must be located so deep that drilling-in will most probably be above the valve).



Such valves are of the “Fail-safe Closed” type. If hydraulic pressure to the valve is lost, it will immediately close. These valves can also be pumped through from the surface even when they are closed. Such valves exist in two versions: ✓ Flapper valves ✓ Ball-valves.



Tubing Hanger



Setting Depth of Safety Valves



Control Line



▪ In offshore wells, at least one safety valve is SCSSV Landing Nipple placed in every well at a depth from 200 ft to 2,000 ft below the seabed. ▪ Depth of safety valve depends on: SPM ▪ well environment (onshore, offshore) ▪ below depth where damage to the safety valve can occur from surface related SSD Top Packer hazards such as impacts, explosions,fires SSD etc ▪ production characteristics (wax or hydrate Producing Zone 2 deposition depth) Btm Packer ▪ characteristics of the safety valve. Bottom No-Go Nipple (maximum and minimum setting depths)



Flow Coupling



Top No-Go Nipple



Top No-Go Nipple



Blast Joint



Perforated Joint



WL Entry Guide Producing Zone 1



PRODUCER COMPLETION SCHEMATIC



Function Of Sub- Surface Safety Valves WRSV SVLN



WRSV Set In SVLN Lock Mandrel



TRSV



Control Line Nipple Profile Lock-Out Mechanism



Packing Profile Packing



CL Port



Piston



Piston Seal Bore



Flow Tube Spring Spring Flow Tube



Flapper



Flapper



Function of Sub- Surface Safety Valves



SCSSV



Wire line SCSSSV Nipple



Control line installation



Types of Down Hole Safety Valves They can be divided into two categories : 1- S. S. C.S.S.S.V. 2 - S. C .S.S.S.V. 1. ( Down Hole ) Sub Surface Controlled Sub Surface Safety Valves ▪ often called velocity valves or Storm® chokes) are wireline retrievable ▪ installed in standard profile seating nipples in the tubing string below the surface tubing hanger. ▪ A subsurface safety valve requires a change in the operating conditions at the valve to activate the closure mechanism. ▪ The velocity valve contains an internal orifice that is specifically sized to the flow characteristics of the well. ▪ The valve is normally open and is closed by an increase in flow rate across the orifice. ▪ This creates a pressure drop, or differential pressure, across the valve that causes it to close. ▪ The velocity valve reopens when the pressure is equalized across the valve.



Subsurface-controlled safety valves SSCSSV Differential pressure controlled velocity valves ▪ Often called velocity valves or Storm® chokes are wireline retrievable ▪ installed in standard profile seating nipples in the tubing string below the surface tubing hanger. ▪ A subsurface safety valve requires a change in the operating conditions at the valve to activate the closure mechanism. ✓ The velocity valve contains an internal orifice that is specifically sized to the flow characteristics of the well. ✓ The valve is normally open and is closed by an increase in flow rate across the orifice. ✓ This creates a pressure drop, or differential pressure, across the valve that causes it to close. ✓ The velocity valve reopens when the pressure is equalized across the valve.



Sub Surface Controlled Sub Surface Safety Valves Activated by maximum flow of the well



▪ Subsurface Controlled Safety valves are restrictions in the flow path held open by a spring. ▪ When the flow rate through the valve becomes so high that the resistance force collapses the spring and the force of the reservoir holds the valve shut. ▪ The well can be reopened by pumping into the well. ▪ This valve has to be reset every few weeks as reservoir pressure falls to ensure that ▪ “wide open flow” would still be adequate to collapse the spring and close the valve. ▪ Once closed, the valve can be re-opened by applying tubing pressure above it, or by means of an equalising valve run on wireline.



Function Of Sub- Surface Safety Valves



Sub Surface Controlled Sub Surface Safety Valves Ambient pressure controlled ▪ This type of valve is normally closed. ▪ The well pressure (hydrostatic or flowing) keeps the valve open. ▪ If the well starts to produce at an increase flow rate ▪ the tubing pressure drops and ▪ valve is closed by a spring and pre-charged nitrogen chamber. ▪ Once closed, the valve can be reopened by applying tubing pressure above it, or ▪ by means of an equalising valve, run on wireline .



Surface-controlled subsurface safety valves (SCSSVs) WRSV



SCSSV -



WRSV



-



TRSV



TRSV



W/L SCSSSV



TRSV Control Line



WRSV Set In SVLN



Nipple Profile



WRSV SVLN



Lock Mandrel



Lock-Out Mechanism



Packing Profile Packing Piston



CL Port Piston



Flow Tube Seal Bore



Spring Spring Flow Tube



Flapper



Flapper



Wireline Retrievable SCSSV ▪ Surface controlled wire line retrievable



▪



▪ ▪ ▪ ▪



DHSV is ▪ run in the open position with a prong on a wire line running tool Closure mechanism is either • ball or • flapper type Held open by hydraulic pressure applied to the valve via control line Retrieval is much easier compared to tubing retrievable valves Have to be pulled prior to wire line operations due to restricted bore The valve is re-opened by applying equal pressures above and below the valve



Annulus Safety Valve Why is an annulus safety valve installed ? ▪ Annulus safety valve is run part of completion string ▪ Us in gas lift wells



▪ In gas lift systems where large amounts of pressurized gas exists in the tubingcasing annulus.



▪ Annulus Safety Valves may be incorporated to contain this gas inventory in the annulus in the event that the wellhead becomes damaged.



Annular Safety Valve - Gas Lift ❑ The ASV contains large amounts of pressurised gas in the tubing-casing annulus – should the well-head become damaged ❑ Provides annular by-pass via a hydraulically operated valve array



Lift Gas



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Corrosion & Erosion



Barrier Concept Barrier element: A barrier element is any device, substance or fluid that prevents the flow of formation fluids into the wellbore. ➢ A barrier is in effect a defence system to avoid or reduce the consequences of accidental well control events. ➢ Barrier(s) may be located downhole (mechanical plugs, columns of fluid), or topside (valves, plugs, BOPs).



Seconda Barrier



Formation Pressure



➢ Even if a barrier element is designed to prevent well flow on it own, it must always be accompanied by other barrier elements. ➢ In other words two barriers must exist at all times



Primary Barrier Formation Pressure



The principles of different barrier types Barrier Definition:  Barrier is any device, fluid or substance that prevents flow of wellbore fluids.



Classes of Barriers 1. Primary 2. Secondary 3. Tertiary



Types of Barriers •



Mechanical • Fluid: ▪ ▪



designed to stop flow by providing a hydrostatic pressure greater than the formation pressure but must have another barrier such as BOPs as a back up



The principles of different barrier types



2



▪ Barrier elements include: ▪ Mud hydrostatic pressure: designed to stop flow but must have another barrier such as BOPs as a back up Formation Pressure



Mechanical barriers ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓



Mud Hydrostatic Pressure



Casing and Cement. Drill string. Drilling, Wireline, Coil Tubing, Workover BOP’s. Wellhead . Deep set tubing plug. Mechanical Barriers Production Packer. Stab-in Safety Valves. Completion String Tubing Hanger



Mud Hydrostati



Barrier Envelope Barrier Envelope



is an envelope consisting of one or several dependent well-barrier elements designed to prevent fluids or gases from flowing unintentionally from the formation, into another formation or to surface. ▪ Pressure control requires a minimum of two independent and tested barriers at all times. ▪ If either of the barrier fail then attempts must be made to reestablish the existence of two barriers before normal operation can continue



▪ A barrier envelop refers to a barrier containing a system of barriers made up of hydrostatic and mechanical barriers or a combination of various mechanical barriers. ▪ The systems within the barrier envelope must be independent of each other so if a barrier fails it will not affect the other barriers.



Example of Barrier Envelope Packer/Tubing Envelope Barrier elements include:



Tubing Spool Outlet Valves



▪ Casing below Packer ▪ Packer ▪ Tubing ▪ Tubing Accessories



Surface casing DHSV Production casing



Tubing Packer Fluid



▪ Tubing Hanger Cement



▪ Xmas Tree Packer



Perforations



Example of Barrier Envelope PACKER/TUBING ENVELOPE Barrier elements include: ▪ Casing below Packer ▪ Packer ▪ Tubing ▪ Tubing Accessories ▪ Tubing Hanger ▪ Xmas Tree



Example of Barrier Envelope Production Casing Envelope ( Annulus Flow)



Barrier elements include:



Tubing Hanger/Hanger Spool



• Production Casing • Side Outlets Valves



• Tubing Hanger • Tubing Head • Casing Head Housing



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Which Barriers Prevent Annulus Flow In the production well schematic in figure identify the main barrier elements (envelope) that prevent annulus flow? Follow Red Arrows 1. Packer 2. Production casing below packer 3. Tubing Hanger/Hanger Spool ( Tubing Head) 4. Tubing spool outlet valves 5. Production tubing



Tubing Spool Outlet Valves



Surface casing DHSV Production casing



Tubing Packer Fluid



Well Fluids



Cement



Packer



Perforations



API connections On all BOPs flanges, three different types of connections are used both as end connections and side outlet connections: 1. Studded connection 2. Clamped hub connection 3. Flanged connection Studded connection



Flanged connection