Sonatrach_Well Intervention and Workovers

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Introduction to Hydrocarbon Exploitation Work over & Well Intervention

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Workovers

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“…any work performed after the initial completion that alters the well performance or mechanical structure”.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Well Servicing & Workovers

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Potential Well Problems Well Servicing and Workover Techniques

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Intervention Techniques

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– Wireline – Coiled Tubing – Hydraulic Snubbing Units – Surface Well Intervention Technique

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Well Servicing & Workovers 

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During the conceptual design stage it is important to identify any potential reasons for workovers and the applicable techniques. When reviewing the impact of well problems and Workover techniques on the initial completion design, it is important to recognise the risk associated with that problem and the potential consequences. Optimising the completio n design around potential well problems and Workover techniques is, like many other issues, a question of balancing risk against likely consequence.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Types of Operations

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Measurements Maintenances

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Workover

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Types of Operations 

Measurements – May involve the status of equipment – Quality of pay zones-borehole connections – Status of reservoir and well equipments etc.

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Maintenances – Simple operations that can be done on a well during production operations

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Workovers – Heavier operations that might require the well to be killed – Sometimes carried out with the well under pressure

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Measurement Operations At the Wellhead – Pressure and temperat ures, variation would mean modification in production conditions.

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– Pressures or loss in pressur es in the annulus to check integrity of packers, casing and production strings. – In artificial lift operatio ns to monitor stress on rods, pumps or gas lift valves. – Safety valve testing etc. At the Tubing – Calibrations and checks – Corrosion or deposit prob lems etc.

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At the Bottom hole – Checking top of sediments – Production logs –density, flow rate or temperature

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Maintenance Operations 

At the Wellhead – Routine operations such as adjusting flow rates – Opening and shutting in well.

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– Replacing faulty parts downstream – Periodic verification of safety valves etc At the Tubing – Operations connected with problems of deposits, corrosions etc – Injection of inhibitors, chemicals, de-emulsifiers, anti foaming agents etc. – Operations for exchange of equipments downhole etc.

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At the Bottom hole – Sand control, further perforations etc – Pumping chemicals etc. ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Workover Operations 

At the Wellhead – Leaks in lower master valves, tubing hanger. – Problems with SSSV control lines etc – Damaged back pressure valves and other wellhead components.

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At the Tubing – Casing or tubing problems/leaks – Collapsed, burst or broken pipe – Tubing partially or totally plugged.

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At the Bottom hole – Leaks in equipments that has seals such as packe rs, locators, slip joints etc. – Gas lift valves, fish, broken rod, pumping problems – Miscellaneous faulty downhole equipment such as sensors, control lines etc.

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Modification in production conditions Restoration to pay zone –bore hole con ditions Change in purpose of well Fishing ©2005 Abalt Solutions Limited. All rights reserved

Potential Well Problems Low Reservoir Pressure: 

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The reduction in reservoir pres sure and hence flowr ates is particularly acute in dissolved gas drive reservoirs. In gas cap and water drive reservoirs, pressure maintenance techniques can often offset the reduction in pressure due to depletion. How to Solve it: – Recomplete the well with either smaller tubing or some form of artificial lift. – Injection

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Potential Well Problems Poor Permeability: 

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Fields with low reservoir permea bility suffer a rapid decline once the fluids near the wellbore are produced. Matrix acidising is only effective in this situa tion if formation damage is also present. How to solve it: – The most effective method of improving productivity in these types of reservoir is to utilise a large hydraulic fracture treatment.

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Potential Well Problems Wellbore Restrictions: 

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Typical causes of restriction s include scale, sand, paraf fin and asphalt etc. Many of these problems may not be apparent during early field life but can become a significant problem as the field matures. How to solve it: – A number of techniques, both mechanical and chemical, exist to remove the restriction. – However, these workover techniques are remedial techniques and consideration should always be given to the prevention of the problem.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Potential Well Problems Control of Water Production: 

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Excessive water production can lead to a number of production problems including – loss of production and eventual well death – expensive treatment and disposal costs, – corrosion and scaling. Recovery from water drive res ervoirs Significant increase in water production – rise in water/oil contact as a result of reservo ir depletion How to solve it: – Squeeze cementing – plugging back and re-compl etion

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Potential Well Problems 

Fingering – Water migrating along a high permeability streak.

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Water Conning – water is drawn up from the aquifer either across bedding planes leading to coning.

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How to solve it: – Reduce off take from wells – plugging back and recompletion

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Potential Well Problems Control of Gas Production: Excessive gas production from a well can result from solution gas in the oil evolving as the pressure declines, or as a result of gas encroachment from the gas cap.

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With pressure decline in saturated oil reservoirs, the gas evolved across the reservoir may migrate to the gas cap.

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However, the gas evolv ed near the well bore as the oil is produced causes an increase in gas saturation and allows the gas to be produced with the oil.

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How to solve it :

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– High gas/oil ratios (GORs) in this case are a function of the res ervoir drive mechanism and cannot usually be remedied by a workover. – An increase in GOR can also occur from a lowering of the gas cap into the producing zone and through channels in the cement or casing leaks. This increase in GOR can be temporarily remedied by squeeze cementing and lowering the perforated interval. ©2005 Abalt Solutions Limited. All rights reserved

Potential Well Problems Mechanical Failures: 

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Mechanical failures of tubing, casing and downhole equipment often require a workover to rectify the problem. Typical problems would include

– casing leaks, either as a result of corrosion or collapse, – tubing failures, packer failures and downhole safety valve failures. 

How to solve it: – Replacement of downhole components by work over units – Expandable tubular ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Potential Well Problems Primary Cement Failures: 

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A poor primary cement job which leav es channels behind the casing can lead to the influx of unwanted fluids and in certain instances casing collapse. How to solve it: – Squeeze cementing – Scab liners – Expandables

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Potential Well Problems Sand Production: 

Failure of reservoir formations and subsequent sand production from wellbore can cause Erosion of tubular and components Productivity impairment Clogging of separators   

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How to solve it: Mechanical sand control – Screens – Gravel pack – Frac pack – Expandables 

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Sand Management– reservoir pressure maintenance ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Well Servicing & Workover Techniques 

The most commonly utilis ed workover techniques include: – Wireline operations; slickline, braided line and electric line. 

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– Coiled tubing operations. – Hydraulic workover operations. – Remedial cementing. – Concentric workover operations. – Full rig workovers.

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Wireline Operations

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Technique used to operate in a producing and injecting well by means of a steel cable, to enter, run. set and retrieve measurement tools and instruments needed for production.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Operations 

Advantages – Work can be done inside tubing without killing

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the well. – Operations performed quickly due to lightweight and mobile units. – Pay zone not damaged during operation – Relatively easy to handle, saving money and number of resources to operate. 

Limitations – Highly skilled personal required to operate. – Risky to work in highly deviated wells – Can work in tension and moderate loads, no rotation and circulation possible. ©2005 Abalt Solutions Limited. All rights reserved

Wireline Operations 

Classification – Checking and cleaning tubing or bottom hole (checking corrosion, clogging, top of sediment etc. – Carrying out measurements (BHT and Pressure,

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locating surfaces, production logging etc) – Running & retrieving operations (setting and pulling SSSV, plugs, chokes, gas lift valves etc)

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Operations 

Slickline. – This is a solid single strand of wire, the commonest size being 0.108in

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Braided line.

– This wireline consists of stranded wire resulting in a higher load capacity than slickline. Commonly used sizes are 3/16 and 5/16in – commonly used in fishing operations where slickline has insufficient strength to impart the required loads. 

Electric line. – This consists of stranded wire and a conductor capable of transmitting an electrical signal to the surface. – any application where an electrical signal needs to be transmitted up or down the well.

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Wireline Operations 

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The main functions of slickline are as follows: – Installation and retrieval of flow control equipment. – Running of pressure, temperature and flow monitoring devices. – Cleaning the tubing. – Bailing fill. – Swabbing the well. – Fishing equipment. Wireline units are installe d on various means of transport including trailers, trucks, boats and barges. Units used on offshore platforms are typically skid mounted. The wireline is spooled on to a reel that is usually hydraulically driven.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Equipment

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Wireline Equipment 

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The minimum surface equipment required to perform wireline operations is: – Wireline winch unit. – Measuring device. – Weight indicator. – Hay pulley and wireline clamp. – Stuffing box. – Lubricator. – Blowout preventer (BOP). – Wireline.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Equipment 

Winch and Motor – Steel drum that holds length of wire – Driven by a diesel or gasoline engi ne or sometimes electrically operated. – Engines rated outp ut depends on working depth . – Winches are either single or double drum. One spool wi th slickline and other with braided line used for considerable tension strength. – The most comm on wireline winch unit is skid mounted and has a double drum, one with 20 000 ft of 0.108in wire and the second with 15 000 ft of 7/32in wire.

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Source :United drilling ©2005 Abalt Solutions Limited. All rights reserved

Wireline Equipment 

Cable – Steel wire drawn in one piece without any welding or brazing in accordance with API SPEC 9 A. – Common diameters are 0.066”,0.072”,0.082”,0.092” and 0.105”. – Three types of wires are used

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Ordinary steel Galvanized steel Stainless steel with good H 2S resistance.

The measuring device – as the name implies , provides the operato r with the location of his tool relative to some datum, usually the swab valve. – The operator uses this device to locate the tool string, monitor the speed, and to avoid running the tool string into the stuffing box when pulling out of the hole. ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Equipment 

The weight indicator – displays the total loa d or line tensio n and is critical to jarring operations to avoid breaking the wire. – Types  

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Hydraulic electric

– The device will also indic ate   

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restrictions in the tubing, changes in fluid density losses or increases in weight when setting or retrieving downhole equipment.

The hay pulley – guides the wire down from the lubrica tor and out parallel to the floor to the winch drum. – The hay pulley is attach ed to the Xmas tree via the load cell for the weight indicator. ©2005 Abalt Solutions Limited. All rights reserved

Wireline Equipment 

Lubricator – Placed on top of the x-mas tree to allow tools to be run into pressurized well. – Serves as intermediary between surface and well. Lower part has quick union on end.

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– Common sections are 8ft long and depend upon length of string that is going to be run. – Widespread diameters are 2” to 4”and series from 3000 to 10,000 psi. – At the base there is a ½” bleed off valve, used when BOP is closed

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Equipment 

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The wireline clamp is used to secure the wire when required e.g. when removing the lubricator. The stuffing box provides the pressure seal on the wire and consists of a packing gland that can be adjusted by means of an external nut. – In the event that the wire breaks and is forced out of the packing, there is a an internal BOP plunger that is designed to seal off the stuffing box. Source:www.uniteddrilling.com

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Wireline Equipment 

BOP or wireline valve – Located between lubricator and top of well head. – provides a means of well control in emer gency situations. BOPs can either be single or double. – The BOP can isol ate pressure with or without wire in the well . The BOP rams have resilient seals which can close and seal around a wire, without damaging or cutting the wire.

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– Dual BOPs are normall y employed for braided line or fishi ng operations.

Source: Well completions-Perrin

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Tool String 

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All equipment placed above specialized tools and run in hole along with them. It is connected to the wire by special socket.

Rope Socket – Threaded on its lower end and connected to the wire by a knot – Spring placed in machine cavity acts as shock absorber. – Used to connect the tools to wireline. ©2005 Abalt Solutions Limited. All rights reserved

Wireline Tool String 

Knuckle Joint – Provides flexibility to the tool strin g in deviated holes etc. – Prevents wire from twisting around due to tool string dragging against wall

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Jars – Makes it possible to hammer with stems at end of stroke to shear pin.and fishing operations. – Use for maintenance – Mechanical jars can move upwar ds/downwards by sudden pulling – Hydraulic jars allow only upward pulling

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Wireline stem or sinker bars – Heavy bars that al low string to be run into we ll despite wellhead pressure and friction. – Aids in the jarring of tools. – Available in sizes of 2,3 or 5 fee t.

Knuckle Joint

Mechanical Jar

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Tools 

Wireline tools fall into 4 categories– Checking and maintenance tools – Running and pulling tools

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– Lock mandrels, downhole tools and others – Fishing tools

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Wireline Tools Checking and maintenance tools – Tools screwed directly on the bottom of wireline tool string. – Checking and cleaning inside of tub ing & bottom of well 

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Swaging tools – Straighten tubing walls that have bee n slightly deformed allowing free passage of wireline tools

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Gage Cutters – Run prior to wire line operations to check the way is clear. – Allows some deposits to be cleared. – Remove corrosion, paraffin etc.

Source: www.rebcooiltools.com

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Tools 

Sand Bailers – Used to take sediment fill

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at the bottom of the well or even clean the bottom – Equipped with a check valve – Mechanical or hydraulically activated. 

Scratchers – Used to clean the inside of tubing. Source: www.rebcooiltools.com

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Wireline Tools Running and Pulling tools – Specialized tools for pulling and retrievin g downhole tools. – Downhole tools are attached to the tool string by mean s of the standard landing and fishing heads located in the upper part of each tool

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Running tools – Run and set downhole tools in well. – Holding on to them by retain er pins and gripp ing dogs – Allow downhole tools to be landed an d locked, then to free them by jarring

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Pulling tools – Gripping and retrieving downhole tools from wel l to surface. – Gripping dogs latch onto fis hing head that can be unseated and pulled up by jarring.

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Combination tools ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Tools

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Wireline Tools Other Tools Locking Mandrel 

– Carry tools screwed on under them. – Landed and locked into landin g nipples integr ated in the tubing or sometimes directly on tubing walls. s r e v o k r o W & n o ti n e rv e t n I ll e W

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Equalizing subs

– Inserted between mandrel and plug and allows pressu re differential to be equalized across assembly before it is unseated.

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Kick over tools

for installing side pocket mandrels in gas

lift operations 

Swabbing tools to start and kick off well ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Wireline Tools Fishing Tools 

Wireline cutters – Designed to cut the wire flush with rope socket when string is stuck.

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Wireline finders – To find upper end of a broken wireline and tamp it down to make it into a nest. – Bell shaped and very close to tubing diameters

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Wireline grabs – Serve to catch wire and bring it to su rface. – Consist of 2 or 3 branc hes with teeth and diameter corresponding to inside tubing.

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Impression blocks – Identify shape and condition of the head of fish – Bell shaped and filled with lead

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Wireline grab

Impression block

Overshot

Overshot – Allows broken equipment to be fished. – Bowl equipped with a grapple (basket) that latches onto head of fish. ©2005 Abalt Solutions Limited. All rights reserved

Electric Line 

The primary use is – Cased-hole Formatio n Evaluation – Production Logging.

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– Perforating, setting bridge plugs and packers etc. Production logging is the term used for any survey which is run to evaluate the nature and behaviour of fluids in the well during production or injection. The applications of production logg ing include: – Well test evaluation. – Determining reservoir character istics. – Evaluating completion efficiency. – Identifying unwanted fluid flow eg thief zones. – Reviewing stimulation treatments, before and after. ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Coiled Tubing Units (CTU) 

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It consists of continuous pipe with a diame ter of ¾” to 1 ½” or even more, coiled up on a spool. Can be run in and pulle d out of a pressur ized well

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Coiled Tubing Equipment 

Injector head – Uses friction drive system actuate d hydraulically. – Directs tubing into the well and supp orts it – Equipped with goosen eck (guide), straightener , depthometer and weight sensor.

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Reel – Diameter about 8ft can contain s the tubing and driven by hydraulic of motor. – Tubing up on the reel is connec ted by reel swivel to the rotation axis allowing pumping to continue

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Tubing – Strip of mild steel rolle d cylindrically and welded longitudinally – Several hundred meters butted togeth er by radial welding to make up coils up to 20,000ft long.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Coiled Tubing Equipment

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Coiled Tubing Equipment 

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Safety Assembly – Stripper with sealing elements and stack of safety rams. – Stripper located above BOP, sealing element actuated hydraulically at a pressure that depends on wellhead pressure. – BOP Stack consists of 

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Pipe Rams-close and seal on tubing Slip rams-hold the tubing Shear rams-cut the tubing Blind rams-total closure over cut tubing ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Coiled Tubing Equipment 

Surface equipment – Power pack consisting of diesel engine driving hydraulic pump required for all equipment. – Control cab with control unit, gages and warning lights needed to operate and monitor. – Hydraulic crane or mast to retrieve safety assembly and injector head.

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Standard Coiled Tubing Operations 

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Coiled tubing units are routinely use d for the following operations: – Nitrogen lifting. – Sand lifting. – Cleaning out the wellbore utilising a downhole motor. – Circulating fluids. – Drill stem testing (DST). – Sand control. – Corrosion inhibitor placement. – Spotting acid, Spotting cement. – Coiled tubing conveyed electric line services. – Inflatable bridge plugs. – Fishing operations.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Nitrogen Lifting 

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Pumping nitrogen down coiled tubing to reduc e the hydrostatic head of the well fluids is utilised in a number of well operations. Lifting unstable wells and circula ting out completio n fluids following a workover are common applications. The injection rate required to bring on the well is a function of the pipe size, depth, fluid characteristics and reservoir performance. Coiled tubing can also be used to provide the requir ed underbalance prior to perforating.

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Sand Lifting 

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Coiled tubing can be used to clea n out sand fill from sumps that has occurred during production or as a result of hydraulic fracturing operations. Coiled tubing’s ability to maintain circulation while running in or pulling out of hole make it ideally suited for this application. If possible sand lifting should be performed with the well flowing.

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This may alleviate the need for injectin g gel, although cross linked polymer is usually injected.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Cleaning Out with DH Motors 

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This technique is utilised when the deposit s in the well are compacted or cemented and is particularly useful in the removal of insoluble scale deposits. A downhole motor is used to drill out the deposit which is then washed to the surface. The downhole motor operates on the Moineau principle which utilises fluid being forced through a progressive cavity to supply the rotational power.

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Clean Out

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Circulating Fluids 

Coiled tubing obviously provid es a convenient and economic means of circulating fluids and is used for such varied purposes as circulating kill fluid, washing drilling mud, and removing paraffin and salt using hot oil or water.

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Drill Stem Testing 

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Coiled tubing is often used as a means of artificial lift to assist wells which will not flow naturally during DSTs. Two methods are used, downho le jet pumping and nitrogen gas lift. – The jet pumping method utilises the coiled tubing to both locate the jet pump module in a landing nipple and subsequently convey the power fluid. The power fluid is usually water, although a combination of water and nitrogen can be used for low GOR crudes. Heavy crude oils may also benefit from applying heat to the power fluid. – The jet pumping techniqu e is most appropriate for crudes with an API gravity of 12 or less. – Nitrogen gas lifting is more suitable for the higher API crudes.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Sand Control

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Limitations on pump press ure and rates limit this application to shallow wells less than 6000 ft. Both resin coated sand and water activa ted plastic can be pumped with coiled tubing. To place water activated plastic: – CT is run in the hole to the interval to be treated, and the well fluids are circulated out to diesel. With the wellbore free of water, the plastic is pumped through the coiled tubing with the annulus shut off. – After the plastic is squeezed into the formation, the coiled tubing is shut in for 12 to 24 hours with sufficient wellhead pressure to prevent backflow of the plastic from the formation.

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Corrosion Inhibitor Placement 

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Coiled tubing has been used in conjunction with an inhibitor valve to atomise corrosion inhibitor and coat the tubular on low rate gas wells with potential carbon dioxide corrosion. However, in many cases the use of inhibito r to prevent corrosion has not proven to be costeffective.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Stimulation 

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Coiled tubing is ideally suited for the selec tive placement (spotting) of acid and can be used in a number of applications, including opening perforations and dissolving acid soluble scale deposits. Using coiled tubing in this man ner avoids having to bullhead the well. Coiled tubing allows acid to be circulated across the perforations and take the returns back up the tubing. In this way smaller amounts of acid can be used at lower pressures and the contact time with the production tubing is reduced.

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CT Conveyed Electric Line Services 

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Coiled tubing provides a conveni ent means of obtaining the functionality of electric line in highly deviated and horizontal wells. The system can be adopted in both cased and open hole. Coiled tubing has certain advantages over other systems in that no downhole wet connections are required and the tools are less prone to damage.

©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Inflatable Bridge Plugs 

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Inflatable bridge plugs can be run through on coile d tubing, set in production liner and subsequently retrieved. The bridge plugs , manufactured by Lynes and Baker Oil Tools, consist of an inflatable element that is set by pumping down the tubing and a hydraulic disconnect which is activated by dropping a ball down the tubing and pressuring up. The tool has the adva ntage of being able to pass thr ough restrictions in the tubing and set in relatively large diameters.

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Fishing Operations 

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Coiled tubing fishing techniqu es are proven successful, especially in the recovery of fish buried under sand, cement or scale. Fishing with coiled tubing allows fill to be cleaned out and the fish washed over and latched during the same operation. Application of this technology has potential in remote or offshore locations where rig availability is a problem or in cases where the CTU is already available on site.

©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Remedial Cementing 

Remedial cementing uses various techniqu es to place small volumes in specific targets. The type of operations fall into two categories:

– Cement squeezes, where cement is squeezed under pressure to seal perforations or defects in the primary cement sheath. – Cement plugs, which are set to isolate part or all of the wellbore.

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Remedial Cementing 

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Remedial cementing is usually performed during the production phase to control the fluids entering the wellbore, or to restore pressure integrity. Common applications include: – Recompletion or perforation squeeze. – Repairing of channels. – Repair of casing leaks. – Supplementing top of cement. – Plug and abandonment.

©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Rig Workovers 

Conventional rig workovers are usually employed to perform the following: – Retrieving and running completion strings. – Repairing or modifying the permanent downhole equipment e.g running scab liners etc. – Changing the completion interval.

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Concentric Workovers 

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Concentric workovers involve the use of a smaller diameter workstring which is run inside the permanent completion. Concentric workover methods include coiled tubing, HWUs and small workover rigs. Coiled tubing and HWUs have the advant age of being able to be run in the well without killing the well.

©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Hydraulic Workover Units (HWU) 

A hydraulic workover or snubbing opera tes on the principle that pipe can be inserted or withdrawn from a well under pressure.

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rs e v o k r o W & n io t n e v r te n I ll e W

The process utilises jointed tubing or drill pipe with a hydraulic snubbing unit to run the tubing string without killing the well, and allows small diameter tubing to be run through the completion.

©2005 Abalt Solutions Limited. All rights reserved

(HWU)

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The unit has to perform three basic functions: – Feed the pipe into and out of the well in a controlled manner against wellhead pressure. – Provide a seal which maintains integrity while at the same time allowing the pipe to be inserted or removed from the well. – Provide a means of plugging the inside of the pipe. ©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Hydraulic Workover Units (HWU) 

Hydraulic workover units have seve ral advantages over conventional workover rigs and greater capability than coiled tubing: – The workover operation can be performed under pressure and in certain cases with the well still flowing. This eliminates the risk of formation damage in sensitive formations resulting from killing the well prior to a conventional workover. – Mobilisation and demobilisation are shorter reducing the overall time a well is off production. – The hydraulic workover unit is flexible, with a lifting capacity up to 340 000 lbs, allowing it to handle relatively large tools. The ability to rotate the pipe enables light drilling and milling work to be performed.

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©2005 Abalt Solutions Limited. All rights reserved

Hydraulic Workover Units (HWU) 

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s r e v o k r o W & n o ti n e rv e t n I ll e W

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The primary use for HWU was for emergen cy and nonroutine well interventions. This use has to so me extent tarnis hed the reputation of HWU, in that most of the experience has been gained under difficult or emergency situations. Indeed, in many cases HWU wa s the only appropria te technique to control the well. However, for some of the reasons outlined above, the HWU is now becoming the preferred well servicing technique for certain situations.

©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Hydraulic Workover Units (HWU) 

Current applications include: – Fishing or milling in casing. – Cleaning casing. out cemented solids in the tubing, liner or – Drilling out bridge plugs. – Washing out frac materials. – Pressure control/well killing. – Circulating out heavy fluids. – Acidising and washing. – Running macaroni tubing to pump nitrogen in wells where depth and pressure preclude the use of coiled tubing. – Running completions under pressure. – Sand consolidation. – Squeeze cementing or plugging back.

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Hydraulic Snubbing Unit 

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Hydraulic snubbing units are made up from modula r units which can be easily transported and rigged up. When locating the unit, ca re should be taken to ensu re that the structure or wellhead can support the weight of the unit together with any forces generated during the snubbing operation. A hydraulic workover unit (HWU) consists of the following components – The hydraulic jack assembly, guide tube, window, travelling and stationary slips, rotary table and power tongs. – The work basket and control panel. – Hydraulic power pack and accessories. – Circulating swivel, kelly hose and pumps. – BOP stack.

©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

BOP Stack Configuration

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©2005 Abalt Solutions Limited. All rights reserved

Hydraulic Snubbing Unit 

The main components of the BOP system are as follows: – stripper rubber 

s r e v o k r o W & n o ti n e rv e t n I ll e W

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is located immediately below the window and is used for running pipe in and out of the hole without using the stripper rams. The stripper rubber is a solid synthetic rubber element that can stretch as couplings etc pass through, and maintain pressure integrity. Allows pipe to be stripped through the rubber under pressure.

– stripper rams  

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Should always be incorporated in a snubbing BOP. The stripper rams provide pressure integrity at pressures above 3000 psi Facilitates the running of downhole tools. ©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Hydraulic Snubbing Unit 

Equalizing loop – This loop runs from below the lower stripper ram to below the upper ram and is used to equalize the

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rs e v o k r o W & n io t n e v r te n I ll e W

pressure above the lower ram before opening it.

choke

– included in the loop to regulate the rate of equalisation. – These chokes are changed out to suit the fluid in the well. 

Vent line – ties in belo w the uppe r stripping ram and is run to safe point away from the snubbing unit. – This line is used to bleed down the pressure between each stripper ram.

©2005 Abalt Solutions Limited. All rights reserved

Hydraulic Snubbing Unit 

Safety Rams – located below the strippe r rams and are used to contain the well pressure in the event of a stripper ram failure or change in the stack. – Safety rams are pipe rams and the nu mber used in the stack will depend on the well conditions and planned operations.

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– At least one set of safet y rams must be contr olled from the basket. – These are the sam e as blind rams used in a drilling BOP and are used to shut in the well when there is no pipe in the stack.

©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Hydraulic Snubbing Unit 

Blind/shear rams – will cut the pipe and clos e in the well in a emergency situation. – The ram and blade must tested prior to to ensure that theytyp willecut thebe size and grade ofrig-u pipe.p,

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Outlet spools – provide access to the wellb ore and sho uld always be located above at least one pipe ram preventer and have double valve isolation.

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choke and kill lines – attached to an outlet spool or ram body and as the name suggests are used to pump fluid into, or take returns from the well. – These lines must have a working pressure equiv alent to the BOPs. ©2005 Abalt Solutions Limited. All rights reserved

©abalt solutions limited - 2005

September – October 2005