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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

Introduction to Hydrocarbon Exploitation Well Control Section By Pratap Thimaiah

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Drilling Engineering -Well Control

Kick

An uncontrolled flow of formation fluids into the wellbore during a drilling operation mainly arising due to the formation pressure being greater than hydrostatic pressure imposed by mud column.

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Causes of Kick  Insufficient mud weight  Low level of fluid column in annulus  Excessive swabbing  Excessive drilling rate in gas bearing formation  Diffusion of gas through mud cake

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Drilling Engineering -Well Control

Insufficient Mud weight  Penetration of geo pressured zone.  Accidental dilution of mud by fluid addition at surface  Dilution of mud by influx from aquifer exposed to open hole.  gradual decrease in mud density due to gas cut and failure to degas.  Poor quality control

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Low level of drilling fluid column

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 Failure to fill hole during tripping  Lost circulation – Mud loss to caverns and vugs – Penetration of depleted zones – Mud loss to fractures as a result of surge pressures, excessive hydraulics etc.

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Drilling Engineering -Well Control

Excessive swabbing  Reduction of bottom hole pressure caused by upward pipe movement  Mud flows down the annulus into the open hole.  Frictional pressure loss in the direction of surface.  Reduced BHP and instantaneous vacuum below bit.

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Excessive drilling rate in Gas bearing formations

 Influx reduces mud density in annulus.

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 Mud cut occurs from: – Swabbing – Fluid diffusion due to negative pressure differential – Expansion of gas as it reaches the surface. – Air entrained in mud from the Kelly air trips.

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Pre-Kick Data

Drilling Engineering -Well Control

 Maximum Working Casing Pressure – Casing and BOP are designed for different expected pressures during each phase. – Determined during well planning-Usually maximum rating of BOP or 80% burst pressure of last casing string.

 MAASP (Maximum Allowable Annular Surface Pressure) – Represents maximum annulus pressure permitted while controlling a kick. – Annular pressure at surface that corresponds to weakest point of the hole. MAASP =0.052 x (Frac - ) x TVD where Frac=fracture pressure at shoe in ppg ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Pre-Kick Data

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 Pump, String and Hole configurations – – – – –

Pump capacity Hole stability Drilling string capacity Annular capacity Casing data (size, weight, burst pressure, shoe depth etc)

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Kick Detection Techniques

Drilling Engineering -Well Control

 Positive Indicators – – – – –

Mud pit level/flow increase Incorrect hole fill up during trip Decrease in stand pipe pressure Increase in pump rate Increase/decrease in drill string weight

 Potential Indicators – Increase in ROP – Lost circulation – Changes in mud density and conductivity.

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Well Control Procedures

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

Control Procedures Involve the following: 1. 2. 3.

Shut in the well-follow predefined procedures Observe shut in pressures and kick volumes Make kill calculations for – – – – – –

Formation pressure BHP Kill mud density Initial and final circulation pressure Drill pipe pressure schedules Weighting material volume required.

– – – –

Drillers method Wait and weight method Concurrent Top kill method

1. 2.

Height and density annular pressure behaviour while circulating

4.

Define weighing up and circulating procedures

5.

Make interpretation for influx

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Well Control Equipment

Drilling Engineering -Well Control

 Wellheads  Control systems  Associated equipment  Blow out Preventers – Annular – Ram Type

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Well Control Equipment

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BOP

Drilling Engineering -Well Control

 Annular Preventer – Doughnut shaped elastic element with bond steel reinforcement. – Extrusion of element into wellbore is effected by upwards movement of hydraulically actuated piston. – Element designed to seal around any shape or size of pipe and to close on open hole. – Facilitates stripping of drill pipe in and out of well, with pressure on wellhead

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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BOP

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BOP

Drilling Engineering -Well Control

 Majority of annular Preventer currently in use are manufactured by – Hydril (types MSP,GK,GL,GX) – Shaffer (spherical) – Cameron (Type D)

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase BOP

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 Ram Preventers – Two Hydraulically actuated horizontally opposed rams which are either designed to seal off an open hole or annulus against pipe of specific diameter. – Working pressure of ram preventers should be atleast equal to maximum anticipated surface pressures ,plus margin for pumping to the well.

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Drilling Engineering -Well Control

BOP

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase BOP  Types – Pipe Rams

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 Designed to centralize and pack-off around one specific size of drill pipe or casing.

– Variable Pipe Rams  Available in different sizes  One set will provide back-up for two different pipe rams.  Have limited hang-off capacity therefore depends upon tool joint size and ram range.

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Drilling Engineering -Well Control

BOP

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase BOP – Hanging Rams  Pipe rams with enhanced load bearing capacities used for floating operations.  Hardening of bearing area

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– Blind/shear rams  Used to cut pipe and seal as blind rams.  Pipe stub accommodated in a recess.  Care should be taken that pipe body is opposite rams and not tool joint.  Bop control systems must be adequate to shear the pipe in use.

– Offset rams  Available for dual completions

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Control Systems

Drilling Engineering -Well Control

 Provides means of individually closing and opening each BOP and valve conveniently, rapidly, repeatedly and at correct operating pressure.  Designed to operate when in emergencies, primary rig power may not be available.  Elements of control systems:

– Power source – Control manifolds – Accumulators – Connecting pipe works/hose bundle and wiring

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Control Systems

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Drilling Engineering -Well Control

Control Systems

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Control Systems -Power Source  Primary power source

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– Electrically driven pumps. – For a 3000 psi accumulator system, pumps should incorporate a pressure switch set to cut in & out at 2800 psi and 3000 psi respectively. – Diesel pumps used on land rigs

 Secondary power source – Air power pumps located on control manifold. – Stand by diesel driven air compressor piped to pumps should be provided at location away from primary power source.

 Battery packs – Where electric panels are used, a battery pack is required

 Manual closing – Extension arms and wheels should be considered for ram preventers.

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Control Systems-Control Manifolds  Equipped with three control manifolds or panels – Central Manifold

Drilling Engineering -Well Control

Located away from the rig floor area. All hydraulic, air-hydraulic or electro-hydraulic Required features are – Regulator to reduce accumulator pressure to operating pressure for ram preventers ,annular preventers and valves. – Control handles or switches – Pressure gauges – By pass valves – Vent line for bleeding off accumulator fluid – Relief valve for pumps – Flow meters.

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Control Systems-Control Manifolds – Driller's Control Panel Located on the rig floor within access.

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Air or electric operated Required features include: – Control for each BOP Stack and to adjust manifold regulators. – Read-outs for accumulator pressures, manifold pressures and flow meters. – Air supply pressure read outs. – Schematic showing kill & choke lines – Visual or audible warning devices

– Remote Manifold Located at safe distance from well access Required features include: – – – –

Controls for BOP Stack Interlocks and covers Visual and audible warning systems Schematic of BOP Arrangement. ©2005 Abalt Solutions Limited. All rights reserved

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Drilling Engineering -Well Control

Control Systems-Accumulators  Hydraulic fluid required to operate the BOP functions is stored in accumulators, pressurized against a nitrogen inflated bladder.  Located near control manifold.  Stores hydraulic energy and high rate supply of fluid for BOP functions.  Operating pressures are 3000 psi.

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Control Systems-Pipe Works/Wiring

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 High capacity conduits for individual functions.  For a particular function, fluid flows from accumulators, through regulators and directly to function.  Control lines should be seamless steel tubing of 1 in minimum nominal size and pressure rating equal to working pressure of control system.

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Associated equipment

Drilling Engineering -Well Control

 Mud control & Monitoring equipment  Mud gas separators  Drill string valves  Rotating heads

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Associated equipment-Mud control & Monitoring

 Pit volume measurement – Calibrated read-out and audio alarm installed in Driller’s station  Flow line measurements – Measures flow line mud return rate  Trip tank – Used to fill hole during trips, measure mud volumes or water into annulus when circulation is lost or logging etc. – Types  Gravity feed  Pump type

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Associated equipment-Mud gas separators

Drilling Engineering -Well Control

 Separates gas from drilling fluids  Provides a means for safety venting the gas and returning usable liquid mud to active system.  Minimizes risk for gas influx circulation during a kick without having to shut down the system  Types – Atmospheric

 Referred to as ‘gas buster’ or ‘poor-boy’ separator.  Simple design and does not require control valves on either discharge lines

– Pressurised

 Operates with moderate back pressure generally 50 psi or less.  Overcomes line pressure losses due to excessive lengths of vent lines

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Associated equipment-Drill String Valves  Used to close in well on the drill pipe bore and to protect surface equipment.  Placed on surface and may be either manual shut-off or automatic check valve type.  Rated at same pressures as BOP & tested at same frequency.  Types

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– Kelly Valves

 Upper kelly valve closes on drill string when kelly is down through rotary table and cannot be lifted.  Lower kelly valve allows closing- in on drill string and removing kelly if required

– Float valves

 Prevents back flow during connections and flow up drill string in the event of a kick.

– Drop-in valves  Held on surface & dropped down to a special landing sub.  Allows pipe to be stripped to bottom and preventing further circulation

– Drill pipe safety valves  Installed when kick occurs, allows drill string to be closed-in.

– Inside BOP

 Surface installed checked valve to close drill string bore.  Available on rig floor as back up and installed above drill pipe safety valve ©2005 Abalt Solutions Limited. All rights reserved

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Drilling Engineering -Well Control

Associated equipment-Rotating Heads

 Installed above BOP and provide seal on kelly or drill pipe.  Drive unit is attached to Kelly, locates in bearing assembly  Applications – Drilling with air or gas – Permit drilling Underbalance. – Diverter for surface hole – Keep gas away from rotary table, important when H2S can be expected

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Kill Method-Driller’s Method  Well shut in after the kick has occurred with appropriate shut in procedures followed.

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 Influx circulated out using original mud in hole.  Once kick is out of hole, the hole is filled with the heavier kill mud.  Two circulations: – First circulation-remove influx – Second circulation-circulate kill mud

 Advantages – Minimum circulation – Minimum idle time – Minimum well information required

 Disadvantages – High annular pressure if kick contains gas – Maximum time with well under pressure – Maximum time spent controlling choke

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Drilling Engineering -Well Control

Kill Method-Driller’s Method

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Kill Method-Driller’s Method

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Kill Method- Wait & Weight (Engineer’s) Method  Influx is circulated out by the kill mud in one cycle.  Requires manipulation of choke to maintain constant bottom hole pressure as the new mud moves from surface to bottom.

Drilling Engineering -Well Control

 The kill may require several circulation cycles with mud density raised in stages.

 Advantages  Lowest wellbore and surface pressure.  Minimum time spent on choke

 Disadvantages  Idle time weighting up with gas migration possible.  Possibility of several cycles if large mud weight increase is necessary.

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Kill Method- Wait & Weight (Engineer’s) Method

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Drilling Engineering -Well Control

Kill Method- Wait & Weight (Engineer’s) Method

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INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase

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Kill Method-Concurrent Method  Mixes the features of Drillers & Engineers Methods.  Applied in cases where surface pressures need to be kept as low as possible and shut-in time minimum.  Circulation starts immediately after observing shut-in pressures using current mud weight.  Mud weight is then increased in stages.  As each stage of increased mud weight reaches the bit, the driller starts pumping next stage.  When the new mud reaches the kill mud weight, circulation continues until new mud reaches the surface.  This method requires more choke manipulation to maintain constant BHP like Engineers method.

 Advantages – Minimum idle time – Control starts immediately – Continuous and smooth adjustment of mud density

 Disadvantages – Slightly more complex calculations – Maximum time spent circulating under pressure. ©2005 Abalt Solutions Limited. All rights reserved

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Well control -Without Circulation

If the influx is gas-drill string out of hole ?  Volumetric method to bleed –off ,allowing gas to expand as it migrate.

Drilling Engineering -Well Control

 Most effective method when the kick occurs during swabbing.  In most cases mud weight is sufficient to prevent further influx before the circulation of weighted mud.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Well control -Without Circulation

X

X Drilling Eng inee ring-We ll Contro l

Kill Fluid

Displace Small Amount of Kill Fluid Into Well.

Gas

X Kill Fluid Settles To Bottom

Gas

Gas Pressure Bled Off at Surface (Process Repeated)

Gas Compressed

Kill Fluid Kill Fluid

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Top Kill Method

 Bullheading

Drilling Engineering -Well Control

– Injection of mud into the closed annulus to force invading fluids back into formation. – Used in cleaning up well bore after a drill stem test in cased holes. – Only used in kick control when no other method is possible. – Disadvantage is that there is a high risk of failure of casing shoe and creation of fissures to surface behind casing.

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Safety

 To avoid or prevent flowing of wellbore fluids!

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 A general rule is that at least two independent and tested barriers should be used.  There are two types of barriers: – Mechanical – Hydrostatic

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Mechanical Barriers  Closeable Barriers: – – – –

BOP Rams Xmas Trees Valves SSV Annular preventers

Drilling Engineering -Well Control

 Closed Barriers: – – – –

Wireline stuffing box Coiled tubing stripper Snubbing strippers Coiled tubing check valves

 Additional Barriers: – – – –

Wireline Plugs Cement Plugs Overbalanced hydrostatic fluid Bridge Plugs ©2005 Abalt Solutions Limited. All rights reserved

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase Hydrostatic Barriers

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 As their name says it all, this type of barrier is provided by liquid.  Typical fluid barriers are: – – – –

Drilling Mud Completion Brines Seawater Fresh Water

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Drilling Engineering -Well Control

Pressure Control Devices

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September – October 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION Development Phase BLOW OUT

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When secondary control fails, then blowouts occur.  Massive influx to the wellbore and ‘gusher’ to surface.  To control this, it maybe useful to close blind rams before abandonment.  Putting blowouts under full control may require drilling of a relief well, through which are pumped very heavy mud or cement to plug off the well affected.  During blow outs special blow out control teams are required.

Types  External Blowout: It is an Uncontrolled flow of influx to the wellbore and through to the surface.  Internal Blowout or Underground Blowout: It is an uncontrolled flow of influx to wellbore and entry into a weak zone ©2005 Abalt Solutions Limited. All rights reserved

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Drilling Engineering -Well Control

BLOW OUT

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September – October 2005