Sonatrachs Multilaterals Horizontal wells

Development Phase

September – October 2005©abalt solutions limited - 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION

Abalt Solutions

Introduction to Hydrocarbon Exploitation

©2005 Abalt Solutions Limited. All rights reserved

Multilateral Wells

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Multilateral Technology

Increase in production rates and improverecovery from multiple zones is possible bydrilling side laterals or separate drain holes(branches) from the primary wellbore.

Development Phase



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Multilateral Configurations

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Multilaterals

Advantages– Increased production from

single well– Accelerated production– Reduction in surface well

equipment & costs.– Ease of monitoring wells.– Future plug backs laid out,

avoiding expensive futurere-drills

Development Phase



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Applications

Some of the key applications are:– Tight reservoirs-Improving drainage architecture– Improving efficiency of EOR– Slot recovery– Injection/Production from same well– Complex drainage reservoirs-accessing

discontinuous intervals.

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Applications

Heavy Oil Reservoirs– Improving steam

injection– Increasing drainage

cover in depleted andshallow reservoirs

– Mitigate water or gasbreakthrough orconning in thin oilreservoirs

Low permeability ornaturally fracturedReservoirs

– Intersecting naturalfractures

– If orientation isknow, dual-opposedlaterals optimizewellbore contact

Satellite Fields– Effective & economic means

of producing outlayingreservoirs

– Producing from smallreservoirs with limitedvolumes.

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Applications

LaminatedFormations– In a layered reservoir,

several laterals can tapmore pay.

– Varying lateralinclinations can drainmultiple thin zones.

Isolated reservoirs– Tapping by-passed pay

zones– Compartmentalised

Reservoirs due to lowpermeability or inefficientinjection water sweep

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Multilateral Well Planning

Considerations

– Drilling methods– Junction design– Well control issues– Drilling issues– Milling problems– Completion requirements– Lateral requirements– Abandonment

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There are 3 main drilling techniques:– Long Radius– Medium radius– Short Radius

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Kick off methodsA lateral can be kicked off using any of the

methods:– Open hole– Cased hole– Composite casing

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Kick off methods

Open Hole kick-off– Cement plug is first set in

open hole where kick offposition is desired.

Disadvantages– WOC takes a very long time– Possible contamination of

drilling fluid– Must have a good cement job– Low reliability in open hole.Advantages– Simple and cheap– No whip stock needed– Suitable for vertical or

deviated holes– Lateral can be same size as

parent hole– Plug can be drilled out to

access lower hole– No overheads

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Kick off methods

Cased Hole Kickoff– Window is first

cut at theposition wherekick off isdesired

– There aftersameprocedure asopen hole.

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Kick off methods

Whipstock kick off– Metal shunt which when set will allow

drilling or milling assembly to drill indirection required.

– AdvantagesPositive kick off and orientation at

desired depth.Reduces total operational time and

prevents problems with metalcuttings.

Allows removal and re-entry oflaterals.

– DisadvantagesAdditional cost of equipment and

personal to run and set whipstockAdditional time due to multiple tripsPossible difficulties in retrieving

whipstock.

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Junction Design

Junction is a point where multilaterals meet themother bore.

It provides isolation of lateral from main boreand formations.

Allows re-entry into lateral. Junction design should consider

– Junction stability– Location of target below junction– Laterals placed in zones of similar pressures– Casing size and completion design– Life cycle well requirements.

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Junction Classification

Multilateral wells are characterized according todefinitions established in the TAML (TechnicalAdvancement of Multilaterals) Forum.

These standards classify multilateral junctionsas Level 1,2,3,4,5 or 6 based on the degree ofmechanical complexity, connectivity andhydraulic isolation.

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Junction Classification

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Multilateral Level 2

The level 2 multi-lateral technologyutilizes an open hole lateral from acased wellbore.– The level of complication raises

slightly since a window millingoperation is needed to open anexit from the casing when alateral is needed above thecasing shoe.

– Isolation of the entire wellbore ispossible by use of a scab linerover the exit window in the mainwellbore.

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The level 3 of multi-lateral is a linerinsertion into the lateral. This requiresre-entry of the lateral, but is usuallydone before the whipstock is removed.– In this completion, the liner is not

physically tied back to the mainwellbore and no pressure isolationis possible without the scab liner orsimilar equipment

Development Phase



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When pressure isolation isneeded, a physical seal isrequired. The junction sealin a level 4 completion maybe cement or one of a fewmechanical specialtysystems.– The complexity and risk

increases with this seal,but the isolation potentialis vastly improved.

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Cased cemented mainbore with un-cementedor cemented liner.

Pressure integrityprovided by additionalcompletion equipmentinside main well bore.

Development Phase



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Cased cementedmain bore withun-cemented orcemented liner.

Pressure integrityprovided byprimary casing atlateral intersectionwithout anyadditionalcompletionequipment.

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Multilateral drilling

Old wells– pre-installed windows and locator/orienting collars are not used– a special packer incorporating a locator/orienting assembly must be

set in the main casing, after orientation with a survey tool,– A window is milled, before the lateral can be drilled.

New wells,– Windows can be installed with the main casing.– Locator/orienting collars are installed below the windows,– A whipstock, run on drill pipe, is then set in the locator/orienting

collar, across the window, to divert drilling tools out through thewindow.

– Once a lateral has been has drilled directionally, it may be left open,a slotted uncemented liner or sand control screen installed, or aliner cemented in place.

– With cased laterals, the liner stub, protruding into the main casing,must then be milled out, and the whipstock milled out or retrieved.

Development Phase



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Multilateral drilling-New wells

1. Install Junction at proposed depth, Orient window based on gyroscopicmeasurements and cement primary casing.

2. Drill out internal sleeve and cement. Set retrievable whipstock and multipositioning tool in profile below window section. Retrieve running tool.

3. Drill lateral borehole and remove drilling assembly .Reorient whipstock todrill opposing lateral. Retrieve whipstock and multipositioning tool. Cleanout main wellbore

4. Set liner assembly, re-entry deployment tool. Run liner into lateral. Setliner setting tool in upper profile and lock liner tie back into pre-cutwindow.

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Multilateral drilling-New wells

5. Release liner setting tool and lift inner cementing string.Cement liner using dual wiper plugs. Retrieve liner settingtool and inner cementing string.

6. Release multi positioning tool and retrieve re-entrydeployment tool.

7. Complete the junction.

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Multilateral drilling-Old wells

1. Attach Whipstock and selective landing tool to millingassembly.

2. Lock selective landing tool to correct profile to be milled.3. Shear off whipstock and mill window through casing.

Remove milling assembly and retrieve whipstock.

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Multilateral drilling-Old wells

4. Clean out main wellbore. Set re-entry deployment tool andselective landing tool to divert drilling assembly and loggingtools. Drill lateral borehole.

5. Install liner on drill pipe guided by RDT for bore hole stabilityand zonal isolation. Pump cement through drill pipe and linerto top of liner. Retrieve tools before cement hardens.

6. Retrieve RDT and selective landing tool.

Development Phase



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Re-entry

Most multilateral wells have thenbeen equipped with conventionalcompletions, with the packer, ifused, above the upper lateral.

Multilateral wells provide nopossibility for re-enteringlaterals through the completion,and only very limited optionseven if the completion is pulled.

Selective access to laterals, viacoiled tubing, would increase thevalue of multilateral wells, bymaking possible selectivestimulation, perforation,production logging, drillingdeeper with coiled tubing andplugging of water-producingintervals.

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Re-entry

Multi-Lateral Re-Entry (‘MLR’)system allows selective re-entryvia the completion.

– This system employs anoriented MLR nipple, setacross the window beforerunning the completion.

– A through-tubing whipstockmay then be set in the MLRnipple, on coiled tubing, todeflect subsequent coiledtubing runs into the lateral.

Most multilateral completions donot allow more than one tubingstring to be installed, making itnecessary to commingle productionfrom the different laterals.

Development Phase



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Introduction to Hydrocarbon Exploitation


Development Phase

Horizontal Wells

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Horizontal Wells

Wells with an inclination angle of 90 degreesfrom the vertical

Milestones in development– 1950 Russians drilled 43 horizontal wells– 1978 Esso, modern horizontal, Alberta– 1979 Arco drilled to overcome high GOR– 1979-83 ELF and Agip drill first horizontal well in

Ropso Mane.– 1989 265 drilled world wide– 1990 1000 drilled world wide– 1992 Over 2500 drilled world wide -75% in North

America

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Horizontal Well Applications

Increased Formation Contact– Tight formations or heavy oil.– Reservoirs with thin beds.

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Reduction in water and gas coning– Water and gas migrate into wellbore along with

oil– OWC risen into a cone shape around wellbore– Resulting in choked off producing zone around

wellbore.– Horizontal wells have lower drawdown and

discourages coning.

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Intersection of vertical Fractures– Limestone & dolomite formations are brittle and

numerous fractures.– Fractures are vertical and difficult for a vertical

well to intersect.

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Horizontal Wells

Types– Short Radius– Medium Radius– Long Radius

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Horizontal Wells- Short Radius

SRW (Short Radius Wells)– Very high build up rate(60-150 degrees/100ft)– Radius range 40-100ft– Requires special articulated motors

– AdvantagesEnables sharp turns in reservoirsBoth motor and drill pipe drivenLaterals can be tied back by special liners

– DisadvantagesLimited extension possiblePoor directional controlSpecial tools and equipment needed

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Horizontal Wells- Medium Radius

MRW (Medium Radius wells)– Build up rate is 8-30 degrees/100ft– Radius range of 200 to 700 ft– Horizontal drain between 1000-3500ft– Typically consists of build tangent and build-

horizontal section.– Two BHA might be required

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Horizontal Wells- Long Radius

LRW (Long Radius wells)– Build up rate of 2 to 6 degrees /100 ft– Uses a common steerable system containing a

bent sub and downhole motor.

– Two profilesSingle build-up section terminating in horizontal

sectionBuild tangent and higher build lateral section.

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Well Profile Design

Considerations when designing horizontal wells:– Target definition– Single curve design– Double curve design

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Well Profile Design

Tangent Definition– Target location– Entry point into reservoir– Length of horizontal drain– Azimuth range of target– Vertical depth– Dip of target– Tolerance in vertical depth & displacement

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Well Profile Design

Single Curve Design– Hole angle is built up from zero at KOP to 90

degrees at reservoir entry point.– Build up tendencies of both formation and rotary

steerable BHA should be known to avoid missingthe target.

– If Build up rate is too low, well path will fallbelow target and vice versa.

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Well Profile Design

Double build curve design– The problem :If build up rate is high, well path

above reservoir and If build up rate is too low,well path below reservoir.

– The solution :Have a tangent section below initialbuild up curve and then build up to requiredangle when reaching reservoir.

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Torque and Drag

Friction between drill string and walls of thewell

Drag is produced when drill string is moving.Torque is produced when drill string is rotating.For optimum horizontal well profile and drill

string components ,knowledge of Torque anddrag is necessary.

HWDP is run along the curved section ofwellbore to counter act forces of bending anddrag.

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Torque and Drag

Torque– Horizontal section

Th = OD x Wm x L where OD=Outside Diameter of tool joint, in144 Wm=Avg buoyant weight of pipe, lb/ft

L=Length of hole or pipe section, ft– Straight sections of hole

T = OD x Wm x L x f x Sin where =angle required and f=friction factor24

– Final build up section For WOB<0.33 X Wm x R where R=Build up radius ,ftTh = OD x Wm x R

144 For WOB>0.33 X Wm x RTh = OD x Wm x R + OD x WOB (WOB-0.33 x Wm x R)

144 144

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Torque and Drag

Drag Forces– Develop during tripping operations

– Horizontal Section

Dh= 0.33 x Wm x L where Dh =drag force in horizontalsection

– Build up curveFo =0.85 x Wm x R

If Fo<0.85 Wm R, then Db= Wm x R3

If Fo>0.85 Wm R, then Db= 0.69 Fo -0.25 Wm x R

– Straight sections of holeD =Wm x L x f x Sin

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Extended Reach Wells

Wells defined with ratio ofMeasured depth (MD) to TrueVertical Depth (TVD)>2.

Employs both directional andhorizontal techniques .

Current wells have achievedreach to TVD ratios >4.

After initial build, most wellsare drilled with constant sailangles(70 to 80 degrees)

Factors dominating designare– Torque & Drag– Hole Cleaning

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ER Projects typically break into– Ultra Long ERD– Very Shallow ERD– Deepwater ERD– Small rig ERD

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(courtesySchlumberger)

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Industry comparison of ERD Wells.Standard or Advanced Technology ?

(courtesy Schlumberger)

Development Phase



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Available Technologies– Casing Floatation– Downhole adjustable Stabilizers– Rotary Steerable Systems– Mechanical Torque/Drag Reducers– Hole condition monitoring systems

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Extended Reach Wells Key Challenges :

– ECD (Equivalent Circulating Density)– Shallow directional control– Hole cleaning

Applications– Extending life of mature fields by kicking off from old

wells– Controlling environmental impact of drilling operations

(Ex Wytch Farm)– Allows access to reserves in environmentally sensitive

areas.– Permits satellite developments from existing platforms– Increase in production– Reduction in surface locations, completion

components etc.

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Benefits– Economic access of reserves.– Brings production forward– Fewer pipelines and satellite production

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Limitations– Excessive torque and drag– Poor hole cleaning in long, high angle hole sections– Buckling of casing or drill string.– Running casing successfully to bottom– Guiding wellbore accurately through pay zone– Less than optimal directional control in complex reservoirs– Wellbore instability

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Future developmentsLow ECD Drilling fluidsPush down and floating casingUnder balanced drilling improves ROPExpandable TubularSteerablesLarge scale 3-D Modelling and visualization.

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Under balanced Drilling

Drilling with Hydrostatic head of drilling fluidless than pressure of formation being drilled.

Addition of air, nitrogen or natural gas todrilling fluid may create under balanced state.

Development Phase



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Why Drill Under Balanced ?

Reservoir Improvement– Reduced formation damage– Reduced stimulation requirements and costs– Increased enhanced recovery

Drilling Problems– Losses– Differential sticking– ROP and BIT Life– Reduced ECD in Long reach wells

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Advantages– Increased ROP– Decreased formation damage– Eliminate differential sticking– Reduction in risk of lost circulation– Improved bit life– Tight hole problems reduced– Increase hole cleaning capability

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Disadvantages– Wellbore stability and consolidation– Increased drilling costs, depending upon system

used– Possible near wellbore mechanical damage– String weight increased due to reduced buoyancy– Possible excessive borehole erosion– Increased torque and drag

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Rig Type– Conventional– Coil Tubing– TTRD– Hybrid design

Development Phase



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Fluid Systems– Gaseous fluids

AirNitrogen

– Two phase fluidsMistFoamGasified Liquid

– Artificial lift systemsAnnularDrill string injection

– Light liquidsLow mud weightGlass beadsWaterCrude

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Fluid selection for UBD Operations-– Compatibility with formation fluids– Bore hole stability and hole cleaning– Compatibility with formation– System stability– Degree of under balance required– Corrosion and temperature– Health and safety

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Gaseous fluids– Initially air was used,but O2 with natural gas could

cause an explosive mixture.– Cryogenic Nitrogen –requires larger logistics in terms

of storage tanks– Natural gas

– Characteristics of air drillingFaster ROPLonger Bit lifeGreater footage per bitGood cement jobBetter productionRequires minimal water influxRelies on annular velocity to remove cuttings

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Mist Drilling– Small amounts of fluids dispersed into gaseous

environment.– Generally used in areas where formation water is

present– Hole cleaning is more difficult, therefore used in

special operations.

– CharacteristicsRelies on annular velocity to remove cuttingsHigh volumes required (more than 30-40%)Pressure generally higher than dry airIn correct GOR leads to slugging.

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Foam Drilling– Liquid and surfactant added to form foam for

drilling.– High carrying capacity and low density– Foam is stable even once it returns to surface.

– CharacteristicsStable foam reduces slugging tendenciesReduced pump ratesStable foam can withstand limited circulation

stoppages without affecting cutting removal orECD.

Breaking down of foam needs to be addressed.Increased surface equipment needed

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Surface Equipment for UBD– Drilling System– Gas generation Equipment– Well control Equipment– Surface Separation Equipment

Development Phase



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Drilling System– Coil tubing unit-Used when hole size <6-1/8”– Jointed pipe-Used when hole size> 6-1/8”

(courtesy lealtd)

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Gas generation equipment– Cryogenic N2

Truck supplying nitrogenNitrogen converter

– Natural gasGas sourceGas compressorsFlow and Pressure regulators

Documents

Sonatrachs Multilaterals Horizontal wells