new aspects of multilateral well construction

52 Oilfield Review

New Aspects of Multilateral Well Construction

José Fraija Hervé Ohmer Tom Pulick Rosharon, Texas, USA

Mike Jardon Caracas, Venezuela

Mirush Kaja Eni Agip Milan, Italy

Ramiro Paez China National Offshore Operating Company(CNOOC)Jakarta, Indonesia

Gabriel P. G. Sotomayor Petróleo Brasileiro S.A. (Petrobras) Rio de Janeiro, Brazil

Kenneth Umudjoro TotalFinaElf Port Harcourt, Nigeria

For help in preparation of this article, thanks to AxelDestremau, Port Harcourt, Nigeria; Robert Dillard and JimFairbairn, Rosharon, Texas, USA; James Garner, SugarLand, Texas; Gary Gill, Calgary, Alberta, Canada; HeitorGioppo and Joe Miller, Rio de Janeiro, Brazil; Tim O’Rourke,Jakarta, Indonesia; and John Spivey, University ofWyoming, Laramie, USA. CBT (Cement Bond Tool), Discovery MLT, ECLIPSE,FloWatcher, MultiPort, MultiSensor, NODAL, Phoenix,PowerPak XP, QUANTUM, RAPID (Reliable AccessProviding Improved Drainage), RapidAccess, RapidConnect,RapidExclude, RapidSeal, RapidTieBack, USI (UltraSonicImager) and VISION475 are marks of Schlumberger.

Multiple drainholes that diverge from a main wellbore maximize reservoir contact. In addition to providing more

drainage area than a single-bore well, these multilateral completions potentially reduce overall drilling risk and

total cost. To meet specific field-development objectives in today’s demanding oil and gas applications, operators

require reliable junctions between primary casing in the main borehole and liners in lateral well branches.

In the pursuit of optimal production, cost reduc-tion and maximum reserve recovery, operatingcompanies in the petroleum industry are placingincreasing emphasis on multilateral comple-tions—separate drainholes, or branches, drilledfrom a single primary borehole. More than 10% ofthe 74,000 new wells drilled each year arecandidates for these types of completions.Multilateral technology is also used for reentrydrilling applications in existing wells.

Basic forms of multilateral wells have beenaround since the 1950s, but early drillingmethods and completion equipment were suit-able in only a few applications. Improvements in well-construction techniques during the 1990sallowed operators to drill and complete anincreasing number of wells with multiple lateralbranches.1 Today, main wellbores and lateralscan be drilled vertically, at high angles or horizon-tally to address various subsurface conditions.

Multilateral well configurations range from asingle drainhole to multiple well branches in hor-izontal-fanned, vertical-stacked or dual-opposedarrangements (next page). Laterals are com-pleted as openholes and with uncemented orcemented “drop-off” liners—casing that is notconnected to the main wellbore. Other comple-tion designs use mechanical assemblies toprovide a strong connection, pressure integrityand selective access at junctions between lateralliners and the primary casing of a main wellbore.

Like any other well completion, multilateralliners often include external casing packers toensure zonal isolation or mechanical screens forsand control. Production from individual lateralscan be commingled or flow to surface through

separate tubing strings. Today, wells also mayincorporate advanced completion equipment tomonitor and control flow from each lateralbranch. Accordingly, drilling and completion risks vary with well configuration, junction com-plexity, well-completion requirements anddownhole equipment.

Multiple laterals increase productivity bycontacting more reservoir than a single-bore well.In some fields, multilateral technology offersadvantages over other completion techniques,such as conventional vertical and horizontalwells or fracture stimulation treatments.Operators use multilateral wells to target severalformations or more than one reservoir and to tapbypassed reserves with a single main wellbore.Multilateral technology often provides the onlyeconomical means to produce isolated reservoircompartments, outlying satellite fields and smallreservoirs containing limited reserve volumes.

Multilateral wells are particularly suited forconnecting vertical and horizontal features, suchas natural fractures, laminated formations andlayered reservoirs. Multiple high-angle or hori-zontal drainholes intersect more natural fracturesand often enhance production better than single-bore horizontal wells or hydraulic fracturing. Amultilateral well should be considered in settingswhere directional or horizontal wells are appro-priate. Directional, horizontal and multilateral wellsoptimize wellbore contact with a reservoir andallow higher flow rates at lower pressure dropsthan single-bore vertical or horizontal wells. 1. Bosworth S, El-Sayed HS, Ismail G, Ohmer H, Stracke M,

West C and Retnanto A: “Key Issues in MultilateralTechnology,” Oilfield Review 10, no. 4 (Winter 1998): 14–28.

2. Betancourt S, Shukla S, Sun D, Hsii J, Yan M, Arpat B,Sinha S and Jalali Y: “Developments in CompletionTechnology and Production Methods,” paper SPE 74427,presented at the SPE International PetroleumConference and Exhibition, Villahermosa, Mexico,February 10–12, 2002.

But there are limits to how long a single hor-izontal section can be before borehole and pipe,or casing, friction limit well outflow. Multilateralwells reduce frictional pressure losses duringproduction by spreading inflow across two ormore shorter lateral branches. For example, dual-opposed laterals reduce flowing friction pressurecompared with a single-bore horizontal well thathas the same reservoir exposure and productionrate (see “Key Design Considerations,” page 68 ).

Multilateral wells require additional initialinvestment in equipment, but potentially reducetotal capital expenditures and development costsas well as operational expenses by decreasingthe number of required wells. This technologyreduces wellhead, platform-riser and subsea-completion requirements, which decreases costand optimizes slot utilization on offshore plat-forms or subsea templates. Multilateral wellsalso minimize the size, or footprint, of surfacelocations and mitigate environmental impactonshore. Fewer main wellbores reduce repeatedexposure to shallow drilling risks.

Lateral junctions are a critical element of mul-tilateral completions and can fail under formationstresses, temperature-induced forces and differ-ential pressures during production. Junctions are

Autumn 2002 53

divided into two broad groups: those that do notprovide pressure integrity (Level 1, 2, 3 and 4),and those that do (Level 5 and 6). Multilateralsuccess depends on junction durability, versatil-ity and accessibility.

Level 3 and Level 6 systems have emerged aspreferred multilateral junctions.2 Level 3 junc-tions incorporate a liner tieback and mechanicalconnection to the primary casing that permitselective access and reentry of lateral branches.Level 6 junctions are an integral part of the pri-mary casing string that provides pressureintegrity and lateral access.

New junction-construction techniques allowthe use of multilateral wells in a wider range ofsubsurface conditions for a growing number ofreservoir applications. However, more complexequipment and well configurations create techni-cal obstacles, operational risks and economicconcerns that operators and service companiesmust address. This article reviews multilateralapplications and classifications. We also discussjunction systems and installations through test-well results and field examples from the USA,Canada, Venezuela, Brazil, Nigeria and Indonesia.

Reservoir Applications Multilateral wells replace one or more individualwells. For example, a dual-opposed multilateralwell replaces two conventional horizontal wells,each drilled from surface with separate casingstrings and wellheads. For areas with shallowdrilling hazards, deep reservoirs or fields in deepwater, a single main wellbore eliminates the riskand high cost of drilling to total depth (TD) twice.Onshore, this reduces the number of wellheadsand the size of surface locations. Offshore, multi-lateral wells conserve platform and subseatemplate slots, and reduce surface-facility anddeck-space requirements.

A primary advantage of multilateral wells ismaximum reservoir contact for increased pro-ductivity or injectivity, and improved recoveryfactors. Several lateral drainholes intersect andconnect heterogeneous reservoir features, suchas natural fractures, streaks of higher permeabil-ity, laminated formations or layered reservoirsand isolated pockets of oil and gas. Maximizingreservoir contact increases wellbore drainagearea and reduces pressure drawdown, whichmitigates sand influx and water or gas coningmore effectively than do conventional verticaland horizontal wells.

Shallow, depleted orheavy-oil reservoirs

Verticallystacked laterals

Horizontally fannedlaterals

Dual-opposedlaterals

Laminated orlayered reservoirs

Main wellbore

Junctions

Low-permeability ornaturally fractured reservoirs

> Basic multilateral configurations. Horizontally spread laterals in fork, fan or spine-rib arrangements target a single zone to maximize production fromshallow low-pressure or heavy-oil reservoirs and fields with depleted pressure. Vertically stacked laterals are effective in laminated formations or layeredreservoirs; commingling several horizons increases well productivity and improves hydrocarbon recovery. In low-permeability and naturally fractured formations, dual-opposed laterals can intersect more fractures than a single-bore horizontal well, especially if stress orientation is known, and can alsoreduce flowing friction pressure during production.

Any new technology has elements of risk andtechnical complexity, so both advantages anddisadvantages must be addressed.3 Loss of a main multilateral wellbore results in lost pro-duction from all the branches. Multilateralcompletions are mechanically more complex thanconventional wells and depend on new tools anddownhole systems. Well control during multi-lateral drilling or completion operations can bedifficult. Also, there are greater risks related tolong-term wellbore access for remedial wellwork or reservoir management.

After consideration of positive and negativeaspects of multilateral technology as well as itslong-term impact on field development, severalreservoir applications become evident. Wells withmultiple laterals are particularly suited for fields

with heavy-oil reserves, low permeability or natural fractures, laminated formations or layeredreservoirs, bypassed hydrocarbons in distinctstructural or stratigraphic compartments andmature production or depleted reservoir pressure.4

Economic development of heavy-oil reservesis limited by low oil mobility, steam-injectionsweep efficiency and recovery factors (see“Heavy-Oil Reservoirs,” page 30). For heavy-oil orother low-mobility reservoirs, lateral drainholesoffer advantages similar to hydraulic fracturingtreatments in low-permeability gas zones.Increased wellbore contact with a reservoir stim-ulates oil production. Horizontal laterals alsoreduce pressure drops across the completionface, mitigate water coning and improve steaminjection in these reservoirs (above left).

Low-permeability and naturally fracturedreservoirs are frequently associated with limitedproductivity, so formation anisotropy is a factor indesigning multilateral wells. Hydraulic fractureslie parallel, not perpendicular, to natural frac-tures. As a result, wells produce as if proppedfractures were much shorter than in a homoge-neous reservoir. Horizontal laterals drilledperpendicular to natural fractures significantlyimprove well productivity by intersecting morefractures (above middle).

In laminated zones and layered reservoirs orheterogeneous formations, wells with verticallystacked laterals improve productivity and reserverecovery by connecting multiple pay intervalsseparated by vertical barriers or permeabilitycontrasts and gradations (bottom left).Simultaneously producing multiple zones helpskeep production rates above the economic limitof surface facilities or offshore platforms andprolongs the economic life of wells and fields.

Multilateral wells can tap and producebypassed reserves in distinct reservoir compart-ments created by depositional environments,formation diagenesis and sealing faults (left).When reserve volumes in individual blocks do notjustify a dedicated single-bore well, multilateralcompletions can connect several reservoir com-partments. Reservoir compartmentalization alsooccurs as aquifer or injected water sweeps pastlow-permeability areas, leaving pockets ofbypassed oil and gas that can be recovered bydrilling and completing multilateral wells.

In a similar fashion, multilateral wells allowdevelopment of small reservoirs and outlyingsatellite fields that are not feasible to produce

54 Oilfield Review

> Heavy-oil reservoirs. In addition to improvingsteam injection, horizontally spread lateralsmaximize production and improve recovery fromheavy-oil deposits and thin, shallow or depletedreservoirs by increasing wellbore drainage area.In reservoirs with thin oil columns, horizontallaterals mitigate premature water and gasbreakthrough, or coning.

> Low-permeability or naturally fractured reser-voirs. Horizontal laterals improve the likelihood of intersecting natural fractures and completingan economic well in naturally fractured forma-tions with unknown fracture orientation. If stressorientation is known, dual-opposed laterals opti-mize wellbore contact with the reservoir.

> Laminated formations or layered reservoirs. In layered reservoirs, several vertically stackedlaterals contact more of the reservoir than asingle-bore vertical well and can tap multipleproductive formations. Varying lateral inclinationand vertical depth of each drainhole can drainmultiple thin formations.

> Isolated reservoir compartments. Multilateralwells often are more efficient than individualwellbores for tapping bypassed hydrocarbons in distinct reservoir compartments or as a resultof partial reserve depletion.

> Satellite fields. Multilateral wells are an effec-tive and economical means of producing outlyingfields and small reservoirs containing limitedhydrocarbon volumes.

Autumn 2002 55

with conventional vertical, high-angle or hori-zontal wells (previous page, top right). Operatorsalso use multilateral wells to exploit low-pressure and depleted reservoirs, particularly forinfill and reentry drilling.5

In mature fields, multilateral wells improveinfill drilling by targeting areas that are noteconomic to produce with a dedicated well-bore. During plateau production, drilling lateralbranches from existing wellbores taps additionalhydrocarbons without abandoning current produc-tion. This strategy improves the flow rate from awell and increases recoverable reserves, allowingmature reservoirs to be produced economically.

Wells with multiple branches help modifyreservoir drainage in tertiary water- or steam-injection projects. Lateral branches sidetrackedfrom existing wells control inflow location andimprove flood patterns as sweep efficiencychanges over time. Producing previously bypassedhydrocarbons and realigning injection patternswith lateral well branches eliminate the need topush reserves toward existing production wells.

Multilateral wells also assist with reservoirconformance to control gas and water inflow.Multiple lateral branches drilled with variablelengths in different layers improve hydrocarbonvertical sweep and reserve recovery. Horizontal

laterals mitigate gas and water coning in somereservoirs, especially those with thin oil zones,gas caps or bottom-waterdrive. Multilateralwells improve recovery during gas-cap depres-surization late in the field life cycle and alsoimprove deliverability in gas-storage projects.6

Operators even use multilateral wells forexploration to sample horizontal reservoir qualityand areal extent, and appraise stratigraphictraps. Another role is reservoir delineation. Byplanning two or more laterals from one mainwellbore, a larger area can be probed directlyfrom a single surface location. This approachincreases flexibility during field delineation byallowing each lateral to be planned based onknowledge gained from drilling the main bore-hole and preceding laterals.

In addition to selecting multilateral configura-tions to address specific reservoir applications,engineers must determine the degree of mechan-ical and hydraulic integrity at lateral junctionsthat is required to optimize production and maxi-mize recovery (below).7 Schlumberger offersmultilateral solutions from reentry drilling andopenhole laterals to advanced RAPID ReliableAccess Providing Improved Drainage junctionsthat provide connectivity, strength, sand exclu-sion and pressure integrity.

3. Vij SK, Narasaiah SL, Walia A and Singh G:“Multilaterals: An Overview and Issues Involved inAdopting This Technology,” paper SPE 39509, presentedat the SPE India Oil and Gas Conference and Exhibition,New Delhi, India, February 17–19, 1998.

4. Ehlig-Economides CA, Mowat GR and Corbett C:“Techniques for Multibranch Well Trajectory Design in the Context of a Three-Dimensional Reservoir Model,”paper SPE 35505, presented at the SPE European 3-DReservoir Modeling Conference, Stavanger, Norway,April 16–17, 1996. Sugiyama H, Tochikawa T, Peden JM and Nicoll G: “The Optimal Application of Multi-Lateral/Multi-BranchCompletions,” paper SPE 38033, presented at the SPEAsia Pacific Oil and Gas Conference, Kuala Lumpur,Malaysia, April 14–16, 1997.

5. Hill D, Neme E, Ehlig-Economides C and Mollinedo M:“Reentry Drilling Gives New Life to Aging Fields,” Oilfield Review 8, no. 3 (Autumn 1996): 4–17.

6. Bary A, Crotogino F, Prevedel B, Berger H, Brown K,Frantz J, Sawyer W, Henzell M, Mohmeyer K-U, Ren N-K,Stiles K and Xiong H: “Storing Natural Gas Underground,”Oilfield Review 14, no. 2 (Summer 2002): 3–17.

7. Technical Advancement of Multilaterals, TechnicalAdvancement of Multilaterals (TAML) Forum, Aberdeen,Scotland, July 26, 1999. Hogg C: “Comparison of Multilateral CompletionScenarios and Their Application,” paper SPE 38493,presented at the SPE Offshore Europe Conference,Aberdeen, Scotland, September 9–10, 1997. Brister R and Oberkircher J:”The Optimum JunctionDepth for Multilateral Wells,” paper SPE 64699, pre-sented at the SPE International Oil and Gas Conferenceand Exhibition, Beijing, China, November 7–10, 2000. Westgard D: “Multilateral TAML Levels Reviewed,Slightly Modified,” Journal of Petroleum Technology 54,no. 9 (September 2002): 22–28.

Level 1 Level 2 Level 3

Level 4 Level 5 Level 6

Level 1 –Level 2 –

Level 3 –

Openhole sidetrack or unsupported junction. Cased and cemented main wellbore with openhole lateralor drop-off liner. Cased and cemented main wellbore with uncemented lateralliner mechanically connected to the main wellbore (red).

Level 4 –

Level 5 –

Level 6 –

Cased and cemented main wellbore with cemented lateralliner mechanically connected to the main wellbore.Cased and cemented main wellbore and uncemented orcemented lateral liner with hydraulic and pressure integrityprovided by additional completion equipment inside the mainwellbore—packers, seals and tubulars.Cased and cemented main wellbore and uncemented orcemented lateral liner with hydraulic and pressure integrityprovided by the primary casing at the lateral liner intersectionwithout additional completion equipment inside the main wellbore.

> Junction classifications. Multilateral wells are characterized according to definitions established in the Technical Advancement ofMultilaterals (TAML) Forum held in Aberdeen, Scotland, July 26, 1999 and recently updated in a July 2002 draft proposal. These standardsclassify junctions as Level 1, 2, 3, 4, 5 or 6 based on degree of mechanical complexity, connectivity and hydraulic isolation.

Precut Windows and Junction Connectivity The prefabricated RapidTieBack nonmilling multi-lateral drilling and completion system usescasing-exit windows machined in advance andcovered with a drillable internal sleeve to con-struct closely spaced laterals in new wells(below). This junction system can be installedquickly with minimal rig downtime in wells with

inclination angles up to horizontal. A key systemadvantage is the capability to complete quad—up to four—laterals at right angles with adjacentcasing windows as close as 6 ft [1.8 m].

RapidTieBack quad junctions are designed tolocate junctions within a reservoir and drill high-angle drainholes using short-radius drillingassemblies. This multilateral system also can be

set above the reservoir, which reduces anglebuild-rates and lateral inclination to minimizestress on junctions.

By eliminating milling operations, precut win-dows provide fast and consistent casing exits,avoid steel-cuttings debris and reduce the risk ofcasing damage. Drill bits with hole-openinggauges further reduce risk while drilling out

56 Oilfield Review

3Drill lateral

branch.

Orientationslot

Orientationslot

Inner drillablesleeve

Precutwindow withcompositecovering

1Cement window

section.

Whipstock

Runningtool

Drillbit

Mono-positioningtool

2Clean out casing and

install whipstock.

Liner

Reentrydeployment

tool (RDT)

Liner tieback

Liner settingtool

Inner sleeve

Inner cementing string

4Install lateral liner

and tieback.

Upper profile

Urethanefiller

5 –6 –7 –

Release liner setting tool and lift inner cementing string. Cement liner using dual-wiper plugs. Retrieve liner setting tool and inner cementing string. Wash over RDT with overshot, release monopositioning tool and retrieve RDT.Install inner template sleeve to hold lateral liner in place.

1 –2 –3 –

4 –

Install junction at proposed depth. Orient windows based on gyroscopic measurements and cement primary casing.Drill out internal sleeve and cement. Set retrievable whipstock and monopositioning tool in profile below window section. Retrieve running tool. Drill lateral borehole and remove drilling assembly. Reorient whipstock to drill opposing lateral. Retrieve whipstock and monopositioning tool. Clean out main wellbore.Repeat for next set of windows. Set liner assembly, reentry deployment tool (RDT) and monopositioning tool in profile below window. Shear assembly off of RDT and run liner into lateral.Set liner setting tool in upper profile and lock liner tieback into precut window.

5Optional

cemented liner.

6Remove RDT.

7Complete junction.

Overshot

> Precut casing windows. Applications for RapidTieBack quad junctions include new wells that require fullbore junctions in shallow heavy-oil reservoirs,low-permeability or naturally fractured formations and mature fields with depleted pressure. This system requires no milling of steel casing, connectsliners to the primary casing of a main wellbore and allows cementing of liners.

Autumn 2002 57

cement and the temporary urethane-filled sleeve.A specially designed wash tool with an orienta-tion key confirms that RapidTieBack profilenipples in the main casing are clear of debris.

Installation of a mechanical tieback sleeveconnects lateral liners with the parent casing foradded stability and provides selective reentryaccess to well branches for remedial work.Laterals can remain openhole or be completedwith uncemented or cemented casing, slotted lin-ers and sand-exclusion screens for additionalborehole stability. A large internal diameterthrough the liner tieback in the main wellboreaccommodates bigger completion hardware,high-volume artificial-lift equipment and reentrytools for future well operations.

A large internal bore allows completion toolsand equipment with larger outside diameters,such as high-volume electrical submersiblepumps and hydraulically or electrically operatedtubing and slickline-retrievable flow-controlvalves, to pass through RapidTieBack quad junc-tions. Placing artificial-lift equipment deeperincreases pressure drawdown for additional pro-ductivity and decreases ultimate abandonmentpressure, which improves reserve recovery.

RapidTieBack quad systems have been usedextensively for heavy-oil applications, but theyare also applicable for multilateral-well comple-tions in low-permeability, naturally fractured anddepleted reservoirs to improve well productivityand reserve recovery by increasing wellboredrainage area and reducing pressure drop acrosspay intervals.

RapidTieBack Quad: Canada and Venezuela Thermal processes for enhanced oil recovery(EOR) inject steam to heat formations, reduceheavy-oil viscosity and promote flow. Multiplelateral branches maximize reservoir contact andimprove productivity for cyclic steam injectionand production, a process historically called “huffand puff.” This technique typically involves atleast two months of steam injection and possiblya shut-in and “soak” period followed by six ormore months of production.

Although about four times more costly thansingle-bore wells in these applications, quad-lateral wells typically increase well productivitymore than sixfold. These multilateral comple-tions also limit environmental impact by reducingthe number of wells, which also minimizes

surface facilities such as steam lines and gather-ing lines. During the past six years, RapidTieBackquad systems have been used successfully toconstruct more than 220 multilateral junctions for steam-soak radial wells in Canada and cyclic steam stimulation (CSS) wells inVenezuela (above).8

The RapidTieBack quad junction allows later-als to be initiated and drilled through closelyspaced exit windows in a short section of primarycasing, which facilitates horizontal steeringbefore reaching the bottom of a productive inter-val. Operators use this system to drill directionallaterals by exiting the primary casing above areservoir and turning horizontal after enteringproductive zones.

Combining EOR processes with multilateral-well technology is extremely effective. In mostcases, production economics and reserve recov-ery exceed expectations, so operators in Canadaand Venezuela plan to continue drilling and com-pleting multilateral wells over the next fewyears. Operators in North and South Americaalso are considering RapidTieBack quad systemsfor well-completion applications other thanheavy-oil reservoirs.

8. Stalder JL, York GD, Kopper RJ, Curtis CM, Cole TL and Copley JH: “Multilateral-Horizontal Wells IncreaseRate and Lower Cost Per Barrel in the Zuata Field, Faja, Venezuela,” paper SPE 69700, presented at the SPE International Thermal Operations and Heavy OilSymposium, Portamar, Margarita Island, Venezuela,March 12–14, 2001.

6 ft

Lateral liner

Main wellbore

CANADA

USA

SOUTHAMERICA

ALBERTA

Caracas

Calgary

VENEZUELA

> Quad-lateral completions. Operators have installed more than 220 RapidTieBack quad junctions inVenezuela and Canada (left). Setting precut windows in a short tangent section improves the junction-construction process and facilitates lateral access. This system provides the option of completing upto four laterals openhole or with liners connected to the main wellbore by a mechanical tieback sleevefor added strength and stability at junctions (right). An oriented diverter set in a reference profile pro-vides selective access to reenter lateral branches for remedial well interventions.

Milling Oriented Windows The RapidAccess multilateral completion systemproviding selective drainhole access helps orientmilled casing-exit windows for openhole laterals,drop-off liners and more complex junction instal-lations (below). It also provides selective lateralaccess for reentry operations. This simple, low-cost

window-milling technique uses a speciallydesigned profile nipple, or indexing casing cou-pling (ICC), installed in parent casing strings toorient commercially available retrievable whip-stocks. Using an ICC eliminates the need toorient precut windows by turning and positioninga string of casing from the surface.

The fullbore ICC provides a permanent datumfor milling casing windows and drilling lateralsfrom 7- and 95⁄8-in., or other standard size, pri-mary casing strings. Installing more than one ICCsupports construction of several lateral junctionsand allows multiple reservoir penetrations foroptimal field development. Five different profiles

58 Oilfield Review

Clean out main wellbore. Set reentry deployment tool (RDT) and selective landing tool in ICC to divert drilling assemblies and logging tools through casing window. Drill lateral borehole. Install liner on drillpipe guided by RDT for borehole stability and zonal isolation. Pump cement through drillpipe and liner into liner-borehole annulus to a point below thepolished-bore receptacle (PBR) on top of the liner. Release drillpipe from liner and retrieve running tool before cement hardens.Retrieve RDT and selective landing tool.

4 –5 –

6 –

Place ICC in casing below proposed lateral depth and cement casing. The ICC is not oriented in advance. Cement casing.Drill out cement. A proprietary coating prevents cement from sticking to an ICC profile. Wiper plugs typically clean the ICC, but a jetting tool is available to clean ICC profiles.Determine ICC orientation with USI UltraSonic Imager log measurements acquired during a USI and CBT Cement Bond Tool evaluation.Attach retrievable whipstock and selective landing tool to milling assembly. Lock selective landing tool with orienting key adjusted to properly position tools in ICC profile.Shear off of whipstock and mill window through casing. Remove milling assembly and retrieve whipstock.

1 –2 –

3 –

Reentrydeployment

tool (RDT)

ICC

Whipstock

Millingassembly

Drill bit

Drill bit

Logging sonde

USI image

Selectivelanding tool

1Install indexing casing

coupling (ICC).

2Clean ICC profile and

determine orientation.

3Install retrievable whipstock

and mill casing exit.

4Install diverter and drill

lateral branch.

5Optional uncemented andcemented dropoff liners.

6Remove RDT and

selective landing tool.

Overshot

>Milling casing windows. The RapidAccess system uses a profile nipple called an indexing casing coupling (ICC), installed in the primary casing to mill exitwindows for openhole laterals. The ICC serves as a permanent depth and directional orientation reference for drilling and reentry operations. This systemprovides fullbore access in 7- and 95⁄8-in. casing, and is a key component of RapidConnect and RapidExclude junctions.

Autumn 2002 59

provide for additional kickoff points and selectiveaccess to laterals for optimal well-construction,completion and production flexibility. The ICCprofiles can be installed in any sequence and atany depth to verify tool orientation throughoutthe life of a well.

The ICC does not require special installationor operational procedures. An ICC is installed andrun like a short joint of casing. This integraldesign with standard American PetroleumInstitute (API) tubular dimensions simplifieslogistics and allows conventional cementingoperations. The ICC does not restrict internalwellbore diameter or limit casing reciprocationand rotation during cementing, which helpsensure an adequate cement bond.

After the casing is cemented, wireline or mea-surements-while-drilling (MWD) survey toolsdetermine ICC depth and directional orientation sothat a selective landing tool can orient a whip-stock and milling assembly in a specific directionat the chosen depth. The ICC position also can bedetermined from USI UltraSonic Imager log dataoften acquired during CBT Cement Bond Tool eval-uations, which eliminates an extra logging run.

Previous casing-exit techniques requiredinstallation of a temporary packer to serve as areference and platform for milling casing win-dows. With packer-based systems, depth anddirectional orientation are lost after retrievingthe packer. Future access to the lateral isextremely expensive, if not impossible. Now, theICC concept provides positive verification of toolorientation and added confidence during themultilateral well-construction process.

A casing window can be milled up to 90 ft [27 m] above an ICC. Two or three windows can be indexed off of the same ICC at differentorientations as long as they are within the 90-ft spacing. Redundant tool-retrieval featuresensure access to lower laterals. Positioning anICC at the proper depth is the primary considera-tion during installation.

A two-stage process using a whipstock fol-lowed by a special reentry deployment tool (RDT)further improves window milling and junctionconstruction compared with systems that justuse a whipstock. The RDT outside diameter issmaller and thus easier to retrieve than standardequipment, which minimizes debris and tool-retrieval problems after drilling.

The ICC is an important element in multilateral-well maintenance, long-term field-developmentplanning and reservoir management. Setting anoriented diverter in the ICC allows selectiveaccess at a junction for lateral reentry. By pro-viding a permanent reference point and support

for through-tubing lateral access, the ICC reducesthe cost and risk of future remedial work and junction construction. RapidAccess open-hole junctions are applicable in shales andcompetent, consolidated formations. The ICCalso provides the foundation for SchlumbergerRapidConnect multilateral completion systemproviding selective drainhole access and connec-tivity and RapidExclude multilateral junction forsolids exclusion (see “Junction Connectivity andStability,” below, and “Junction Strength andSand Exclusion,” page 63).

Junction Connectivity and Stability In early multilateral junctions, maintaining selec-tive branch access was possible only with precutwindows or more complex junctions. This madeplanning for future laterals difficult because junc-tion depth had to be determined in advance. Inaddition, precut windows with drillable sleeveslimited casing integrity. Building on RapidAccesswindow-milling solutions, RapidConnect and

RapidExclude junctions create a structural con-nection between lateral liners and the primarycasing that allows selective access to wellbranches and the main wellbore. Each wellbranch is cased, but typically only the main well-bore is cemented.

Conventional anchoring systems withmechanical liner hangers or latching mechanismsoften extended into the main wellbore, prevent-ing access to laterals and the main wellbore.Mill-over liners provided temporary access to thelateral and main wellbore, but these junctionseventually collapse under loads caused byformation temperatures and stresses, pressuredepletion, subsidence and high pressure differ-ential when high-volume electrical submersiblepump are used. In contrast, RapidConnect andRapidExclude designs provide mechanicalintegrity at a junction in the event of forma-tion instability and movement over the life of a well (above).

Junction cross section

Template

Maintains mechanical integrity afterformation collapses on junction.

RapidConnect Junction

Unsupported junction moves intomain wellbore after formation

collapses on junction.

Junction cross section

Conventional Mill-Over Liner

Finite-element analysis

Deflection of 3.51 in. intothe main wellbore with a

10-psi load

Negligible deflection with a 1000-psi load

Finite-element analysis

Connector Liner

> RapidConnect junction versus mill-over liner. Constructing a lateral junction by milling over the top of a liner that extends into the main wellbore has several disadvantages (top left). Formation forceseventually push liners back into the main wellbore, restricting access below that point or collapsingthe junction completely. RapidConnect and RapidExclude connectors and templates improve junctionmechanical integrity and reliability (bottom left). These junctions withstand pressures 100 to 150 timesgreater than a mill-over junction. Loads on the junction are transferred to the primary casing by theconnector and template interlocking profiles. Finite-element analysis verified structural integrity of theRapidConnect system. A load of 10 psi [69 kPa] on a mill-over junction results in more than 3.5 in. ofdeflection in 95⁄8-in. casing (top right). However, a 1000-psi [6.9-MPa] load on a RapidConnect junctionresults in negligible deflection (bottom right).

These two systems achieve connectivity atmilled casing windows by assembling junctioncomponents downhole to close dimensional tol-erances. The resulting high-strength connectionsare suited to multilateral applications in unsta-ble, unconsolidated, weakly consolidated orincompetent formations. There are two maincomponents of these systems, a template and aconnector, that fit together to provide consistentjunction connectivity.

The template with a precut window and guiderails is placed next to a milled casing-exit win-dow. These rails match profiles on a connector.The template is installed in an ICC as part of themain wellbore completion, and the precutwindow is oriented adjacent to the previouslymilled casing window for a lateral. Using ICCprofile nipples allows precise tool orientationduring installation.

The interlocking guide rails and connectorprofiles orient and divert the liner and connectorthrough the template window into a lateral. The top of the connector then locks into place inthe upper section of a template to resist linermovement. The concept is similar to tongue-and-groove connections.

This technique creates a strong structuralconnection. The RapidConnect junction achievesa collapse-strength rating of 1500 psi [10 MPa].The smooth transition from main wellbore to lat-eral facilitates subsequent reentry and remedialoperations. Integral through-tubing lateral accessand selective isolation simplify future operationsand facilitate production control.

An optional ICC installed in advance at mini-mal cost allows the flexibility to drill andcomplete other lateral branches in the future.

Unlike precut windows, the ICC provides com-plete casing integrity until an exit window ismilled. If unplanned laterals are required in a well-bore where there is no ICC, the RapidConnectsystem can be installed using a conventionalpacker as the reference datum and tool platform.

Schlumberger evaluated RapidConnect andRapidExclude equipment and procedures in anexperimental well at the Gas TechnologyInstitute (GTI) facility in Catoosa, Oklahoma,USA, to validate the junction-construction pro-cess for milled casing windows (above). Thisfull-scale testing was in addition to conventionalcomponent, subassembly and system-levelqualification tests performed during the stan-dard product-development process. The systeminstallation and junction construction weresuccessful, and the system was fully functionalafter retrieval from the test well. Several

60 Oilfield Review

Template Connector

Profile nipple

Upper packer

RapidConnect template

RapidConnectconnector

Selectivethrough-tubingaccess (STTA)

Selective landing tool

Lower packer

Set template and selective landing tool in ICC or on a packer belowmilled window after running lower completion equipment. Positiontemplate opening across casing-exit window. Retrieve templaterunning tools. Insert connector downhole until the lower end engages in the polished-bore receptacle (PBR) on top of drop-off liner and the upperend lands in the template. Retrieve running tools. Complete junction installation.

1 –

2 –

3 –

Set tubing and packer for upper lateral. Tie into template PBR ifhydraulic isolation is required at the junction.Set a selective through-tubing access (STTA) device with a lockingprofile and a deflector in the template to divert tools into the lateralfor remedial interventions.Install an internal sleeve to isolate a lateral from the main wellbore.

4 –

5 –

6 –

1Install template.

2Install connector.

3Junction complete.

5Optional lateral

access and reentry.

6Optional isolationof upper lateral.

4Install remaining

completion equipment.

> Junction connectivity and strength. The RapidConnect and RapidExclude systems use RapidAccess ICC profiles to construct junctions that connect lateralliners to milled exit windows in primary casing strings. A high-strength junction is constructed in the well, not prefabricated. Two main components areassembled downhole to close dimensional tolerances without precut windows and orienting the casing from surface. The first component, a template withprecut window and guide rails, is set across a milled window. The second component, a connector, physically anchors lateral liners to the template.

Autumn 2002 61

RapidConnect field installations and a full-scaleRapidExclude junction test at the Catoosa site confirmed junction performance and deploy-ment procedures.9

RapidConnect Junction: Nigeria In March 2000, TotalFinaElf ran the first 7-in.RapidConnect junction in Ofon 26, a new welllocated offshore Nigeria (right).10 The main bore-hole penetrated two productive intervals, while asingle lateral branch targeted a fault-isolated section of the upper zone. The welldesign called for a cased and cemented mainwellbore with a cased lateral liner mechanicallyconnected to the primary casing, but notcemented at the junction.

Prior to drilling and completing the upper lat-eral, TotalFinaElf individually gravel packed thetwo producing zones in the main wellbore belowthe proposed lateral. An isolation packerbetween the two screen assemblies allowedselective production from either interval. Tosupport multilateral equipment and comple-tion operations, the 7-in. production casing ofthe main wellbore, which was set at 2883 m[9459 ft], included an ICC for depth reference anddirectional orientation.

The operator oriented a commercially avail-able whipstock in the ICC, milled a window in the7-in. casing between 1916 and 1920 m [6286 and6299 ft] and drilled a 6-in. lateral drainhole to2730 m [8957 ft]. Maintaining formation stabilityand lateral connectivity at this junction depth andhigh angle was a major concern.

A lower 4-in. drop-off liner attached to anupper 41⁄2-in. temporary liner was run into the 6-in. lateral. The upper liner prevented loss ofborehole diameter or hole collapse between the7-in. casing window and the drop-off liner duringcementing operations. Stand-alone sand-exclusion screens without a gravel packcontrolled sand influx and stabilized the produc-tive interval sufficiently, but a water zone abovethe screen depth had to be isolated from thejunction. The operator chose external casingpackers to isolate the sandface before cement-ing. Ported collars allowed cement to be placedin the annulus across from the water zone.

The 4-in. liner assembly included standardwire-wrapped screens for sand control, a primaryand a backup ECP, two ported collars, a polished-bore receptacle (PBR) for a subsequent tiebackliner and a quick disconnect to release the 41⁄2-in.liner. A 23⁄8-in. internal washpipe facilitated fluidcirculation and cementing. A sliding sleeve in the41⁄2-in. liner provided a way to circulate cementout of the annulus below the junction.

9. Ohmer H, Brockman M, Gotlib M and Varathajan P:“Multilateral Junction Connectivity Discussion andAnalysis,” paper SPE 71667, presented at the SPE AnnualTechnical Conference and Exhibition, New Orleans,Louisiana, USA, September 30–October 3, 2001.

Indexingcasingcoupling(ICC)

9 5⁄8-in.casing

QUANTUMproduction packer


Selectivelandingtool

QUANTUM production packer

RapidConnect connector

Sliding sleevewith profile nipple

Portedcollar

PBR Portedcollar

External casingpackers

Cement

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Cement

Sand-control screens


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QUANTUM gravel-pack packer

Bottom packer

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N

AFRICA

NIGERIA

PortHarcourt

Lagos

> Nigeria offshore multilateral completion. TotalFinaElf installed a RapidConnect system to completethe Ofon 26 well in Nigeria, West Africa (middle). The trajectory of the main wellbore targeted twoproductive zones; a single lateral branch tapped a fault-isolated section of the upper zone (top). Thetwo lower zones were completed with standard sand-exclusion screens and gravel packed individu-ally. The operator ran a drop-off liner consisting of stand-alone wire-wrapped screens, a primary anda backup external casing packer (ECP) to isolate the sandface before cementing, two ported collars, a polished-bore receptacle (PBR) and a disconnect to release the running string and a temporary 41⁄2-in. liner to stabilize the lateral during completion operations (bottom). A 4-in. tieback liner then wasset in the PBR of the drop-off liner and locked into the RapidConnect template.

10. Ohmer et al, reference 9.

The workstring tubing, 41⁄2-in. liner and 23⁄8-in.washpipe were retrieved after cementing thedrop-off liner and cleaning out excess cementabove the 4-in. lateral tieback PBR. This left the4-in. drop-off liner in the 6-in. openhole, 18 m [59 ft] from the 7-in. casing window. The junctionwas deployed in two runs: the first to place aRapidConnect template adjacent to the 7-in.milled casing window; the second to tie back into

the drop-off liner and complete the junction witha RapidConnect connector.

On the first trip, the template was seated inthe upper isolation packer below the junction.The second trip stabbed a seal assembly on thetieback liner into the 4-in. PBR on the drop-offliner and locked the connector into the template.A sliding sleeve located in the RapidConnectstinger and shifted by coiled tubing allowed

special conformance-control chemical gels to bepumped into the annulus to further seal the junc-tion and prevent water influx.

Production tubulars and completion equipmentfor the upper main wellbore completion were con-nected into the top of the RapidConnect template,and an isolation sleeve was run across theRapidConnect junction to isolate the lateral.Multilateral technology increased productivity andextended the economic life of this well by allow-ing selective production from multiple zones.

62 Oilfield Review

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13 3⁄8-in. casing16-in. casing

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INDONESIA

ASIA

AUSTRALIA

N

Jakarta Java Sea

> Indonesia multilateral completion. Repsol YPF, now China National Offshore Operating Company (CNOOC), installed a RapidConnect system to completeEast Rama field Well AC-06 in the Java Sea, Indonesia (upper left). Each lateral branch targeted two pay intervals (left and right). The lower 6-in. lateralwas completed with a liner consisting of a 4-in. Weatherford expandable sand screen (ESS) and expandable isolation sleeve (EIS) assembly and 41⁄2-in.blank pipe below a 7-in. liner packer at 2406 m [7894 ft] MD. The upper 6-in. lateral was completed with a liner assembly comprising 4-in. ESS, 22 m [72 ft] of 4-in. EIS, 41⁄2-in. blank pipe and a 41⁄2-in. TAM International external casing packer (ECP) that was connected to the main wellbore and RapidConnect tem-plate by a tieback liner and the RapidConnect connector (middle).

Autumn 2002 63

RapidConnect Junction: Indonesia Developing outlying offshore fields in SoutheastAsia adds substantial oil production and recover-able reserves for the region. These types offields, however, often are located beyond exist-ing development patterns. Operators install smallplatforms with minimal facilities to reduce cost,but this limits the available slots for developmentand infill drilling.

For example, the East Rama field platform inthe Java Sea, Indonesia, had eight wellheadslots and limited weight capacity (previous page).Six slots were already in use when two “sacrifi-cial” vertical wells drilled by the Schlumbergermultipurpose service vessel (MPSV) Bima identi-fied an untapped block of oil reserves. Optimalfield development and reserve drainage requiredfive wellbore entry points in the reservoir.

Repsol YPF, now China National OffshoreOperating Company (CNOOC), decided that twomultilateral wells were the best solution. Actingas the primary contractor, Schlumberger collabo-rated with Diamond Offshore Drilling, M-I DrillingFluids, TAM International and Weatherford onthis project. Each of the two laterals for EastRama AC-06, the first multilateral well, targetedtwo pay intervals. This completion did not requirehydraulic isolation at the junction, so the opera-tor chose the RapidConnect system.

In January 2002, a RapidConnect junctionwas installed to complete Well AC-06.11 Aftercementing 95⁄8-in. intermediate casing at 1875 m[6152 ft] measured depth (MD) and 1196 m [3924 ft] true-vertical depth (TVD), DiamondOffshore Drilling drilled a directional 81⁄2-in. bore-hole to 2430 m [7973 ft] MD, just above thereservoir. The rig contractor then cemented a 7-in. casing string that included a primary and abackup ICC with different profiles. The first ICCwas at 1890 m [6201 ft] MD; the second ICC wasplaced 19 m [62 ft] deeper as a contingency.

The first 6-in. lateral was drilled directionallyto 2608 m [8557 ft] MD using an M-I DrillingFluids synthetic oil-base drill-in fluid andSchlumberger VISION475 43⁄4-in. MWD/logging-while-drilling (LWD) system. After TD wasreached, the lateral liner with a 4-in.Weatherford expandable sand screen (ESS) andexpandable isolation sleeve (EIS) assembly and41⁄2-in. blank pipe was installed below a 7-in.liner packer at 2406 m [7894 ft] MD.

After the liner packer was set and the ESS andEIS assembly were expanded, a 7-in. QUANTUMgravel-pack packer with a plug was set in themain wellbore at 1920 m [6300 ft] MD to isolatethe first lateral and lower completion during

drilling and completion of the upper lateral. Ahigh-viscosity fluid was circulated on top of theisolation packer as a debris barrier.

A selective landing tool run in conjunctionwith the Schlumberger VISION475 system accu-rately determined the downhole orientation ofthe upper ICC. The next run set the selectivelanding tool and a Weatherford whipstock in theupper ICC at 1890 m MD. A 7-in. casing windowwas milled from 1880 to 1884 m [6168 to 6181 ft]MD in less than 21⁄2 hours using a SchlumbergerPowerPak XP extended power steerable down-hole motor. The upper 6-in. lateral wasdirectionally drilled with the same type of drill-influid that was used in the lower lateral.

A 7-in. QUANTUM packer and temporary linerwere run above 78 m [256 ft] of 4-in. ESS, 22 m[72 ft] of 4-in. EIS, 41⁄2-in. blank pipe and a 41⁄2-in.TAM International external casing packer, whichwas set at 6300 ft MD. The ESS and EIS sandfacecompletion were expanded and the ECP wasinflated with cement. The liner disconnect wasreleased, and the upper QUANTUM packer andtemporary liner were retrieved. The whipstockand QUANTUM packer plug were retrieved fromthe wellbore.

Installation of a RapidConnect template andconnector on a tieback liner connected the upperlateral completion assembly with the main well-bore and completed the Level 3 junction. Anelectrical submersible pump set in 95⁄8-in. casingabove the 7-in. liner hanger finalized the comple-tion; production from each lateral branch wascommingled. From start of drilling to first produc-tion, this well was completed in a record 36 days.

At a stabilized oil rate of 874 m3/d [5500 B/D]and 128,864 m3/d [4.5 MMscf/D] of gas, WellAC-06 produces three to four times more oil thanthe best conventional wells in the field. This mul-tilateral well also achieved the highestproductivity level—32 B/D/psi [0.74 m3/d/kPa]—for East Rama field. Well AC-02 and Well AC-03 single-bore completions produced at 7 and12 B/D/psi [0.16 and 0.28 m3/d/kPa], respec-tively. The productivity improvement demon-strated by this well proved that multilateral technology is cost-effective for developing satel-lite fields and bypassed reserves.

Junction Strength and Sand Exclusion Multilateral junctions can experience connec-tivity problems because of unstable formationsand high mechanical loads that adversely affecttheir mechanical integrity. In formations that are prone to sand production, solid particlesentering through junctions cause serious prob-lems. Schlumberger developed a multilateralsystem to construct junctions that exclude sandand better support the loads that are created byformation instability.

Based on proven RapidAccess andRapidConnect concepts, the RapidExclude multi-lateral junction for solids exclusion prevents sandinflux (above). This system is an additionalcompletion tool for layered, faulted and compart-mentalized reservoirs, including wells that

11. Caretta F, Drablier D and O’Rourke T: “Southeast Asia’sFirst Multilateral with Expandable Sand Screens,”Offshore Engineer (April 2002): 55–56. Tanjung E, Saridjo R, Provance SM, Brown P andO’Rourke T: “Application of Multilateral Technology inDrilling an Offshore Well, Indonesia,” paper SPE 77829,presented at the SPE Asia Pacific Oil and GasConference and Exhibition, Melbourne, Australia,October 8–10, 2002.

Polished-borereceptacle (PBR)

Junction cross-sectional views

RapidExcludejunction

> High-strength junctions and sand exclusion. The RapidExclude system is based on RapidAccess andRapidConnect designs. A modified guide-rail profile excludes sand and provides additional mechanicalintegrity. This system resists junction loads up to 2500 psi [17 MPa] and excludes particles as small as 40 microns. This profile view shows engagement between the template and connector of a 95⁄8-in.RapidExclude system (top). Left to right, these cross sections represent slices from top to bottom of theassembly (bottom). The two components begin as concentric pipes and then diverge until there are two separate bores.

penetrate different pressure regimes. Continuousengagement between a modified template-locking rail and connector profile excludesformation grains and solid particles. TheRapidExclude system controls sand influx inunconsolidated or weakly consolidated reser-voirs. This high-strength junction also providesjunction stability in unstable shales or formationswith high stresses.

Most conventional junctions exhibit collapseresistance in the 10 to 100 psi [0.07 to 0.7 MPa]range and have an open gap of more than 1 in.[2.5 cm]. This enhanced junction exhibits collapsestrength that exceeds 2500 psi [17 MPa], andexcludes formation sand grains and solid parti-cles as small as 40 microns.

A 95⁄8-in. RapidExclude system was qualified inJune 2002 at the GTI Catoosa facility inOklahoma. A test well was completed with 95⁄8-in.casing that included a RapidAccess ICC. Field-proven procedures from previous RapidConnectinstallations were used to mill the casing-exitwindow and construct a junction at 970 ft [295 m]in a shaly sand. Junction components wereretrieved as part of this full-scale qualificationtest to evaluate installation reversibility.

The connector was retrieved with a conven-tional spear by applying straight pull. Next, thetemplate was retrieved, again by straight pull.Both components were in good condition andfully functional. The selective reentry deflector,intervention tools and an isolation sleeve wererun and retrieved successfully by a slickline unitto complete the system qualification. TheRapidExclude system performed as expected and was qualified for commercial installation. InNovember 2002, Schlumberger successfullyinstalled a RapidExclude junction in Venezuela.

Junction Pressure Integrity The prefabricated RapidSeal multilateral comple-tion system providing selective drainhole accessand connectivity with a pressure-sealed connec-tion forms a high-strength symmetrical junctionwith hydraulic integrity between two adjacentlaterals and the main wellbore. This system wasdeveloped through a joint research and devel-opment project between Agip, a division of Eni,and Schlumberger.

Early Level 6 junctions consisted of two full-size liners attached to a joint of primary casing.This configuration simplified junction construc-tion, but required a large borehole that resultedin loss of two or more intermediate casing sizes.

The sudden jump from large parent casing tosmaller lateral liners was also a limitation.

Schlumberger and Agip addressed theselimitations by developing a novel metal-formingtechnology. Unlike the RapidConnect andRapidExclude systems, which are assembleddownhole, a RapidSeal junction is manufacturedin advance as one piece. Currently, this systemcombines two 7-in. outlets below 95⁄8-in. casingor two 95⁄8-in. outlets below 133⁄8-in. casing toform a junction.

The manufacturing process reduces initialoutside diameter of the system by plasticallycompressing the two lateral outlets to less thantheir expanded diameters in a special mechanicalpress. This ensures even stress distributions,consistent system geometry and accurate dimen-sional tolerances and allows a compressedjunction to pass through the preceding casingstring, which minimizes wellbore telescoping.

The unique hybrid design of this dual-outletjunction increases resistance to both internalburst and external collapse pressures. Two out-lets are welded onto a stiffener, or structuralmember, made of high-strength material. Onlythe ductile outlets, not the stiffener, sustainplastic deformation. A proprietary processensures full weld penetration along the stiffener-outlet interface.

The RapidSeal system uses a combination ofstrong, ductile components to reduce failures andtubular stresses in the outlets, and maintain thestrength of a junction after it is compressed andreformed. When this system is deployed at theproper depth, a wireline-conveyed expansion toolreforms the outlets to their original size andcylindrical shape in a single trip (next page).Compared with systems that use a mechanicalswedge, this technique greatly reduces installa-tion time.

The reforming process, which takes about 45 minutes, is monitored and controlled in realtime on the surface. This procedure ensures asmooth expansion and confirms that final outletgeometry meets API specifications for internalpipe dimensions. Pistons in the two saddles ofthe expansion tool apply force to simultaneouslyopen and reform both outlets symmetrically.Electric power from the wireline operates a pumpin the tool that provides sufficient hydraulic pres-sure to develop 1.5 million lbf [6.6 million N] offorce in a 133⁄8-in. RapidSeal junction.

An adapter provides a smooth transition froma single bore to the two outlets and connects theoutlets to the main junction bore. The bottom of the junction assembly is a steel frame inside a fiberglass guide that functions as a standardguide shoe and protects the outlets duringinstallation. The steel structure also acts like a whipstock to guide tools out of the junction outlets during drilling and completion of eachlateral branch.

The symmetrical design of RapidSeal junc-tions ensures a smooth transition from the mainwellbore to each branch, allowing standarddrilling tools and completion assemblies to passthrough the junction. Service-pressure ratings for95⁄8-in. and 133⁄8-in. RapidSeal junctions are 1200psi [8 MPa] and 2200 psi [15 MPa], respectively.

After extensive laboratory testing, aRapidSeal junction with 95⁄8-in. parent casing andtwo 7-in. outlets was installed, expanded andcemented successfully in a deviated experimen-tal well at the GTI Catoosa test facility inOklahoma.12 Two 61⁄8-in. directional brancheswere drilled out of the junction. The first branchwas completed with an uncemented 4-in. liner;the second branch was completed with acemented 4-in. liner. The test objective was toevaluate the RapidSeal system before the firstcommercial field installation. Components, toolsand procedures performed successfully duringthis test installation. The 133⁄8-in. RapidSeal sys-tem has been qualified in laboratory tests.

RapidSeal Junctions: Brazil, Nigeria and Indonesia Petrobras installed the first commercialRapidSeal system in an onshore well at Macau,Brazil. This 95⁄8-in. junction was oriented andinstalled above the reservoir at 518 m [1700 ft]MD. The two outlets were expanded to originalround geometry within API dimensional toler-ances and cemented in place. The expansionprocess required 6 hours, including trip time,with only 30 minutes of nonproductive time. The operator directionally drilled two 7-in. lateral branches using a PowerPak XP

64 Oilfield Review

12. Ohmer H, Follini J-M, Carossino R and Kaja M: “WellConstruction and Completion Aspects of a Level 6Multilateral Junction,” paper SPE 63116, presented atthe SPE Annual Technical Conference and Exhibition,Dallas, Texas, USA, October 1–4, 2000.

Autumn 2002 65

1Install junction.

3Install cement retainer and

cement primary casing.

2Expand junction outlets.

4Drill out cement retainer

and wiper plugs.

7Complete junction and

install production equipment.

5Drill and completefirst lateral branch.

6Drill and complete

second lateral outlet.

Clean out main wellbore to top of junction outlets. The RapidSeal profile provides a positive depth indicator.Set and orient deflector in RapidSeal profile to divert drill bit and liner assembly into first outlet. Clean out cement and drill first lateral borehole. Run liner-hanger packer andcasing. Install slickline plug in profile nipple below liner hanger to isolate lateral. Retrieve deflector.Set and orient a deflector in the RapidSeal profile oriented to divert bit and liner assembly into second outlet. Clean out cement and drill second lateral borehole. Run liner-hangerpacker and casing in second lateral branch. Install slickline plug in profile nipple below liner hanger to isolate lateral. Retrieve deflector. Set DualAccess system in main wellbore to complete both lateral branches.

4 –5 –

6 –

7 –

Drill main borehole. Under-ream and enlarge openhole section across junction location. Set RapidSeal system on primary casing. Position wireline-conveyed expansion tool saddles in RapidSeal outlets. Verify junction directional orientation to ensure proper expansion of outlets. Real-time process control and monitoring at surface confirm simultaneous expansion and final geometry of outlets. Retrieve expansion tool. Using the RapidSeal profile for depth verification, set wireline-conveyed cement retainer above junction to prevent a pressure differential and increase reliability. Cement junction.

1 –2 –

3 –

RapidSealsystem

Wireline-conveyedexpansion tool Cement

retainer

Wiper plugs

Drill bit

RapidSealprofile

Liner-hangerpacker

Deflector DualAccesspacker system

> Junction pressure integrity. The RapidSeal system is manufactured in advance, not constructed downhole, to achieve pressure integrity. This TAML Level 6 system includes a prefabricated section of parent casing with two smaller outlets. The symmetrical outlets are compressed to pass through thepreceding casing and then reformed to original geometry by a wireline-conveyed modular expansion tool. The expansion process is controlled and moni-tored from surface in real time and performed in a single trip.

positive-displacement motor (PDM) and 6-in. by7-in. eccentric, bicentered polycrystalline dia-mond compact (PDC) bits (above).

The first branch with a cemented 41⁄2-in. linerfor zonal isolation down to the reservoirextended 644 m [2112 ft]. The second branchwith a cemented 41⁄2-in. liner extended 568 m[1864 ft]. A DualAccess system with isolationpackers set in each lateral and a multiport production packer in the main wellbore washydraulically connected by separate tubing

strings to an Intervention Discriminator and aMultiPort bypass packer with multiple portingabove the laterals. Hydraulic flow-control valvesallow selective isolation or production of upperand lower lateral branches. FloWatcher inte-grated permanent production sensors monitorpressure, temperature and flow rate from eachwell branch.

The DualAccess system is retrievable foraccess to the main wellbore and reentry of bothbranches. After extensive and successful testing

of both laterals for pressure integrity andaccessibility, DualAccess completion equipmentwas retrieved to perforate and complete thewell. The first lateral branch was completed with31⁄2-in. production tubing and a progressing cavitypump (PCP). The second lateral branch was completed with 31⁄2-in. tubing and an electricalsubmersible pump.

Petrobras and Schlumberger are collaboratingtogether to develop procedures for offshoreinstallation and operation of a 133⁄8-in. RapidSeal

66 Oilfield Review

0

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3 1⁄2-in. hydraulic flow-control valves

3 1⁄2-in. FloWatcher productionmonitor (pressure, temperatureand flow rate)

Pressure-relief valve

7-in. tubing

Intervention Discriminator

SOUTHAMERICA

BRAZIL

Perforations

N

Macau

Rio de Janeiro

> Brazil Level 6 multilateral field test. The first commercial installation of a 95⁄8-in. RapidSeal systemwas performed onshore for Petrobras in Macau, Brazil (upper right). Each lateral targeted two produc-tive intervals (lower right). A DualAccess completion system was installed temporarily for extensivetesting and evaluation of advanced flow-control and monitoring equipment (left). This system consistsof tubing strings with seal assemblies for each lateral liner, a packer to isolate the annulus betweenproduction strings, and the primary casing and an Intervention Discriminator to selectively accesseach lateral.

Autumn 2002 67

system in Brazil. Schlumberger has also installedRapidSeal systems in Nigeria for Agip, and inIndonesia for CNOOC.

Agip recently installed a Level 6 junction tocomplete the Idu ML 11 well in Idu field onshoreNigeria. The objective was to produce two sepa-rate intervals—Zones I and L—with two lateralbranches from a single main wellbore. Agipdrilled to the proposed junction depth at 2000 m[6562 ft] and under-reamed the hole to 171⁄2-in.for RapidSeal system expansion.

The junction was oriented before expandingthe outlets and cementing the primary casing.The operator drilled both lateral branches with61⁄8-in. PDC bits using synthetic oil-base mud(OBM) and cemented 41⁄2-in. liners in place. Thefirst lateral extended 693 m [2274 ft]; the secondlateral extended 696 m [2283 ft]. Each outlet wastied back to surface independently using aDualAccess packer system (above). At initialrates of 2250 BOPD [358 m3/d] from Zone L and2000 BOPD [318 m3/d] from Zone I, this well is

producing better than originally forecast andmore like two separate directional wells.

Advanced, or intelligent, completion compo-nents are evolving to meet operator needs, andmultilateral completions are becoming increas-ingly sophisticated. Many wells now includedownhole equipment to monitor production,selectively control flow from lateral branches andmanage reservoirs more efficiently.

CNOOC recently drilled and completed thefirst TAML Level 6 multilateral well in Indonesia

4 1⁄2-in. liner-hanger packer

4 1⁄2-in. liner

Zone I perforations

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PortHarcourt

Lagos

> Nigeria Level 6 multilateral completion. Agip drilled two lateral branches using a RapidSeal junction in theonshore Idu ML 11 well (top). The first branch extended 693 m [2274 ft]; the second lateral extended 696 m [2283 ft](right). Each outlet was tied back to surface independently using a DualAccess packer system (left).

and the world’s first Level 6 intelligent completionto increase recoverable reserves and reducewell-construction costs. A RapidSeal junctionwas installed to complete the NE Intan A-24 wellin the Java Sea (above). This well in 23 m [75 ft]of water required less time to drill—just 25days—and cost about $1 million less than theAC-06 well, a Level 3 multilateral completion inEast Rama field drilled to about the same depthwith similar lateral lengths.

After the 95⁄8-in. RapidSeal junction wasoriented, expanded and cemented in place at2770 ft [844 m] MD, both lateral branches weredrilled with M-I Drilling Fluids synthetic OBM.The first lateral extended 1655 ft [504 m] MD andwas drilled with a 61⁄8-in. PDC bit. The second lat-

eral extending 2335 ft [712 m] MD was drilledwith a 6-in. by 7-in. bicentered bit using aPowerPak PDM that had a 1.83° bent housing.CNOOC completed the first lateral with 31⁄2-in.premium sand-control screens. The second lat-eral utilized 41⁄2-in. premium sand-controlscreens. Each branch included an ECP for zonalisolation.

Advanced well-completion equipment installedabove the junction included downhole hydraulicvalves to control flow and sensors to measurepressure, temperature and flow rate for eachwell branch. A Schlumberger electrical sub-mersible pump with a downhole MultiSensorwell monitoring unit for submersible pump com-pletions and a variable-speed drive at the surface

lifts hydrocarbons to the surface through 41⁄2-in.tubing. A surface control and data acquisition(SCADA) system and multiphase flow meters onsurface monitor pump parameters and well per-formance, and transmit data to CNOOC in realtime via the Web.

Key Design Considerations The first factor to consider when planning a mul-tilateral completion is whether it is a new orexisting well. New wells offer engineers thefreedom and flexibility to design multilateralwells from the bottom up. NODAL productionsystem analysis and reservoir modeling helpestablish optimal lateral length and tubing size,which determines primary and intermediate

68 Oilfield Review

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9 5⁄8-in. RapidSeal junction

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Hydraulic flow-control valve

No-go profile Shear disconnect

FloWatcher sensor

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MZ multizone isolation packer

MultiSensor unit

ASIA

AUSTRALIA

INDONESIA

N

Jakarta Java Sea

> The world’s first intelligent Level 6 multilateral completion. CNOOC recently drilled and completed the NE Intan A-24 well, the first TAML Level 6 multilat-eral in the Java Sea, Indonesia (lower right). After orienting, expanding and cementing the 95⁄8-in. RapidSeal junction at 2770 ft [844 m] MD in place, the oper-ator drilled two lateral branches (upper right). The first branch extended 1655 ft [504 m] MD; the second lateral extended 2335 ft [712 m] MD. Each lateralwas completed with an external casing packer and sand-control screens. An orienting device, or deflector, ensured correct insertion of completion equip-ment in junction outlets. Advanced completion equipment—hydraulic flow-control valves and sensors to measure pressure, temperature and flow rate foreach well branch, a Schlumberger electrical submersible pump with a downhole Phoenix artificial-lift monitoring system and a variable-speed drive on sur-face—made this the first “intelligent” Level 6 multilateral well (left).

Autumn 2002 69

casing sizes. Completion options and well configurations are more limited for existingwells, but many older wells are candidates forreentry using multilateral technology.

Another consideration is junction type, whichdepends on the required degree of mechanicalintegrity and pressure integrity at each lateral,formation stresses, and the need for reentryaccess to individual branches. An openhole lateralwithout junction connectivity may be sufficientwhen lateral production is commingled, junctionsare in competent formations or lateral access isnot required. A Level 6 system may be moreappropriate if selective production or injection ineach lateral is desirable, if the junction is locatedin a weakly consolidated formation or if lateralaccess is required.

Reservoir knowledge is crucial when plan-ning multilateral wells. In exploration or earlydevelopment wells, there may not be enough

information to plan a complex well trajectory. In this situation, operators can drill a low-costvertical well with contingency plans for one ormore laterals, depending on informationobtained while drilling and completing the mainwellbore. Horizontal and multilateral wells alsoare used at this stage to better delineate thereservoir from a single surface location. In latterstages of field development, a considerableamount of reservoir information is available, somore complex well trajectories can be designedto target specific formations, reservoir compart-ments or bypassed reserves.

In economic terms, multilateral wells do notrepresent two or more wells for the price of one.In a few cases, multilateral completions doublewell output, but based on industry averages,increases of 30 to 60% are more likely.Historically, for multilateral wells to be prof-itable, capital expenditures should increase by nomore than 50%. This means that overall well-construction economics should improve by about40%. Optimal multilateral completions are basedon economic evaluation of several alternativesthat rely on forecasts of reservoir performance.

In many situations, numerical simulationusing a single-well or field-wide model isrequired to provide an accurate forecast onwhich to base project economic analysis.Numerical simulation requires more knowledgeof the reservoir, takes longer to set up andrequires more computational time than analyticalmodels. However, numerical models can accountfor effects such as multiphase flow and gravity,complex reservoir geometry and heterogeneousreservoirs. The multisegment well module inECLIPSE reservoir simulation software modelsfluid flow and frictional-pressure losses throughwellbores, annuli, lateral branches and well-completion valves.13 This advanced modelingcapability provides more realistic estimates ofmultilateral-well performance (above left).

Evolving Technology, Increasing Acceptance Following a trend similar to acceptance of hori-zontal wells in the early 1990s, operators in thelate 1990s began to ask, “Why not drill a multi-lateral well?” Today, rather than asking if amultilateral well is applicable, the question oftenis, “What type of well configuration and multi-lateral system is best suited to meetfield-development and production require-ments?” Multilateral wells are not just anaccepted technology, but an essential tool fordeveloping hydrocarbon reserves worldwide.

Exploiting reservoirs with multilateral wells isa viable means of reducing total capital expendi-tures and field-operating expenses, andsignificantly improving production in today’s mostchallenging petroleum arenas. As confidence inmultilateral technology grows, smaller reservoirslike satellite fields currently under considerationfor development in the North Sea, and frontierfields in the Gulf of Mexico, Southeast Asia,West Africa and the Middle East will be devel-oped with multilateral wells.

Multilateral-completion systems vary incomplexity. RapidConnect and RapidExcludejunctions provide enhanced strength and sandexclusion for added durability and more reliablereentry access to lateral well branches in bothnew and existing wells. RapidSeal systems offerthe flexibility to optimize flow from each lateralfor production and conformance control, to pro-duce separate reservoirs with different initialpressures or to inject in one lateral while produc-ing from the other.

There is an increasing trend toward minimizingconventional rig interventions. Using standardcoiled-tubing equipment, for example, theDiscovery MLT multilateral tool system providesselective access to lateral junctions. A flow-acti-vated bent-sub controls tool orientation, whilepressure feedback provides real-time confirma-tion at surface that the correct well branch hasbeen entered. The acid-resistant tool allowsplacement of well-treatment fluids. This systemfacilitates reentry, cleanout and stimulation oper-ations in openhole laterals, drop-off liners orjunctions constructed in existing wellbores.

Multilateral completions were one of the key oilfield technologies to emerge during thepast decade. It is extremely important to screenand select well-completion systems for multilat-eral wells within the context of reservoirconditions, field-development requirements, totalcost and overall risk.14 These techniques serveproduction companies best when thorough risk-reward analysis is performed. An integrated,multidisciplinary team is required to plan, designand implement multilateral wells properly.

Today, service companies continue to invest inresearch and new product development to provideoperators with more reliable tools and systems forinstalling multiple drainage points in reservoirs. Inthe near term, two challenges remain: further opti-mization of equipment and installation consistency.This technology is still evolving, but as long asimproving net-present-value is a primary businessobjective, multilateral technology will continue tobe a leading source of economic gains throughoutthe oil and gas industry. —MET

13. Afilaka JO, Bahamaish J, Bowen G, Bratvedt K, Holmes JA,Miller T, Fjerstad P, Grinestaff G, Jalali Y, Lucas C,Jimenez Z, Lolomari T, May E and Randall E: “Improvingthe Virtual Reservoir,” Oilfield Review 13, no. 1 (Spring2001): 26–47.

14. Brister R: “Screening Variables for MultilateralTechnology,” paper SPE 64698, presented at the SPEInternational Oil and Gas Conference and Exhibition,Beijing, China, November 7–10, 2000.

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> Reservoir simulation and multilateral-well mod-eling. Using ECLIPSE reservoir simulation soft-ware and a coarse, structured grid, this examplecompares a conventional horizontal well that hasa single 4000-ft [1220-m] lateral section with aLevel 6 multilateral well that has two dual-opposed 2000-ft [610-m] laterals (top). Cumulativeproduction from a dual-lateral well greatlyexceeds the output of a single-bore horizontalwell when horizontal permeability (k) varies (bot-tom). To accurately predict production inflow, thearea around a wellbore must be modeled indetail. Each discrete wellbore segment has indi-vidual local pressure and fluid properties. TheECLIPSE simulator also uses a fine and unstruc-tured grid to model wellbore segments and reser-voir flow around complex multilateral trajectories.

new aspects of multilateral well construction

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