`HYDROCARBONS
`
`ISTITUTO DELLA
`ENCICLOPEDIA ITALIANA
`FONDATA DA GIOVANNI TREC CANI
`
`Exhibit 2002
`
`IPR2016-00598
`
`
`
`©
`ALL RIGHTS RESERVED
`
`Copyright by
`ISTITU11) DELLA ENCICLOPEDIA ITALIANA
`
`FONDATA DA GIOVANNI TRECCANI S.p.A.
`2007
`
`M.l.T. LIBRARIES
`
`
`
`
`
`MAR 3 1 2089
`
`Recexveo
`
`Primed in Italy
`
`Phot.o]il.h and priming by
`MARCHESI GRAFICI-IE EDITORIALI S.;1A.
`Via Flaminia, 995l99‘7 - 00189 Roma
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`I This mum! mavbenrwuctod hvcnuiirleht Iawttltlu 1‘: Us. Cede!
`
`Upstream technologies.
`L Novel well and production architecture
`
`i3.1.1 Introduction
`
`5:
`
`computations necessary for their effective
`day-to-day use. All of the tremendous developments
`in all aspects of many different operations were
`focused on the same basic production scheme:
`developing, completing, and producing from a
`vertical well. Today. the art, science. and technology
`of drilling and completing a vertical well have
`reached a very high level of maturity.
`In spite of all efforts, however, production from
`some reservoirs proved highly challenging and
`beyond the existing capabilities of the industry. Even
`though large amounts of oil and gas were known to
`exist underground. the available techniques and
`production architectures were not sufficient to allow
`their economical exploitation. For example, the
`Austin Chalk formation in Central Texas was known
`
`to contain large volumes of hydrocarbon, but the
`productivity of wells drilled into it was random and
`unpredictable. For years operators grappled with
`trying to find a consistent suitable production
`scheme, but with very limited success. A similar
`situation existed in the Rospo Mare reservoir.
`offshore Italy in the Adriatic Sea. operated by Elf
`with Agip as a main partner. After a great deal of
`work. the collaborative efforts of Elf, Agip and
`lnstirut Francais du Petrole led to the conclusion that
`production of this field required different production
`architecture. They finally decided that the best way
`to produce from the fi'actured carbonate reservoir
`was by drilling a horizontal hole and intersecting the
`existing natural fractures in the formation.
`Even though horizontal drilling had been
`attempted in the l940s_. it had been completely
`abandoned as too cumbersome and inefiicient. The
`
`general belief among experts was that many of the
`beneficial results of a horizontal hole could also be
`
`achieved by hydraulically fracturing a vertical well.
`In fact, theoretical developments had shown a direct
`
`185
`
`' For over a century, the centrepiece of production
`igirebitecttue and associated technologies of the oil
`gas industry has been a vertical well. The
`=.-u uction philosophy has been quite simple: based
`"ii the best available geological and geophysical
`ilata, locate the most likely underground spots for
`"
`accumulation of oil and gas, drill a vertical hole,
`ease and cement it to give it long life and to prevent
`fiigration of reservoir fluid into adjacent zones. The
`1.: jority ofthe initial wells were completed
`-a ole along the producing zone to facilitate the
`__ peded flow ofoil. But this model soon proved
`,
`to cause later production problems: excessive and
`controlled water and gas flow accompanied by
`id drop in reservoir pressure and well
`ductivity. lack of access to the zone in poorly
`Iidated formations, and very limited remedial
`. ces and treatments to address flow problems.
`new technologies were developed by the oil and
`and other industries, the production schemes
`I ged to take advantage of the new developments.
`orig the borrowed technologies are reservoir
`-
`eering theories from hydrology, the use of
`I charges for perforation based on military
`r»
`hnology, cementing materials from construction
`Stries, computer modelling and simulation from
`'1 and aeronautical engineering, and many more.
`'
`technologies developed by the industry itself
`_ also proved tremendously valuable in all phases
`operations. Notable among these are electrical
`g, hydraulic fracturing, Logging While
`= mg (LWD), 3D seismic, new drill bits, and
`'_ puterized on—site data acquisition systems.
`— r
`ication of these technologies required the
`opment of new tools and equipment, materials.
`the engineering know-how to perform
`
`I
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`.
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`' -u-"1: NEW DEVELOPMENTS: ENERGY, TRANSPORT, 5USTAlNABlLlT‘I"
`I
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`NEW UPSTREAM TECHNOLOGIES
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`correspondence between the two production
`methods. While horizontal drilling was an unknown
`territory with a very small basis of technical and
`operational support, hydraulic fracturing was a
`well-established and common practice in the
`industry, with all the required tools, equipment,
`materials and technologies in place. Lack of
`technical and operational support base for horizontal
`wells also meant scarcity of know-how, higher risk,
`and greater cost. In spite of these obstacles, it was
`decided to undertake the project, and thus began the
`next generation of production architecture, which is
`shaping the industry at the present time. The success
`of this pioneering effort has led to the development
`of an entirely new production architecture that is
`based on a horizontal well as its centrepiece. From
`the main bore multiple lateral branches are extended
`into the same or other reservoirs, thus substantially
`increasing contact with the hydrocarbon-bearing
`formation. Evolution of this system led to
`recognition that effective production management
`based on this complex scheme requires the ability to
`control and regulate flow from or into different
`branches, and thus recognition of the need for
`downhole flow regulators and intelligent wells.
`Since success of horizontal holes depends on much
`more accurate placement in the reservoir, new and
`advanced drilling and navigation systems had to be
`developed to augment the existing technology. Tools
`and techniques of reservoir description also had to
`undergo major changes to allow better definition of
`the distribution and flow of oil and gas, which led to
`downhole sensor technology development. To take
`full advantage of the above developments, one also
`needs hybrid simulators and decision-making
`processes to economically optimize fluid flow into
`or out of the reservoir. All of these procedures have
`led to the formation of a new frontier in oil and gas
`production, one that is likely to shape the future of
`oil and production.
`Below we review historical, technical and
`operational aspects of each of these technologies. In
`particular, the discussion covers horizontal holes.
`multilaterals. intelligent downhole flow regulators, and
`the technologies that enable their effective utilization.
`These enabling technologies include geosteering,
`permanent downhole measurement devices, and novel
`completion techniques, among others.
`
`3.1.2 Horizontal drilling
`
`History of horizontal drilling
`The first modern horizontal holes were drilled
`
`in France: two in Lacq and one in Castéra-Lou
`
`..
`
`(Giger et at, 1984). All ofthese were land wells.
`The main objective of the first two wells was to
`understand and develop the technology that was
`required for effective production of Rospo Marc
`reservoir, offshore Italy in the Adriatic Sea. The
`first two of these were drilled in Lacq Supérieur at
`the relatively shallow depth of around 2.000 Ft (600
`m). The first well, Lacq 90, was drilled in 1979, and
`its horizontal section was 360 ft (108 m) long,
`completed with an un-cemented sloned liner. The
`next well, Lacq 9], had a horizontal section 1,120 ft
`(336 In} long. Various completion techniques were
`tried in this well to isolate part of the well and to
`reduce flow of water. The third well, Castéra-Lou
`1 l0, was used to demonstrate the feasibility of
`drilling at a depth of9,000 ft (2300 m} and to
`experiment with various completion techniques.
`This well penetrated l,000 it of reservoir (300 m),
`with a 490 ft (147 nl) horizontal section. and
`
`produced at a rate of 440 bblld (barrels of oil per
`day) or 70 m3ld. its production was more than eight
`times higher than the neighbouring vertical wells,
`thus proving the viability of the concept.
`Rospo Mare, the next horizontal well, was
`drilled in the main target ofthe research. The
`formation is a carbonate with very low porosity
`where much of the oil is contained in natural
`
`tinctures and vugs. The reservoir fluid is heavy oil,
`with AP] gravity of l 1° and viscosity of 300 CP. The
`vertical pilot hole was 9 SIB" (_about 24.4 cm) and
`the horizontal open hole was 8 IE2" (about 21.6 cm)
`in diameter. The vertical location of the horizontal
`
`section was 230 ft (70 m) above the oil/water
`
`contact. The horizontal section penetrated 2,000 ft
`(600 tn) of the reservoir. This well produced 3,600
`bbl/d (570 m3!d}, more than twenty times that of the
`other wells in the same field.
`
`The next major development in horizontal
`drilling was led by Maersk Oil & Gas in Dan field.
`Their main intent was also to improve productivity
`of the low permeability chalk. l-lowever,
`accomplishment of their production objectives
`required the creation of multiple fractures in the
`horizontal hole. To do this, they needed to
`successfully install and cement a liner in the
`horizontal section in order to isolate the well for
`
`multiple fracture treatments. Furthermore, creation
`of multiple fractures required new cementing.
`techniques and materials for horizontal wells,
`highly specialized downhole tools. multiple trips,
`and several milling and cleaning operations, as well
`as specialized fracturing materials and techniques.
`All these issues were addressed and resolved
`
`l
`
`through collaborative efforts between Maersk,
`l-lalliburton and Baker Oil Tools (Brannin at at'.,
`
`186
`
`ENCVCLOPAENA or Hvoaaflfi
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`
`
`
`
`0; Darngaard et al., 1992; Owens et all, 1992).
`*. '_ result was a successful completion of long
`and cemented horizontal holes with multiple
`- and substantially higher productions.
`In spite of this spectacular success, the growth of
`ntal hole technology was relatively slow. It took
`- than a decade and many successes and failures
`re the industry developed the required equipment,
`.. ‘ques, technologies and comfort—level to consider
`" ontal drilling as a viable option for field
`loprnent.
`
`_
`'
`_
`
`ff";-. uctivity of horizontal wells
`Several different equations have been developed
`' computation of the productivity of horizontal
`, s. Because of the complexity of the problem, most
`':-“these are approximations of the analytic solutions;
`er, they are accurate for engineering
`putations.
`'Babu and 0deh’s solution (1989) considers the
`a o-steady state flow. Assuming the reservoir
`u etry defined in Fig. 1, and that there is no
`ation damage, their solution for the flow rate q is
`I
`
`qi
`
`7138- to-3b.!':E(_a,,—p,fi
`B,u(1n-"i'—a +1nc,,— 0.75 +s,)
`the productivity index, J, is given by:
`7.03-10* b,.*'iE
`U2
`Hp(In C"';,A
`—0.75 +53)
`
`W
`
`- q is the flow rate, stbfd (stock tank barrelfd); A
`drainage area of the horizontal well, R2; 3 is the
`am.-:fiO1'1 fluid volume factor, rbfstb (reservoir
`lfstock tank barnel):.,u is the oil viscosity. cP; b is
`drainage distance of horizontal hole in y direction,
`=CH is the geometric factor; 19, and k, are the
`eability in directions x and z, in mi) (where x, y,
`-z are coordinates of a point in the reservoir); fig is
`average reservoir pressure in drainage volume, psi;
`
`UPSTREAM TECHNOLOGIES. NOVEL-WELL AND PRODUCTION ARCHITECTURE
`
`puf is the average flowing bottomhole pressure, psi; r,,.
`is the wellbore radius, ft; .93 is the skin resulting from
`partial penetration.
`The approximate expression for CH is:
`
`1nC,, 6.28hJJ;[3
`a+ H
`3 ’<_z1__si (am-
`_
`
`—1n(sin%‘l)—0.s ln(%
`
`1.088
`
`where a is the drainage distance of horizontal hole in x
`direction, it; h is the drainage distance of horizontal
`hole in z direction, it: x0 is the x coordinate of centre
`of well; 20 is the z coordinate of centre of well.
`Denoting by L the length of horizontal hole, if L=b
`(fully penetrating well), then 5320. If L<b, then the
`partial penetration skin, SR, is given for two special
`cases.
`
`In the first case:
`
`a rgflil; 0.75}:
`vi ;
`\C
`
`where k_,, is the permeability in direction y, then:
`
`SR =
`
`b
`
`Pm: (Z ' )
`[Inf + c.251n-:i~1n(sin 18:: 2 )~1.s4J
`
`P”=i:2JIEiF(2£ia')+
`+orslF<ee)eF(es)J}
`
`where F denotes a function.
`
`Pressure computations are made at mid-point along
`the well length, y,,,,«d=(y] +y2)/2. The. values of
`-‘(L/2b). Fl(4ymn+L)/2b] and Fl(4J/m-rL)/lb] in the
`above equations are computed by replacing y with the
`appropriate arguments in:
`
`F(y)= ~(y)[0.l45-+ iny -0.l37y2]
`
`F0’) ={2 —y)[0.l45 + ln(2 -y)- 0.13? (2 -y)]
`y =4.Vgio‘i'L 2,,
`2b
`
`In the second case:
`
`J;_< 1.33;: >_:h_
`Viv};
`\"lr‘;.:
`Yuk:
`
` - 1. Horizontal hole layout
`__,- I-r reservoir.
`
`
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`INEW DEVELOPMENTS: ENERGY. TRANS?0flT, SUSTAINABILITY
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`187
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`NEW UPSTREAM TECHNOLOGIES
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`This gives:
`
`SR = Pr-_r:+ + Pry
`
`=6.2sb2[(tM+@)+
`
`air
`
`r_,.
`
`3:5
`
`52
`
`P *
`
`3‘
`
`These equations indicate the main applications‘.-sf
`horizontal holes and the conditions under which they?
`provide the best production results. Consider a
`horizontal hole with an ellipsoidal drainage radius of--5 i
`5.000 ft (around 1,500 rn). Suppose the intent is to
`drill a horizontal hole with a radius of 0.4 it ( 12.2 cm '
`We will assume four different formation thicknesses '.
`150, I00. 50 and 25 it. or46, 30. I5 and "L5 m) and
`three different hole lengths (2.000. L000. and 500 it, -
`or, 610. 305 and 152 m). We further assume ten
`different values of Ir,/ky { 0.5 through 10}. For each
`case we will compute the ratio of well production to
`that ofa similar wcil in a uniform permeability
`formation. The results are shown in Fig. 3. The data
`show the following important points:
`- Thinner formations yield better production resul .-
`3
`relative to a vertical well.
`- The impact of formation penneability anisotropy’
`more prominent in thick formations. This effect is-
`oflen masked by the higher productivity of thicker}
`formations.
`
`'
`
`-
`
`-
`
`Effect of penneability anisotropy increases as
`length increases.
`in thick formations, behaviour of short horizontal
`well lengths is about the same as a vertical well.
`- Horizontal holes can create spectacular results in‘.
`wells with high effective vertical permeability,
`such as some of the naturally fractured reservoirs
`of the Middle East.
`The above analysis shows that horizontal holes
`not offer a panacea for every production scenario.
`Their effectiveness diminishes in thick. highly
`laminated and heterogeneous formations.
`From the above reported .Ioshi‘s equations. if
`L.-’h3>l and L!2tt<€ 1, then:
`
`Fri’: ~1)("”‘}?“ ill; +’.::’ +2?)
`
`Pm will have the same form as given earlier.
`above.
`
`Another set of equations are those derived by Joshi
`(1988). For the case of an isotropic formation
`(l:,=k_,,=k,=)'t} (Fig. 2), the equation for flow is given
`by:
`
`q_
`
`Zrtkhfip“T
`#B[|n +£]n h J
`
`L
`
`Zr“,
`
`[/2
`
`or —2£ [[15 + 0.25 +(
`
`2,eH_)4]u.s
`
`L
`
`wll-(all
`
`L 2 {L25
`
`where Ap is t.he pressure drop and 20: is the large axis
`of the horizontal drainage ellipse around a horizontal
`well (see again Fig. 2), and r,” is the equivalent radius
`of a presumed circular drainage area.
`For the case of anisotropic formations, where
`horizontal permeability is not equal to vertical
`permeability, tkflitéky). the solution developed by Joshi
`and modified by Econotnides er of. {I991} gives:
`
`F
`
`2J'l:d.'H}iAp
`.-T7
`»B['n“—“%"“9"+§Eln.,.lim]
`
`q:
`
`Znkhlsp
`*2-H
`L/4
`
`_£iB hit
`
`= E
`kl’
`
`13
`
`This is the same as the expected flow from an
`infinitely conductive vertical fracture. This simple
`observation was one of the reasons for slow initial
`
`2,3 is the minor axis of the ellipse represented
`in Fig. 2.
`
`acceptance of horizontal holes. The argument used
`that since one can get the same effective production
`
`Fig. 2. Flow geometry
`in a horizontal hole.
`
`
`
`188
`
`ENCYCLOPAEDIA or n-rot!‘
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`
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`UPSTREAM TECHNOLOGIES. NOVEL WELL AND PRODUCTION ARCHITECTURE
`
`L4
`
`I
`0.2 4
`
`E:
`
`I
`
`.9 on
`
`.95335-ch1.I
`
`
`
`productionratio
`
`‘.3
`
`l‘-J-
`
`3
`
`4
`
`5
`
`fl
`
`7
`
`3
`
`9
`
`Ill
`
`kit/kv
`
`that it decreases the reservoir energy available for oil
`production. Thus, delayed gas production is also
`beneficial for reservoir economics.
`
`Joshi ( 1988) offers the following equation for
`computation of the maximum gas-free oil production:
`
`= l.535(9a —Qg)lt[}t3 —Ut — t',.)2]
`ln(r;_./r,,.)
`
`q""”
`
`where gm, is the ntaximurn gas lice oil production rate:
`9” is the oil density, g/cm’; 9g is the gas density. g/em3;
`2,. is the distance between the gasfoil interface and
`perforation top; r‘, is the reservoir drainage radius, ii‘.
`To use this equation for horizontal holes, one needs
`to substitute rm. (effective wellbore radius) for r,,:
`
`rfl?= IE‘
`
`L
`“ a[l + .-'a=— (1.x2)2][hx2r,,.]h*1
`
`where the expressions for at and r,” are as given
`earlier.
`
`The expression for rnaximurn water-free oil
`production rate, q,., is given by Giger et at’. ( 1984) in
`the form:
`
`kAp I23
`,=1.s3-1o-3——
`Jun
`L
`‘J
`
`A more rigourous solution to determination of
`critical crestittg rate (see below) for horizontal holes is
`provided by Guo and Lee (1992).
`
`Horizontal hole operational challenges
`Together with all of its benefits, the drilling and
`completion of a horizontal hole poses operational
`challenges that must be overcome for its successful
`
`efits of the initial horizontal holes was the delayed
`2. . uction of coning water (Giger era1., I984).
`__ Many oil reservoirs include large volumes of gas
`“L tare usually trapped above the oil zone. With
`uction, because of its lower density and viscosity,
`gas can cone through the oil zone and flow out of
`_
`-1: reservoir. The negative effect of gas production is
`
`-'
`
`Ill! NEW DEVELOPMENTS: ENERGY. TKRNSPORT. SUSTAINII-BILITY
`
`189
`
`
`
`'
`
`'
`
`In a less expensive vertical well with a long
`draulic fracture, there was no compelling reason to
`a horizontal hole with all of its associated
`‘
`' plications. higher costs. and lower operational
`bilities. With time and experience the industry has
`ed the short-comings of the above argument.
`It ulic fractures seldom deliver the theoretical
`
`a uction levels {simply because of the difference
`een theoretical and actual fracture behaviours;
`
`eshy, 2003).
`
`'
`
`r and gas coning in horizontal holes
`The produced fluid from many oil and gas
`' oirs is a mixture of water together with oil and
`'. The volume of produced water increases with
`oir age. In addition to the connate water present
`th oil and gas. water can come from three other
`- es: bottom-water (through eoningj, edge-water,
`urgected water {through high conductivity channels).
`rig, processing, and disposing of the produced
`-r require large operational and capital expenses.
`= addition. many reservoirs use water flooding as a
`"" " "l for maintaining reservoir pressure as well for
`« ing the oil out of the formation. Thus, it is
`'ous that delaying and reducing the production of
`ter will add to reservoir value. One of the observed
`
`_,
`
`
`
`
`
`.
`
`-
`
`Since drilling a horizontal hole costs more and
`takes longer, part of the added cost is offset by
`openhole completions.
`- Cemented completion of horizontal holes is still
`uncharted territory for many operators and
`therefore preference is given to alternative
`completions.
`More discussion of horizontal hole completions .'
`presented later in this chapter.
`
`3.1.3 Multilateral wells
`
`‘
`
`
`
`Fig. 4. Different hole layouts in a horizontal hole: A, undesirable orientation with respect to oilfwater contact:
`B. hole tracking oil./water contact; C. the same as B, but with a shorter and better placed hole.
`
`190
`
`ENCYCLOPAEDIA or HYDRGI --
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`NEW UPSTREAM TECHNOLOGIES
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`implementation. Among these complications is the
`hole navigation. The production outcome of a
`horizontal hole depends greatly on the location of
`the hole relative to the formation. For example.
`delaying water production requires placing the
`horizontal hole close to the top of the reservoir.
`Without water or gas, best production results come
`from a hole which is at the centre of the reservoir.
`
`Given the complex geology and structure of most
`reservoir formations. placing the well at the desired
`part of the formation can become a daunting task.
`Consider the structure shown in Fig. at A. A straight
`horizontal hole in this formation will intersect the
`
`water zone and lose most of its advantages. The
`success of the horizontal hole depends on the ability
`to steer the well properly within the reservoir. For
`example. the case shown in Fig. 4 B satisfies the
`requirement for distance from the olllwater contact.
`but it could face operational problems due to hole
`curvature and the possibility of debris collection at
`the bottom of the well, thus impeding flow of
`reservoir fluid. A shorter and better placed hole can
`offer better production results, as shown in Fig. 4 C.
`Obviously the challenge here goes beyond planning
`and drilling operations. It mandates superior
`reservoir mapping and characterization.
`At the present time, most horizontal holes are
`completed openholc. The main reasons for this
`choice are:
`- The main benefit of horizontal holes comes from
`
`their long contact with the permeable reservoir.
`Casing and perforating these holes reduces this
`contact. However, whenever completion operations
`require hydraulic fracturing, the horizontal holes
`are in fact cased, cemented, and perforated to
`facilitate effective fracturing.
`- Contrary to initial fears, in many formations hole
`stability has not been a big problem. This is
`specially true in those areas where the maximum in
`sin: principal stress is horizontal. Concerns about
`hole stability have sometimes been addressed by
`placing slotted or perforated liners inside the
`horizontal section.
`
`Side-tracking ofl" of an existing well and drilling a
`branch well has long been an established practice of‘
`the oil and gas industry. In the past. the use of this
`technique was limited to problem wells where
`continuation of the existing well path was either
`impossible or very costly. The process consisted of
`placing a high strength cement or mechanical plug
`inside the well to divert the bit into a new path. But
`doing this left the original hole plugged and
`inaccessible for future production or operations.
`With the feasibility and benefits of horizontal
`wells verified by actual applications, industry
`innovators quickly considered extension of the
`process for more robust production schemes. Sev '
`.
`groups. mostly in the North Sea. began planning for
`completion architectures involving production from "
`multiple horizontal holes connected to a mother
`'
`bore. Among these were groups such as Maersk,
`BEB, N0l‘5l( Hydro, BP, and service companies
`as Halliburton and Baker. Although the side-tracldn;“~;
`technology was mature and well-established, new
`technologies were needed to allow the selective
`re-entry of various laterals, as well as commingled
`production from them.
`The technology for side-tracking and drilling
`of existing wells had been in existence for many
`years. Almost all of these side-tracked wells were
`mandated by drilling problems that made
`continuation of the existing bore either impossible on :
`very costly. But in all these applications, the original
`
`_
`
`'
`
`
`
`UPSTREAM TECHNOLOGIES. NOVEL WELL AND PRODUCTION ARCHITECTURE
`
`Classification of multilateral wells
`Classification ofrnullilateral wells is based on
`
`the properties and capabilities of the junction. The
`various levels of multilaterals are described below:
`
`Level I. This is the simplest type of multilateral.
`The two bores are open above the junction which
`olfers no mechanical or hydraulic strength or
`isolation (Fig. 5A). This type ofjunction may be
`suitable for applications where the junction is within
`the pay zone. However. the system does not offer
`any options for flow control. nor is the well suitable
`for re-entry for remedial work.
`Level 2. In this type of multilateral. the main
`bore is cased and cemented but the lateral is
`openhole (Fig. 5 B}. The lateral may include an
`uncemented, slotted or perforated liner for
`mechanical protection. The advantage of this type of
`junction is that it allows re-entry into the main bore,
`as well as installation of flow control devices. This
`
`system is common in applications where all the
`junctions and laterals are within the pay zone. Its
`main disadvantage is poor access to laterals in case
`there is need for re-entry and service work.
`Level 3. In this system. the main bore and lateral
`are both cased. but only the main bore is cemented
`(Fig. 5 C). The lateral casing may be attached to the
`main casing through a liner hanger. This type of
`junction provides access to the lateral in case there is
`need for it.
`
`The main advantage of the next three levels of
`multilaterals is that they allow placement of the
`junction outside the pay zone.
`Level 4. In this system, both main bore and
`laterals are cased and cemented. and this provides
`flow isolation within the well system (Fig. 5 D}.
`However, the junction may not have sufficient
`mechanical strength. This type of multilateral may
`be suitable for cases where thejunction is placed
`within a strong and competent formation.
`Level 5. In this system. also known as a
`downhole splitter, the junction is mechanically
`isolated from the flow conduit (Fig. 5 E}. Both main
`bore and laterals are cased and cemented. This
`
`system is suitable for high pressure andfor high
`temperature applications. It also allows selective
`re-entry into the main bore and laterals for remedial
`service work. However, installation of dual flow
`
`lines requires larger size rnain hole. which adds to
`the drilling cost.
`Level 6. In this system, the two strings of casing
`are mechanically connected together at the junction
`such that the connection itself provides pressure
`isolation as well as mechanical strength (Fig. 5 F).
`One option for the construction of such systems may
`be the use of expandable pre-fabricated junctions.
`
`
`
`; and hydraulic isolation was necessary to
`-
`‘N d internal reservoir pressure during
`action from the laterals.
`Access. Full utilization of the system required
`‘rive access to each of the laterals at any given
`.This feature was necessary to perform the
`us well services during the wells life.
`These three requirements, connectivity,
`"on, and access (abbreviated by their
`yms CIA) became the standard reference for
`teral definitions until it was replaced later
`"number system.
`The first comprehensive plan for installation of a
`‘ ateral well was prepared by a joint team
`-.u D
`'sed of Mobil Germany and I-lalliburton
`-
`. l Research Centre. The target was the deep
`fields in Soelingen, Germany. The main intent was
`one the overall drilling costs of the deep High
`I , High Temperature (I-{Pl-KT] wells in this field,
`ncreasing well productivity by selective
`' ulic fracturing of the laterals when required for
`productivity. This plan was approved for
`_ g by the European Community under the
`‘e project. However. the complex nature of the
`(deep HPHT operations) caused this plan to be
`-a by plans to drill the multilateral off ofa well
`Forties field offshore UK. operated by BP. In this
`" .. . target the intent was access and production of
`passed by water flooding operations. This
`teral was later successfully executed in 1996
`(la er al._. 1996).
`- The first actual installation of a multilateral well
`
`-
`
`successfully completed through collaborative
`'ng, development and operations by Norsk Hydro
`' Hallibutton in well Oseberg l2C in the central
`_
`_
`I Sea in April 1996 (Jones er nl., 1997). More
`__ u ation about the details and features of this
`is presented later in this Chapter.
`
`'
`
`-was abandoned and replaced by the side-tracked
`ch. In the new drilling model, the desire was to
`.-.. ortally drill a second well. re-establish contact
`‘ .. the mother bore. and continue production from
`(or multiple} branches. It was quickly
`ized that the success of such completions
`ded on satisfying the following criteria:
`Connectivity. This meant the lateral is connected
`rnain well such that standard oilfield tools
`
`_ be deployed within the entire wellbore system
`performing conventional well services.
`_,.'§s1olari'on. The junction needed to be
`' ulically and mechanically isolated from the
`‘on. This feature was required to satisfy two
`rtant system needs: mechanical integrity of the
`n was needed to satisfy North Sea
`tions to withstand external formation
`
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`191
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`NEW UPSTREAM TECHNOLOGIES
`
`Levels 2 and 3 may not be suitable when there is
`possibility of sand or solid production. Having a
`borehole support device provides a means for re—entry
`if this becomes necessary.
`When there is possibility of solids production, a
`level 4 cemented junction offers a barrier to solid
`production and may be a better choice. The full ID
`(Inside Diameter) access through the intersection
`provides additional operational flexibility, such as
`deploying tools below thejnnction. It is suitable for
`high rate injection or production wells. It can also
`allow use of large IDXOD (Outside Diameter) isolation
`andfor completion equipment for high rate stimulation.
`Level 4 laterals can also be upgraded to a level 5
`junction by placing a seal-bore packer or PBR
`(Polished Bore Receptacle) in the lateral.
`A level 6 junction can also be installed in a level 4
`lateral by using a PBR or seal-bore packer in the
`lateral below the window.
`
`Junction construction
`
`Construction of the junction is one of the most
`critical parts of multilateral well construction. As the
`requirements of the junction increase, so do the
`difficulties and costs associated with its construction.
`Several critical considerations are involved in selection
`
`of the location and properties of the junction in
`multilateral wells. including the following.
`Junction location. The location of the junction is
`often dictated by the drilling and production
`requirements- Ideally it should be placed in a
`competent rock and located so as to minimize the
`drilling costs and difficulties while enabling maximum
`access and penetration into the reservoir. In the initial
`
`applications of multilateral wells, the junction was
`located in the slanted part of the well above the pay
`zone. Whenever the reservoir formation is a compete
`rock, drilling advancements have made it possible
`,
`easily place the junction in the horizontal section
`.
`the well and within the pay zone itself. This ability ..
`locate the junction substantially simplifies the .—..
`
`requirements for hydraulic isolation. But when the ._.._E_.
`zone is not mechanically competent to maintain
`'
`junction stability during the well life. the junction
`must be placed somewhere else. In such application;
`one needs to consider building a more complex
`_
`junction, preferably a level 5 or 6 type ofjunction.
`'_ ‘
`Jrmcn'on orientation. Afier selecting the location
`H ''
`the junction. the next question is orientation ofthe
`junction with respect to the main bore: above. below;
`to the sides. Advancements in directional drilling
`provide flexibility to reorient the lateral from any
`direction into any other direction to fit the junction, :-I
`production requirements. However, the mechanical
`stability of the junction depends on its orientation "
`respect to the magnitudes and orientations of the
`principal stresses. In an experimental and numerical.
`study of this problem, Papanastasiou er al. (2002) __
`that the most stable direction for the lateral is u :
`'
`
`with the maximum in sitar stress. They also found
`as expected. failure occurs initially in the inte -
`‘ -
`.
`area between the two wells and spreads outward. '
`in siru stresses were not equal (which is usually the I
`case), junction failure preceded wellbore failure.
`
`Fig. 5. Level I to 6
`(A to F) multilateral
`junctions.
`
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`
`Case history: first high level multilateral well
`As mentioned earlier, the first advanced
`multilateral well was drilled in 1993 and was the
`
`_
`
`_
`
`.-
`
`-
`'
`
`L
`
`
`
`
`
`tof collaboration between Norslt Hydro and
`I burton. Development of the hollow whipstock
`‘Q 1; was critical to the implementation of this
`it }was led by Weatherford. The target well was
`-
`; 12C in Oseberg C‘ platform. which was
`. cted for production of Oseberg Field in the
`'1 North Sea, with recoverable reserves of l .6
`
`I
`
`.. s of barrels. Oseberg C is a fully integrated
`.-i that produces through horizontal holes.
`; formation is a medium to coarse grained
`“zone in the Middle Jurassic Brent group (Jones
`3 .1997). In addition to the main productive
`on, Oseberg, large quantities of oil were
`' to be present in the Ness channel sandstone
`. lies above the Oseberg formation. The amount
`In Ness formation was not sufficient to justify
`. ction of another dedicated platform or to allot
`- r - slots in Oseberg C platform for its
`ion. Yet the large volumes of oil present in it
`a slrong incentive for the d