primary cementing equipment

8/17/2019 Primary Cementing Equipment

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Surface Mixing and Pumping Facilities

Major components of surface-cementing equipment are:

• mixers or blenders

• pumping/displacing unit

• cementing or plug-release head

Mixing Equipment

Dry cement must be mixed with the proper amount of water to ensure that slurry andset-cement properties are as designed.

For most slurries the jet mixer produces a uniform mixture. !pecial mixingequipment is sometimes required for high-density cement high-"iscosity cement

and jobs for which precise composition and blending of all additi"es is particularlycritical #such as liner and squee$e-cementing operations%.

&he jet mixer induces a partial "acuum at the "enturi throat drawing in the drycement. 'igh stream turbulence then pro"ides thorough mixing # Figure ( Schematic of jet mixer and typical job-site setup%. &he jet mixer is simple

reliable and rugged and can handle )* sac+s of cement per minute.

Figure 1

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,atch mixing and/or blending is achie"ed through use of propeller- or impeller-typemixers paddle mixers ribbon blenders pneumatic mixing and rotation of thecement tan+ #similar in appearance to those used in construction%. Figure # pneumatic blender % and Figure #ribbon blender % illustrate pneumatic and ribbon

types.

Figure 2

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Figure 3

nly a limited amount of cement can be mixed in a batch unit. 'owe"er se"eralunits can be combined to pro"ide continuous operation on large jobs. ,atch mixerspro"ide the most accurate and thorough mixing of all slurry components.

Density measurements are made to gauge consistency and control the mixingoperation. 0ariations during a job can result from nonuniform blending of drycomponents changes in water/cement ratio or air entrainment in the sample.

Density is measured either on samples with balances #two types% or continuouslywith radioacti"e de"ices or a force-balanced 1-tube.

Pump-Skid Truck

&he typical slurry-pumping unit # Figure 2 % is truc+-mounted and contains dieselengines and displacement tan+s that are accurately graduated so that water or mud

"olumes can be controlled to place the slurry downhole properly.



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Figure 4

3n operation the pumper draws slurry from the mixer in a predetermined "olumecalculated from sac+s and yield. Meanwhile displacing 4uid is drawn from storage totwo open tan+s on the pumper. &he slurry is followed immediately by the 4uid whichis gauged by the alternate draining and 5lling of the two tan+s.

6ementer or pump-s+id styles "ary greatly from small portable units to large truc+-mounted systems. Most wor+ is done at less than )*** psi but pressures up to**** psi #(78** +9a% can be handled with proper equipment. 9umping rates are

dependent on mixing capacity. 'igh rates are (* to () bpm. hen nearing the end of displacement slow rates are preferred to decrease the possibility of plug or casingdamage.

Cementing Heads

6ementing heads pro"ide a connection for pump-truc+ and rig-pump lines into thecasing and a receptacle for the plugs. Modern heads pro"ide a quic+-change cap thatcan be remo"ed to insert the cement plug # Figure ( cement head with manual plug release%.



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Figure 1

Most cementing heads are designed to hold one or more plugs and are loaded beforethe actual cementing operation. 9lugs are selecti"ely released into the casing fromthe head. hen casing rotation is desired an adapter swi"el is used between thetopmost collar and the head and the casing is suspended by the rotary table slips.

&he ad"antage of using a cementing head that pro"ides space for two plugs is that itallows for continuous pumping; that is pumping of the cement can proceed while thetop plug is being dropped.

Conventional Casing Jos and Equipment !pplications

&he con"entional two-plug casing job is illustrated in Figure ( #Principal equipmentused in typical two-plug primary cement job %.



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Figure 1

< predetermined "olume of slurry is pumped into the casing between two wiperplugs. &he bottom plug ruptures when it seats; the top plug is solid. &he top plug isdisplaced with mud or completion 4uid. Flow stops and pressure builds when the topplug lands. 6hec+ "al"es in the 4oat shoe to pre"ent bac+4ow of the hea"ier columnof slurry in the annulus.

"uide#Float S$oes and Collars

3n most cases except in certain shallow wells a round-nosed shoe is run on thebottom joint to guide the casing past borehole irregularities encountered while thestring is run. &hree types of shoes are commonly used:

• guide shoes without "al"es of any +ind

• 4oat shoes with a chec+ "al"e that pre"ents slurry bac+4ow

• di=erential or automatic 5ll-up types


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6ollars ha"e basically the same features as shoes Figure #Regular type guide shoe %

Figure 2

Figure #Down jet type guide shoe %



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Figure 3

Figure 2 #Insert self ll-up oat !al!e %



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Figure 4

Figure ) #Standard oat collar %

Figure 5

Figure > #Standard oat collar with double demale threads %



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Figure 6

Figure 7 #Insert !al!e oat shoe with self ll-up unit %



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Figure 7

Figure ? #"ement ba#e collar with latchdown plug and sealing slee!e %.



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Figure 8

&hey are commonly +nown as ba@e collars #without "al"es% 4oat collars anddi=erential or automatic 5ll-up collars. Aocated one or more joints abo"e the shoethe collar in addition to 4oat and 5ll-up functions acts as a seat for pump-downwiper plugs.

!ince cement immediately below the wiper plug may be contaminated the collarshould be positioned to minimi$e the amount of contaminated cement pumped outaround the shoe.

hen 4oat equipment is used it pre"ents 4uid from bac+4owing up the casing as thecasing is run in the hole. &his causes the casing to B4oatB downhole because it ispartially empty and somewhat buoyant. &o control buoyancy e=ects with 4uid when

using 4oat shoes or 4oat collars from a surface 5ll-up line.

%iper Plugs and &isplacement Concepts

iper plugs are used to separate cement from preceding or following 4uids # Figure ( top and bottom wiper plugs%. &he bottom plug also remo"es mud from the wall ofthe casing and pre"ents this mud from accumulating beneath the top plug and beingdeposited around the lower casing joints.



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Figure 1

hen the two-plug system is used the operator should "erify that the bottom plug isin fact placed in the bottom position in the cementing head. < mechanical de"iceshould be used to gi"e "isual proof when the top plug lea"es the head.

< bottom plug is not recommended with large amounts of lost-circulation material inthe slurry or with badly rusted or scaled casing since such material may collect onthe ruptured diaphragm.

Displacement of the top plug should be carefully monitored. Fluid behind the plugshould be determined from calibrations on cementing-unit tan+s or by measuring outof a storage tan+.


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• pre"ent di=erential pressure stic+ing

• +eep casing out of +ey seats

&wo general types of centrali$ers are spring-bow and rigid$ &he spring-bow type hasgreater ability to pro"ide stando= where the borehole is enlarged. &he rigid type

pro"ides more positi"e stando= where the borehole is to gauge. !pecial close-tolerance centrali$ers may be used on liners.

3mportant design considerations are positioning method of installation and spacing.6entrali$ers should be positioned on casing

• through inter"als requiring e=ecti"e cementing

• adjacent to #sometimes passing through% inter"als subject to di=erential

stic+ing and may be used on casing that passes through the doglegs and isthereby subject to +ey-seat stic+ing.

6orrect positioning requires a caliper log of the wellbore so that locations correspondwith to-gauge sections of the borehole. 3nstallation method depends on the type ofcentrali$er: solid body split body or hinged. &he hinged type is most commonlyinstalled.

6entrali$ers are held in their relati"e positions on the casing by either the casingcollars or mechanical stop collars. &he restraining de"ice #collar or stop collar% shouldalways be located within the bow-spring type centrali$er so the centrali$er will bepulled not pushed into the hole. &herefore the bow-spring type centrali$er shouldnot be allowed to ride free on a casing joint.

Aoad-de4ection cur"es may be used for determining the spacing required to achie"edesired stando= # Figure ( centrali%er with proper stop collar location and exampleload-deection cur!e%. &he stando= required to pre"ent di=erential-pressure stic+ingis normally less than that required to centrali$e casing for good displacement

eCciency.



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Figure 1

&he lateral load imposed on a casing centrali$er is the combined e=ect of centrali$erspacing casing weight hole angle and weight of casing below the centrali$er anddogleg #a minor e=ect%.

Equations to calculate lateral load are a"ailable in orld ilBs "ementing &andboo'(Suman et$al$) *+,,) p$ 22. &hese can be programmed for calculators and aree=ecti"e design aids. Data is also a"ailable from manufacturers and from


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be placed within the cement inter"al to ensure uniform cement distributionopposite critical $ones.

Production casing 9lace one centrali$er immediately abo"e the shoe and oneat the top of each of the bottom six joints. &hey should be placed on e"ery

joint through the producing $ones and extending (** feet abo"e #and below if

applicable%. ther potential problem $ones +ey seats stic+ing areas etc.should also be protected with centrali%ers$

.iners 1se centrali$ers if clearance and hole conditions permit.

Stage cementing 6entrali$ers should be spaced o"er the cemented inter"alabo"e the stage collar and one joint below since there is no casing mo"ementin such jobs. hen used the external pac+er acts as the lower centrali$er.

Tale (* Rules of thumb for centrali%er spacing in !ertical holes$ Source/ 0orld 1il"ementing &andboo'$

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