Tiếng anh chuyên ngành Thiết bị dầu khí (Petroleum equipment)

The mud moves up the annular space between pipe and holeor casing, carrying the drilled rock in suspension.At the surface, the mud leaves the hole through the return line and falls over

Unit Drilling Rigs

Rigs are generally categorized as onshore (land) or offshore (marine) Onshore rigsare all similar, and many modern rigs are of the cantilevered mast, or "jackknife" derricktype This type of rig allows the derricktobe assembled on the ground, and then raisedtothevertical position using power from the drawworks, or hoisting system These structuresare madeupof prefabricated sections that are moved onto the locationbytruck, barge,helicopter, etc., and then placed in position and pinned togetherbylarge steel pins Somecantilevered land rigs have their mast permanently attachedtoa large trucktoenhance theirportability Figure 1 shows a typical large land rig with a drilling mast

Figure 1: Drilling rigOffshore drilling rigsfallinto one of several categories, each designed to suit a certain typeofoffshoree n v i r o n m e n t :

• Bargerigs

• Submersibler i g s

• Jack-uporself-elevatingr i g s

WestAfrica,theinland watersofthe Louisiana swamps, or the shallows ofLakeMaricaibo,V e n e z u e l a Bargerigsaregenerally capableofdrillinginwaterdepthsoflessthan12ft(3.7m),or,in the case of a posted barge, perhapsto20ft(6.1 m) A

posted barge has alower hullthat rests on the bottom and an upper deck that

issupportedbyposts from the lowerh u l l SUBMERSIBLE RIG: A submersible rig is a larger version of a posted barge, and

is capable of workinginwater depthsof18ftto 70ft(5.5 mto2.14 m) Often the hull of asubmersible rig will have steel floats or "bottles" thatcanbefilledwith water (balllasted)tohelp stabilize the vessel onbottom

JACK-UP RIG: This is a self-elevating drilling rig, illustratedinFigure 2 , designed tooperate in depths from 30ftto 350ft(9 mto107 m).Afterbeing towedtothe location(orinsomecases being self-propelled), the legs are loweredbyelectric or hydraulic jacks until theyrestonthe seabed and the deck is level, supported perhaps 60ft(18 m) above the waves.Most jack-up rigs have threetofive legs, and are either vertical or slightly angled forstability The legsmayhave steel feet, called "spud cans,"ortheymaybe attached to a largesteel mat When moving to a location the legs are raised high above the deck, creating asome what cumbersome vessel that must move at slow speeds andonlyin good weather.The derrick, or mast, on a jack-up may be located over a drilling slot indentedinone side

of the structure, or the drill floormay becantilevered over the side of the deck, allowing therig to service wells on stationary platforms, or caissons, offshore

SEMISUBMERSIBLE RIG: Unlike the other offshore vessels, the semisubmersibledrilling rig does not rest on the seafloor This rig is a floating decksupportedbys u b m e r g e d p o n t o o n s a n d i s k e p t s t a t i o n a r y byaseries of anchors and mooring lines, and, in some cases, position-keepingpropellers

"Semis" can either move under their own power or must be towedtotheirlocation.Theyhave a water-depth-operating rangeof20ftto 2000ft(6 m to 600 m), and differfrom each other principally in theirhullconfiguration and their number of stabilizing

columns Most types have a rectangular deck; others may be wedgeshaped,p e n t a g o n a l ,

oreven triangular The two most usualhullarrangements are a pair of parallelpontoonsoranindividual pontoon at the footofeach stabilizing column The columns andpontoons are ball lastedtoprovide a low center of gravity, addingtothe semi's stability.Although the semicanoperate in deeper water than a jack-up, it is stilllimitedbythecapabilities of the mooring equipment and the "riser" (the conduit thatconnects the drill floortothe sub-sea equipment located at the borehole on thes e a f l o o r ) DRILLSHIPS: Drillships are most often utilized for extremely deep water drilling atremote locations A "floater" like the semisubmersible, a drillship must maintain itsposition at the drilling locationbyanchors and mooring lines, orbycomputer-controlleddynamic positioning equipment A series of controllable pitch propellers, or "thrusters,"shift position and speedtomaintain the ship over the wellbore The drilling slot, or

"moon pool," is through the ship's midsection, as showninFigure 6 and Figure 7 Mostdrillships have greater storage capacity than other typesofrigs, allowingefficientoperation atremotel o c a t i o n s

STRUCTURE RIGS: Structure rigs are mounted on a fixed drilling and productionplatform, with all necessary auxiliary equipment secured on the deck The derrick andsubstructure are usually capable of skidding to different positions on the platformstructure; following the drilling and completion of multiple wells, the rigmaybe dismantledand removed during the production phase of the program Subsequent remedial work onthese platformsmayrequire the rig to be replaced.Insome cases, theconfigurationofwellsonthe platform allows a jack-up rig to service the location Permanentdrilling and production structures varywidelyin design and capabilities A few of themost common designs are:

Thedrawworks is a spool or drum upon which the heavy steel cable (drilling line)

is wrapped From the drawworks, the line is threaded through the crown block atthetopofthe mast and then through the traveling block, which hangs suspended from thecrown block(Figure 1 )

Byreeling inorletting out drill line from the drawworks drum, the traveling blockand suspended drillstemcanbe raisedorlowered.Inordertosafely manage the movement ofsuch a heavy load with precision, the driller relies on an electrical or hydraulic brakesystem to control the speed of the traveling block and a mechanical brake to bring ittoacomplete stop The drawworks also features an auxiliary axle,or

"catshaft," with rotating spools on each end called "catheads." One spinning cathead isused to provide power to tighten the drillpipe joints via a cable from the cathead to therotary tongs The other cathead is for "breaking out" or loosening the pipe joints when thepipe is being withdrawn ins e c t i o n s

Thewire rope drilling line that is spooled onto the drawworks drum undergoes acertain degree of wear as the block is raised and loweredinthe derrick For this reason theline is routinely "slipped" (moved onto the drawworks drum) and replaced with a newsection from the continuous spool on which itisstored The line is clamped at the storagespool endbya deadline anchor The hook is attached to the traveling block and isusedtopickupthe drillstem via the swivel and kelly when drilling, or with elevators whentripping intoorout of theh o l e

Unit Rotating system

I Reading comprehension

Theswivel allows the drillstemtorotate while supporting the weight of drillstring inthe hole and providing a pressure-tight connection for the circulation of drillingfluid.Thedrilling fluid enters the swivelbywayof the "gooseneck," a curved pipeconnectedto

a high pressure hose Connectedtothe swivel is the kelly, a three-, four-, or six-sided40ft(12.2m)lengthofhollow steel, which is usedtotransmit the rotary movement of therotary table to the drillstring (The term drillstem refers to the kelly and attached drillpipe,drill collars, and bit The term drillstring refers to the drillpipe and drill collars However,most folks in theoilpatch disregard these rules and use whichevertheyplease!) The kellycock is a special valve on the end of the kelly nearest the swivel, which can beclosedtoshut in the drillstem A lower kelly cock is also available on the bottom end of thekelly to perform the same functionwhenthe upper kellycock is not accessible Theflatsided-kelly fits through a corresponding opening in the kelly drive bushing, whichinturn fits intothe master bushing set into the rotary table The rotary table is turnedbythe rig's powersource, the table turns the bushings, the kelly bushing turns thekelly,thekelly turns thedrillpipe, and so on down to the bit Note thatinp l a c e ofthis conventional rotatingsystem, many modern rigs have gonetothe use of power swivels and top-driveu n i t s

up and downin thederrick while maintaining a pressure-tight system The circulatingdrilling mud moves through the swivel,kelly,drillpipe, and drill collars, exiting through thebit at the bottom of the hole The mud moves up the annular space between pipe and hole(or casing), carrying the drilled rock in suspension.

At the surface, the mud leaves the hole through the return line and falls over a vibrating screen called the shale shaker This device screens out the cuttings

anddumpssomeofthem into a sample trap and the rest into the reserve pit Once cleaned of large cuttings, the mud is returnedtoa mud tank, from which it can be once again pumped down the hole Fine particles are removedbycentrifugal forcebyflowing them u d

8through desanders, desilters,ora centrifuge A degasser is used to remove small amountsofgas picked upinthe mud from the subsurfacef o r m a t i o n s

Unit Controlling system

I Reading comprehension

Controlling the subsurface pressures encountered while drilling is an importantpartofthe operation One ofthepurposes of the drilling mud is to provide a hydrostatic head

of fluidtocounterbalance the pore pressure of fluids in permeable formations However, for

a variety of reasonsthewell may "kick"; that is, formation fluidsmayflow into the wellbore,upsetting the balanceofthesystem, pushing mud outofthe hole, and exposing the upperpartofthe hole and equipment to the higher pressures of the deep subsurface If leftuncontrolled, thiscanlead to a "blowout," with the formation fluids forcefully erupting fromthe well, often igniting, and endangering the crew, the rig, and thee n v i r o n m e n t

Theblowout preventers are a seriesofpowerful sealing elements designedtoclose offthe annular space between the pipe and hole where the mud is normally returning to thesurface.Byclosing off this route, the well canbe"shut-in" and the mud and/or formationfluids forcedtoflow through a controllable choke, or adjustable valve This choke allows thedrilling crew to control the pressure that reaches the surface andtofollow the necessarysteps for "killing" the well and restoring a balanced system Figure 1 shows a typical set ofblowout preventers, includingtheannular preventer, which has a rubber sealing element that

is hydraulically squeezed to conform tightly to the drillpipeinthehole

Figure 1 BOP systemAlso shown are ram type preventers These include pipe rams,whichclose around thepipe with rubber-lined steel sealing elements,andblind rams, which seal offthewellborewhen there is no pipeinthe hole Shear rams are a type of blind ram that can crimpthepipeintwowitha powerful hydraulic force to seal off the hole Blowout preventers areopened and closedbyhydraulic fluid stored under 1500to3000 psi (10,000to20,000 kPa)inanaccumulator The choke manifold houses the series of positive and/or adjustablechokes that are usually controlled from a remote panel on the rig floor Often, a rig that isencountering frequent gas kicks will also have a mud-gas separator, which saves thedrilling mud that is expelled along with a large flow of formation gas, and separates the gasfor safe flaring at some distance from therig

When akick(influxofformation fluid) occurs, rig operators or automatic systemsclose

the blowout preventer units, sealing the annulustostop the flow of fluids out of thewellbore.Denser mud is then circulated into the wellbore down the drill string, up theannulus and outthrough the choke line at the baseoftheBOPstack through chokes (flow restrictors) until

downhole pressure is overcome Once “kill weight mud”extends from the bottomofthe well to the top, the well has been “killed” Iftheintegrity of the well isintact, drillingmaybe

resumed Alternatively, if circulation is not feasible itmaybepossible to kill the

wellby"bullheading", forcibly pumping,inthe heavier mud from thetop through the kill line

connection at the base of the stack This is less desirable becauseofthe higher surfacepressures likely needed and the fact that much of the mud originallyin the annulus

mustbeforced intoreceptiveformationsinthe open hole section beneaththe deepest

casings h o e

Exploitable reservoirsofoil and gas are increasingly rare and remote,leadingtoincreased subsea deepwater well exploration and requiring BOPs to

remainsubmergedforaslong asa year in extreme conditions As a result, BOP assemblies

have grownlarger and heavier (e.g a single ram-type BOP unitcanweigh in excess of30,000 pounds), while the space allotted for BOP stacks on existing offshore rigs has not

growncommensurately Thus a key focusinthe technological development of BOPs over

the last two decades has been limiting theirfootprintand weight whilesimultaneouslyincreasing safe operatingc a p a c i t y

Unit Casings and the casingh e a d

I Reading comprehension

Suppose anoilwell were just a “holeinthe ground,” with no protection During thedrilling, soft earth or high formation pressures would probably make the well-borecavein,orcollapse Therefore, a well completed and produced without protectionwouldbevery wasteful.Inthat unprotected well, oil and other reservoir fluids would leak,

or seep from the well-bore into other formations.Inordertothose phenomena,

casingstringsare used to protect the well-bore during drilling After the well is completed,

the casing strings continuetoprevent cave-ins and leakage, or seepage from thewell-bore.Casing is a steel pipe ranging from less than 41/2 inches OD to more than 20 inches OD.Casing pipe put together with leakproof connections is called a casing string Throughout the drilling, more thanonecasing stringmaybe set in the well-bore Drilling continuesinside each casing string after it is set So, The first casing string installed has thelargestOD

Figure CasingsThecasing string that completes the well-bore to a producing formation is called

theproduction casing.The production casing has the smallest OD compared with other

casing strings in the well-bore.Ifthewell is completed withonlyone casing string, that string

play the role of the production casing Usually, the first string installed is thesurface casing.Hence, the surface casing is the casing with the largestOD.Sometimes, a conductor

casing is set before the surface casing.The first casing string installed is always the shortest

casing stringinthe well-bore.Ifnoconductor casing is set, the shortest casing string in thewell-bore is thesurface casing This first string of casing is heldin

place with cement Ifonlyonestringofcasing is usedtocomplete the well, the productioncasing is heldbycement all the way to the producing formation Normally , it is the surfacecasing that is completely cemented in At the bottom of the string, the production casing,like the surface casing, is cemented in place.Ina two casing-string completion, theproduction casing is run inside the surface casing To support the production casing from

the surface, acasing headisused.

Thecasing head has a bowl which supports the casing hanger This casing hangersupportstheproduction casing The casing head screws into or is welded onto the top of thesurface casing Or, at the well head, the weightoftheproduction casing is actuallysupportedbythe surfacec a s i n g

Some wells are completed with three casing strings An intermediate casing stringmay be set inside the surface casing

Then the production casing is set inside the intermediate casing The intermediatecasing is longer than the surface casing but shorter than the production casing It is usedwhen formation pressures and drilling depths make three casing strings necessary When

an intermediate casing string is used, it is supported at the topbya casing head set on thesurface casing Then,tosupport the production casing from the surface, a second casinghead is used A well completed with three casing strings has two casing heads Theuppermost casing head supports the production & intermediate casing The lowermostcasing head sits on the surface casing and supports the cementedinplace casing in a wellcompleted with three casings t r i n g s

Finally, The surface casing is usually:

- supportedbya casingh e a d

- cementedinp l a c e