hpht well design

8/13/2019 HPHT Well Design

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NOVODRILL / ONGC / TRANSOCEAN

HIGH PRESSURE DRILLING REFRESHER

APRIL 2012

1. WELL CONTROL REFRESHER

2. HP/HT WELL CONSIDERATIONS

2.1 Well Designs -Nee !"# $%%$'e s("e )l$%e*en'L"ss $n +i%, )"'en'i$l

2.2 E&i)*en' #e&i#e*en's $n #es'#i%'i"nsHig(e# )#esses $n 'e*)e#$'esH#$'es $n '(e *& g$s se)$#$'"#

2. D#illing Fl&isG$s En'#$in*en'

Te*)e#$'e E!!e%'s S'$'i% s Dn$*i%

2.3 O)e#$'i"n$l P#"%e$l #e&i#e*en's !"# HP/HT 4ellsFinge#)#in'ing5 Fl"4 C(e%,s5 C(e%, T#i)s $n %i#%&l$'ing

+i%, De'e%'i"n $n Res)"nse

. WELL TO 6E DRILLED -

Well Design Dis%&ssi"nsP#"7le* P#ei%'i"n $n Res)"nse is%&ssi"ns

3. OPERATIONAL PROCEDURES TO 6E USED

8. E9ERCISES

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1. WELL CONTROL REFRESHER

WELL CONTROL CONCERNS ARE THE SA:E AS FOR EVER; WELLT;PE

CAUSES OF +IC+S

1. NOT +EEPING THE HOLE FULL2. SWA66ING. DRILLING INTO HIGHER PRESSURES

PREVENTION OF +IC+S

1. +EEP THE HOLE FULL2. DO NOT SWA6. 6E AWARE OF INCRESING PRESSURE TRENDS

PRESSURE TREND INDICATORS

< CHANGE IN ROP )"si'ie $n neg$'ie

< == E9PONENT< HOLE PRO6LE:S

< 6AC+GROUND GAS< CONNECTION GAS

< TRIP GAS< TE:PERATURE DOWNHOLE< SHALE DENSIT;< SHALE CAVINGS< DELTA FLOW< PIT GAIN

IF IN DOUBT WE FLOW CHECK

+IC+ INDICATORS

< DELTA FLOW< PIT GAIN

IF THE WELL IS FLOWING WE CLOSE IN THE WELL AND KILL IT

+ILL :ETHODS

< WAIT AND WEIGHT< DRILLERS :ETHOD< 6ULLHEADING

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2. HP/HT WELLS - INTRODUCTION

If a given rig and operation is deemed to be capable of handling conventional kicks thento determine the HP/HT requirement the differences between the two well types must bedefined

The additional requirements / considerations for HP/HT over conventional well controlcan be summarised as follows!"

21 #ell $esign

% &ore 'asing (trings / (tronger casings required)% *ormation *racture +radients &uch 'loser to *ormation Pressures% ,apid 'hanges in $ownhole Pressure / Temperature

22 $rilling and -ick Handling .quipment

% (urface Pressures will be Higher% (urface Temperatures will be Higher% $ownhole Temperatures will be Higher% +reater ,isk of Hydrates% Influ 0olume to be Handled at (urface is Potentially +reater

2 $rilling *luids

% Heavier % Higher ,heology to carry weighting material% $ifferent Influ +as ehaviour in 3il &uds

24 -ick $etection

% $ealing with *ormation 'harging .ffects% 5uantifying (tatic and $ynamic #ell 'haracteristics


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2.1 WELL DESIGN

% :"#e %$sing s'#ings / S'#"nge# %$sings #e&i#e>

&ost wildcat wells are designed to use a final hole si6e of 7 1/28 so that in theevent of well problems a contingency liner / casing can be set and the well finishedoff in 9 :/78 or ;8 hole

:"s' HP/HT esigns 4ill ($e '(e ? 8/@ / ? B/@ "# 10 /3 "# B%$sings

7eing se' in '(e *$in )#esse '#$nsi'i"n "ne.

The selection of this casing shoe in the transition between normally andoverpressured formations is critical

% *ormation *racture / Pressure +radients

The fact that these gradients get closer the deeper we go is well documented andimpacts strongly on kick tolerance calculations

#hen a well is engineered certain assumptions must be made about pressures andstrengths of formations These can be right or wrong so the information we aregathering from the well as we drill it is vital to support or challenge theassumptions made

% ,apid 'hanges in $ownhole Pressure / Temperature

These are common in HP/HT wells 3n #ildcat wells < etreme caution must beeercised as the pressure transition can be as much as === psi increase in only:=m of drilled depth

>t the same time that the pressures rise downhole then so do the temperaturesIncreasing temperatures can be good indicator of rising pressure regimes

3nly certain formations are capable of trapping such pressures Typically these are(hales or &arls They must be fairly plastic They may have some porosity but it isunlikely that they will have any vertical permeability otherwise the pressure wouldhave leeched away over +eological time Typically again< as the pressure gradient

increases then so does the water content of the shales This can be spotted by twomechanisms *irstly reduction in (hale density and secondly increase in

background gas levels for a given ,3P *or each foot drilled< more water iscontained within the drilled cuttings This water contains gas and as this gas isreleased at surface the background gas levels will rise

The skill required is to go far enough into the transition 6one to get a strong casingseat but not so deep as to having the well ?blowing around your ears?

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2.2 ASSESSING EUIP:ENT REUIRE:ENTS

The salient HP/HT needs which will need to be met by this equipment are!"

% (urface Pressure will be Higher @ This implies the use of 19


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2.. DRILLING FLUIDS

The differences between drilling fluids for HP/HT wells as against conventional wells arefourfold

% Heavier % Higher ,heology% $ifferent 'omposition to Provide Temperature (tability% $ifferent Influ +as ehaviour in &ud

G$s En'#$in*en' in '(e :&

>nother problem that comes hand in hand with heavier muds is gas entrainment >ny gelstrength which is sufficient to hold barytes will have no difficulty holding gas This meansthat the mud will carry a residual amount of gas in it at all times Typical background gaslevels are one or two percent 3ne way to illustrate this phenomenon is to circulate the

well after setting casing or a liner .ven though no new hole has been drilled< the gasdetector will be showing some residual level of gas

In Production Tests the surface separation equipment usd to separate any gas out ofproduced oil will include a heaterThe heater is used to heat the oil >s the oil is heated itgives up the dissolved and entrained gas much more readily

This phenomenon also applies to gas in mud I! '(e *& is ("''e#5 i' 4ill #ele$se g$s*"#e #e$il .In a circulated well the temperature of the mud coming out of the flow linewill not vary much during constant circulation If the pumps are stopped at any time thenthe mud at the bottom of the well will heat up as heat soaks in from the surrounding rock

This means that $n 'i*e '($' %i#%&l$'i"n ($s s'"))e '(e#e 4ill 7e ("' s)"'s in '(e*&.These hot spots will give off entrained gas more easily than the constantly circulatedmud and this will be picked up by the gas detector as an increase in +as Aevels

'are must be taken not to over"react to increasing gas levels from such situations#e epect that C"nne%'i"n G$s5 Se g$s $n T#i) G$s leels 4ill 7e (ig(e# '($n7$%,g#"&n g$s leels #hat we have to respond to is a trend increase in these levels

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2.3. HP/HT OPERATIONAL PROCEDURES

The foregoing tet has highlighted the problems we might face on High Pressure wellsThese factors are now taken into consideration when detecting and handling kicksasic kick indications and response are the same for all wells< ie!"

% *low ,ate or Pit 0olume Increase

% #hen the kick has been detected the well will be closed in in the same manner forall wells

% *inally the methodology which must wells will be killed Dtypically the wait andweight method but increasingly the $riller?s &ethodE is the same for all wells

+i%, Ini%$'"#s

High pressure wells ehibit additional characteristics which confuse kick detection Theseare!"

% *ormation 'harging

% (tatic vs $ynamic $ownhole Temperatures

F"#*$'i"n C($#ging %"*7in$'i"n "! 7$ll""ning $n !il'#$'e ine%'i"n

+iven that with the effects of .'$< the formation is eposed to a greater hydrostatic headduring circulation than when the well is static< formation charging must be epected

Static well conditions Effects of ECD pushing wellbore ba

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How this manifests itself is in the wellbore giving back fluid once the pumps have beenswitched off The speed at which mud is returned and the volumes vary from well to welland even within a given well as mud weight and well depth increases

This flow back is a product of the ballooning effect shown in the figure above and

possibly the release of any filtrate which has been forced into the wellbore formations dueto the etra hydrostatic head applied by the .'$

&ost &ud *ilter 'akes are not totally effective in preventing filtrate invasion into thewellbore formations If there is any invasion then there will be local ?charging? of theseformations up to the prevailing .'$ pressure at that point in the wellbore

#hen the pumps are stopped< the local formation pressure will be be higher than thehydrostatic head of mud at that point so flow back from the formation into the well borecan occur

C$n 4e )#ei%' e$%'l 4($' '(ese '4" )(en"*en$ 4ill 7e in $ 4ell >P#"7$7l N"' Therefore to quantify these it is necessary to carry out etensive flow checks on the welluntil a pattern emerges These flow checks could be = or 49 minutes but should beobserved and recorded diligently

It is typical that the 8flow back8 rate from formation charging should decrease with timeduring a given flow check

.actly how this manifests itself will only be evident when the flow check is carried out

>t first< rig crews can find watching the well apparently flowing an alarming eperienceso it is advisable to discuss this effect in detail and illustrate by carrying out regularchecks on what constitutes normal behaviour for the well

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S'$'i% s Dn$*i% D"4n("le Te*)e#$'es $n '(e i*)$%' "! '(is

3n HP/HT wells< downhole temperatures are typically in the range of == " 9=F*

>t the well design stage these are estimated and during drilling electric logs will confirm

or deny the accuracy of these estimates

If the well is left uncirculated then it is a reasonable assumption that the mud in theborehole will assume the temperature of the surrounding formation

This phenomenon is important to consider when looking at the tools that can be run inHP/HT wells >ny tool with electronics< elastomers or oil in them will be sensitive to hightemperatures

This means we need to consider our choice of electric logging tools< A#$/ $ andeven Bars The most powerful Bars are typically Hydraulic Cars 3n some wells the

hydraulic poil can boil and in these cases the more traditional mechanical Car D eg the$ailey AI Bar E is a better choice The strike blow is less than a Hydraulic Bar in normalwells which is why they are not used so much but the hydraulic Bar may not be striking atall when used in very hot wells

It may seem Galien to be circulating for no apparent reason but on such wells sometimesits safer to keep circulating and cooling the well down rather than run the downholecomponents right up to their designed temperature ratings

*rom the $rilling 'ontractors perspective the same concerns apply to any ,ig based.quipment which have elastomers in them This means the 3P and surface manifolding

needs to have elastomers capable of coping with the anticipated temperatures (ubsea3Ps have a ready supply of cooling water around them and will reduce thetemperatures being eperienced by the 3P when compered to those on say a Aand ,ig orBack up rig > lot of ,igs now are putting temperature sensors on the 3Ps to eliminatesome uncertainty

*rom the #ell Production Testers perspective< again the higher temperatures need to beconsidered #hen the well is flowing on a production test the produced fluid is all atambient reservoir temperature $ownhole tools need to be designed to cope with the hightemperatures and the surface equipment will see almost as high temperatures as thedownhole equipment when in flowing mode This is why there are very few HP/HT Test

(preads around the world and why when planning a well with the intent to Test it isimportant to Glock in a (pread which can be available at the time required In practicethis may mean committing to an HP/HT Test (pread for quite a while before it is actuallyneeded

The mud sitting in the tanks on the rig is probably in the range 7=F* " 19=F* depending oncirculation pattern< water depth< tank capacity< ambient temperature etc

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'onsequently< as the mud system goes from static to dynamic< a cooling effect on thewellbore is unavoidable This means that $!'e# e'ene %i#%&l$'i"n '(e 4ell7"#e 4ill7e s&7s'$n'i$ll %""le# '($n 4(en '(e 4ell ($s 7een le!' s'$'i% !"# s"*e 'i*e.

.very time the pumps are stopped then the heat source from the surrounding rock will

heat up the transition 6one towards the wellbore and finally heat up the mud that is sittingin the wellbore

This is a natural phenomena and is to be epected

If the well were to be closed in after etended circulation then as the mud could notepand as it heated up it is reasonable to epect the shut"in pressure at surface to rise

This is in fact what happens in practice

>s with *ormation 'harging it is phenomenon that rig crews are not necessarily familiar

with< so again a demonstration of the effect is desirable

This can be done at the casing leak off test If the cement/floats/pocket drill out takes afew hours then this circulation will have cooled the surrounding formations sufficientlyfor the phenomenon to be observed

Having drilled the pocket and circulated to an even mud weight< quickly pullback into thecasing shoe< shut off the pumps and close the well inThe pressure build up gives a 8finger print8 for the well

This temperature effect acts in addition to the formation charging effect and the onlyreadily discernible difference at surface is that the temperature effect will give a straightline relationship between closed in surface pressure and time for longer than might beepected for *ormation 'harging .ffect

In some cases the straight line relationship can indicate potential required mud weights inecess of 2= ppg to regain 8control8 of the well

'ommon sense must prevail and it must be remembered that pore pressure will not eceedoverburden pressure in a well otherwise the reservoir fluids would already have escaped

1=

Time

Press. Build Up following

Kickdditional!ud"eight#e$uirement

%ingerprinting Press. BuildUp


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In practice we may not actually know how much of the effect is due to 'harging and howmuch to Temperature It really does not matter too much anyway< provided that we checkthe behaviour and have established what constitues normal behaviour

$espite understanding why we have these apparent well flows on HP/HT wells < it still

goes against all we have been taught to pull out of the hole on a well which has apparentlyflowed 9 or 1= barrels once the pumps were switched off

'onsequently< it is therefore epedient on trips to observe the flow check as mentionedabove and then carry out a 9 or 1= stand wiper trip The bit should then be put back on

bottom and bottoms up circulated &ud salinity< weight< temperature and gas levelsshould be observed during this circulation If the well is flowing hydrocarbons< gas levelswill rise If the well is flowing formation water< salinity and mud weight will changeTheonly fluids we are going to find in these wells will be water< gas< condensate< oil or a miof these#hen our drilling fluid weighs 197 ppg and resembles toothpaste in teture thenany of the above influes are easily spotted by loss in mud return weight and huge

differences in background gas levels and Hydrocarbon 'hromatograhic breakdown

> lot of HP/HT wells have ended up Gchasing their tails because higher gas levels areseen when circulating bottoms up after a wiper trip The response has been to increase&ud #eight to control the gas This would in a regular well Gdo the trick but on HP/HTwells the gas levels will stay the same or even go up

>ny time that the well has been static< the mud at the bottom of the well will heat up andwhen we circulate it to surface we will see higher gas levels This on its own should not beyour cue to raise the mud weight

:& :$n$ge*en' "n Hig( P#esse Wells

*rom the above tet it can be seen Cust how many confusing effects could be taking placein the well $espite anything you may be told to the contrary< in a #ildcat well these

phenomena are not predictable with any degree of accuracy'onsequently< the only practical way to handle these phenomena in a safe manner is to!"

aE Try to keep all mud properties and drilling parameters as constant as possible foras long as possible

bE >lways circulate bottoms up following a short< check trip prior to pulling out

of the hole completely

(ince we can only measure the mud at surface and guess what is happening downholethen the yardstick to apply is " Di 4e ($e P#i*$# C"n'#"l >

If the answer is ;es

then the mud system has been effective in that role

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12/17

O)e#$'i"n$l P#"%ees !"# S$!e H$nling "! Hig( P#esse +i%,s

H$nling +i%,s "n Hig( P#esse Wells

The main mechanical weakness in the system in most cases is the Poor oy &ud +as

(eparator

$ifferent 3perators took different views on the safe throughput of a given Poor oy .arlyPoor oys had ;K vent lines which clearly put more back pressure on the system whenventing gas than say a 12K vent line would create (ome companies would produce graphsshowing how much gas could be produced through the Poor oy These graphs are Cust

based on theoretical modelling >s we know this is not always correct and since if thegraph is not right then you will only find out when the liquid seal blows then a saferoption is to Cust reduce the kill speed so that the gas throughput is decreased drastically toa level that is not even close to what could blow a sealIn practice when circulating out an influ the 'hoke manifold is warm or hot as mud

passes through it If there is gas breakout then the effect is like a refrigeration cycle Thechoke manifold gets colder downstream of the chokes >t first this looks like condensation

but even when working on the equator the choke manifold will then develop a coating offrost on it 'ondensation can be epected and is not something to be concerned abouthowever if when circulating frost develops on the P& then its time to slow thecirculation rate down until the gas cut mud has been circulated out If gas is comingthrough the chokes then to maintain the kill the choke will need to be closedIn most normal kills once they get under way theres very little adCustment of the chokerequired D because you are circulating a homogeneous fluid around @ the mud that was inthe annuus above a potential influ E >nother indication of gas coming through thechokes is a different noise coming from the choke manifold >t times there is slugging too

$uring kills attempts to shut down as much background noise as possible

There is no ecuse for not knowing what is going through the 'hoke manifold at any time

>ny well kill operations must be planned as multiple speed kills

This means checking slow circulation rates not only of = strokes per minute as is usualbut also of 1=< 19 and 2= strokes per minute (ometimes the pumps can not run as slowlyas 1=spm but the minimum reliable running speed should be determined well ahead oftime and not left to finding out Gthe hard way during an incident

>s a policy it is suggested that the well be killed at = (P& until frosting appears on the&anifold < the well starts slugging or theres a change in the sound coming from themanifold

etter (afe than (orry

> further precaution is to discuss the deficiencies of the Poor oy with the ,ig 'rew andeplain what happen if the equipment capabilities are eceeded

>s mentioned earlier the temperature sensors on the 3P and choke equipment must bemonitored during well killing operations

The manufacturers of the elastomeric products specify a continuous working temperatureand a short term eposure temperature that the equipment is designed for

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-illing operations should be carried out within the 3P working temperature envelope

If temperatures begin to eceed the designed levels then the only recourse available is toslow down the kill operation or stop it completely until the 3P components cool

+lycol should be employed as the gas reaches the choke line D.asily recognisable by arise in Pchoketogether with a change in tone and a chilling effect downstream of the chokeitself E

+iven the known weaknesses in the kick handling system< measures should be put in placeto spot failures in this equipment< should they occur we must ask ourselves 8If there isgoing to be a failure< how will I detect it and how can I make it safe)8

There are well documented #ell 'ontrol $isasters which could have been contained hadthe ,ig 'rew been in a position to trace the immediate source of gas around the rig floorand implement a contingency plan

Practically speaking this implies!"

aE -eeping a (ubsea T0 camera at the 3P during killing operationsbE &onitoring of the liquid seal blow off area at the Poor oy &ud +as (eparator

Having taken a kick and handled it safely the equipment must be prepared for the netone To ensure that the equipment is ready two main checks are required!"

1 'heck for erosion due to the high solids content of the mud2 *lush the system with water to clear any residual barytes to prevent blockages

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WELL TO 6E DRILLED

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Well Schematic (DRAFT)

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.2 Well S)e%i!i% P#"7le* P#ei%'i"n

1. +i%,s

The area we are drilling in is fairly well mapped with close outstep wells +iven the three

known D or predicted E pressure ramps we will be controlled drilling as we approach theseso are unlikely to go flying into over pressures #e will have 3il based mud in the hole forall of these ramps so can use the usual detection tools of gas levels< amounts of cavings etcto indicate pressures coming up Laturally we have to be super careful when drillingahead but probably the main source of any kick would be if

DiE we swabbed in the well orDiiE didnt appreciate the difference between static and dynamic bottom hole pressuresDiiiE $rilled into losses < causing a drop in hydrostatic head which reduced the primary

control on a 6one above this

2. L"sses

Aosses could be epected in the well These would most likely L3T be catastrophic butmore probably Cust down to the .'$ created when circulating a heavy mud around

. H"le Cle$ning

Lot epected to be a problem in this well given that it is 0ertical and the high mudweights will have high rheology If the mud weight did not follow the pressure ramp

properly there could be ecessive caivings produced and these could create a holecleaning / hole pack off problem

3. Di!!e#en'i$l S'i%,ing

'are needs to be taken once the reservoir section has been penetrated #e anticipate highpressures in the reservoir but there is always the chance that the modeling has given us amud weight considerably heavier than we needed +iven oil based mud and drilling in ashale< it will be hard to detect this 3nce the sands are penetrated then the differentialsticking effect can be considerable The usual precautionary practices should be used-eep string moving and if we need to shut down for whatever reason try and do so with noH> across this section

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3. E9ERCISES

3.1. #e are drilling away in 12 MK hole at

hpht well design

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