Horizontal Well Control Theory

8/12/2019 Horizontal Well Control Theory

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1 V1.0C

Sedco Forex is now drilling several developmentwells a year in which the final section is horizontal.

As one of the aims for the operators is to enhance thefinal production of their reservoirs it is probable thatthe numbers of such wells will continue to increase.

To date the procedure has been to drill the wells withthe standard policies and practices laid out in the wellcontrol manual.

Is this adequate ?

What are the differences between horizontal andvertical wells, or even deviated wells and verticalwells which could give us problems ?

Research & Engineering

Slide No.1 © Sedco Forex Jul’93

Te c h n o l o g y Tr a n s f e r Ho r i z o n t a l We l l Co n t r o l

H o r i z o n t a l We l l

C o n t r o l



2 V1.0C

If we look at the four main areas of well control wecan ask three questions

What, if any, are the differences ?

How, if at all, will it effect us ?

What should we do about it ?




Horizontal Well Control

We will consider the similarities and differencesin the four main areas of well control ;

Kick Avoidance

Kick Detection

Shut-in

Kick Control

- Drilled Kicks

- Swabbed Kicks



3 V1.0C

Whilst a horizontal well is being drilled it is normallyfor development purposes. This means that there is

previous experience in the area and the formationpressures should be well known. This should help inchoosing the correct mud weight.

We must not be complacent as there is a growingtendency towards early production with fewerappraisal wells being drilled.

The main dangers for a kick whilst drilling come from

allowing the mud weight to drop,mud going into losscirculation zones, or drilling across a fault to a highpressure zone.

As you are tripping in a known producing zone then itis always possible to swab the well in. If the well isswabbed, the production zone could be veryextensive leading to large influx volumes.

There is also the problem of cuttings build up on the

low side of the well, which may increase the tendencyto swab by reducing the annular clearance.




Kick Avoidance

Known Formations

Fewer Appraisal Wells

Drilled Kick

– Mud Weight Drop

– Sealing Fault to Higher Pressure Zone

– Loss Circulation

Large Section of Reservoir Exposed

Cuttings Bed on Low Side



4 V1.0C

The geometry of the well does not alter the fact thatformation fluid coming into the well will displace

drilling fluid from the well.

We need to continue to emphasise the need forcontrol of the mud pits to ensure that gains are notdisguised by mud transfers. A reliable flow paddlesystem will assist in faster detection of kicks.

As we saw in earlier work unless the formation goesunder balance then it is very unlikely that a flow check

will be positive especially in OBM. Any influxswabbed into the horizontal section is unable tomigrate and will produce a negative flow check.A negative flow check does not mean there is noinflux

Again it comes back to proper control of the trip tankwhilst coming out of the well.




Kick Detection

Influx In = Mud Out

Early Detection Best

– Flow Rate Increase From Well

– Pit Volume Gain

Good Trip Monitoring Essential



5 V1.0C

If the influx remains in the horizontal section then theinflux will not reduce the hydrostatic pressure in the

annulus. The SIDPP and the SICP will then remainvery similar.

Currently these pressures are used to help estimatethe influx density. This estimate will not work in ahorizontal well

We do not need to know the influx type for successfulwell control. We can always assume a worst case of

gas.The new MDS system will allow influx typing in WBMfrom a measure of system compressibility duringshut-in.




Shut-In

If the influx is in the horizontal section

SIDPP ≈ SICP

Influx Type Unknown

Assume a Worst Case, Gas



6 V1.0C

The well is shut in. If it was a drilled kick we wouldnormally work out our pumping pressure schedule

and proceed from there. Can we just use thestandard kick sheet ?

If we are off bottom we need to get back to bottombefore trying to circulate out the kick. The well was incontrol before we started tripping so we need to getrid of the influx to regain control.




Kick Control

Once we have shutin on a horizontalwell what do we do next ;

How do we fill our kick sheet ?

OR

How do we get back to bottom ?

Lets look at both in turn.



7 V1.0C




Exaggerated Horizontal Well

MD 10,000 ftT VD 5,000 ft

OMW = 10 ppg

SCRP = 500 psi @ 4 bbl/minSIDPP = 1000 psi

10,000 ft of 5" Drill Pipe @ 0.017224 bbl/ft

If we look at an extreme horizontal well we couldenvisage some thing like this.

A 10,000 ft measured depth well with a true verticaldepth of 5,000 ft and a horizontal displacement of5,000 ft. Even though it is unrealistic it allows us tomake some points

Suppose that we shut in a kick with a drill pipepressure of 1000 psi and that the original mud weightwas 10 ppg

The pre-recorded SCRP was 500 psi at a pumpingrate of 4bbl/min

The drill string is comprised solely of 5" drill pipe witha capacity of 0.017224 bbl/ft.



8 V1.0C




Standard Wait & Weight

KMW = SIDPP ÷ 0.052 ÷ TVD + OMWKMW = 1000 ÷ 0.052 ÷ 5000 + 10KMW = 13.85 ppg

ICP = SCRP + SIDPPICP = 500 + 1000 = 1500 psi

FCP = SCRP x ( KMW ÷ OMW )FCP = 500 x ( 13.85 ÷ 10.00 ) = 692 psi

String Volume = 10,000 x 0.017722 = 172.2 bblTime to Bit = 172.2 bbls ÷ 4 bbls/min = 43 mins

BHP @ Shutin = 1000 + ( 10 x 0.052 x 5000 ) = 3600 psi

Suppose we now apply the standard well controlmanual wait and weight method.

We can find our required kill mud weight from theSIDPP and the TVD of the well.

This will also enable us to work out our initial and finalcirculating pressures.

We then need to find the time taken for the kill mud toreach the bit. For this we must use the measureddepth of the well to calculate our string volume. This

gives us a time of 43 minutes to kill the drillstring.As a final calculation we could work out our bottomhole pressure prior to starting the well kill operation.From the SIDPP and the hydrostatic pressure we get3600 psi



9 V1.0C

From all the preceding work we can now plot ourpumping pressure schedule and use that to kill the

drillstring and eventually the well.

This is probably the procedure that would beemployed today on any Sedco Forex rig that took akick in a horizontal well.




Pumping Pressure Schedule

Time

I n i t i a l C i r c u l a t i n g P r e s s u r e

0

20 0

40 0

60 0

80 0

1000

1200

1400

1600

0 43

0

20 0

40 0

60 0

80 0

1000

1200

1400

1600

F i n al C i r c ul a t i n g

P r e s s ur e



10 V1.0C

But the aim of any well control operation is tomaintain a constant bottom hole pressure which is

equal to the formation pressure.

We previously saw that the bottom hole pressurewhen the well was shut in was 3600 psi so any wellcontrol method we use should maintain this pressure.

However if we look at the bottom hole pressure wewould impose by following the normal vertical wellwait and weight method we can see that it peaks at

21 1/2 minutes and is about 300 psi above that whichis required for well control.

At this point the kill mud has reached the TVD of thewell. If we were to stop the pumps and record theSIDPP it would be zero. The standard kick sheetassumes that as the kill mud is half way to the bitthen the SIDPP would be halved. It requires that aback pressure is held on the choke to control theBHP, and allow for the remaining SIDPP, whilstcirculating.




BHP During Well Kill

TIme ( Mins )

B H P ( p s i )

3400

3500

3600

3700

3800

3900

4000

0 21.5 43

Perfect Kill

W&W Kill



11 V1.0C




Two Questions

We can see there is a need for a better approach tothe Kick Sheet. We need to decide two things ;

How to divide the well up by depth ?

How to find the pressure at each depth ?

There is more than one answer to each question.



12 V1.0C

The idea of both of these methods is to simplify thewell into straight line segments that make it easier to

find the TVD at certain MDs.

Both methods require that the end point of eachsection is defined with a measured depth and avertical depth. Both use different approximations todefine these points. Once these points have beenfound the TVD at any measured depth can be foundfrom simple trigonometry.




Four Section Methods

Rather than consider the well as one continuallyvarying profile from the vertical to the horizontal twomethods have been proposed which split the well intofour sections.

Vertical Section

30° Section

60° Section

Horizontal Section



13 V1.0C




Four Section - TVD Method

Vertical section

30°Section

60°Section

Horizontal Section

30°

60°

KOP

KOP + 0.5( TVD - KOP )

TVD

One suggestion has been to split the well into foursections using the TVD and the kick off point, KOP.

The thick black line shows the actual well and thegrey shading shows the effect of using theapproximation.

The attractive idea of this proposal was that the drilleronly need know his KOP and TVD to work out thevertical depth at any measured depth. Unfortunatelythere are so many different geometries that this wouldnot work in all cases. For example the 60° projection

in this slide would underestimate the bottom holepressure for that section by making you think thatyour TVD was less than it actually was.



14 V1.0C




Vertical section

30°Section

60°Section

Horizontal Section

30°

60°

Four Section - Geometric Fit

The other method of splitting the well into foursections is more complex. This time the sections are

chosen by drawing tangents to the well profile. Thetransition from one section to another is thus assuredto fit the well profile and a close estimate of TVDcould be found.

The main problem with this method is that thesimplest direct way to do it is to physically drawtangents on a well profile plot. The method requiresthat you already have access to a full set of well

deviation data which you then try to simplify.



15 V1.0C

Irrespective of which of the four section proposals isused the next step is similar. Once the well is split the

methods then go on to use the cosine of the angles tofind the TVD at the end of each section of measureddepth. As only two angles, 30° and 60° are used, thecosine could be simply considered as a multiplicationfactor.

The above example shows one way of finding therequired information. This could be considered as thesame as filling out the pre kick data sheet.

The reality is that whilst drilling a horizontal well theinformation linking TVD to MD will be readilyavailable. The use of some intermediate step such asdrawing tangents only adds to the complication and isanother potential source of error.




TVD Data Sheet

BOREHOLE DRILL STRING DATA MEASURED TRUE VERTICAL DEPTH

SECTION DETAIL CAPACITIES bbls/ft DEPTH DEV OF COSINE MD X COSINE DEV

No. D/STRING ANNULUS D/STRING ANNULUS SECTION CUM ANGLE OF DEV SECTION CUM

1 RISER C/L 0.01746 0.0087 450 0 1 450

2 5" DP 9 5/8 CSG 0.01746 0.0489 2300 2750 0 1 2300 2750

3 5" HW 9 5/8 CSG 0.0087 0.0489 450 3200 0 1 450 3200

4 5" DP 9 5/8 CSG 0.01746 0.0489 1128 4328 0 1 1128 4328

5 5" DP 9 5/8 CSG 0.01746 0.0489 1287 5615 30 0.866 1115 5443

6 5" DP 9 5/8 CSG 0.01746 0.0489 911 6526 60 0.4985 459 5902

7 5" DP 8 1/2 OH 0.01746 0.046 756 7282 60 0.4985 377 6279

8 5" DP 8 1/2 OH 0.01746 0.046 4000 11282 90 0 6279

9 5" HW 8 1/2 OH 0.0087 0.046 270 11552 90 0 6279

10 6 1/2" DC 8 1/2 OH 0.0087 0.046 120 11672 90 0 6279

11

12

TOTAL MD 11672 TVD 6279

( After Drilling And Production Training Centre, Horizontal Well Control Course )



16 V1.0C




10 Section - Measured Depth

The simplest way to split the well up is to do it bymeasured depth, as is done with the current kick

sheet.

The well can be split into ten convenient sections ofmeasured depth and then the TVD found for the endof each section of measured depth.

This information is easily found from the directionaldriller, survey personnel or from any survey program.There will always be several sources of this

information on the rig whilst a horizontal well is drilled.The time to find out about this is before it is requirednot after. It should be regarded as part of your pre-recorded data.



17 V1.0C

Once the well has been split up we then need to findthe standpipe pressure required to keep the bottom

hole pressure constant as the kill mud is pumped.

The basic calculation of the initial and final circulatingpressures remains the same. We need to find somemeans of calculating the pump pressure at the pointsin between.

The initial look at the exaggerated right angle wellshowed us that the use of the measured depth of the

kill mud gave a bad answer. The obvious next step isto look at reducing the pressure uniformly with thevertical depth position of the kill mud




Pumping Pressure

Calculations remain the same for :

Initial Circulating Pressure, ICP

Final Circulating Pressure, FCP

But how do we reduce ICP to FCP as thekill mud is pumped :

Measured Depth of Kill Mud ?

Vertical Depth of Kill Mud ?

We have seen that the measured depthapproach gives a bad answer.



18 V1.0C

The required kill mud weight and the initial and finalcirculating pressures are all found as normal.

There is then one new item that has to be found. TheIncremental Kill Gradient. This finds the reduction instandpipe pressure as the kill mud is pumped downeach foot of the vertical depth.

The reduction along each component of the drillstring can then be found from its vertical depth timesthe kill gradient. This can then be taken from the

initial circulating pressure to find the circulatingpressure at the end of each of the drill stringcomponents.

In this case the final circulating pressure is reachedwhen the kill mud reaches the TVD of the wellirrespective of whether it has reached the bit.




INITIAL CIRC FINAL CIRC INCREMENTAL

PRESSURE PRESSURE TVD KILL GRADIENT

2 0 2 6 - 1 8 7 7 ÷ 6 2 7 9 = 0 . 0 2 2

SECTION PRESSURE PRESSURES DRILL STRING ANNULUS

DECREMENT =

BORE SECTION TVD X INITIAL CIRC PRESSURE

HOLE INCREMENTAL K ILL MINUS CUMULATIVE BBLS STROKES BBLS STROKES

SE CT IO N SE CT IO N GR ADI ENT CUMULATIVE DECREMENT

No. TVD DECREMENT SECTION CUM SECTION CUM

1 450 11 11 2015 8 69 69

2 2300 55 66 1960 40 341 410

3 450 11 77 1949 4 34 444

4 1128 26 103 1923 20 168 612

5 1115 26 129 1897 22 188 800

6 450 11 140 1886 16 136 936

7 377 9 149 1877 13 113 1049

8 70 597 1646

9 2 20 1666

10 1 12 1678

11

12

[ ]

TVD Kick Sheet

( After Drilling And Production Training Centre, Horizontal Well Control Course )

1877 6279 0.022- ÷ =



19 V1.0C

The standpipe pressure graphs produced from thestandard kick sheet and the TVD kick sheet are

compared above.

We can see that the TVD kick sheet reaches the finalcirculating pressure after about 1050 strokes. Thecirculating pressure is then held constant as the killmud is pumped along the horizontal section.

This method has allowed us to reduce the standpipepressure by about 50 psi as the kill mud starts into

the horizontal section.But if we consider how we find our final circulatingpressure there is something odd. The final circulatingpressure is the amount by which the slow circulatingrate pressure will INCREASE because of the kill mudin the string. As the string is not yet full of kill mudthere must be some pressure increase still to comeas it enters the horizontal section. Yet the finalcirculating pressure has been reached and we cannotallow any further increase for risk of breaking downthe formation




TVD Vs Standard

Kick Sheet

Total Strokes

C i r c u l a t i n g P r e s s u r e ( p s i )

1850

1900

1950

2000

2050

0 200 4 00 60 0 800 1000 1 200 14 00 160 0 1800

TVD Kick Sheet

Standard Kick Sheet



20 V1.0C

From the previous slide we can see there is aproblem. The circulating pressure should not remain

constant as the kill mud is pumped along thehorizontal section. It should increase and yet wecannot increase the final circulating pressure. We canimprove the calculation if we consider the circulatingpressure to have two parts.

The first, the static pressure reflects the reduction inthe SIDPP as the kill mud is pumped down thedrillstring.

The second, the dynamic pressure reflects theincrease in the pump pressure as the kill weight mudis pumped along the string.

The actual circulating pressure comes from thecombination of these two effects.




Split the Pressure

The calculation can be greatly improved at the expense ofa slight complication. Instead of finding a singlecirculating pressure. We find its two components ;

Static Pressure

– the SIDPP during the drillstring kill

Dynamic Pressure

– the pump pressure whilst killing the drillstring

The circulating pressure becomes the sum of the two.





22 V1.0C

On the other hand as the kill mud is pumped alongthe pipe the heavier mud will increase the dynamic

pressure.

This should increase from the initially recorded slowcirculating pressure to the calculated final circulatingpressure.

This depends only upon how far along the drill pipethe kill mud is. The FCP - SCRP is effectively thecalculated increase in pump pressure.

When MDP equals MDT , kill mud at bit, then thedynamic pressure is the same as the FCP. WhenMDP is small then the dynamic pressure is similar tothe SCRP




Dynamic Pressure

The DYNAMIC pressure at any time in the kill is relatedto the MD of the kill mud. The DYNAMIC pressure willINCREASE as the mud is pumped.

It can be found at any time in the kill from ;

Where MDP is the measured depth of the kill mud atthat time and MDT is the total measured depth of thewell

Dynamic Pressure = SCRP + FCP - SCRP( )MDP

MDT



23 V1.0C

The circulating pressure whilst the kill mud is beingpumped to the bit is simply the sum of the static and

dynamic pressures. The main thing to ensure whensumming up the Dynamic and the Static pressure inthe well is that both calculations were done for thesame physical point in the string.




Circulating Pressure

The CIRCULATING PRESSURE at any time is then :

STATIC PRESSURE + DYNAMIC PRESSURE

The pressures must be calculated with the kill mud at thesame place in the string.



24 V1.0C

If we look at how we can apply this concept to a kicksheet we could produce a new kick sheet, instead we

have chosen to produce an extension to our existingkick sheet.

The aim is to keep the process as consistent andsimple as possible. The standard Sedco Forex kicksheet is filled out as normal to section G1. Theinformation required for the extension is then filled outin the top section of the extension.

The ten sections of measured depth are then put inthe first row of the calculation sheet. The calculationof the circulating pressure is then carried out line byline.

The pump strokes vs pressure information can thenbe plotted back on the original kick sheet.



Te c h n o l o g y Tr a n s f e r Ho r i z o n t a l We l l Co n t r o l Horizontal Kick Sheet

WELL CONTROL KICK SHEET( Horizontal Extension )

Complete the standard Sedco Forex kick sheet up to Section G 1. You should then fill out this sheet to allow you to calculate your pumping pressure graph. You need totransfer the following information to this sheet.

Measured Depth = ........................ ftTrue Vertical Depth = ........................ ftSlow Circ Rate Press= ........................ ps iSIDPP = ........................ ps iF i na l Ci r c Pr e ss ur e = ........................ ps iStrokes To Bit = ........................ stks

You can then find the Pressure Increase :

Pressure Increase = F.C.P. - S.C.R.P. = ........................ ps i

You should then break the well up into ten sections of measured depth, ensure the well profile is adequately described, and place the values in Row A of the tablebelow. You should then proceed through the calculations line by line until the table is full. Once the table is full the values can be used to draw your pressure againststrokes graph as normal. The rest of the kick sheet is then filled out as usual.

1 2 3 4 5 6 7 8 9 1 0

A M.D . 0

B M.D. Rat io Row A ÷ Measured Depth 0

C St ro kes Strokes To Bit x Row B

D Dyn am ic Pressu reSCRP + ( Pressu re In c x Ro w B )

E T.V.D . at M.D. in Row A 0

F T.V.D. Rat io Row E ÷ True Vert ical Depth 0

G S t a t ic P r e s su r e S I DP P - ( S ID P P x R ow F )

H Ci rcu la t ing Press .Row D + Row G



25 V1.0C

We can look at how this would work in practise withthe completed sheet above.

All the information has been transferred to theextension sheet. The well has been broken into tenuniform sections of measured depth. The verticaldepths corresponding to each of the measureddepths are put in row E. Remember this informationshould be pre-recorded.

Although in this example the ten steps are exactly

equal this is not a requirement of the sheet. It wouldwork with any ten measured depth points. It isprobable that the most readily available points wouldbe at the survey depths. The ten surveys bestdescribing the well could be chosen.

Once the sheet is filled out we can plot our pumpingpressure schedule.



Te c h n o l o g y Tr a n s f e r Ho r i z o n t a l We l l Co n t r o l Worked Example

WELL CONTROL KICK SHEET( Horizontal Extension )

Complete the standard Sedco Forex kick sheet up to Section G 1. You should then fill out this sheet to allow you to calculate your pumping pressure graph. You need totransfer the following information to this sheet.

Measured Depth = 1 1 6 7 2 ftTrue Vertical Depth = 6 2 7 9 ftSlow Circ Rate Press= 1 7 0 0 ps iSIDPP = 32 6 ps iF i na l Ci r c Pr e ss ur e = 1 8 7 7 ps iStrokes To Bit = 1 6 7 8 stks

You can then f ind the Pressure Increase :

Pressure Increase = F.C.P. - S.C.R.P. = 177 ps i

You should then break the well up into ten sections of measured depth, ensure the well profile is adequately described, and place the values in Row A of the tablebelow. You should then proceed through the calculations line by line until the table is full. Once the table is full the values can be used to draw your pressure againststrokes graph as normal. The rest of the kick sheet is then filled out as usual.

1 2 3 4 5 6 7 8 9 1 0

A M.D . 0 1 1 6 7 2 2 3 4 3 5 0 2 4 6 6 9 5 8 3 6 7 0 0 3 8 1 7 0 9 3 3 8 1 0 5 0 5 1 1 6 7 2

B M.D. Rat io Row A ÷ Measured Depth 0 0 .1 0 . 2 0 .3 0 .4 0 . 5 0 .6 0 .7 0 . 8 0 . 9 1 .0

C St ro kes Strokes To Bit x Row B 0 1 6 8 3 3 6 5 0 3 6 7 1 8 3 9 1 0 0 7 1 1 7 5 1 3 4 2 1 5 1 0 1 6 7 8

D Dyn am ic Pressu reSCRP + ( Pressu re In c x Ro w B ) 1 7 0 0 1 7 1 8 1 7 3 5 1 7 5 3 1 7 7 1 1 7 8 9 1 8 0 6 1 8 2 4 1 8 4 2 1 8 5 9 1 8 7 7

E T.V.D . at M.D. in Row A 0 1 1 6 7 2 3 3 4 3 5 0 2 4 2 6 3 5 5 5 4 6 1 4 0 6 2 7 9 6 2 7 9 6 2 7 9 6 2 7 9

F T .V .D . R at io R ow E ÷ Tr ue Ve rt ic al De pt h 0 0 . 18 6 0 . 37 2 0 . 5 58 0 .7 3 6 0 . 88 5 0 . 9 78 1 1 1 1

G S t a t ic P r e s su r e S I DP P - ( S ID P P x R ow F ) 3 2 6 2 6 5 2 0 5 1 4 4 8 6 3 8 7 0 0 0 0

H Ci rcu la t ing Press .Row D + Row G 2 0 2 6 1 9 8 3 1 9 4 0 1 8 9 7 1 8 5 7 1 8 2 7 1 8 1 3 1 8 2 4 1 8 4 2 1 8 5 9 1 8 7 7



26 V1.0C




TVD Kick Sheet Vs Extension to Kick Sheet

Total Strokes

C i r c u l a t i n g P r e s s u r e ( p s i )

1800

1850

1900

1950

2000

2050

2100

0 200 4 00 60 0 800 1000 1200 1 400 160 0 1800

TVD Kick Sheet

Extension

We can now compare results from the extension tothe kick sheet with those from the the previously

examined TVD kick sheet. The most obviousdifference is that the extension sheet goes to aminimum value before increasing to the finalcirculating pressure. This increase comes about asthe heavy weight kill mud is pumped along thehorizontal section.

Another point to note is that the schedule is moreuniformly described by the ten points on the

extension than the ten points on the TVD sheet. Thiswould make it easier for the choke operator to follow.



27 V1.0C

If we look at what is going on down hole during allthis then we can see several bottom hole pressures

depending upon which method is used.

Re-stating the goal of well control as maintaining aconstant bottom hole pressure we can see that onlyone of the methods does this. The standard kicksheet is the worst approximation. This gives anexcess pressure of about 125 psi in this case. TheTVD kick sheet is slightly better giving an excess ofabout 75 psi.

They could be regarded as additional safety factorsbut their potential size should be appreciated beforeusing them as such. Once a well geometry is decidedit is relatively simple to check on the possible extrapressures incurred by using the standard kick sheet.The formation breakdown is one obvious potentialproblem with too high a pressure.

If a correction for deviation is required then theextension to the kick sheet could be used




Comparison of

Bottom Hole Pressures

Total Strokes

B o t t o m H

o l e P r e s s u r e ( p s i )

3400

3450

3500

3550

3600

0 20 0 400 600 800 1000 1 200 14 00 1600 1800

Standard

TVD Sheet

Extension



28 V1.0C

If we consider influxes off bottom we shouldremember that the only way we will pick up the

swabbed influx is from the kick sheet.

The influx will not migrate out of the horizontalsection. It will not reduce the hydrostatic whilst it is inthe horizontal section. This means that the flow checkwill be negative even with a large influx.

The danger is that when we run back to bottom theinflux may be displaced out of the horizontal section

by the BHA. Once in the vertical it could reduce thehydrostatic enough for the well to flow. The horizontalsection could then produce very quickly.

This means that we have to be especially vigilantwhilst running back in and be ready to shut the well inat the first signs of flow.




Swabbed Influx

Trip sheet shows influx

Negative flow check

Run back to bottom

At some point gas displaced to vertical

Well goes underbalance and flows



29 V1.0C

The running back in of the drill string may eventuallyforce the influx out of the horizontal section into the

vertical.

If the well is shut in the correct sequence of thevolumetric stripping method will ensure that thecorrect bottom hole pressure is maintained byallowing controlled expansion of the influx on the wayup. You are assuming a worst case by allowing forthe gas expansion all to occur in a vertical section.

If you get back to bottom without seeing any flowthere is still the potential for the well to gounderbalance when the swabbed influx is circulatedout of the horizontal section.




Kicks Off Bottom

Controlled Volumetric Stripping

No gas expansion until gas out of the horizontalsection

Bottom hole pressure maintained by correct useof Pstep and Vstep

Once on bottom use the kick sheet if required orcirculation to remove swabbed influx








Summary 2

Drilled Kick

– Change required to kick sheet

– Proposal based on measured depth

– Split static and dynamic components

Swabbed Kick

– Displace influx to vertical and cause flow

– Volumetric stripping

– Worst case assumption for vertical section

Documents

Horizontal Well Control Theory