spe-4923-ms
TRANSCRIPT
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Publication 425
. SPE 4 ?3
September 2973
ROCK CUTTING BY JETS: “
A PROMISING METHOD OF OIL WELL 13RILLZXG
by
R. Feenstra, A. C. Pols & J, van Steveninck
,
Paper to be offered for presentation at the
103rJ AIM Annual hkcting in Dallas, Texas, 24- 2S Februq- 2974.
. .
KONIXKLIJKE/SH12LL
EXPLORATIE EN PRODUKTH2 L.-U30RAT03MR-M
RIJSWIJK, THE 2?13THERLAF?DS
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ONT NTS
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bstract
Introduction
Laboratory experiments
Field experiments
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Looking ahead
Conclusions
Acknowledgement
.,
References
Tables I - W
I?igwes 1-12 -
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Ew
In
1
1
10
13
13
14
15
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ABSTRACT
This paper deals with the results of experimental research work performed in
laboratory and In the field on high-pressure jet drilling. Threshold pressures have be
found to be five times the rockfs “true tensile strength, irrespective of drilling fluid
properties and bottom-hole pressure.
However, bottom-hoIe pressures and drilling flu
have a major effect on bit performance,
similar to the hold-down phenomena in
conventional drilling. These results have been obtained with conventional drilling fluid
and laboratory ecluipment designed to simuiate d“own-hole pressures. Following single-
nozzle exq)eriments,
criteria have been established for constructing laboratory bits
.,
(1, 4 in) and fieIcl bits (9 5/8 in). ‘ ~
Field bits have been run in Tertiaxy shales bcIow 1700 ft depth, using conventio
5000 psi pressure service. These runs indicate that jet bits cut to-gmgc holes, with
abnormal de~tiation tendency, faster than conventional bits. The small nozzles (2-3 mm
ID) required for acceptable hydraulic” power demand have shown to be practical, thank
to effective straining of the drilling fluid.
It can be concluded. that the method of jet drilling rock in oil wells looks feasibl
and promising. Further evaluation of this method in the near future seems justified.
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ROCK CUTTING BY JETS:
A PROMISIN-G METHOD OF OIL WELL DRILLING
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INTRODUCTION
In the course of time, an increasing number of investigations on jet cutting
kinds of material, such as rocks
1,2,3
45
, metals ‘
, and wood6 have been re~_ted
serve various applications.
This paper deals with one particular application of je
viz cleep-well drilling for hydrocarbon exploration and production. A number of
.
7,8,9
have been published on this subject ,
, some of which refer to jets purposely
containing abrasives,
,7
termed ‘jetted particll? drilling .
Since such abrasives com
fluid handling considerably and do not appear to be absolutely necessary for mak
hole we have restricted ourselves to conventional drilling fluids.
A large part of our investigation has been performed with the aid of three
laboratory-type drilling machines,
which permit tests on both micro-bits (Ii in)
full-scale bits (6+ -
9 5/8 in). In view of the application of jets in deep wells,
has been taken to simulate hydrostatic pressures x they exist in the field on t
hcle bottom. These have been found to have a m-ajor effect on the bit-penetration
for various drilling fluids.
1?ollowing experiments with single :~ozzles,
?.aborato~ bits have been cles ig
imp?.”oved further and developed for fieid. use. Field runs on 9 5/$ in bits ~ using
conventional equipment and pumps, served to verify the feasibility of the jet dril
concept. Further efforts are evidently needed to evaluate the jet drilling method.
10
is encouraging that one of these , I
a field test pm gramme, is supported by a n
of oil companies jointly. Such a combined effort is of paramount importance to
eva hate and develop this new method of drilling to its full potential in a reasona
period of time. This paper aims to contribute to that ultimate goal.
. .
LABORilTC)RY EXPER13iE NTS
~uipment used
Three laboratory machines (Figs.
1-3) have been used for jet drilling
experiments. Their ratings are given in Table 1.
The largest machine was recen
modified for high-pressure service
; its new ratings are given in parentheses.
All machines are equipped with a pressure vessel in which experiments ar
performed on rock samples. The rock samples are jacketed (e, g. painted or co
with plastic sheet), except for one circular spot within an O ring at the bottom
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pressure vessel,
which serves to discharge the filtrate flow through the rock po
atmospheric pressure (Fig.
4). The fluid pressure inside the pressure vessel is
simulate the differential pressure between the hydrostatic head of the mud colum
the hole and the pore pressure in the rock at drilling depth. It is this differentia
pressure that affects drilling rates at depth. The pressure in the pressure vesse
maintained by throttling the mud flow downstream of the pressure ~essel.
.
Test
procedure
Threshold pressures are derived from tests with a 3 mm nozzle (I?ig. 4)
mounted eccentrically by 40
jetted with a certain nozzIe
five rotations at 30 fim (=
mm, 10 mm above the rock sample. Water o~*mud
pressure drop and an ambient pressure of 50 bar.
10 seconds), the rock surface is inspected. The tes
repeated with roughly 1070 higher nozzle pressure drop until a groove is cut in
rock surface (Fig, 5), The last nozzle pressure drop is considered to be the
threshold. pressure. “
The penetration rate of a laboratory bit is measured by lowering the bit
the rock at an increasing rate,
after the circulation pressures and bit-rotary sp
have been set. As long as the rate of lowering is below the potential cutting ca
of the jets, the rock will *be removed at the same rate as the bit is lowered, b
soon as the rate of lowering the bit exceeds its potential cutting capacity, the b
approach the hole bottQm. This can easily be detected because the bit pressure
increases as a result of choking the nozzles by the hole bottom, and a moment
the bit will ‘touch the rock, leading to some” rotary torque atid an increase in b
reading, The rate of lowering at the moment of increasing bit-pressure drop, b
lozd, or torque is recorded ~~sthe bit’s penetration rate in the rods drilled at
prevailing bit-pressure drop,
rotary speed, back pressure and fluid properties.
.
Threshold
pressures
The nozzle pressure drop has to exceed a certain threshold before the roc
surface is damaged by the jet. This pressure has been determined (Table 119 fo
various rocks and test conditions, using the single nozzle test set-up discussed
before. It has been found that the threshold pressure is related to the rock’s t
strength, the ratio bein”g roughly 5:1 (Table II). McClain & Cristy
11
have also
threshold pressures for Indiana limestone and Berea sandstone that are five tim
the tensile strengths of the rocks
as
measured by C heatham & Gnirli
12 (TabIe
These measurements refer to atmospheric conditions.
l?ol*tunately, we have fou
that differences in ambient pressure (betxveen O and 100 bar) have no effect on
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rock’s threshold pressure.
Consequently, both cavitation and chip hold-down apparen
do not affect threshold pressures, If these findings il.so hold for other types of roc
a prediction can be made of the. minimum pressure required to penetrate a particula
type of rock at any depth. In this respect,
it would be. very convenient if the rock’s
tensile strength could be reasonably correlated with some kind of existing log, so
minimum pump-pressure recpi~e,ments for jet drj.lling in a given field might b,e
determined in advance without taking cores.
Practical consequences
------ ------ ------ ----
In order to estimate the pump-pressure rating for field application of jet drill
the tensile strengths of a number of rocks have been collected from the literature
(TabIes IV and V)12’ 13.
The strongest sedimentary rock shown in these tables reclu
a nozzle pressure drop of 680 bar (’3 900 psi) to initiate penetration. Making allowan
for excess nozzle pressure drop for fast drilling and string pressure losses, this
would require say 15000 “psi pump-pressure rating,
which is within the rating of
commercially available frac pumps.
Some rocks may present problems, e.g.
the handling of loose pebbles when
jetting conglomerates, or the destruction of large boulders of chert, Conventional
clrilling may then be necessary.
If a large piece of chalk bearing flintstone is
cncounte red,
.
it may also be broken up along weaker veins of.
Challi,
as experienced
in the laboratol~. Particular basalts may requir~ a minimum nozzle prcssute drop
of 1S50 bar (27 000 psi), an unrealistic figure for the near future. In conclusion,
find that jet drilling will be clifficult, if not impossible,
in some particular formatio
I?or such’ exceptional rocks, however, jet bits can be equipped with a set of conven
cutting means
formations.
Drilling fluids
------
---.--
(diamonds or rollers) so as to cope with short intervals of these
Threshold pressure
compositions (Table VI}.
destruction which occurs
values. appear to be the same for water and muds of vari
However,
on exceeding the threshold, the amount of rock
during five revolutions has been observed to be different
~~,ater and muds. These observations on groove depth may provide an inciication Of
happens during drilling. ‘
w Table 11 shows that the ‘Brazilian’
tensile strength of Solcnhofen limestone is
‘considerably lower than its uniaxial tensile strength and that threshold pressure
correlates better with the unia.xinl tensile strength,
3?ail*hul*st~~ has shown that,
for @rticulal* rock types, the Brazilian test will always gik+e too low values.
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At elevated ambient pressure,
shallower grooves are cut by mud jets than by
water jets under the same conditions. The reduction in groove depth in the permeable
rocks is ascribed to a phenomenon very similar to static hold-clown, because it coul
be overcome by closing the pore drain valve to allow the pore pressure to rise to
the ambient (bore-hole) pressure. We shall see later that the same effect is
encountered under identical conditions when drilling with jet bits, instead of cutting
a groove with one jet during five revolutions.
At atmospheric ambient pressure, much deeper grooves are cut by mud jets
than by water jets.
This is attributed to” the ‘emergence during expansion at the nozz
of air entrained in the mud (not in water), which creates almost unsubmerged
conditions for the jet. The effective length of a free jet (approx. 100 nozzles
cliameters2) is much greater than that of a submerged jet (4-8 nozzle Cliameters14).
The effect observed is therefore pronounced for large nozzle stand-off, as could
occur after five revolutions. During drilling, when nozzle stand-off is kept small
enough all the time,
the drilling rate at atmospheric ambient pressure is not higher
for mud than’ for, water. ”
The rock-destruction mechanism
One would expect that compressive forces,
resulting from the jet impact, or
shear forces,
resulting from the radially emerging flow would cause. rock destruction.
,15
‘ Further cavitation might play an important role .
Since the compressive strength of most rocks is more than five times their
t~nsi~e strength, and their average threshold pressul*e equal to five times their tensi
strength, a rock is unlikely to fail because of compressive forces. The same concisi
has been drawn by Powell & Simpson
16
17
and Forman & Secor
, who talc ulated that
failure of a semi-infinite elastic solid can be expected when the maximum impact
16
or between 14 and 25 times
17
pressure is 20 times .
the tensile strength, which is
much higher than the pressures found experimentally. It can thus be concluded that
compressive forces resulting from jet impact are unlikely to cause rock destruction.
Leach & V7alker2 indicated that surface shear stresses are negligible.
Cavitation cannot occur when the ambient pressure &xceeds the nozzle pressure
drop as occurs in deep wells. Rock destruction by a water jet has been found to be
the same at near-atmospheric and high ambient pressures. From this, it ,can be
concluded that cavitation is of’ no, importance for jet drilling at any depth.
The most probable explanation for the me clxmism of rock destruction is that
high-pressure fluid causes local extension of the rock by penetration into pores and
cracks. It is well-known that, in permeable rocks, an increase in p~qe-fluid pressur
le~ds to a reduction in rock compression.=
One can visualise this by considering the
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reverse of consolidation (soil mechanics).
Locally, the effective grain stress will
become tensile and, as the tensile strength of rock is low relative to compressive
strength, tensile faiIure can be expected at moderate fluid pressurq. The effect of
17
pore-fluid pressure has been confirmed by calculations by l?orman & tSecor , wfho
have found theoretical threshoid pressures of 2.5 to 3.5 times the tensile strength.
Earle’8 has found theoretical threshold pressures of 4 to 6.2 times the tensile stren
of permeable rock, which agrees very well with the experimental values,
It is more difficult to visualise the same failure mechanism in impermeable r
but even very dense rock contains pores and” cracks.
These will be filled with high-
-pressure fluicl when the jet is above them,
which is an ideal situation for crack
propagation.
Bits
A proper
fluid-jet bit is,
in fact, nothing more than a nozzle holder. Two
examples are shown in Figs. 6 and 7; one is a typical laboratory bit, O. D. 36 mm,
equipped wit h 8 nozzles of 1 mm ID,
as has been us”ed for most experiments; the
other is a 9 5/8 in bit” equipped with 16 nozzles of 3 mm ID afte~* field use. We sha
discuss a few particular features of these bits.
t
Raclial nozzle spacing
-------- ------ ------ --
Groove experiments have shown that one nozzle cuts a groove about 3 nozzle
cliameters wide. The nozzles in a bit will have to be placed such that the grooves
by them touch each other to avoid rock crushing by the bit body.
McClain and Cristy report
11
that the distance bet~~-een two grooves can be gre
because the ridges between the grooves break away owing
to the jet action (hydraulic
kerfing). However, they experimented in the open air.
Submerged rock at high amb
pressure does not break up so easily.
Drilling tests with mud as a drilling fluid ha
denlonst~’ated that .a 10% larger distance than 3 nozzle dian~ters between the ~ooves
is not advisable, because then high ridges*
would be left at the hole bottom (Fig. 8
These riclges are appxrentty strengt\lened by a pressure differential across the mud
cake (static hold-down). With water as a drilling fluid, such a mud cake does not
occur and smooth hole bottoms are obtained, indicating that some %ydraulic Iierfing
may then occur.
* ft is remarkable that only three ridges appem* where one would expect seven.
is apparently some keriing,
but M soon as one of tile two ~*idges bordering a
disammnrs. there is sufficient room for the jet to emerge.
Consequent ly, the
Th
gro
pre~~urc distribution on the remaining ridge ~vill change-and become insufficient
removal of that ridge. Misalignment of the bit may also cause a ridge pattern as
shown in Fig. 8, but it has been checked that this was not the case here.
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Spacer
.
- ----
A spacer serves to keep the nozzles a safe distance off bottom, thus preventin
them from being damaged. .
In the field, a spacer is required.
The following leads for spacer design have
been obtained from laboratory experiments and confirmed by field experience:
- A spacer should be designed to withstand not only wear but also appreciable shoc
loading, Jetted hole bottoms are frequently rough and irregular, in particular in
non-homogeneous rock.
- A spacer must cover the entire radius of the hole since it is not known where th
, strongest spots in non-homogeneous rock are encountered. “
- A spacer should not be located too close to jets since these may adhere to it,
thereby cutting a smaller groove at a wrong location.
A conventional bit, provided with tlm required arrangement of nozzles, would
seem to be t~e best way to meet these requirements and leaves open the possibility
of drilling conventionally through exceptional rocks too strong to be purely jetted,
concluded before. So far we have preferred a diamond bit to a roller bit. ‘
In the laboratory, the penetration rate expc riments liave been perforined with
spaceless bits (I?ig. 6), while the nozzle stand-off has been kept in excess of a lo
limit of roughly 1 nozzle cliameter by a device on the drilling machine actuated by
bit pressure drop, as mentioned before.
This arrangement excludes any mechanical
cutting by a spacer, which has been found to improve the reproducibility of the
measurements of bit penetration rate.
Nozzle size
------- -----
The nozzles in the hits shown in Figs. 6 and 7 are all needed to ctlt the hole
hence it is essential that none of them becomes plugged.
.This requires effective n
straining menns,
since for reasonable circulation rates small nozzles, ranging from
2 mm or less to 3, perhaps 4 mm, have to be used. In the laboratory, it has pro
fe~sible to use bits with only 1 mm nozzles (Fig. 6) without problems, despite the
use of weighted muds (12 lb/gal), thanks to the straining of the mud in the high-
-pressure line. A. similar straining system has been used successfully in the fieId
with 2. and 3 mm nozzles.
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Penetration rates
,
The penetration rate of the laboratory bit shown in Fig. 6 has been measured
the: way described before.
The effect on penetration rate of differential pressure (ho
clown), rotary speed,
bit pressure drop, rock type and drilling-fluid composition has
been investigated.
Differential yressure (hold-down~
----- ----- ---- ----- ----------
The cliffe rential pressure between the static head of the mud and the poro
pressure is known to cause reduction of conventional drilling rates by chip hold-down
19
effects . A similar effect has been found for jet drilling as is shown in Fig. 9. T
ma=gnituck ~f Lhis reduction (55% at 50 bar ambient
with conventional drilling, probably because bottom
Bit rotary syeed
------ ----- ---
Bit rotary speed has no effect on penetration
sufficiently high.
This follows from Fig. 10, which
pressure) compares favorably
balling20’21
does not Occ ul”.
rate, provided the rotary speed
shows that the penetration per
~evolution is inversely proportional to rotary speed,
and that there is an upper limit
to penetration per revolution,
Only because of this limit, may ehmted rotary speeds
be rec~uired to achieve mzcsimurn penetration rates, particularly at a bit pressure dr
very -much in excess of the threshold pressure.
The value of. this limit has been fou
to clepend on rock ‘type, fluid properties and bit design.
lleproducibility of the value
the limit is poor. Theoretically,
at a combination of very low rotary speed and a b
pressure drop slightly in excess of the threshold pressure, the penetration per :
revolution should be limited to roughly seven nozzle diameters, because beyond this
14
clistance the fluid velocity decreases below the velocity in the nozzle .
When taking into account the small size of the test bit and of the nozzles, we
feel that for full-size bits there is no urgent need for extremely high rotaly speed
(turbines) in excess of what can be obtained with modern rotary drive. Slow rotary
speeds are to be avoided. In jet drilling, it is pose
very maximum speed because the torque is low. ”
Bit messure dro~
Me o run the rotary drive at i
-----------------
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The penetration rate increases proportionally to the excess bit pressure d~’op
over the rock’s thrc s11oM pressure, as is shown in 1?ig. 11. From this fi=~re, the
negative effect of a low rotar~r speed at high bit pressul*e drop can also be noted.
The ‘rate of increase with bit pr~ssure clro~ depends on rock type, fluid composition,
hold-down differential pressure and, hit design.
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Rock t~c
------ --
The rock determines the nozzle pressure drop at which penetration will comme
(the threshold pressure) as dis~ussed before.
It also affects the rate of increase in
penetration rate with the excess bit pressure
drop. For instance, when circulating
water, the penetration rate was founcl”to increase 1100 mzn/min per 100bar excess
bit pressure drop in Obernkirchen, sandstone and 180mm/min per 100 bar excess b
pressure clrop. in a quartzitic sandstone.
Drilling-fluid conl~osition
-- --- - - - - - - --- - -- -- - -- .-
The highest penetration rates are obtained when using water as a jetting fluid,
irrespective of bottom-hole pressure.
At zero holcl-down pressure,
the same high penetration rates result u%en usin
unweightecl clay water muci (say s. g,
1.2 01”10 lb/@,
but, when using a barytes-
lden mud, the penetration rate in Gildenhausen sandstone, for insv.:lce, is h~lved.
This is attributed to bridging below the jet immediately upon the jets impact,
resulting in prcssurti build-up in the pores being harnpcrecl,
With [he lighter mud,
the rc is a spurt 10ss at a rate ecpal to water
22
, which is apparent l:i- sufficient to
achieve the same penetration rate as with water.
At elevated differential pressure ‘(5O bar), penetration rates v;ere measured t
vary with mud compositions and
roclis
The results obtained in Oke r:: iirchen sat:dst
are as follows:
Unwei~ ~ed clav water mud was used as a standard fluid (pe~* 1000 kg tap watc?r:
300
li~
LimburSfia clay to simulate clrillecl solids, 60
li~
bentonite, 2 kg sodium
llexamet~i]llos~]llate ancl some soclium hydroxide).
This mucl yielch?d ~ penetration rat
of l-OUghly 45% Of th:lt with lvater ,
one of the best rates of all muds tested.
Addition of bar- to the clay mud to raise the specific gravity from 1.2 to 1.4
caused the penetration rate to drop to 1490 of the rate ~~ith water.
Subsec~uent clil~:
back with tap vmtcr until the s, g.
was 1.2 again did not fully restcz.e the penetratio
.
late; it became 23% of the rate with water.
.
.
While thinning the lighter muds (s. g. S 1, 2) the vhosphate cement was founci
affect penetration rate in that the higher contents yielded higher pens: ration .,ratcs.
The barytes mud (s. g. 1.4) has originally only been thinned \vi:il phosphates.
Upon addition of 20 g/1 cluebracho and stii~un hydroxide, . the ~isco~i~~ droPped
considerably (Marsh funnel 53 to 32
s, plastic viscosity from 8 to 7 CP and Bingham
yield from 35 to 9 lb/100 ft) but no effect on penetration rate was noticed.
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A mud very-similar to the standard fluid (containing 330 kg instead of 300 kg
Limburgia clay in 1000 kg tap water),
but with CMC as ~-iscosifier and filtrate loss
reducer (5 kg in 1000 kg tap whte.;),
instead of bentonite (60 kg in 1000 kg water),
showed a penetration rate of 25% (instead of 45%) of that with water. This result
adding 2% w bentonite to a slurry of 220 kg Limburgia clay per 1000 kg tap water.
This caused a 25?G increase in penetration rate.
A knolin mud, consisting of kaolin, water
penetration of 40% the rate with water, despi~~
Reduction of the water loss to 14 ml/30 min by
in penetration rote,
13iscussion
.. **,*.** s
might mean that bentonite is favorable for the penetration rate. We checked this
and Calgcm (s. g. 1. 2), caused a
the high API water 10Ss (M ml/30
‘tidding bentonite prod ucecl no change
The most harmful effect on penetration rate was due
to the adclition of barytes
This even caused reduction of the penetration rate without a pressure difference
between bore hole and pores being present. l’here is, of’ course, a. pressure differ
\
‘1
immediately below the jet between the stagnfition pressure of the fluid awl the pres
in the pores.
The barytes partiClcs will bric~gc thC?Se pL)~L’e~mmediately, the~~by
reducing the pressure build-up in the pores.
l’urther, we found that bentonite may sometimes bp beneficial for the penetrat
rate. This may be clLv2to bentonite particles plugging pews far aheacl cf the area
where rvc
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FIELD EXPERIIIENTS
The step from the
which have to be solved
-1o-
laboratory to the field usually introduces a number of problem
satisfactorily before economic evaluation is feasible. A numb
of fielcl runs have therefore been made to locate possible barriers and find means of
overcoming these.
,
,.
‘rest prep
ar at ions
,It was expected that conventional rig equipment would be adec uate, provided tha
the formations selected were weak enough to be jetted purely with the aid of the
available pumps.
NAM’s Groningen gas field offered a suitable section of Tertiary
“shales below 1700 ft depth. A IfAIU rig suitable for 5000 psi surface pressure and
ecluipped with two Gardner Denver PZ 9 pumps could be made available,
Three sections of .Tertiary, 300-700 ft thick, have been jetted in’ three different
wells with 9 5/8 in bits, one of which is shown in Fig. 7. Some of the precautions
talien to prevent problems are discussed below.
)?luicl circulation
----------------
In :iew of the small nozzles (2 and 3 mm ID), used in the bits, ati effective
straining system was provided,
Apart from ch~cking shale shakers and conv~iltlod
strainers in t?lc pumps
‘ suction and discharge for proper functioning, hvo additional”
strainers (l?ig.
i2) fvex“e also usccl
; one in the tool joint below the kelly and one
in~idb a collar close to the bit. On every connection made, the upper str~liner was
~eplaced by a clean one,
already placed into the” single to be added. This strainer
served to pick up pieces of iwbbe~* {worn packing),
etc. and any material that had
bypassed
scale etc
0.2 -0,5
Tripp~n~
. . .
any screen in some way. The down-hole strainer served to catch dirt,
from added drill pipe.
The holes of bbth thick-walled strainers were
mm smaller in diameter than the nozzle,.~. “
While running into the hole, di@ might miter the nozzles and plug them, for
instance while mnning into a lbridger, while scraping dirt from the hole wall or whe
solids inside the bit bridge across the nozzle opening.
To avoid this, the nozzles we
plugged from the outside of the bit with rubber-covered rivets. These i’ivets can be
pumped out of the nozzles with about 100 psi pressure.
lIoreovcr, a float valve was
installed to prevent back flow also after the’ ri~’ets have been pumped out. These
precautions are perhaps unnecessary since laborato~~ tests have shown that when a
bit with open nozzles is pushed into soft shale,
the shale indeed enters the bit but i
extruded again when circulation is stm*ted.
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Drilling
.
----.-
$ilince thin streaks of stronger rock might be encountered, the bits used were
clesigned to diamond drill, if necessary.
Therefore, between six and twenty
collars (8 in OD), 30 ft length),
were used and stabiIised by a stiff-bottom
bit - stat -
short collar (strainer) - stab - collar - stab - collars etc.
drill
assembly:
Test results
All bits reached bottom without troubles. On starting circulation the nozzles
appeared open,
and on starting rotation, the bits appearc?cl to drill r.t little or ilo bit
load. No significant ecluipment troubles were encountered, Some observations made
are discussed below.
.
Bit Ioad------- --
Al though, in principle,
no bit load is recluirerl to jet the forrnntion, in practice
. an ins$,rurnent .is ncecled which can tell the driller ~vhere the bit is v:ith .re.spect to t
hole bottom. The weight indic~.to~’ can do this when sufficient load on bit can M
tolerated because part of slackecl--off weight may be absorbed by dm ~ of CO1lJXSanc
stabilisers. A 10-15000 lb bil load on the 9 5/8 in Mts was useci or jet drilltr.g in
order to make sure that the bit was on bottom,
so that the penctr:’.:’.on rate was
maximum owing to minimum nozzle stal~d-off, At very low bit Ior.d [0-3000 lb)
significantly lower penetration rates were experienced, The same R: .lLes for i rrcguI
i.,
lowering of the bit by the driIIe~*.
Penetration rate
cuttings and bits
------- ------ ------ ----- ------- --
At optimum cot:ditions,.
penetration rates averaged 5-6 ft/nlim These Mes
might also be obtained conventionally; however,
only Io~* some time because of the
occurrence of clay balls.
Clay balls were not experie need whiie je:zing, but tk.e wat
clriHing fluid mudded up quic
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-12- ‘
Several times thin streaks of stronger rock were encountered, which had to be
diamond-drilled. Then the bit load increased suddenly but could be restricted to about
30-35000 lb for a minute or so until the streak hml”bcen fully penetrated. This
combination of jet bit and diamond bit,
one of which is really cutting at a given time,
performed well. It is particularly reciuirwl in non-homogeneous medium to very strong
.
rocks, where the high penetration rate and the long bit life of jet bits will be of much
greater importance than in soft shales and sands.
Both the diamonds and the nozzles were hardly damaged (Fig. 7) during these .
short test runs. Although it is too early to ci.raw firm conclusions, it seems feasible
to develop jet bits with a very favorable life comparable with that of diamond bits
rather than roller bits.
Torque and r.~. m.
------- ------ ---
At the low bit loads applied,
very low torque was measured, being large ly due
to friction of the drill string and being governed by r. p. m. NO signs of vibrations
were observed. In general, elevated rotary speeds favoured bit penetration, so that
120-180 rpm ~~as most freclucntly applied.
~Iud strainers
------ ------ -
The use
far more than
of strainers was found to kc essential. The top-strr.inersf cap~~city was
requirecl, so that much longer periods of circulation could haye been
possible. On one occasion, the down-hcle strainer was filled with plastic coating
material from the drill pipe, indicating that plastic-coated drill pipe may not be
compatible with jet drilling.
JI’ithout the strainers, nozzle plug~ting could not Imye been
avoided.
IIole deviation and hole gauge
------ ------ ------ ----- -- -
From the test, it was inferred that the way of drilling affected very much the
size and the course of the hole. Jetting at very low bit load produced a larger hole
size, hole deviation and dog leg severity than jetting at reasonable bit load. In the
latter case the hole usually hardly appeared over gauge, no dog legs occurred and
the deviation chan=md insignificantly.
It is evident that string st:lbilisation can ~i~~y be
effective in a hole which is cut reasonably to gauge. This, in turn, is gre~~tl~ affected
by the design of the jet bit and the drilling practices.
,,
.
.-
.
.
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.
-13-
LOOKING AHEAD -
so far jet drilling appears feasible and promising; therefore more extensive
investigations are needed than have hitherto been performed worlci-wicle. It is
encouraging that at least eight oil companies are aware of the potential of the method
10
and jointly support a field test programme
. These field runs should disclose what
is currentIy feasible at pump pressures exceeding 10 000 psi. They will yield
experiences with recent bit designs and high-pressure eclu;pment and thus provide
.
some indication of the economic
viability of. drilling by jets in the future. It is
evident that such an effort provides an excellent opportunity for LJ1 industries
involved to improve not only the hardware but also the bits, the performance of
which clete~*mines the success of the method.
The experience
gained with high-pressure pumping v(ill extend the f.eld of
application for existing methods of drilling.
I or
instance, v~-henhigh-fluid pressures
for continuous service can be supplied at reasonable costs
turbine-driven cliamoncl bits
can be powered much better than at present,
which shouki raise their pe rforrnance
considerably.
This already is valid for pump pressures in the 5000 psi range, for
pressures many rigs are suited,
in particular in expensive operations.
With respect to the performance of jet bits,
aci.clitional laboratory-research seem
..
imperative to develop” design criteria and to gain insight into the jet-d rillinc process,
required for the correct interpretation of the field rcsuIts and the furtj:er bit iicvelop
mcnt. In the bit development in the laboratory we have so far experiet}cecl tl]:~t bit
performance ctepends very much on bit design. Since jet drilling will umioubtedly
cause n significant increase in rig cost,
and this is to be offset by hig?:er penetration
rate and long., r bit life, it is justified to spcncl many future effo~’ts on improving bit
performance.
Only with the best bits and operational, teckr~ques can the full potential
of the jet,-dril]ing method, -lso in small hole size, be clisclosed and u ilised.
CONCLusIONS
-
1.
2.
3.
4.
5.
The threshold pressure for cutting rock is rough~y fi’(e times the ro~.k’s tensile
strength, irrespective of drilling-fluid composition ar.d do~vn-hok pressures.
The bit penetration rate is roughly proportional to the nozzle pressure drop in
.
excess of the threshold pressure.
Elevated rotary table speed is required for maximum jet bit performance.
Chip hold-down pressure reduces jet-bit performance significantly.
No abnormal deviation problems have been experienced in the field. - -
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,
,
6.
7.
8.
9.
10.
1~,
12.
13.
14.
.
-14-
The hole jetted correctly is- to gauge.
Cutting recovery in the field was ‘~ood. “
Laboratory testing of a variety of bits has yielded useful design criteria; for
instance, the radial distance between nozzles
must not exceed three nozz~e
diameters.
.
A spacer must be resistant to wear and shock loading, it must cover the entire
radius of the hole,
and be located at some distance from the jets. The spacer
function can be performed by conventional, cutting means that also cope with rocks
that are too strong to be jetted..
Inert solids in mud are much more harmful to the penetration rate than active cl
Weigilted muds may yield a reduction in penetration rate
even if hold-clown pressu
is absent,
Rock failure is due to the penetration of high-pressure fluid into the pores a]~d
cracks of the rock.
.
Hydraulic kerfing
cannot occur under clown-hole conditions with plastering muds.
In the laboratory,
nozzles as small as 1 mm could be used without insurmountable
problems. In the field good experience has been gained with 2 and 3 mm nozzles.
The strainers used were adecluate to prevent pluggin:; of the nczzlcs.
15. In the field, 9 5/S in holes could be jetted in weak, formations at very satisfacto~
rates using 5000 psi equipment.
AU< h’O’N~EDGE MEIJT
. .
The authors wish to think the Management of .Shell Internationmle Research
Maatschnppij, The Ha~me, the Netherlands, for permission to publish this paper.
The help given by many colleagues is gratefully acknowledged.
.
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,.
.
.
.
-15-
RE’FE13ENCES
1.
2.
3,
4.
5.
6.
7,
8.
9.
10,
.-
“11.
12,
13.
14.
7
7
I?armer, I.W. ,
“Penetration of rocks by water jet impact;’. Ph.D. Thesis,
University of Sheffield, April 1965.
Leach, S. J. & Walker, G, L. ,
“Some aspects of rock cutting by hig$ sp’eed w
jets”, Phil. Trans. Rov, Sot.
London, Series A 260, July 1966,
Brook, N. & Summers, D.A. ,
~JThe penetration of ~tock by high-speed \Vater
Int. J. Rock hlcch. 31in. Sci.., Q, pp. 249-258.
Imanaka, 0. et al. ,
“Experimental study of machining characteristics by liqui
-2,,
Wcrn .
ets of high power density uP to 198
Paper G3, 1st Int. Swnp. On J
Cutting Techn, Coventry, April 1972. “
Kee, W.R. & Kurko, M.C. ,
‘Tlevclopment of a jet cutting maciline system”.
Papep G5,
1st Tnt. SunP.
on Jet Cutting Techn. , Coventry, APril 1972s
Bryan, E.L. ,
“High energy jets as a new concept in wood machining”.
170rest Products Jouri~al 8, Aug. 1963, 8, pp. 305-312.
Wyllie, M.R. J. ,
pl’oc, 8th World “Petroleum Congr
“Jetted particle drilling”. _
~IOSCOw1972.
hIaurer, W. C. & Hcilhccl
“Hyclraulic jet clrilling”. ~PE pa~~er ~43
19G9.
fiIaurer, ~;’. C., Heilhecker, J.K. ~ Lovet W=W. s
ltHigh ~ressurc jet drilling’
sPE Paper S988, 1972.
[
-
8/16/2019 SPE-4923-MS
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.
.
-16-
15. Kohl, R.Es ,
~tRock tunneling with high speed water jets utilizing Cavitation d
Technical report 713-1.’ Hydronautics Inc. , June 1968.
16. Powell, J. II. & Simpson, S.P. , “’theoretical study of the mechanical effects
water-jets impinging on a semi-infinite elastic “solid”.
Int. J. Rock Mech. Mi
~, 1969, pp. 353-364.
.
17, I?orman, S.E. & Secor, G. A.,
‘fThe mechanics of rock failure due to water
impingement”.
SPE -paper 4247, January 1973.
IS. Earle, E. N.,
“Unpublishecl results”.
Shell Development Company. -”
19. Gamier, A.J. & Van Lingen, N.H. ,
“Phenomena affecting driIling rates at
Trans. AIME 216, 1959, 2.32.
20. Feenstra, R. & Van I.eeuwen, J. J.hl. ,
“Full-scale experiments on jets in
impermeable rock drilling”. Jour. Pet. Tech. , hIarch 1964,
21. Van Lingen, N. H. , “Bottom sca~:enging
- A major factor governing penetratio
rates at depth”. Jour. I>et. ‘recht, February 1962*
22.
Darley’, ~f.C.H. ,
“Designing fast drilling fluids”. Jour. Pet. ‘.re@&.
April
22. l?airhurst, C, ,
‘‘Cln the validity of tile
‘Brazilian’ test for brittle materials”.
Int. J. Rock .31ech. J[ining Sci. 1, ~~~’~, PP. 535-5469
-
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.
.
.
-17-
.
Ratings of the drilling machines - TABLE I
Machine
Max, pump pressure
, bar
, psi
Max ambient pressure, bar
.
, psi
Rotary speed
, rpm
Stroke
, cm
Pump power
, HHP
Max. bit size . , in
31zx. bit load
, tons
15 tons
400
5800
200
2900
30
- 3000
25
120 “
5
15
.
high pressure
1000
14600
500
7250
30-300
23
550
6
3.5
50
tons
200
2900
200
2900
11-1120
75
1600
10
50
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.
.
-18-
‘/
Threshold pressures and tensile strentihs of some test rocks,
as measured at KSEPL - TABLE II
I
Rock
Gildenhausen sandstone (oIc1llot)
Oberrkirchen sandstone
lGreywacke sandstone
b
uville limestone
Vaurion limestone
~Carrara marble
Bo.varian granite “
Belgian limestone
‘Solenhofen limestone
~Basalt
I
~Belgian cplartzitic sanc stone~ “ ~
‘Brazilian’ tens
uniaxial tensile
pressure.
rhreshokl
pressure,
bar
100
220. .
230
160
360
280
300
425
800
785
770
le strength of
strength. ‘i%e
Solenhofe n 1
latter gives
.
.
Tensile strength, *
bar
25
49
52
28
m
55
63
91
100
200
1~~
.—
87
100
190
Ratio of thresh
pressure an
tensile streng
4,0
4,5
4.4
5.7
5.3
5.1
4.8
~ 4.7
8.0’
3.9
5.4
Uni
~ The ter.sile strengths of most rocks have beer. measurecl with a simple Brazilian
with solid cylinders of equal length and dimne:er.
It should be noted that the
nms:one differs considerably from its
the better correlation with threshold
1
1
)
\
I
.,
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.’
. .
. . .
.
-19- “
.
Threshold pressures as measured by Oak Ridge National I.ahoratory
11
- TABLE I
Threshold pressure
Rock
I
==++-R-
erea sandstone
138
2000
%orgia granite
414
6000
Tensile strenah after
Gnirk & Cheatham
12
*
—-
psi
635
26
380
I
Ratio of threshold
pressure and
tensile strength
5.5
5.25
.....
Some tensile strengths, by Gnirk & Cheatl~am
12
- TABLE IV .
Rock
Indiana limestone ‘
Carthage marble “
Danby white marble
Berea sandstone
Virginia greenstone
Tensile strengths .
+==
10s0
I
74.3
865 \ 59.7
38C
26.2
280
I
19.4
.
.
. .
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-20-
.
Tensile strength of some I?rench rocks
13
- TABLE V
Rock’ type Origin
Tensile strength,
barx
Granite
Granite
Granite
Granocliorite
Granoc.liorite
Granocliorite
Microgranite
13asalt
Basalt
Andesit
O Aite
r
Igneous rocks
I
Quartzite
Quartzite
Crystalline limestone
Crystalline limestone
Crystalline limestone
Calcareous schist
Calcareous schist
Porphyrorde ‘
Gypsum
Chalk
Limestone
Limestone
Limestone
“Limestone
Limestone
Limestone
Limestone
Sanclstone
Ligron
St. Germain de Modeon
Senoncs
Plouclalmezeau
I?lamanville “
Cap de Long
Corbigny
St. Jean le Ccnteilier
Raon l’lltape
Volvic
Salies du Salat
Metamorphic rocks
TiSmes
Cherbourg
lIosset
VilIette
Montcenis Zone H
Montcenis Zone I
Montcenis Zone 111
Genis
Sedimentary rocks
CormeiHes en Parisis
Guerville
.
HmltevilIe
Marquise
MontaIieu
Pagny
EuvilIe
St. Maximin
St. Vaast Ie Mello
-1’ehel
131
90
134
128
~34
114
212
180
370
77
218
.
110-282
158-254 “
89
101
74-128
34-105
27-97
76-134
12.1
2.67
136
90
100
89
50
7.5-13.3
6
111-169
* For anisotropic rocks,
both the lowest and highest values are c@oted.
It has been assumed that the lowest value determines the threshold
..”
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.
.
-21-
Drilli ng-mucl compositions and properties - TABLE VI
Composition ‘
Tap water ‘ , kg
Bentonite , kg
Limburgia clay , kg
Ba~yies
?
kg
Calgon
s
kg .,
r
roperties
Specific gravity’ ,
kg/1
hlarsh funnel ,s
l?ann plastic vise. , cP
17ann Bingham yield, lb/100 ft2
API filtrate loss
, ml/30’
pH
1
1000
60
--
10(),$
93
12
55
16
9.1
2“
1000 .
60
1.5
1.04
34
6
4
12
8.8
3
1000
52
260
415
2*7
1.42
74
11
47
6 “
9.2
~ Sodium hydroxide added to ofi:e.in a reasonable pH value.
. .
-
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o
z
I
1
E
n
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.
*
a
FIG,
3.
HIGH-PRESSURE DRILL
NG MACHINE
., .
...” . ..
FIG. 5. TYPICAL GROOVE IN ROCK SURFACE
.
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.
*
Ro:atable shaft .=
.
Seal —— K
---2
.:. -:...
/tzi
Fluid in .
1
.
re
I’2.= Pressure vessel
/“
.
“’
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c
.-
E
E
w
m
i=
td
5
.-
IL
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b
FIG. 8. THREE RIDGES ON HOLE BWTOM INDICATE INSUFFICIENT
OVERLAP
Penetmt ion mte
mm/min
6kI
500
400
I
300
2
c
bb
1
I
I
I
1
1
I
n
I
O 20 40 60 80 Iw
120
140
160 1[
Difktential pssure
Bit asin fig. 6
Bit rotary speed 358rpm
Clay-water mud, s .g. 1.2
Gildenhausen sandstone
Bit
pressure
mp
200
bar
.,
)
bar
f lG. 9. PENETRATION RATE DECREASES WITH INCREASING STATIC HOLD-DOWN PRESSURE
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4.0
2.0
I.c
f-- Fknetrction rate
~ limited to approx.
4.5mm/w.
\+ \
*.
mmaiiiizxx--l
\
+ ,,
50
lg@
200
400
. 300
rpm
F&tory speed
FiG.10.THE PENHRATKN H? I%N’XJJTZI?4ISINVERSELYPROFCRTIONALTOROTAR
.80C
Goc
40[
20(
SPEED ANO HAS
AN UFPER LIMITOF ROUGHLY4.5
mm/rev.
rixmc lmscnw c 1
5“
6
/
—
1
2
3
4
5
6
‘pm
153
215
275
358
505
660
2
1
/
5
I
F
1
. 250
300
.
.
Bit
pn?ssu”mdrop
;0 ba
x
FIG.11.PENETRA1-IGNRATE INCREASES PR12F12RTIONALLYWITH EXCESS B T PRESS
.::
‘.
.
EXCEPT AT A COhli3 NATlGN OF
i-ii~i-iSIT-PRESSURECROPANI)
LOW ROTARY
ii :
.
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FIG,
12. STRAINER USED DURIJ’JGFIELD EXPERIMENTS