Society of PetroleumEngineers
Slimhole Drilling Hydraulics
R.A. Delwiche, Dl3 Stratabit; M.W.D. Lejeune, Consultant; P.F.B.N. Mawet, Consultant;
and Roland Vighetto, Total
Copyright 1992. Society of Petroleum Engineers Inc.
This paper was prepared for presentation at the 67th Annual Technical Conference and Exhibitionof the Society of Petmleum Engineers held in Washington. DC. October 4-7. 1992.
This paper was selected for presentation by an $PE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper.
as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to wrrection by the author@).The material, as presented, does not necessarily reflecl
any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publicationreview by EditorialCommitteesof the Soclety
of Petroleum Engineers. Permissionto wpy is restrictedto an a b s t r a c t s . Illustrationsmay not be copied. The abstract should wntain wnspicuousacknowledgment
of where and by whom the paper is presented. Write Librarian, SPE. P.O. Box 833836. Richardson. TX 750833836 U.S.A. Telex, 730989 SPEDAL.
Abstract
Introduction
Drilling in small diameters is not new : the mineral
industry currently drills slim holes in hard rocks. In this
context, the drill string rotates at high speed very close to
the hole wall, which is in general of good stability.
Two main different technics are used in drilling.
Conventional drilling in sedimentary formations use small
rods rotating at a low speed inside a large hole (the
pipehole diameters ratio is about 0.30). This conventional technic is largely experienced all around the world
and empirical rules are deduced to help drilling designers.
Mining drilling (through hard formations) consists in
small rods rotating at a high speed but inside a hole with
nearly the same dimensions (the rodhole diameters ratio
is about 0.90).
To transfer that drilling method to the oilfield and
keeping high rotation speed and small annulus, many problems occur due to the sedimentary type of formations
drilled, and hydraulics become crucial for following points
of view : the lifting up of cuttings in the annulus (no ball i i up), the well bore stability, the cleaning of the bit, the
differential mud pressure in the annulus, the hydrodynamic lubrication between rods and the well bore.
Therefore, it is essential in slimhole to investigate
drilling hydraulics, using basic theoretical equations derived from fluid mechanics.
The developed model takes into account mud rheology, drill string rotation -and eccentric position of drill
string. Outputs are annulus thickness, drilling parameters
(including mud flow), and mud characteristics, all to be
respected to reduce slimhole drilling problems. The final
output is the compromise which integrates all these requirements for a successful operation.
Tests r e a l i i in a slimhole well have allowed to validate the theoretical assumptions.
In order to reduce costs (depending strongly on the
drilled hole diameter) in petroleum expensive exploration
wells, the idea was to transfer mining technology to drill
sedimentary formations. But an accurate knowledge of
hydraulics is essential in this case because hydraulics in
the annulus between rods and formations drilled are crucial in the point of view of wellbore stability, cuttings removal and transportation.
This theoretical approach allows a better understanding of phenomena occurring in the annulus and thus an
optimization of hydraulic parameters for a successful
slimholedrilling.
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SPE 24596
SLIMHOLE DRILLING HYDRAULICS
Slimhole drilling characteristics and
implications on drilling parameters
Slidole drilling is different from oil-well and
mining drilliigs because of :
- the important rod rotation speed (N(xpm)),
- the very slim annulus (Plannulus),
- the (soft) sedimentary formations drilled
- the mud characteristics.
These 4 main different characteristics make absolutely essential the drilling hydraulics study from the basic equations of fluid mechanics (see figure l).
Main requirements on drilling hydraulics
Drilliig parameters such the annulus dimensions,
the drilliig mud characteristics and the mud flow rate
have to be chosen in order to ensure :
a) a sufficient cuttings entrainment along the annulus (no
balling up)
----> annular mud velocities profile as uniform as
possible,
--> annular mean velocity greater than the cuttings
sedimentation velocity;
b) the wellbore stability
----> small velocity gradient to minimize the shear
stresses close to the wall of the borehole,
---> the annulus pressure lower than the formation
breakdownpressure,
---->no chemical reactions between the drilling fluids and
the formation;
c) optimum bit performances
---->minimum mud flow rate to cool it,
---> minimum mud flow rate to avoid bit clogging;
d) a minimized mudpower consumption
----> adequate choice of mud rheology characteristics,
----> mud flow rate adjusted.
These above conditions have to be respected simultaneously for successful slimhole drilliig. It's possible
with the adequate annulus dimensions, (rheology,
viscosity, chemistry) mud characteristics, and adjusted
mud flow rate.
Implications on hydraulic drilling parameters
1. To keep an]rullar mud velocities mofile as u f o r m
possible (to ensure carrvine effect on cuttings. and t~
avoid bJline uD)
The velocities profile depends on the annular flow
regime :
a) ifturbulent, velocities are constant but two difficulties
appear : shear rate (slippage velocities) and thus shear
stress close to the wall of the borehole are too high
(dangerous for the wellbore stability in soft formations
drilled), and pressure circulation losses are important
(proportional to square mud flow rate (ie %q2)), and thus
the annulus pressure. So, it's better to avoid it !
b) if laminar, velocities profile depends on mud
rheology.
The 3 main rheological models to study the
behaviour of various mud types are newtonian, binghamian, and oswaldian. A wide constant velocities zone is
possible to be reached (see figure 2) with an important
yield value if bighamian mud (YP>>),or with low rheological index if oswaldianmud (n<<).
2. To obtain annular velocitv =eater than the cutsedimentationvelocity
In order to ensure a sufficient carrying effect on
cuttings (to avoid balling up or having stuck pipes), it's
necessary to keep all along the annulus a mud velocity
greater than the cuttings sedimentation velocity. It's a first
approximation assuming that all forces acting on cuttings
are in the same direction. But in small annuli, if rod rotation speed is high, cuttings and mud particles follow an
helicoidal trajectory, so drag forces and gravity effects
are not parallel anymore.
The cuttings sedimentation velocity depends on
cuttings density, cuttings shape, cuttings dimensions,
mud density, viscosity and rheological characteristics.
(see figure 3). These parameters are influenced by the
formation drilled, and by the bit used, but also by the rod
rotation speed changing cuttings path.
It's in general recommended to have mud velocity
of about 0.5 m/s. But a more detailed study of the
optimization of all these parameters is on project.
.. .
3. m
z
e shear stress close the wall of the borehole
IJ
I kee~lagsrnallvelocitv sadgal
Shear stresses close to the wall of the borehole can
erode it, and cause caving. This phenomena is very dangerous because in this case, the rotating rods are not supported anymore by the wall and can break. It strongly depends on the velocity gradient, function of the mud
annular velocities curve. As seen before, a Nbulent flow
regime causes very important velocity gradients near the
wall of the borehole, and thus, high shear stresses along
the drilled formation can generally not be admitted. A
laminar flow regime induces lower velocity gradients and
thus lower shear stresses. So, it's recommended, in soft
sedimentary formations, to keep a laminar flow regime
inside the annulus.
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Slimhole drilling characteristics
SPE 24596
SPE 24596
R. DELWICHE, M. LEJEUNE, P. MAWET, R. VIGHETI'O
4. To obtain an annulus pressure lower than the
An adequate choice of mud density and
rhwlogical characteristics, and a mud flow rate
adjusted (minimum) can avoid this leak-off problem.
5. To ensure o~timumbit performance$
In order to avoid any clogging at the
bottomhole, it's important the mud flow rate is
sufficient to cany up all cuttings drilled. The cuttings
discharge depends on the rate of penetration (rop), the
drilled cross-section area (R) (coring or full-hole
drilliig).
It's possible to define the optimized annulus
dimensions to avoid too important pressure losses, for
a maximum mud flow rate given (by an economic rop
(for example)). Following a logical way, it's possible
to design core barrels, rods and bits with these
"hydraulic" dimensioning considerations, combined
with geologist's requirements, and mechanical strength
laws. The starting point of this design can be either the
core dimension required for geological analysis, or the
diameter drilled for economical reasons. Till now, design of core barrels was mainly driven by mechanical
rules and geologist's requirements. The hydraulic aspect was only empirical. (see figures 4,5,6)
Adjusted mud flow rate definition
Mud cuttings canying capacity can be defied
as a function of the ratio of the drill cuttings discharge
and the mud flow rate (x%). Depending on the type of
formation drilled, on the bit used, and the mud
rhwlogy, maximum ratios can be defied (x%). So
we can find the minimum mud flow rate in order to
ensure sufficient canying effect, which can be expressed as :
q (mudflow rate) > rop. $21 x%
Ill
It's important to minimize pressure circulation
losses, in order to minimize power consumption, to
keep annulus pressure lower than the formation fracturation pressure.
Pressure circulation losses can be expressed as :
where p :mud density
f : fluid friction factor (depending on mud
rhwlogy, annulus dimensions, and flow regime)
L :length
0annulus :hydraulic diameter
v :averaged annular velocity
AL, : couette coefficient (taking into account
the fluid helicoYdal trajectory)
y : crescent coefficient (taking into account
the rod eccentricity in the borehole).
Many requirements, as described above, exist
on slimhole drilling hydraulics. We can try to respect
all of them by a right choice of the mud flow rate.
In short, conditions to respect are the following
ones : laminar annular flow regime ( to avoid
turbulent regime), annulus velocity greater than
cuttings sedimentation velocity, minimum flow rate to
ensure sufficient carrying effect (q (mud flow rate) >
rop. R / x%), minimum flow rate to minimize pressure
losses and annulus pressure and to cool the bit.
So, if the type of formation drilled, dimensions
of bit, rods used are given, for a mud chosen, it's possible to define the mud flow rate satisfying all these
requirements. The plot (see figure 7) summarizes all
these conditions. This type of investigation has already explained some unsuccessful slimhole drilling
tests, based on conventional drilling empirical rules.
Slimhole specific problems
All requirements described before need a very
accurate hydraulic model. In order to have a good correlation, a mud rheological model more complex than
Bingham or Oswald has been defied.
Moreover, rods rotation at a high speed in a
small hole (slim clearance) causes new hydraulic ef-
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Another way of caving formation is to obtain an
annulus pressure greater than the formation
breakdown pressure. The annulus pressure is composed by the static pressure (function of mud density
and of depth), andthe dynamic pressure (function of
pressure circulation losses (depending on mud
characteristics, annulus dimensions, depth, and mud
flow rate)).
Lower annulus clearance expected, higher the
choice of mud rhwlogy is important. This dimension
deeply influences the circulation losses. A large YP
(in laminar regime) strongly increases the losses if
annulus clearance is small. This ratio " YP/0annulus"
is an important parameter about circulation losses and
can explain main differences observed between
conventional and slimhole drilligs.
SLIMHOLE DRILLING HYDRAULICS
fects as the Couette effect (related to helicoidal path followed by cuttings and mud particles), the crescent effect
(related to the rod eccentricity inside the hole), and the
ability of hydrodynamic lubrication (important to model
the torque caused by mud on rods).
Before describing specific slimhole drilling effects,
the table 1resumes the main differences between conventional oil-well and slimhole drillings.
Modellization of actual mud
In conventional drilling, muds are modellized with
classical rheological models l i e Bingham or Oswald.
The relation between shear rate and shear stress is usually
deduced with a standard rheometer @am). The use in
conventional drilling is to define the mud model with only 2 points of the rheological relation. These points are
corresponding to highest shear rates. This approach can
be justified in the case of conventional drilling. But in
slimhole drilling, a more accurate mud model is required,
mainly to cover the smaller shear rates in a better way. In
order to have a larger correlation, a mud rheological model more complex than Bingham or Oswald has been defined This model is defined by 3 parameters ( zo ,k and
n), instead of only 2 in classical models. The relation between the shear rate noted " y' and the shear stress noted "
T'can be expressed as :
r = r 0 + k yn
[41
On figure 8, differences between Binghamian, Oswaldian and 3 parameters models estimations can be
pointed out, compared to the actual rheological curve
(mainly for the smaller shear rates).
Many muds used in conventional and slimhole
drilhgs are not exactly Binghamian or Oswaldian, but
between both. In conventional drilling where annulus
clearances are quite large, an approximativemodellization
doesn't deeply influence annulus losses predictions. But,
in slimhole drilling, because of thin clearances used, the
estimation of dynamic pressure in the annulus is very sensitive to the choice of mud model, and smaller the annulus clearance, more this prediction is difficult.
Annulus pressure, as explained before, is a very important factor to be estimated with accuracy in relation
with the wellbore stability. This annulus pressure (AP)is
the sum of the hydrostatic and dynamic components.
The use in drilling industry is to express this annulus
pressure by the equivalent irculating density @CD) as
follow, where "g" = 9,81 m/s and " Z is the depth :
5
AP (bars)= Pstatic + Pdyn. = ECDgZ
[5]
The sensitivity of this prediction following the choice of
the mud model is tested on conventional and slimhole
configurations for the same mud as described in table 2,
and for usual mud flow rates.
It can be pointed out that differences between ECD
estimations following the mud model chosen vary from
only 1%in conventional configurations (PET 13"3/8), up
to 25% in very slim holes (SH 3"7/8). Smaller the annulus, higher this sensitivity of the ECD estimation to the
choice of mud model is important (about 8% for SH 5"
and about 15% for SH 4318).
This analysis shows that the accuracy of the mud
modellization in s l i o l e drilling is essential for accurate
predictions of ECD and thus to reach a successful drilling
operation.
Couette effect
An important difference between conventional and
s l i o l e drilligs consists in rod rotation speed. This characteristic related to the annulus thickness influences the
trajectory of cuttings and mud particles.
By viscous effect called "Couette effect", rotating
rods force mud to be in rotation. In consequence, the trajectory of cuttings and mud particles becomes helicoydal
and not straight anymore. This effect, which is small in
conventional configurations, influence the annulus pressure by increasing the length of the mud path and the trajectory for cuttings because, if gravity and buoyancy
forces acting on cuttings remain vertical, entrainment
force (tangent to the mud trajectory) is inclined.
The increase of length trajectory is characterized by
the "AL,"coefficient, which is the ratio between lengths of
the helicoidal path and the straight trajectory. Because of
the complexity of mud rheological model, "AT.," coefficient is estimated in computing resulting velocities from
tangential (influenced by the rod rotation speed) and axial
velocities (function of mud flow rate).
The first approach was to compose averaged tangential and axial velocities. But this didn't take into account mud rheology and annular flow regime. So the 2nd
approach consists in composing 2D tangential and axial
velocities profile. Resulting velocities profile is characterized by a variable angle function of the position in the
annulus. A numeric integration gives then averaged pitch
of the helicoTdal trajectory, and thus the "AL,"coefficient.
(see figure 11)
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All these effects were modellized and will be described here after. This theoretical basis is developed on a
APPLE MACINTOSH in Fortran language. This hydraulic module is implemented in a software including mechanics and rods behavior simulator on IBM PC in C language.
SPE 24596
SPE 24596
R. DELWICHE, M. LEJEUNE, P. MAWET, R. VIGHETTO
this hydraulic software is coupled with a mechanical software simulating the drill string behavior inside the hole.
This mechanical software takes into account boundary
conditions, forces and vibrations produced by the bit at
the bottom of the hole, torque on rods coming from mud,
etc and predicts in 3D rods deformation and rods
stresses.
...
decreases.
The evolution of "Couette" effect depends on mud
rheological characteristics, flow regime, mud flow rate,
rod rotation speed, rod diameter and annular clearance.
The diagram (see figure 11) was determined by experiment and is valid for one mud. More the mud is viscous,
more the "Couette" effect is important, more the "pedalo"
effect occurs for higher rod rotation speed.
The main difficulty consists in the determination of
this limit between laminar and turbulent flow regimes.
Tangential and axial flows are not independent. The limit
between laminar and turbulent globalized regimes is function of both flow components, of mud rheology, etc.. .Experiments in laboratories of HydroMechanics are in progress in order to precise the relation between axial Reynolds number and tangential Taylor number describing
the limit between laminar and turbulent flow regimes.
The shape of this function is showed on figure 1 2
Crescent effect
Another specific effect concerning slimhole drilling
hydraulics is the "crescent" effect. Inside the hole, rotating rods don't remain concentric. In conventional
drilling, rods are small in front of hole diameter and rods
position doesn't influence annular losses. But, in s l i i o l e
c ~ ~ g u r a t i o nratios
s,
between rod and hole diameters
come close to 1. For such ratios as used in s l i i o l e (bigger than 0,75), the eccentric position of rods inside the
hole influence annulus flow and losses. More the rods are
eccentric, more annular losses decrease. This effect (see
figure 13) is taken into account by the " Y "coefficient,
&fhed as the ratio between losses with eccentric rods
over losses with concentric rods.
In order to estimate this coefficient, the velocities
profile in eccentric rods is needed. To determine that, the
classical Reynolds equation generalized to rheological
models like Bingham, Oswald or 3 parameters one is solved by finite differences with a very thin grid. On figure
14, some results of this software for oswaldian muds are
showed for eccentric rods. This figure shows the axial velocities profile in an eccentric annulus (E = 0,80) for an
oswaldian mud.
The "crescent" effect depends on the mud characteristics, the ratio between rod and hole diameters, and the
rod eccentricity. In order to h o w the rod eccentricity,
Experimental results
Importance of experimental validation
It's very important to validate all this theoretical
modellization with experimental results. Oil companies
try to understand phenomenas occuring while drilling
slimholes and TOTAL is one of them.
A collaboration between TOTAL and DBS was decided and experimental results were analysed by DBS for
comparison with theoretical predictions.
During an exploration drilling in Gabon, TOTAL
takes the required time to realize tests in order to obtain
the global effects of the rod rotation speed on the total
pressure losses. For many different depths, sets of tests
were realized, consisting in varying the mud flow rate and
the rod rotation speed. For each couple of these values,
the total pressure losses in the system were recorded with
an acquisition set and pressure gauges of which sensibility was estimated to 5%.
Mud characteristics
Mud characteristics .are very important parameters
to know for accurate predictions of pressure losses when
the annular clearances are thin. For each set of tests, mud
characteristics were accurately noted, with complete Fann
curves, specific gravity, temperature, The choice of mud
characteristics and the mud modellization are very crucial
in slimhole drilling.
...
The theoretical point of view has deduced that bingharnian muds (with large yield point) cause too important pressure losses in thin annulus, and are not proper for
such drillings. The dynamic component of the annular
pressure is much more important in slimhole than in
conventional drilliings.
Experiments c o n f i i that fact. Slimhole wells tested with such binghamian muds were unsuccessful. On
site, it was confirmed that oswaldian muds (without a too
large yield point) were more suitable.
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These approaches assume that velocities profiles
can be composed in 3D if laminar regime exists. If annular flow regime is turbulent, rotating rods don't influence
the whole annular clearance, but only a part, decreasing
with Reynolds number. This effect is called "pedalo effect", by analogy with the phenomena occurring when
fluid is sheared. Thus, for increasing rod rotation speeds,
Couette effect increases up to a critical velocity and then
SLIMHOLE DRILLING HYDRAULICS
Tested configurations, Presentation of results
Only three sets of results are presented in this
paper, which are noted 578P1172,425P1210 and 425P2078. Hole geometry, BHA and mud characteristics
are collected in tables 4, 5 and 6 respectively. Note
that annular clearances are thin. The rod /hole (or casing) diameters ratio are approximatively equal to
0.85.
For each case, 2 diagrams are presented.
Fit,the evolution of total pressure losses in
function of the mud flow rate and that for different rod
rotation speeds. theoretical predictions are represented
by a continue curve and experimental results are plotted.
theoretical and experimental results. This software is
commonly used for conventional drilling, but its results are not guaranted for holes smaller than 6 inches
and this software doesn't take into account any rod rotation effect It can be noticed that REED TOOL software results are quite far from experimental results.
This point of view shows the limitation of
conventional drilling software in slimhole wells and it
shows also that slimhole drillings induce special effects which are not common in conventional drillings.
On the second serie of diagrams (see figure 16,
18,20), the ratio of annular pressure losses without or
with rod rotation speed is showed in front of " a R / V .
Statistical analysis of experimental samples shows that
scattering of experimental results is quite large.
It can be noted that the "pedal0 effect" is not
observed. Because of geometric considerations, and
mud viscosities, rod rotation speeds are too low and
don't exceed the critical rod rotation speed.
It can be also noted that correlation between
theory and experiments for "couette" and "crescent"
effects is acceptable.
The second plot shows the influence of the ratio
" o R/U" (which means the ratio between rod tangential velocity and mud axial averaged velocity) on the
ratio between the annular pressure losses with rod rotation speed (DP N#O) and the annular pressure losses
without rod rotation speed (DPN=O).
Conclusions
Hydraulic studies have been made to get a better
accuracy in slimhole drilling than in conventional hydraulic program.
Analysis
First, it's important to note that to consider with
accuracy the "crescent" effect, we need the howledge
of the exact position of the rods inside the hole (centered or plus or minus eccentric) (remember figure 13).
It's possible to determine this postion if you assume
knowing the hole deformation, centrifugal forces,
etc... But there always remains a doubt on the experimental estimation That's the reason why, on graphs
showing total pressure losses in function of mud flow
rates, "error bars" were placed to represent this uncertainty.
If we consider first graphs (see figure 15, 17,
19), it can be observed that correlation between
theoretical predictions and experimental results is
quite good. Differences don't exceed 15% in any case.
Higher rod rotation speed, higher pressure losses. This
fact is coming from the influence of "Couette effect".
For case n02 (referenced 425P1210), the REED
TOOL software was tested in order to compare with
Preliminary validation on real wells have showed some good correlation between theory and practice, but there are still some work to be done to reach
total validation in all cases and especially to take into
consideration the "crescent" effect" more accurately.
This theoretical approach will help the operators
in the future to drill more successfully slimhole wells
and to adjust more safely the hydraulic and mechanical parameters.
Acknowledgements
The authors thank D.B.S. a BAROID Company
(Belgium) and TOTAL (France) for permission to publish this paper. They are grateful to the Laboratories
of HydroMechanics of Professeur ALEJEUNE of the
University of LIEGE (Belgium) for their helpful collaboration
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Tested configurations were in coring, beginning
to approximatively 1200 m depth (cfr table 3). The
operator has used polyglycerols muds with potassium
carbonates, which are almost perfect oswaldian muds.
Yield points are very low. During tests, the inner tube
of the core barrel was removed, with the result that
pressure losses recorded were only due to inner rods
and annuli.
SPE 24596
SPE 24596
R.DELWICHE,M.LEJEUNE, P.MAWET, R.VIGHETTO
References
AP annular pressure (bars),
DP pressure losses (bars),
ECD equivalent circulatin density (kg/m3>,
g
specific gravity (m/s ),
k
consistence index (Nhn2s-I' or lbs/100 ft2S-" ),
L
lengthb),
n
rheological index (dimensionless),
N
rod rotation speed (rpm),
Pdyn. dynamic pressure (bars),
Fstat. hydrostatic pressure (bars),
q
mud flow rate (m3/s),
R
rod radius (m),
rop rate of penetration (mh),
U
axial averaged velocity (m/s),
v
averaged velocity (m/s),
x
admittable volumetric ratio "cuttings/mud (a),
o angular rod rotation speed (rad. S-I),
W U ratio between rod tangential velocity and mud
axial averaged velocity) (dimensionless)
YP yield point (IV/rn2 or lbs/lOO ft2),
&pth(m),
p mud density (kghn3,
AL couette coefficient (dimensionless),
Ct drilled cross-section area (m2),
y mud shear rate (s-I),
0ann.hydraulic diameter (m),
Z mud shear stress (Nm2 or lbd100 ft2),
yield point stress (N/m2 or lbs/100 ft2),
Zo
W crescent coefficient (dimensionless).
1. T.W. Beihoffer, D.S. Dorough, DD. Schmidt :
"Development of an inhibitive cationic drilling
fluid for s l i i o l e coring application", SPE 19953
2 D.J. Bode, RB. Noffke, H.V. Nickens : "Well
control method and practice in small diameter
wells", SPE 19526
3. K. Floyd : "Slimhole haul in savings", Drilling,
july 1987
4. C.M.Hoffman, P.W. Lawrence : "Add reserves in
existing shallow wells by deepening with slimhole
drilling operations", SPE 15249
5. G.M. Lloyd, D.J. Bode, H.V. Nickens : "Practical
application of real-time expert system for
automatic well control", SPE 19919
6. G. Margueritat : "Exp6rience de forage en tt2s petit
diamBtre", P6trole et techniques, nov. 1985
7. G. Peterson :"Modem exploration by deep slim
hole drilling and wire line coring", GWA
8. B. Rehm :"Horizontal drilling applied in slim
holes", Petroleum Eng. Int., feb. 1989
9. S.H. Walker, K.K. Millheim :"An innovative
approach to exploration and exploitation drilling :
the slimhole high-speed drilling system", SPE
19525
1
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Nomenclature
SPE 24 59 6
-
Table 1 Comparison between conventional and slimhole drilling
IConfiguration
I
noted
A
ROD :
CASING :
0rodIIZIcasing :
ANNULUS
0 int. (mm) :
A
P
FLOW AREA (cm2) :
-
SH 3"7/8
I
1 Configuration
I
SH 4"3/8
1000
1000
3"1/2
3
"
1
/
2
3"7/8
4"3/8
0 , 9 2 8
1000
3"1/2
5"
0,7
1000
5"
13"3/8
0,37
89
99
14.13
89
127
64,46
127
340
781,24
-
-
89
111
34,55
Table 2 Drilling configurzations tested to point out the sensitivity of ECD prediction
in function of the choice of mud rhelogic model
( cfr figures 9 and 10 )
...
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Parameters
l0il-welldrilling
l~limholedrilling
0 r o d l 0 hole =
labout 0,30
labout 0,85 and more
annulus clearance
large (more than 50 rnrn) slim (less than 20 mm)
rod rotation speed (rpm) small (up to 150-200 rpm) high (200 to 800 rpm)
losses inside rodr
about 90% of total losses about 10% of total losses
about 10% of total losses about 90% of total losses
losses inside annulus
couette effect
weak
.important
crescent effect
important
inexistant
need of an accurate model
no need much precision
mud rheolo~icalmodel
TOTAL
ACTUAL OPERATIONS
9'718 hole
bimne b
A drilling
waer base mud
drilled blind
7718 hole
bicone bi drillinp
salt saturated mud
with PHPA
'
continuous mrin
5'718
CHDI%
hole enlwgmg 7718
Side badc SSBm
&I 12 DC's
CHD134 rods
convenlionalcementing
cement lo 4OOm
Corlng
6"7/8 hole
mntinuousmring
Potyptycerols mud wilh
rrolasslum carbonates MW-1.25
0
0
w.
2
B
0
4"1t4 hole
mntinuousiy mred
CHD~01 *tern
25' mre
Potyptycerols mud uilh
potassium carbonales MW-1.2
P
U
%
.
2G
ZUons wob
4Mpm
60 Vmin
CHDlOl rods
as =sing 17
3" hole
CHD 76 system
42mm
P~lyglycerolsmud with
potassium carbonates M W - 1.2
113lons wob
50(YBo rpm
3WU) Vmin
-
Table 3 TOTAL actual operations for tested well
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Drllllng
drilled 15'
CONVENTIONAL
DRILLING
--
I
SLIMHOLE
DRILLING
I
MINING
DRILLING
I
I~~~
13"
I200
1600
I
I
rod rotetion speed ( r p ~
+
I
sedimentary
mlning
I
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I
hole diameter (inch)
drilled formation
I
-
Fig. 1 Differences between conventional, mining and slimhole drillings
-
Fig. 2 Comparison between newtonian, binghamian and oswaldian mud models
about rheologic relations and velocities proflles in laminar regime
'1
CUlTINGS SEDIMENTATION
VELOCITY (#2)
MUD-RETURN
VELOCITY (#I)
-
t
CUlTNGS CARRYING
VELOCITY (#3* 42)
-
I
I
Fig. 3 Velocities and forces acting on cuttings
1
4
3
P
8
2
2
1
0
0
1
2
3
4
S
ma. cleanace(mm)
-
6
7
1
Fig. 4 Influence of the annulus clearance on pressure
losses
I
I
0.0
05
1.0
15
20
25
mud flow rate (Us)
-
Fig. 5 Optimized annulus clearances
3.0
-
2 x%max
1
3
4
formation I mud ratio (%)
s
Fig.7- Determination of the optimized mud flow rate
Fig.6 Globalized optimized design
of a core barrel
N.B. :Fano shear rate (shl)= FPnn velocities(rpm) 1.70
0
0
I00
200
m
400
MO
600
Fano rotation velocilks (rpm)
Fig.& Comparison between rheologic models
ECD (PET13"3/8)
1,030
I
ECD (SH 3"7/8)
2.60
Bin. model
I
2.40
-
2,20
-
2.00
1,8O
1.60
'
Fig.9- Influence of the choice of mud rheologic model
on the equivalent circulating density (ECD)
in conventional drilling (cfr table 2)
I
Osw. model
Fig.10- Influence of the choice of mud rheologic model
on the equivalent circulating density (ECD)
in slimhoie drilling (cfr table 2)
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"o
a :resulting angle (gives the helix pitch)
Vr: resulting velocity
Fig.11- "Couette" effect and "pedalo" effect for an oswaldian mud :
comparison between theoritical predictions and experimental results in laboratories
- , - , - , - , - , - , - , - , - , la
="' *'S'01'5
(adimenrional nunberfortangentlal No
(adirnensional nunberforaxial Now)
when :W:amragadadalwbdly
0:annu b r d e a n n s e
R :mdndlua
v:mudvlrosiW
n = e f l:rod rotation .p.ad(rpm))
€0
1
--
I - . - . - . - . - . - - - * - . - . - I
OO
200
400
ea
000
loo0
lzoo
1100
lea
1000
2000
Taylor
Fig.12- Influence of rod rotation speed on transition between laminar and turbulent globalized flow regimes
Fig.13. "Crescent" effet :
influence of the rod eccentricity on the "psi" coefficient
Fig.14- Velocities proflle in annulus clearance
with eccentric rod (e=0.80) for an oswaldian mud
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V: tangential velocity (N(~m),mud)
W :axial velocity (W=Q/Sannulus)
I
I
PV
14
,
0.014
Table 4- 578P1172characteristics
Mud flow rate (Ymin)
Flg.15 578P1172 : Total pressure losses
in function of mud flow rateand rod rotation speed
Fig.16 578P1172 :Effect of the rod rotation speed
on the annular pressure losses
I
I
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I
BHA
Casing
MUD .
127,O 0e(mn)
5
112,mi (mm)
Shoe depff 1214m
@mnhols
4.25
Totaldepth
121h
Dr**
CMDIOl
108,O 0e(mn)
94.0 0e(mn)
8 3 0 Oi(mn)
78.5 0i upset(mm)
SG
bANN MM
VANN 300
'ANN 200
CANN 100
FANN 6
30
18
13
9
2
gel0
1
FANN3
2
gel10
2
P
AV
p6trole
15
0,015
n
K
0.737
0,182
0.737
0,381
W
Pv
6
12
12.527
0,012
1,26
39
si
OSW
Table 5- 42531210 characteristics
42W1210
100
-
80
,
0
Total N=O
0 Total N=200
Total N ~ 5 0 0
Reed result
A
A
100
200
250
300
350
Fig.17- 425P1210 : Total pressure losses
in function of mud flow rate and rod rotation speed
Fig.18- 425P1210 :Effect of the rod rotation speed
on the annulai-pressure losses
400
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bin
HA
MUD
5
Shos dspbS1214m
@mhde
425
TobJdqxh
am
mpps cmror+
312mH
127.0 Oe(mn)
112.~0i(W
108.0 O a ( W
94.0 ~ a ( m
83.0 Oi(nn$
78,s OirpSa(nn$
FMIV200
FMIV 100
FAMI6
FA MI^
24
14
11
7
2
r
SG
P
1.2
/
gdo
gdro
1
2
w
AV
12
0.012
n
K
0,777
0.110
0.777
0.053
YP
PV
4
10
1,916
0,010
M
Table 6-425P2078characteristics
I Total
N=O
Total N=300
Total N=460
Mud now rate (vmin)
Fig.19- 425P2078 : Total pressure losses
in function of mud flow rate and rod rotation speed
Fig.20- 425P2078 :Effect of the rod rotation speed
on the annular pressure losses
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b"