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© 2005 PetroSkills LLC, All Rights Reserved
LIFTING CAPACITYLIFTING CAPACITY
The primary function of the The primary function of the drilling fluid is to clean the holedrilling fluid is to clean the hole
2 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Poor hole cleaning may be Poor hole cleaning may be responsible for up to 70% of all responsible for up to 70% of all drilling problemsdrilling problems
Drag forces on a particle will Drag forces on a particle will determine how fast a particle will determine how fast a particle will fall through a fluidfall through a fluid
3 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Gravity will cause the Gravity will cause the particle to fall through particle to fall through the fluidthe fluid
When the drag forces are When the drag forces are equal to the acceleration equal to the acceleration due to gravity, the due to gravity, the particle will reach its particle will reach its terminal velocityterminal velocity
4 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
For a spherical particle, the settling For a spherical particle, the settling velocity is represented by the velocity is represented by the following equationfollowing equation
Settling velocity is a function of the Settling velocity is a function of the diameter of the particle, drag diameter of the particle, drag coefficient, viscosity of the fluid and coefficient, viscosity of the fluid and density differencedensity difference
V
d
Cs
p p f
d f
113 4
1 2
.
/
5 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
The drag coefficient can be The drag coefficient can be determined from Figure 5-1 if the determined from Figure 5-1 if the particle Reynolds number is particle Reynolds number is knownknown
Unfortunately, the settling Unfortunately, the settling velocity is required to determine velocity is required to determine the Reynolds numberthe Reynolds number
e
sfpp
VdR
46.15
6 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Based on Figure 5-1, an equation Based on Figure 5-1, an equation can be written for portions of the can be written for portions of the graphgraph
For a Reynolds number of 1 or For a Reynolds number of 1 or less, the equation isless, the equation is
pd RC /24
7 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
8 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Substituting into equation 5-1 Substituting into equation 5-1 yieldsyields
Equation 3 would be used very Equation 3 would be used very seldom unless the drilling fluid is seldom unless the drilling fluid is extremely thickextremely thick
V
d
s
p p f
e
8 289
2
,
9 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Between a Reynolds number of Between a Reynolds number of 500 and 200,000, the drag 500 and 200,000, the drag coefficient can be assumed to be coefficient can be assumed to be 0.440.44
Equation 5-4 resultsEquation 5-4 results
V
d
s
p p f
f
171
1 2
/
10 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
11 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Equation 5-4 is used when Equation 5-4 is used when drilling with thin drilling fluids drilling with thin drilling fluids such as watersuch as water
Between a Reynolds number of 1 Between a Reynolds number of 1 and 500, the drag coefficient is a and 500, the drag coefficient is a curved line and can be estimated curved line and can be estimated by the following equationby the following equation
12 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Substituting into equation 5-1 Substituting into equation 5-1 yieldsyields
6.0
5.18
p
dR
C
V
ds
p P f
e f
346 61 6
0 6 0 4
0 71
..
. .
.
13 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
14 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Equation 5-6 is used for most Equation 5-6 is used for most drilling fluidsdrilling fluids
Calculate the settling velocity, Calculate the settling velocity, then check to make sure the then check to make sure the particle Reynolds number particle Reynolds number corresponds to the equation corresponds to the equation usedused
15 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
In order to clean the In order to clean the hole, the drilling fluid hole, the drilling fluid velocity must exceed velocity must exceed the settling velocity of the settling velocity of the particle so that the the particle so that the net particle velocity is net particle velocity is up the holeup the hole
V V Vp f s
16 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
If the hydraulics are designed If the hydraulics are designed properly, annular velocity is properly, annular velocity is fixedfixed
Settling velocity must be Settling velocity must be changed by manipulating mud changed by manipulating mud properties such as viscosity or properties such as viscosity or mud weightmud weight
Viscosity is the preferred methodViscosity is the preferred method
17 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Example 5-1 shows how Example 5-1 shows how increasing the mud weight can increasing the mud weight can affect hole cleaningaffect hole cleaning
18 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Given:Given:Average cutting size 0.5 inch
diameter spheres (13 mm)Mud Viscosity = 50 cpSpecific gravity of cuttings = 2.52 (or
21 ppg) (2520 kg/m3)Case I: Mud Weight = 10.0 ppg
(1200 kg/m3)Case II: Mud Weight = 12.0 ppg
(1440 kg/m3)
19 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Determine:Determine:The slip velocity of the cuttings in
both mud weights
Case I:Case I: Using equation 5-6Using equation 5-6
m/min) (25.91 fpm 01.851050
10215.06.346
71.0
4.06.0
6.1
sV
71.0
4.06.0
6.1
6.346
fe
fPps
dV
20 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Case II:Case II:
Calculate the Reynolds Number Calculate the Reynolds Number to make sure you are using the to make sure you are using the correct equation (should be correct equation (should be between 1 and 500 for eqn 5-6)between 1 and 500 for eqn 5-6)
m/min) (21.32 fpm 00.701250
12215.06.346
71.0
4.06.0
6.1
sV
21 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Both are between 1 and 500Both are between 1 and 500
e
sfpp
VdR
46.15
131
50
01.85105.046.15pR
130
50
00.70125.046.15pR
22 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Symptoms of sloughing or hole Symptoms of sloughing or hole cleaningcleaningDrag or tight hole on trips or
connectionsHigh torque levelsFill after trips or while making
connectionsDifficulty getting logs to bottom and/or
difficulty in running casing
23 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
A sloughing problem is a hole A sloughing problem is a hole cleaning problemcleaning problem
If a hole sloughs, the cleaning If a hole sloughs, the cleaning capacity of the well must be capacity of the well must be increasedincreased
24 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Example 5‑2 shows how the Example 5‑2 shows how the lifting capacity of the mud can be lifting capacity of the mud can be enhanced by changing the enhanced by changing the viscosity of the mudviscosity of the mudWhile developing deep gas While developing deep gas reserves in the Wind River Basin, reserves in the Wind River Basin, Wyoming, it is necessary to Wyoming, it is necessary to penetrate approximately 3,000 penetrate approximately 3,000 feet of Waltman shalefeet of Waltman shale
25 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
The Waltman is reported to be The Waltman is reported to be both water sensitive and both water sensitive and abnormally pressuredabnormally pressured
The shale was normally drilled The shale was normally drilled with a 14.0 ppg mud (1680 kg/mwith a 14.0 ppg mud (1680 kg/m33))
However, there was no indication However, there was no indication that the shale was over that the shale was over pressuredpressured
26 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Example 5-2 shows how to Example 5-2 shows how to increase lifting capacity with increase lifting capacity with viscosityviscosity
Want a 9.0 ppg (1080 kg/mWant a 9.0 ppg (1080 kg/m33) mud ) mud to have the same lifting capacity to have the same lifting capacity as the 14.0 ppg (1680 kg/mas the 14.0 ppg (1680 kg/m33) mud ) mud in the Waltman shalein the Waltman shale
27 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Find the particle size where the Find the particle size where the slip velocity equals the annular slip velocity equals the annular velocityvelocity
71.0
4.06.0
6.1
6.346
fe
fppsf
dVV
63.0
4.06.04.1
6.346
fp
fes
p
V
d
28 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
First must calculate the power First must calculate the power law constants for the mudlaw constants for the mud
7365.060
100log32.3log32.3
300
600
n
(2908) 6072.0511
60
511 7365.0300
nk
29 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the viscosity at the Calculate the viscosity at the annular velocity of 98 fpm (29.9 annular velocity of 98 fpm (29.9 m/min)m/min)
v
DDk
n
n
DDph
n
phe
200
3
124.2
cp127
98
525.126072.0200
7365.03
17365.02
525.12
984.27365.0
e
30 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate maximum particle size Calculate maximum particle size and check the Reynolds Numberand check the Reynolds Number
mm) (29.5 inch 16.11421
14x127x6.346
9863.0
4.06.04.1
pd
194
127
981416.146.1546.15
e
sfpp
VdR
31 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the viscosity of the 9.0 Calculate the viscosity of the 9.0 ppg mud (1080 kg/mppg mud (1080 kg/m33))
cp417
96.346
98
92116.1
6.346
67.1
4.04.1
6.1
67.1
4.04.1
6.1
fs
fppe
V
d
38
417
98916.145.15pR
32 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting CapacityClass problemClass problemHole size = 8 ¾” (222 mm), Dp = 4 ½” (114
mm)MW = 9.8 ppg (1180 kg/m3), Q = 275 gpm
(1.04 m3/min)Particle diameter = 0.5” and 1” (13 and 25
mm)100 rpm reading = 2250 rpm reading = 17
Calculate the slip velocity for both Calculate the slip velocity for both particlesparticles
33 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
v
DDk
n
n
DD
v ph
n
phe
)(200
3
124.2
1
2log32.3
n
n
i
i
drdv
k
22
5.24
ph DD
Qv
Wdr
dv 7.1
34 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
AnswersAnswersn = 0.3718k = 3.2597 (1.5614)v = 119.6 fpm (36.5 m/min)Equivalent thickness μe = 131 cp
0.5” particle = 57 fpm (17.4 m/min)1.0” particle = 126 fpm (38.4 m/min)
35 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate Calculate nn
1
2log32.3
n
3718.017
22log32.3
n
36 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate Calculate kkCalculate the shear rate at 50 rpm
Calculate k
85507.17.1
Wdr
dv
(1.5614) 2597.385
173718.0
n
i
i
drdv
k
37 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the annular velocityCalculate the annular velocity
22
5.24
ph DD
Qv
m/min 36.5 or fpm 6.119
5.475.8
2755.2422
v
38 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the viscosity at an Calculate the viscosity at an annular velocity of 119.6 fpm annular velocity of 119.6 fpm (36.5 m/min)(36.5 m/min)
v
DDk
n
n
DD
v ph
n
phe
)(200
3
124.2
6.119
5.475.82597.3200
3718.03
13718.02
5.475.8
6.1194.23718.0
e
cp 131e
39 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the slip velocity for the Calculate the slip velocity for the 0.5” diameter particle (13 mm)0.5” diameter particle (13 mm)
71.0
4.06.0
6.1
6.346
fe
fPps
dV
m/min) (17.4 fpm 578.9131
8.9215.06.346
71.0
4.06.0
6.1
sV
40 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the slip velocity for the Calculate the slip velocity for the 1” diameter particle (25 mm)1” diameter particle (25 mm)
71.0
4.06.0
6.1
6.346
fe
fPps
dV
m/min) (38.4 fpm 1268.9131
8.92116.346
71.0
4.06.0
6.1
sV
41 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Check the particle Reynolds Check the particle Reynolds numbernumber
e
sfpp
VdR
46.15
33
131
578.95.046.15pR
146
131
1268.9146.15pR
42 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
What happens if the hole is What happens if the hole is washed out to 12 ¼” (311 mm)?washed out to 12 ¼” (311 mm)?The annular velocity will be reduced
in the washout
22
5.24
ph DD
Qv
m/min 15.8 or fpm 52
5.425.12
2755.2422
v
43 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the viscosity at an Calculate the viscosity at an annular velocity of 52 fpm (15.8 annular velocity of 52 fpm (15.8 m/min)m/min)
v
DDk
n
n
DD
v ph
n
phe
)(200
3
124.2
52
)5.425.12(2597.3200
3718.03
13718.02
5.425.12
524.23718.0
e
cp 322e
44 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the slip velocity for the Calculate the slip velocity for the 0.5” diameter particle (13 mm)0.5” diameter particle (13 mm)
71.0
4.06.0
6.1
6.346
fe
fPps
dV
m/min) (11.9 fpm 398.9322
8.9215.06.346
71.0
4.06.0
6.1
sV
45 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the slip velocity for the Calculate the slip velocity for the 1” diameter particle (25 mm)1” diameter particle (25 mm)
71.0
4.06.0
6.1
6.346
fe
fPps
dV
m/min) (26.2 fpm 868.9322
8.92116.346
71.0
4.06.0
6.1
sV
46 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Check the particle Reynolds Check the particle Reynolds numbernumber
e
sfpp
VdR
46.15
9
322
398.95.046.15pR
40
322
868.9146.15pR
47 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
48 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
49 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
50 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
The CCI is the Carrying Capacity The CCI is the Carrying Capacity Index for a drilling mudIndex for a drilling mud
There are only three hole There are only three hole cleaning variables that can be cleaning variables that can be controlled at the rigcontrolled at the rigMud weightAnnular VelocityViscosity
51 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
The hole cleaning variables that The hole cleaning variables that cannot be controlled on the rig cannot be controlled on the rig are:are:Diameter of particleDensity of particleTo an extent, hole enlargement
52 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
From empirical data, it was From empirical data, it was found that hole cleaning was found that hole cleaning was usually adequate when the usually adequate when the product of the mud weight, product of the mud weight, viscosity and annular velocity viscosity and annular velocity was equal to approximately was equal to approximately 400,000400,000The equation determining the The equation determining the CCI is:CCI is:
53 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
= Mud weight in ppg
K = drilling fluid viscosity, equivalent cp
= Annular velocity, feet per minute
000,400
vKCCI f
f
v
SI Units
000,000,14
vKCCI f
54 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
YPPV
YPPVn
2log32.3
)(511 )1( YPPVK n
)479.0
(511 )1( YPPVK n
SI Units
55 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
If the CCI is 1.0 or greater, hole If the CCI is 1.0 or greater, hole cleaning is assumed to be cleaning is assumed to be adequateadequate
The value of The value of KK can also be can also be determined from a chart of yield determined from a chart of yield point and plastic viscositypoint and plastic viscosity
56 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
57 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Example 5-3 in the book with the Example 5-3 in the book with the 14 ppg mud (1680 kg/m14 ppg mud (1680 kg/m33), and ), and annular velocity of 98 fpm (29.9 annular velocity of 98 fpm (29.9 m/min)m/min)PV = 100 – 60 = 40YP = 60 – 40 = 20 (10)n = 0.7365
Calculate the K valueCalculate the K value
58 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the K valueCalculate the K value
)(511 )1( YPPVK n
cpK 310)2040(511 )7365.01(
59 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
310
60 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the CCICalculate the CCI
000,400
vKCCI f
1.1
000,400
9831014CCI
61 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Class problemClass problemHole size = 8 ¾” (222mm)Dp = 4 ½” (114mm)
MW = 9.8 ppg (1180 kg/m3)Q = 275 gpm (1.04 m3/min)Plastic Viscosity = 14Yield Point = 12 (6)
Calculate the Carrying Capacity Calculate the Carrying Capacity Index or CCIIndex or CCI
62 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the annular velocityCalculate the annular velocity
22
5.24
ph DD
Qv
m/min 36.5 or fpm 6.119
5.475.8
2755.2422
v
63 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Determine Determine KK from the graph from the graph
64 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
12
14
276
65 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Or you can calculate the Or you can calculate the K K value value
)(511 )1( YPPVK n
cpK 276)1214(511 )6211.01(
YPPV
YPPVn
2log32.3
6211.0
1214
12142log32.3
n
66 © 2005 PetroSkills LLC, All Rights Reserved
Lifting CapacityLifting Capacity
Calculate the CCICalculate the CCI
May need more viscosity or May need more viscosity or annular velocityannular velocity
000,400
vKCCI f
81.0
000,400
6.1192768.9CCI
67 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
Hole cleaning in a Hole cleaning in a vertical well is a vertical well is a function offunction ofAnnular velocityParticle diameterMud viscosity, andMud density
71.0
4.06.0
6.1
6.346
fe
fPps
dV
68 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
If the annular velocity of the drilling If the annular velocity of the drilling fluid exceeds the settling velocity of fluid exceeds the settling velocity of the particle, the particle will be the particle, the particle will be carried out of the holecarried out of the hole
If not, the particle must be ground If not, the particle must be ground smaller until the settling velocity is smaller until the settling velocity is lower than the annular velocitylower than the annular velocity
VVp p = V= Vff – V – Vss
69 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
In a directional well, In a directional well, the particle velocity the particle velocity is still a function of is still a function of the velocity of the the velocity of the fluid and settling fluid and settling velocity but they are velocity but they are no longer directly no longer directly opposingopposing
The particle will The particle will seek the low side of seek the low side of the holethe hole
70 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
A cuttings bed A cuttings bed will form on the will form on the low side of the low side of the hole unless the hole unless the annular velocity annular velocity is high enough is high enough to erode the to erode the cuttings bedcuttings bed
ShakerWellbore
Cuttings
Mud
Cuttings Bed
71 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
After a cuttings bed is formed, the After a cuttings bed is formed, the fluid in the annulus will have to fluid in the annulus will have to erode the cuttings bed in order to erode the cuttings bed in order to carry the cuttings up the hole carry the cuttings up the hole
The bed will continue to grow The bed will continue to grow narrowing the annular space and narrowing the annular space and causing an increase in the annular causing an increase in the annular velocity until the rate of erosion velocity until the rate of erosion equals the rate of depositionequals the rate of deposition
72 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
Experiments were conducted in Experiments were conducted in the laboratory to determine how the laboratory to determine how mud viscosity, flow regime and mud viscosity, flow regime and annular velocity affects hole annular velocity affects hole cleaning in a directional wellcleaning in a directional well
Three drilling fluids were used. Three drilling fluids were used. The first was water, which has a The first was water, which has a very low viscosity and is always very low viscosity and is always in turbulent flowin turbulent flow
73 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
The second fluid was a lightly The second fluid was a lightly gelled mud with a low viscosity. gelled mud with a low viscosity. The viscosity was low enough so The viscosity was low enough so that the fluid was in turbulent flow that the fluid was in turbulent flow even at lower annular velocitieseven at lower annular velocities
The third fluid was a higher The third fluid was a higher viscosity mud. Even at high flow viscosity mud. Even at high flow rates, the flow was still laminarrates, the flow was still laminar
74 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
Water PV = 1 YP = 0, always turbulentMud PV = 3 YP = 2 (1), always
turbulentMud PV = 19 YP = 17 (8), always
laminar
ResultsResults
0° and 10°0° and 10°Wells with inclinations between 0° and
10° behave the same as vertical wells
75 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
Increasing annular velocity and viscosity will improve hole cleaning
71.0
4.06.0
6.1
6.346
fe
fPps
dV
76 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
0
10
20
30
40
0 20 40 60 80Inclination, degrees
Cu
ttin
gs
Co
nc
en
tra
tio
n
Turb. Water 115'/min Turb. Mud 115'/min Lam. Mud 115'/min
Lam. Mud 172'/min Turb. Mud 229'/min Lam. Mud 229'/min
Laminar Mud PV= 19 YP= 17Turbulent Mud PV= 3 YP= 2Turbulent Water PV= 1 YP= 0
77 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
10° to 30° 10° to 30° At velocities
less than 120 fpm (37 m/min), the cuttings will settle to the low side of the hole and slide down the wellbore
ShakerWellbore
Cuttings
Mud
78 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
Within a short distance, they will again end up in the higher velocity portions of the annulus and be carried up the hole
ShakerWellbore
Cuttings
Mud
79 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
The hole cleaning capacity of the mud at this inclination is not as efficient as vertical wells
At annular velocities above 120 fpm (37 m/min), the cuttings are not able to form a bed on the low side of the hole, but rather are carried up the wellbore along the low side in slugs or dunes
80 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
0
10
20
30
40
0 20 40 60 80Inclination, degrees
Cut
tings
Con
cent
ratio
n
Turb. Water 115'/min Turb. Mud 115'/min Lam. Mud 115'/min
Lam. Mud 172'/min Turb. Mud 229'/min Lam. Mud 229'/min
Laminar Mud PV= 19 YP= 17Turbulent Mud PV= 3 YP= 2Turbulent Water PV= 1 YP= 0
At flow rates in excess of 180 fpm (55 m/min), the cuttings are carried smoothly along the low side of the hole
81 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
30° to 60°30° to 60°Hole cleaning is the most critical at
inclinations between 30° and 60° with the inclinations between 40° and 50° being the most difficult
A cuttings bed forms at 40° with an annular velocity less than 150 fpm (46 m/min)
At 50°, a bed would form at annular velocities of 180 fpm (55 m/min)
82 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
Not only can a cuttings bed form rapidly at these inclinations, but the cuttings slide down the wellbore on the low side of the hole when the pump is turned off
ShakerWellbore
Cuttings
Mud
Cuttings Bed
Slumped Cuttings Bed
83 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
In directional wells with inclinations less than 40°, the cuttings will fall to the bottom of the hole
Poor hole cleaning will be evidenced by fill on bottom
84 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
In high inclination or horizontal wells, the cuttings will fall to a maximum inclination
Poor hole cleaning will be evidenced by excessive drag while pulling the bottomhole assembly through the section where the cuttings quit falling
While tripping in the hole, bridges will be encountered in this section
85 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
6060oo to 90 to 90oo
Above an inclination of 60°, cuttings bed development does not get any worse
A cuttings bed will build up reducing the annular area which increases the annular velocity
As the annular velocity increases, the drilling fluid will erode the bed faster
At some point, an equilibrium will be reached between the deposition and erosion of the cuttings bed
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Directional WellsDirectional Wells
Annular velocityAnnular velocityAnnular velocity is the variable that
will affect hole cleaning the mostIncreasing the viscosity may actually
reduce hole cleaning at lower flow rates
At higher flow rates, viscosity makes less of a difference
0
10
20
30
40
0 20 40 60 80Inclination, degrees
Cu
ttin
gs
Co
nc
en
tra
tio
n
Turb. Water 115'/min Turb. Mud 115'/min Lam. Mud 115'/min
Lam. Mud 172'/min Turb. Mud 229'/min Lam. Mud 229'/min
Laminar Mud PV= 19 YP= 17Turbulent Mud PV= 3 YP= 2Turbulent Water PV= 1 YP= 0
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Directional WellsDirectional Wells
Fluids in turbulent flow have relatively flat velocity profiles; whereas, the laminar velocity profile is much more pointed
In laminar flow, there can be a significant difference between the velocity of the fluid in the center of the annular space as compared to the velocity near the pipe and hole walls
Laminar Turbulent
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Directional WellsDirectional Wells
Pipe movementPipe movementDrill pipe movement is an important hole
cleaning consideration in directional wells Both rotation and reciprocation will
increase the hole cleaning capacity in a directional well
When reciprocating the drill pipe, the annular velocity around the tool joint increases aiding hole cleaning
89 © 2005 PetroSkills LLC, All Rights Reserved
Directional WellsDirectional Wells
As an example, if the annular velocity in a 4 1/2 (114mm) by 8 1/2 inch (216mm) annulus is 120 fpm (36.6 m/min), then the annular velocity around 6 1/4 inch (159mm) tool joints would be 208 fpm (63.4 m/min) or a 73 percent increase
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Directional WellsDirectional Wells
Rotation will also aid hole cleaningWhile drilling with a steerable system
in the oriented mode (slide mode), the drag in a horizontal well increased
After the connection was made, rotation was resumed and the drag in the well decreased
In this case, the increased drag was due to a cuttings buildup in the well
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Directional WellsDirectional Wells
As in vertical wells, washouts As in vertical wells, washouts will impair hole cleaningwill impair hole cleaning
The annular velocity in a The annular velocity in a washout will be reduced making washout will be reduced making hole cleaning more difficulthole cleaning more difficult
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Directional WellsDirectional Wells
If the washout is at an inclination of If the washout is at an inclination of 35° to 55°, the cuttings accumulation 35° to 55°, the cuttings accumulation can slide down the hole when the can slide down the hole when the pump is turned offpump is turned offHole cleaning in formations that are Hole cleaning in formations that are sensitive to hole erosion can be sensitive to hole erosion can be difficult difficult The high annular velocities required The high annular velocities required to clean a directional well can to clean a directional well can enlarge the hole causing a reduction enlarge the hole causing a reduction in annular velocity in annular velocity
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Directional WellsDirectional Wells
However, it should be However, it should be remembered that the formation remembered that the formation of a cuttings bed will reduce hole of a cuttings bed will reduce hole size causing an increase in size causing an increase in annular velocity anyway, which annular velocity anyway, which can still lead to erosioncan still lead to erosion
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