Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1
Подождите немного. Документ загружается.
Downhole
Motors
865
Figure
4-191.
Downhole turbine motor design.
(Courtesy
Eastman-
Christensen
Co.)
866
Drilling and Well Completions
Table 4-1
09
Turbine Motor, 6V4-in. Outside Diameter,
Circulation Rate 400 gpm, Mud Weight 10 Wgal
Number Optimum Differential Thrust
of
Torque* Bit
Speed
Pressure Load
Stages (ft-ibs) (rpm) (Psi) Horsepower'
(1000
Ibs)
212 1412 807 1324 21 7 21
31 8 2118 807 1924
326
30
'At optimum speed
Courtesy Eastman-Christensen
about center even when a side force on the bit is present during directional
drilling operations.
There are of course variations on the downhole turbine motor design, but
the basic sections discussed above will be common to all designs.
The main advantages of the downhole turbine motor are:
1. Hard to extremely hard competent rock formations can be drilled with
turbine motors using diamond
or
the new polycrystalline diamond bits.
2.
Rather high rates of penetration can be achieved since bit rotation speeds
are high.
3.
Will allow circulation of the borehole regardless of motor horsepower or
torque being produced by the motor. Circulation can even take place when
the motor is installed.
The main disadvantages of the downhole turbine motor are:
1.
Motor speeds and, therefore, bit speeds are high, which limits the use of
roller rock bits.
2.
The required flowrate through the downhole turbine motor and the
resulting pressure drop through the motor require large surface pump
systems, significantly larger pump systems than are normally available for
most land and for some offshore drilling operations.
3.
Unless a measure while drilling instrument is used, there is no way to
ascertain whether the turbine motor is operating efficiently since rotation
speed and/or torque cannot be measured using normal surface data (i.e.,
standpipe pressure, weight on bit, etc.).
4. Because
of
the necessity to use many stages in the turbine motor
to
obtain
the needed power to drill, the downhole turbine motor is often quite long.
Thus the ability to use these motors for high-angle course corrections can
be limited.
5.
Downhole turbine motors are sensitive to fouling agents in the mud;
therefore, when running a turbine motor steps must be taken to provide
particle-free drilling mud.
6.
Downhole turbine motors can only be operated with drilling mud.
Operations
Figure 4-1
92
gives the typical performance characteristics
of
a turbine motor.
The example in this figure is a 6$-in. outside diameter turbine motor having
212
stages and activated by a 10-lb/gal mud flowrate of
400
gal/min.
Downhole Motors
867
Circulation
Rate
400
gpm
Mud
Weioht
10
ppg
-
-
\
-c
Preaaure
-
-
Horsepower
-
300
*O0.
;
a
E
r
100
1500
a
500
lo00
1500
2000
Bit
Speed
(rpm)
Figure
4-192.
Turbine motor, 6Yi-h. outside diameter, two motor sections,
21
2
stages,
400
gal/min,
1
0-lb/gal mud weight.
(Courtesy
Eastman-Christensen.)
For
this example, the stall torque of the motor is
2,824
ft-lb. The runaway
speed is
1,614
rpm and coincides with zero torque. The motor produces its
maximum horsepower of
217
at a speed of
807
rpm. The torque at the peak
horsepower is
1,412
ft-lb,
or
one-half of the stall torque.
A
turbine device has the unique characteristic that it will allow circulation
independent of what torque
or
horsepower the motor is producing. In the
example where the turbine motor has a lO-lb/gal mud circulating at
400
gal/
min, the pressure drop through the motor is about
1,324
psi. This pressure drop
is approximately constant through the entire speed range of the motor.
If the turbine motor is lifted off the bottom of the borehole and circulation
continues, the motor will speed up to the runaway speed
of
1,614
rpm. In this
situation the motor produces no drilling torque
or
horsepower.
As
the turbine motor is lowered and weight
is
placed on the motor and thus
the bit, the motor begins
to
slow its speed and produce torque and horsepower.
When sufficient weight has been placed on the turbine motor, the example
motor will produce its maximum possible horsepower of
217.
This will be at
a speed
of
807
rpm. The torque produced by the motor at this speed will be
If more weight is added to the turbine motor and the bit, the motor speed
and horsepower output will continue to decrease. The torque, however, will
continue to increase.
When sufficient weight has been placed
on
the turbine motor and bit, the
motor will cease to rotate and the motor is described as being stalled. At this
condition, the turbine motor produces its maximum possible torque. Even when
the motor is stalled, the drilling mud is still circulating and the pressure drop
is approximately
1,324
psi.
1,412
ft-lb.
868
Drilling and Well Completions
The stall torque
Ms
(ft-lb) for any turbine motor can be determined from
[86]
(4-138)
where
q,
=
hydraulic efficiency
q,
=
mechanical efficiency
n,
=
number of stages
7,
=
specific weight of mud in lb/gal
q
=
circulation flowrate in gal/min
p
=
exit blade angle in degrees
h
=
radial width of the blades in in.
Figure
4-193
is the side view of a single-turbine stage and describes the geometry
of the rotor and stator.
The runaway speed
Nr
(rpm) for any turbine motor can be determined from
(4-139)
where
qv
=
volumetric efficiency
rm
=
mean blade radius in in.
The turbine motor instantaneous torque
M
(ft-lb) for any speed
N
(rpm) is
M
=
Ms(l-$)
The turbine motor horsepower
HP
(hp) for any speed is
2
nM ,N
HP
=
-
33,000
(’
-
$)
(4-140)
(4-141)
The maximum turbine motor horsepower is at the optimum speed,
No,
which
is one-half of the runaway speed. This is
N
2
No
=
I
(4-1 42)
Thus the maximum horsepower
HP,,,
is
HP,,
=
xMJ,
2( 33,000)
(4- 143)
The torque at the optimum speed
M,
is one-half the stall torque. Thus
(4-144)
M,
M,
=
-
2
Downhole Motors
869
Stator
t
Figure
4-193.
Turbine rotor and stator geometry
of
a single stage.
(Courtesy
Smith
International, Inc.)
The pressure drop Ap (psi) through a given turbine motor design is usually
obtained empirically. Once this value is known for a circulation flowrate and
mud weight, the pressure drop for other circulation flowrates and mud weights
can be estimated.
If the above performance parameters for a turbine motor design are known
for
a
given circulation flowrate and mud weight (denoted as
l),
the performance
parameters for the new circulation flowrate and mud weight (denoted as
2)
can
be found by the following relationships:
Torque
M,
=
(
;rM1
M,
=
[$]MI
(4-145)
(4-146)
Speed
N,
=
(9%
(4-147)
870
Drilling and Well Completions
Power
HP,
=
(:]HP,
HP,
=
(:)HP,
Pressure drop
*P2
=
(4- 148)
(4-149)
(4-1
50)
(4-151)
Table 4-1 10 gives the performance characteristics for various circulation
flowrates for the 212-stage,
6
$in. outside diameter turbine motor described
briefly in Table 4-109 and shown graphically in Figure 4-192.
Table
41
11 gives the performance characteristics for various circulation flowrates
for the 318-stage,
6
$-in. outside diameter turbine motor described briefly in
Table 4-109. Figure 4-194 shows the performance of the 318-stage turbine motor
at a circulation flowrate
of
400
gal/min and mud weight
of
10 lb/gal.
The turbine motor whose performance characteristics are given in Table 41 10
is made up of two motor sections with
106
stages in each section. The turbine
motor whose performance characteristics are given in Table 4-111 is made up
of
three motor sections.
Table
4-110
Turbine Motor, 6%-in. Outside Diameter, Two
Motor Sections,
212
Stages,
Mud
Weight
10
Ib/gal
Circulation Optimum Differential Thrust
Rate Torque' Bit Speed Pressure Maximum Load
(gpm)
(ft-lbs)
(rpm) (Psi) Horsepower*
(1000
Ibs)
~ ~~~
200 353
403 331
27 5
250 552 504
517 53 8
300 794 605
745 92 12
350 1081
706 1014 145 16
400
1421
a07 1324 21 7 21
450 1787 908
1676 309 26
500
2206
1009
2069 424 32
'At
optimum speed
Courtesy Eastman-Christensen
Downhole
Motors
871
Table 4-111
Turbine Motor, 6%-in. Outside Diameter, Three
Motor Sections, 318 Stages, Mud Weight 10 lblgal
Circulation Optimum Differential Thrust
Rate Torque* Bit
Speed
Pressure Maximum
Load
(9pm)
(ft-lbs)
(rpm) (Psi) Horsepower"
(1000
Ibs)
200 529 403 485 40 8
250 827
504 758 79 12
300 1191 605 1092
1
37 17
350 1622
706 1486 21 8 23
400 2118 807 1941 326 30
450 2681
908 2457 464 38
*At
optimum
power
Courtesy Eastman-Christensen
Circulation Rate
400
gprn
Mud Weight
10
ppo
5000
4000
2
3000
P
"
c
U
0
3
P
I-
2000
lo00
0
500
400
300
200
100
2500
2000
0
a
u
1500
f
e
0
?!
500
500
lo00
1500
2000
Bit
Speed
(rprn)
Figure 4-194.
Turbine motor, 6%-in. outside diameter, three motor sections,
31
8
stages,
400
gal/min,
1
0-lb/gal mud weight.
(Courtesy Eastman-Christensen.)
872
Drilling and Well Completions
The major reason most turbine motors are designed with various add-on motor
sections is to allow flexibility when applying turbine motors to operational situations.
For straight hole drilling the turbine motor with the highest possible torque
and the lowest possible speed is of most use. Thus the turbine motor is selected
such that the motor produces the maximum amount of power for the lowest
possible circulation flowrate (i.e., lowest speed). The high power increases rate
of penetration and the lower speed increases bit life particularly if roller rock
bits are used.
For deviation control drilling the turbine motor with a lower torque and the
shortest overall length is needed.
Example
1
Using the basic performance data given in Table 4-1 10 for the 6 +-in. outside
diameter turbine motor with 2 12 stages, determine the stall torque, maximum
horsepower and pressure drop for this motor if only one motor section with
106 stages were to be used for a deviation control operation. Assume the same
circulation flow rate of 400 gal/min, but a mud weight of 14 lb/gal is to be used.
Stall Torque.
From Table 4-110 the stall torque for the turbine motor with 212
stages will be twice the torque value at optimum speed. Thus the stall torque
for 10 lb/gal mud weight flow is
Ms
=
2(
1421)
=
2,842 ft-lb
From Equation 4-138 it is seen that stall torque is proportional to the number
of stages used. Thus the stall torque for a turbine motor with 106 stages will
be (for the circulation flowrate of 400 gal/min and mud weight of 10 lb/gal)
M,
=
P,842(g)
=
1,421 ft-lb
and from Equation 4-146 for the 14-lb/gal mud weight
M,
=
1,4,1(
g)
=
1,989 ft-lb
Maximum Horsepower.
From Table 4-1 10 the maximum horsepower for the
turbine motor with 212 stages is 217. From Equation 4-143 it can be seen that
the maximum power is proportional to the stall torque and the runaway speed.
Since the circulation flowrate is the same, the runaway speed is the same for
this case. Thus, the maximum horsepower will be proportional to the stall
torque. The maximum power will be (for the circulation flowrate of 400 gal/
min and mud weight of 10 lb/gal)
Downhole Motors
873
HP,
=
217(
-)
1421
2842
=
108.5
and from Equation 4-149 for the 14-lb/gal mud weight
HP,
=
108.5(
$)
=
152
Pressure Drop.
Table 4-110 shows that the 212-stage turbine motor has
a
pressure drop of 1,324 psi for the circulation flowrate of 400 gal/min and a
mud weight of 10 lb/gal. The pressure drop for the 106 stage turbine motor
should be roughly proportional to the length of the motor section (assuming
the motor sections are nearly the same in design). Thus the pressure drop in the
106-stage turbine motor should be proportional to the number of stages.
Therefore, the pressure drop should be
=
662 psi
and from Equation 4-151 for the 14-lb/gal mud weight
Ap
=
662(
s)
=
927 psi
The last column in Tables 4-110 and 4-111 show the thrust load associated
with each circulation flowrate (Le., pressure drop). This thrust load is the result
of the pressure drop across the turbine motor rotor and stator blades. The
magnitude of this pressure drop depends on the individual internal design
details of the turbine motor (i.e., blade angle, number of stages, axial height of
blades and the radial width of the blades) and the operating conditions. The
additional pressure drop results in thrust, T (lb), which is
T
=
xriAp (4-1
52)
Example 2
A
6$-in. outside diameter turbine motor (whose performance data are given
in
Tables
41
10
and
41
11)
is
to
be
used for a deviation control direction dritling opera-
tion. The motor will use a new 8-$-in. diameter diamond bit for the drilling
operation. The directional run is to take place at a depth
of
17,552 ft (measured
874
Drilling and Well Completions
depth). The rock formation to be drilled is classified as extremely hard, and
it
is
anticipated that 10 ft/hr will be the maximum possible drilling rate. The mud weight
is to be 16.2 lb/gal. The drilling rig has a National Supply Company, triplex mud
pump Model 10-P-130 available. The details of this pump are given in Table 4112
(also see the section titled “Mud Pumps” for more details). Because this is a
deviation control run, the shorter two motor section turbine motor will be used.
Determine the appropriate circulation flowrate to be used for the diamond
bit, turbine motor combination and the appropriate liner size to be used in the
triplex pump. Also, prepare the turbine motor performance graph for the chosen
circulation flowrate. Determine the total flow area for the diamond bit.
Bit
Pressure
LOSS.
To obtain the optimum circulation flowrate for the diamond
bit, turbine motor combination, it will be necessary to consider the bit and the
turbine motor performance at various circulation flowrates: 200,
300,
400
and
500 gal/min.
Since the rock formation to be drilled is classified as extremely hard,
1.5
hydraulic horsepower per square inch of bit area will be used as bit cleaning
and cooling requirement [87]. The projected bottomhole area of the bit
4
(hZ)
is
R
A,,
=
-(8.5)‘
4
=
56.7 in.‘
For a circulation flowrate of 200 gal/min, the hydraulic horsepower for the bit
HPb (hp) is
HP,
=
1.5 (56.7)
=
85.05
The pressure drop across the bit Ap
(
si) to produce this hydraulic horsepower
at a circulation flowrate of 200 gal/min is
b
p.
85.05( 1,714)
200
*Pb
=
=
729 psi
Table
4-112
Triplex Mud Pump, Model
10-P-13
National Supply Company, Example
2
input Horsepower
1300,
Maximum Strokes per Minute,
140
Length
of
Stroke,
10
Inches
Liner
Size
(inches)
5%
5
%
5Y4 6 6%
Output per Stroke (gals)
2.81 3.08
3.37 3.67 3.98
Maximum Pressure (psi)
5095
4645 4250 3900 3595