Journal of Applied Science and Engineering, Vol. 18, No. 3, pp. 303-308 (2015)
DOI: 10.6180/jase.2015.18.3.11
Drilling Hydraulic Parameters Design Method
under the Limited Circulating System
Bearing Capacity Condition
Zhichuan Guan, Yuming Liu, Qiandeng Li, Yuqiang Xu* and Hua Pang
School of Petroleum Engineering, China University of Petroleum (East China),
Qingdao 266580, P.R. China
Abstract
Hydraulics design is important for achieving the maximum bit hydraulic horsepower or jet
impact force and improving the bottom hole cleaning. The existing hydraulic parameters design
method is suitable for the low pump capacity. As the large-power-and-high-pressure pump is widely
used on the drilling site, the existing hydraulic parameters design method is not sufficient to make the
drill bit obtain the maximum hydraulic energy. In this paper, a new hydraulics design method is
presented, and a larger bit hydraulic horsepower can be achieved compared to the existing design
method. A contrastive analysis under different modes of pump pressures is conducted using the new
design method, which shows that the improvement of the limited pump pressure can significantly
increase the bit hydraulic horsepower. The circulating system pressure bearing capacity should be
improved as much as possible.
Key Words: Ground Pump, Circulating System, Bit Hydraulic Horsepower, Hydraulic Parameter,
Design Method
1. Introduction
As the world energy consumption increases, considerable effort has been expended on how to explore and
utilize energy resources [1-8]. Drilling is widely used to
explore the onshore and offshore oil and gas across the
world. Hydraulic parameters design is an important part
of the drilling design, which aims to achieve the maximum bit hydraulic horsepower, clean the rock fragments
near the bit, carry the drill cuttings to the surface, and improve the rate of penetration (ROP) under given ground
pump conditions. Many studies [9-19] have been conducted on the hydraulic parameters design, but most of
which focus on the bit and circulating system, not on the
ground pump. As the development of the oil and gas exploration, drilling pumps with large power and displacement and high pressure are manufactured to meet the onsite needs [20-22]. The existing hydraulic parameters
*Corresponding author. E-mail: auyuqiang@163.com
design method was designed based on the low pump capacity (i.e. low power and displacement, low rated pressure). Therefore, the existing hydraulic parameters design
method needs further discussion. Furthermore, when the
pump pressure increases, the pressure bearing capacity
of the circulating system has limited the use of the pump
pressure. It is necessary to investigate how to make full
use of the capacity of the ground pump to maximize the
drill bit hydraulic power.
2. The Existing Hydraulic Parameter Design
Method and the New Method
The general steps of the existing hydraulic parameter
design method are as follows [23]: (1) Determine the minimum displacement that ensures the drill cuttings to
be carried to the surface; (2) Divide the entire wellbore
into several well sections and calculate the circulating
system pressure loss coefficient for each section; (3) Determine the pump cylinder diameter. Select the smallest
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Zhichuan Guan et al.
cylinder size whose rated displacement is bigger than
the minimum cuttings-carrying displacement; (4) Determine the hydraulic parameter optimization criterion, accordingly calculate the first and the second critical
depth, and then calculate the optimum displacement and
determine the bit nozzle size and other jet parameters.
In this study, the maximum bit horsepower is selected as
the hydraulic parameters design criterion. The hydraulic
design method for selecting other criterion such as the
maximum bit jet force is similar.
In the step 3, the purpose of selecting small-diameter
cylinder is to obtain a larger rated pump pressure to overcome the pressure loss of the drilling fluid in the circulating system. As the improvement of the pump capacity,
the rated pressures of different-size cylinders are sufficient to meet the drilling requirements in most cases. The
performance parameters of the 3NB1600 pump are shown
in Table 1. When the circulating system pressure bearing
capacity is smaller than the rated pressure of the pump
cylinder, the maximum allowable operating pressure of
the ground pump is actually the circulating system pressure bearing capacity. In this case, the pump displacement becomes the primary consideration instead of the
cylinder size.
The bit hydraulic horsepower is a function of the
pump displacement, and the optimum pump displacement can be found corresponding to the maximum bit
hydraulic horsepower on the bit hydraulic horsepower
-displacement curve, as shown in the example.
Based on the analysis above, the general steps of hydraulic parameters design under the limited circulating
system pressure bearing capacity can be expressed as
follows:
Step 1 and step 2 are similar with the existing design
method.
Step 3: determine the optimum pump displacement corresponding to the maximum bit hydraulic horsepower through formulas or by drawing curves.
Step 4: choose the cylinder whose rated displacement is
closer and larger than the optimum displacement
with the rated pump pressure larger than the circulating system pressure bearing capacity.
Step 5: calculate other bit hydraulic parameters.
3. Comparison of the Two Design Methods
The analysis above shows that the existing hydrau-
lic parameter design method should be improved when
ground pump performance parameters change. The comparison of the new method with the existing method is
shown in the example below.
The drilling parameters are as follows: two 3NB1600
drilling pumps, a 241.3 mm drill bit, 140 m drill collars
with an outer diameter of 241.3 mm and inner diameter
of 71.4 mm, internal flush drill pipes with an outer diameter of 139.7 mm and inner diameter of 118.6 mm. The
circulating system pressure bearing capacity is 18 MPa
based on common experiences; the circulating pressure
loss coefficient of ground pipelines Kg is 1.07 ´ 10-3
MPa.s.L-1.8; the fluid density is 1.60 g/cm3 at the depth of
3000 m; the plastic viscosity is 0.045 Pa.s; the minimum
annular velocity is no less than 0.6 m/s.
The first two steps of the two design methods are
similar:
(1) Determine the minimum cuttings-carrying displacement Qa.
The minimum annular velocity:
(1)
Because the minimum annular velocity is no less than
0.6 m/s, Va takes the value of 0.6 m/s. Therefore, the minimum cuttings-carrying displacement:
(2)
where r is the fluid density, g/cm3; dh is the wellbore diameter, cm; dp is the drill pipe outer diameter, cm.
(2) Calculate the circulating pressure loss coefficient at
this depth.
Table 1. Performance parameters of 3NB1600 drilling
pump [24]
Cylinder
size
(mm)
Pump
stroke rate
(times/min)
Rated
displacement
(L/s)
Rated pump
pressure
(MPa)
190
180
170
160
150
140
130
120
120
120
120
120
120
120
120
120
51.9
46.6
41.5
36.8
32.3
28.2
24.3
20.7
20.7
23.1
25.9
29.2
33.2
38.1
44.2
51.9
Drilling Hydraulic Parameters Design Method under the Limited Circulating System Bearing Capacity Condition
305
(8)
(3)
The pressure drop at the drill bit:
(9)
(4)
The drill bit nozzle flow area:
(10)
(5)
The circulating pressure loss coefficient of the whole
system at the depth of 3000 m:
The jet velocity:
(11)
The jet impact force:
KL = mD + a = 0.0158
(12)
where mpv is the fluid plastic viscosity, Pa.s; dpi is the
drill pipe inner diameter, cm; dc is the drill collar outer
diameter, cm; dci is the drill collar inner diameter, cm; Lc
is the total length of the drill collar, m; B is an constant
for inner flush drill pipe, which is 0.51655; K c is the
drill collar circulating pressure loss coefficient.
The next steps of the existing hydraulic parameter
design method are as follows:
Choose the smallest-size cylinder while ensuring that
the rated displacement is larger than the minimum cuttings-carrying displacement. In this example, select the
120 mm cylinder whose rated displacement is 20.7 L/s
and rated pump pressure is 51.9 MPa, according to Table
1. Set 18 MPa as the limited pump pressure because the
ground pump pressure is no more than 18 MPa.
The first critical well depth:
(6)
Below the first critical well depth, the drilling pump
works in the rated pump horsepower state, and the drill
bit horsepower decreases with the increase of the pump
displacement. The drill bit horsepower reaches its maximum value at the rated pump displacement, so the optimum pump displacement to achieve the maximum bit
horsepower is the rated pump displacement. Because
the depth of 3000 m is less than the first critical well
depth Dp c , the rated pump displacement 20.7 L/s is selected as the optimum displacement.
The circulating pressure loss at this displacement:
(7)
The bit hydraulic horsepower:
The next steps of the new hydraulic parameters design
method are as follows:
When the drilling pump pressure is limited, the output pump pressure ps is a constant of 18 MPa, so the bit
hydraulic horsepower:
(13)
Let
dPb
dP
= 0, so b = ps - 2.8 KLQ1.8 = 0.
dQ
dQ
Therefore, the optimum displacement:
(14)
Because
d 2 Pb
dQ 2
0. 8
= -504
. KL (
pr 1. 8
) < 0, the bit hydrau28
. KL
lic horsepower corresponding to the optimum displacement is the maximum bit hydraulic horsepower. Therefore, the 140 mm cylinder is selected whose rated displacement is 28.2 L/s, according to Table 1.
The circulating pressure loss:
(15)
The maximum bit hydraulic horsepower:
(16)
Comparing the two methods, the bit hydraulic horsepower of the new method is 10.02% larger than the existing method, so the new design method will achieve a
better bottom hole cleaning effect and larger ROP.
The curve of the relationship between the bit hydraulic horsepower and different displacements can be
306
Zhichuan Guan et al.
drawn from Eq. (13), as shown in Figure 1. The dash lines
indicate the values of the bit hydraulic horsepower corresponding to the rated displacements when selecting
the two different sized cylinders. It can be seen from Figure 1 that selecting the 140 mm cylinder in the new design
method can make the bit hydraulic horsepower achieve
the maximum value under limited pump pressure while
selecting the 120 mm cylinder cannot achieve it.
The comparison of the hydraulic design parameters
when choosing different cylinders is presented in Table
2. It can be seen from Table 2 that when choosing the 140
mm cylinder rather than the 120 mm cylinder, the drill
bit horsepower and jet impact force increase, which indicates better bottom hole cleaning when using the new
design method. The drill bit pressure drop and the jet
velocity decrease because the parasitic pressure loss in
the circulating system increases as the displacement increases.
4. New Method Analysis
4.1 Comparison of the Bit Hydraulic Horsepower
under Different Limited Pump Pressures Using
the Same Drilling Pump
In the example, increasing the circulating system pressure bearing capacity from 18 MPa to 20 MPa with other
parameters unchanged, calculate the maximum bit hydraulic horsepower under these two different limited pump
pressures using the new design method, and the result is
shown in Table 3, where P1 is the bit horsepower corresponding to 18 MPa and P2 is the bit horsepower corresponding to 20 MPa.
It can be seen from Table 3 that increasing the limited pump pressure can greatly increase the bit hydraulic horsepower because the increase of the pump power
supply will directly provide more energy for the drill bit.
Therefore, increasing the limited pump pressure is favorable for increasing the ROP.
4.2 Comparison of the Bit Hydraulic Horsepower
under Different Ground Pumps
Redesign the hydraulic parameters in the previous example using the 3NB1000 drilling pump and the 3NB1600
drilling pump under the limited or not limited pump pressure. The limited pump pressure is assumed to be 18 MPa.
Select the 140 mm cylinder for the 3NB1000 pump whose
rate displacement is 27.1 L/s and rated pump pressure is
24.3 MPa. Select the 160 mm cylinder for the 3NB1600
pump whose rate displacement is 37.58 L/s and rated
pump pressure is 39.3 MPa. The relationship among the
maximum bit hydraulic horsepower at the optimum displacement, different well depths and different limited
pump pressures is shown in Figure 2.
Figure 2 indicates that: (1) for the same pump, the
maximum bit hydraulic horsepower under the not limited pump pressure is much larger than that under the
Figure 1. Relationship between the bit hydraulic horsepower
and displacements.
Table 2. Comparison of the hydraulic design parameters when choosing different cylinders
Cylinder size
(mm)
120
140
Optimum
displacement (L/s)
Drill bit
horsepower (kW)
Pressure drop at
the drill bit (MPa)
Jet velocity
(m/s)
Jet impact Force
(kN)
20.70
28.16
296.15
325.81
14.31
11.57
128.41
115.45
4.25
5.20
Table 3. Comparison of the bit hydraulic horsepower under different limited pump pressures
Well depth (m)
3000
3500
4000
4500
5000
5500
6000
6500
7000
P1 (kW)
P2 (kW)
326
385
308
363
292
344
279
328
267
314
256
302
247
290
238
280
230
271
Drilling Hydraulic Parameters Design Method under the Limited Circulating System Bearing Capacity Condition
307
ing capacity of the ground pipelines and other drill tools
should also be improved. Otherwise, the incidents of frequently breaking drilling tools will offset the benefits of
using high pressure and power pumps [25].
5. Conclusions
Figure 2. The maximum bit hydraulic horsepower under different drilling pump pressures at different depths.
limited pressure; (2) when the pump pressure is not limited, using a pump with larger rated pressure can get
a larger maximum bit hydraulic horsepower; (3) when
both of the pump pressures are limited, the maximum bit
hydraulic horsepower for the 3NB1600 drilling pump is
a bit larger than that for the 3NB1000 drilling pump at
the shallow well section, but with the increase of the well
depth, the maximum bit hydraulic horsepower for both
pumps becomes consistent. The reason is that the rated
displacement of the 3NB1600 drilling pump cylinder is
sufficient to reach the optimum displacement at the shallow well section, while the rated displacement of the
3NB1000 drilling pump cylinder cannot, and hence the
bit hydraulic horsepower using the 3NB1600 drilling
pump is a bit larger than that using the 3NB1000 drilling
pump. However, with the increase of the well depth, the
optimum displacement corresponding to the maximum
bit hydraulic horsepower decreases with the change of
drilling parameters, and thus the rated displacements for
both pump cylinders are larger than the optimum displacement. It can be seen from Eq. (14) that the optimum
displacement only changes with the limited pump pressure, so the maximum bit hydraulic horsepower using
the two different drilling pumps are consistent. Although
the power capacity of the 3NB1600 drilling pump is
larger than that of the 3NB1000 pump, but it cannot perform its maximum capacity because of the limitation of
the circulating system pressure bearing capacity, which
also reflects the importance of improving the circulating
system pressure bearing capacity.
Although larger bit hydraulic horsepower, better cuttings-cleaning effect and larger ROP can be achieved
with the increase of the pump capacity, the pressure bear-
(1) The existing hydraulic parameter design method that
selects the small size cylinder to obtain a larger pump
pressure to overcome the pressure loss along the wellbore is suitable for the low ground pump capacity.
(2) A new hydraulic parameter design method under the
limited circulating system pressure bearing capacity
is presented, and a larger maximum bit hydraulic
horsepower can be achieved using the new design
method.
(3) The maximum bit hydraulic horsepower using different ground pumps under limited or not limited pump
pressures are analyzed. The effect of using the new
design method greatly depends on the limited pump
pressure. The circulating system pressure bearing capacity should be improved as much as possible.
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Manuscript Received: Mar. 27, 2015
Accepted: Aug. 4, 2015