Note: Descriptions are shown in the official language in which they were submitted.
~2~
DO;,I~OI~ SCRE~ M~TOR
The invention relates to positive displacement hydrau-
lic machine~, and in particular, it deal~ with a downhole
screw motor~
The invention may be most ef~iciently used in positive-
displacement downhole motors used a~ a drive for a rock-
~brea~ing tool in drilling oil and ga~ wells.
The inven-tion may al~o be u3ed in turbodrills.
Two radically different methods are used nowadays for
drilling wells. ~ne method i8 a rotary drilling method,whe-
rein the drive of a rock-breaking-tool - bit - is di~po~ed
on the ground level, and the bit is rotated through a strin~
of drill pipes. l'he ~econd method involves the employment of
downhole hydraulic machines dispo~ed directly above the bit.
The drill pipe string remain~ stationary in this case. The
~econd method ha~ a number of ObViOUB advantages: there are
no energy lo6ses for rotating the drill pipe string; the lo-
ad on the drill pipes is lowered, hence, the number of emer-
gency situations in the well ~haft i~ reduced.
Downhole screw motors are most wide~pread u~ed amcng
all types of àownhole motor~ employed nowadays in practical
drilling applications. These motor~ feature ea~y operation
and maintenance they are compact and make it pos~ible to
work ~ith drilling muds of largely varying density and ViB-
cosity (cf. Gusman M.'l'l, Baldenko D.F., et al. Downhole Screw
Motors for ~ell Drilling. ~ edra Publishing l~ouse 7 198l)o
~uch hydraulic motors generally compri~e a ca~ing, an output
shaft having radial and thrust bearings1 and working members
- 2 ~
consistin~ of two elements: an outer rubberized ~leeve or
stator having in~ernal helical teeth and a rotor and shaft
havin~ outer helical teeth accommodated in the stator. The
number of tee-th of the sleeve is greater than the number of
teeth of the shaft by unity ~o that the interior of the work-
ing members is divided into high and lo~ pressure chambers
by their mutual engagerrlent when a liquid is pumped through
the working members. Under the action of the resultant pres-
sure diff'erence, the rotor starts moving relative to the sta-
tor, the a~is of the rotor describing a circle about the ax-
is of the stator. 'l'his rotation is tran~mitted to the output
shaft of the rotor. Usually a flow of liquid is used as a
source of energy for operation of the motor, but the hydrau-
lic motor can also f'unction using an aerated li~uid or com-
prèssed air.
l~owadays aow~hole motors used for drilling ~ells gene-
rally have the whole flow of` liquid passing between the ro-
tor and stator.
- One of the main di~advantages of such motors is the
dependence of their output parameters on -the inlet flow of
workin~ liquid. A9 the production requirements in drilling
well~ do not frequently take into account energy capabilities
of dov~nhole motors, the latter are often used under unfavour
able conditions when speed and pressure differences are too
high thus resulting in premature f`ailure of parts and a~serab-
lies of the motor.
To elirninate this disadvantage, conoid nozzles are mo
unted in the axial passage of the rotor (cf. USSR Inventor's
3 ~ 2~
Certificate lio. 436595~ Clo E 21 B 4/0~, 1972), the flow of
working liquid being throttled through the nozzles.
The characteristic of such motore i~ dropping, i.e.
the output shaft speed decrease~ with a growth of the load
torque much fa~ter than in hydraulic motors that do not have
such nozzles. As the load increases, thi~ result~ in a strong
6peed decrease until the output motor ~haft stops at low load
torque values thus resulting in a lower output torque,hence,
in a lower efficiency of drilling.
It i9 an object of the invention to improve efficiency
of drilling.
Another object of the invention is to improve characte~
ristics of the motor having a nozzle provided in the a~ial
passage of the rotor.
Finally, it is an object of the invention to increase
the output ~orking torque of a motor having a nozzle in the
axial passage of the rotor.
These and other object~ are accompli~hed by that in a
downhole motor comprising a ~pindle section and a motor sec-
tion comprising working mernbers - a stator and a hollow ro-
tor having an axial paseage communicating with a ~orkin~
liquid high-pressure zone and accommodating a flow regulat-
or having a nozzle, according to the invention, the nozzle
has two chamber~ dieposed in series in the direction of work-
ing liquid flow: an admission chamber and a delivery c.hamber,
the sur~ace~ o~ the chambers washed with the working liquid
being conjugated along a break line, the a~mular portion of
the admission chamber~ which is adjMcent to the break-line,
being convex with respect to the direction of working liqui~
flo~J, and the cro~s-eectional area of the ~dmiesio~ chsmber
at the outlet thereof being smaller than the cro~ss-section~
al area thereof at the inlet.
The invention makes it po~sible to increase torque and
speed of the output motor shaft thereby improving efficiency
of well drilling. When ~orking liquid enters the nozzle,jete
~tall at the break line to form a powerful vortex in the ad-
mission chamber, the vortex energy increa~ing as the pres-
~ure difference increases so as to reeult in an increaee in
the hydraulic resistance of the nozzle and causing an in-
creaee in the flo~ of liquid pa~ing between the rotor and
stator.
~ he regulator according to the invention is very com-
pact; it can be easily in~talled in any motor and may be re-
placed without di~a0sembly of the hydraulic motor.
1~ one embodiment of the inventio~, the nozzle i~ made-
-up of t~o member~; a buehing and a rod mounted ineide the
bushing, the admiesiQn and delivery chamber~ being defi~ed
by the surfacee of the bushing and rod and are annular in
shape.
In another embodiment, the rod ie cylindrical,and the
bushing is internally provided with an annular projectio~ de-
fining -the convex portion of the admission chamber surface~
In ~till another embodiment of the invention, the bu~h-
ing i~ cylindrical7 and the rod i8 provided with an annular
projection defining the convex portion of the admiesion
chamber surface.
_ 5 _ ~ ~5 ~
In a further embodim~nt of the inventiorl, the bushin
and rod have annular proàections, each projection defining
a convex portion of the admission chamber surface.
All embodimentE of the invention make it possible to
improYe s~ability of~the motor characteristiG, i~e. to di-
minish the dependence of ~peed on the load at the output
shaft. This is achieved because liquid jets flowing along
the curvilinear surface of the admission chamber stall at
the break-line to form a ~pace with an intensive vortical
flowO The higher the pressure diff`erence at the working memb-
ers (rotor and stator)~ hence at the nozzle, the more in-
teIlBiVe i8 mi~ing of liquid jets, the higher is the resist-
ance of the nozzle ~nd the greater i8 the amount of liquid
that passes through the wor~ing members of the motor. This
facility make~ it possible to cau~e a greater amount of li-
quid to pass through the helical surfaces of the rotor and
stator than in case conoid nozzles are used.
This result, i.e. an increa~e in the flow of liquid
through the helical 3urfaces of the rotor and stator upon
an increase in the load at the output shaft, can also be
obtained using other structural mean~; however, the general
idea of the invention will remain unchanged.
In order to lower ~pecific load at the nozzle, several
nozzles are preferably provided in the ~xial passage of the
rotor. ~peration of the apparatu~ as a whole will in such
case remain the same.
Other objects and advanta~es of the invention will be
come apparent from the following detailed description of spe-
~so~æ~
cific embodiments illustrated in the accompanying drawings,in which:
~ ig. 1 is e lon~itudinal section view of a downhole
screw motor having one embodiment o~ a nozzle of a regulat~
or mounted in the axial passage of the rotor;
Fig. 2 i8 a longitudi~al ~ection of a ~low regulator
with a nozzle; enlarged Yiew;
Fig. 3 i~ a diagram showing flows of` liquid passing
through the noz~le;
Figs. 4,5, 6 show various structural embodiments of
nozzles;
~ ig5. 7, 8 show experi~entally obtaine~ energy charac-
teristics for prior art and this invention.
A downhole screw motor (~ig. 1) comprises a motor sec-
tion 1 and a spindle section 2. 'l'he motor section 1 includes
working members: a stator 3 and a hollow rotor 4 mounted
therein. The rotor 4 has an a~ial passage 5 communicating
with a high-pressure zone of liquid, and a flow regulator 6
is mounted in this axial passage. The rotor 4 is connected,
in the lower part thereof`, to a cardan shaft 7 whichg in
turn, is connected to an out~ut shaft 8 of -the spindle sec-
tion 2. A radial bearin~ 9 and a thrust bearing 10 secured
to the shaft 8 are installed in a casin~ 11 of the spindle
section ~, between a nipple 12 and a stab sub 13. A sub 14
is provided in the upper part of the mOtor f`or connectin~
to a drill pipe string. A rock breaking tool (not shown
in the drawing) is connected to the lower part of` the out-
put shaft 8.
- 7 - ~ ~5 ~
The flow regulator 6 (~ig. 2) comprise~ a removable
casin~ 15 in which there is mounted a nozzle 16 made e.g.
of a ceramic material. Sealing ring~ 17 and 1~, e.g., of
rubber are provided between the casing 15 and rotor 4 and
also between the nozzle 16 and ca~ing 15.
~ 'he nozæle 16 i~ made-up of two chambers disposed in ~e-
ries in th~ direction of the flow of workin~ liquid; an ad-
~ission chamber A and a delivery chamber B~ Surfaces 19 and
20 of the admi~sion chamber A and delivery chamber B, respec-
tively, are conjugated along a break line 21. An annular por-
tion 22 of the ad~i~sion charnber A, which iB adjacent to the
break line 21, is convex with re~pect to the direction of
flow of working liquid. ~iameter ~ of the inlet section of
the chamber A is greater than diameter d of the outlet sec-
tion OI the same chamber A. In other words, the cro~s-sec~
tional area of the admis~ion chamber A a-t the inlet thereo~
i9 larger than the cro~-sectional area at the outlet of the
sam~ chamber A.
~ he surface 2ù of the delivery chamber B may have any
appropriate confi~uration~ ~owever, it i8 preferred that the
shape of the chamber B be such a~ to offer maximum po~sible
resistance to the flow of ~orking liquid pas~ing through the
nozzle 16. 'l'he ~urface 2û OI the chamber B is formed similar-
ly to the surface 19 of the chamber A by rota-tin~ a curve
about the axi~ û-û convex with respect to the direction of
flow of working liquid.
Both curve~ forming the chambers A and B inter~ect each
other in the longitudinal ~ection of the nozzle 1~ at a point
which is equivalent to a break point. ~uch points forrn the
intersection line 21 in space, which iB equivalent to the
break line.
The downhole screw motor functions in the following man-
ner.
~ ihen the drill pumps uisposed at the ground level are
switched on, drilling Mud i~ supplied through a drill pipe
string to the working members of the motor section 1 (see
~ig. 1)~ q;he flow i~ divided directly upstream the working
members: the main part of the flow will pas~ between the ~ta-
tor 3 and rotor 4 to impart motion to the latter; the other9
smaller part of the flow wiil pas~ throu~h the passage 5 of
the ro-tor 4 and flow regulator 6 mounted in the passage 5.
Having pas~ed through the working members, both part~ o~ the
flow are again forming a ~ingle flow which gets to the face
through the inner hole of the shaft 8 in the ~pindle section
2.
q~orque provided in the motor section 1 is transmitted
from the rotor 4, via the cardan shaft 7, to the shaft 8 and
further to the rock-breaking tool (bit).
'llhe amount of resis-tance torque overcome by the motor
depends on cooperation of the bit and the rock being broken.
During operation of the motor, the motor torque, as well as
the load or resistance torque 9 undergo changes.
The torque in motOrs oI such a type i~ known to be pro-
portional to the pressure difference at the workin~ members
(in the working zone of the Motor characteri~tic) at a con-
stant flow of a working liquid. A~ the motor resistance tor-
g ~ 2~
que created ùurin~ rotation of the bit increa~es, in theprior art motor the amount of liquid passing between the ro-
tor and stator decreases proportionally with ~ P, ~herein P
is the pressure difference at the motor. rl'hus the characte-
ristic of the motor becomes dropping~ and the speed of the
output shaft 8 materially decrease~.
In the motor accordin~ to the invention; the flow of li-
quid gettin& -to the admission chamber A (Fi~. 3) mOVeS in a
kind of two flows: the main flow along the axis 0-0 of the
nozzle 16 moves from the chamber ~ through the outlet secti-
on thereof of the diameter d, which i~ formed by the break
line 21; the other, peripheral part of the flow washes the
surface 19 of the chamber A. At -the break line 21, this pe-
ripheral flow 8tall6 and is intensively mixed ~ith the main
central flow. 'lhe peripheral flow will be hereinafter re-
ferred to as a resis-tance flow.
Therefore, an inten~ive mi~ing of the main flow and re-
sistance flow results in a decrea6e in the energy of flow
that gets to the chamber B. The greater the pre~sure di~fe-
rence at the working members - stator 3 and rotor 4, and res-
pectively, at the nozzle 16, the stronger i9 the mixing of
liquid flows, the smaller is the amount of liquid flowing
from the chamber A to the chamber B, and the greater is the
amount of liquid admitted to the working members.
As ~hown in ~i~. 4, the nozzle 16 i:s made-up of two
members: a bushing 23 and a cylindrical rod 24 interconnect-
ed by bridges 25. Similarly to the abovedescribed structure,
the no~zle 16 ha~ two a~nular chambers disposed in ~eries
~20
1 iJ -
in the axial direction: the ad~i~rion chamber A anu the de-
livery chamber B having their sur~aces 19 and 2~ washed
with wor~ing liquidD The chambers A ar.d ~ are defined by
the urfaces of the bushing 23 and rod 24.
The ~urface of the bushing 23 is formed by rotatin2 abo-
ut the axis 0-~ a curve which is convex with respect to a ge-
nerant of a cylinder of a radius R, wherein R is the minimum
distance from the axis 0-0 of the nozzle 16 to a line which
is equivalent to the break line 21 formed by intersection
of the surface 19 of the ch&mber A with the ~urface 20 of
the chamber B. In this case, simil2rly to the abovedescribed
embodiment of the invention, the surface 20 of the chamber
B is ~ormed by rotating a~ arbitrary curve about the axis
0--00
An annular projection is provided on the in~er surface
of the bushing 23 to form the conve~ portion 22 o~ the ad-
mis~ion chamber A.
During operation o~ the embodiment of the regulator,
the same IeGUlt i9 obtained a9 in the de~ice 3ho~wn in ~ig.3.
The only difference resides in that the resistance f'low mov--
ing from the center away from the cylindrical sur~ace of the
rod 24 i~ reflected back to the periphery of the admission
chamber A to take part again in mixing with the main flow
(~econdary mi~ingj.
Fig. 5 show the nozzle 16 also having the buhing 23
and the rod 24 and two chambers: the admis~ion chamber A
and the deliver~ chamber ~. In this embodiment o~ the nozzle
16, the bushing 23 is cylindrical and the rod 24 is made ~Yith
~2~
an annular projection 27 ~ef`ining the convex portion 22 of
the surface 1~ of the admiæsion chamber A. rl'he surface of the
bushing 23 washed with wor~ing liquid is c~lindrical, and
the surface of the rod 24 in the chamber B is defined by
rotating about the axis 0-0 a curve which is convex with reæ-
pect to a generant of a cylinder of a radiu~ R, wherein R
is the minimum posæible distance from the axis O-V of the
nozzle 16 to the line 21 which is equivalent to a breaking
line formed by intersection of the areas of the 6urface of
the rod 24 (in the chamber A) and surface of the rod 31
(in the chamber B).
Unlike the motor shown in ~ig. 3, here the resistance
flow, which mOVeG along a curvilinear surface away from the
center of the nozzle towards its periphery, is reflected
from the cylinarical ~urface of the bushing 23 towards the
center and again, but with a lower energy, and takes part
in the mixing with the main ~low.
The nozzle 16 shown in Fig. 6, similarly to the two
above-described embodiments, has two members: the bushing
23 and the rod 24 interconnected by bridges 25. The nozzle
also has two chambers disposed in series in ~he axial direc-
tion: the admission chamber A and the delivery chamber ~ hav-
ing their ~urfaces 19,20 washed with working liquid.The bu-
shing 23 has an annular projectlon 28 and the rod 24 has
an annular projection 29. Each of the projectionæ 28~29
defines the convex portion 22 of the surface 19 o~ the admiæ-
sion chamber A. ~he surfaces of the bushing 23 and rod 24
disposed within the chamber A are formed by rotating about
~ ~5
- 12 -
the axis 0-0 curves each of which is convex with respect
to a generant of a cylinder of a radius R, wherein R is the
minimum possible distance from the axis 0-0 of the nozzle 16
to a respective line ~Ihich is equi~alent to the break line
21.
Operation of this flo~ regulator is distinguished in
the fact that here two resistance flows are formed: one
which moves along the curvilinear surface of the bushing
23 from the periphery to~7ards the center of the nozzle 16,
and the other which moves alon~ the curvilinear sur~ace of
the rod ~4 frorr, the center of the nozzle 16 towards the pe-
riphery tnereof. 'i'hese flows intersect one another within
a ring defined by radii R and R' so as to contribute to a
further mixing of liquid flows.
Therefore, in the abovedescribed er.1bodiments of the mo-
tor according to the invention~ with the presence of two
parallel flows one of which has its own a~iliary resistance
flows the energy of the latter increases with an increase
in the pressure difference, i.e. as the motor is loaded with
an e~ternal torque, the dependence o~ the amount of liquid
passing through the working mernbers and aleo through the
nozzle 16 on the motor loading conditions i8 of a complicat-
ed character. It can be, however, shown that use in the flow
regulator of the nozzles con~tructed as described here will
rnake the energy characteristic of the motor stable to a gre-
ater ex-tent thus bringing about, quite naturally, an increase
in its loading capacity and a very srnall decrease in the mo-
tOr output shaft speed.
~25sO~J2B
- 13 -
~ igs. 7 and 8 show energy characteristiCs, i.e. rela-
tionships between the relative pressure differential values
~P and rotation f requency ~ of the output shaft 8 ~ arld the
relative torque value ~, of a prior art scre~ motor and the
screw motor according to the invention.
Study of the characteristics given in the drawins
sho~s tllat a zone S of stable operation of the motor in
Fi~;. 8 is 18~o larger tnan a zone ~; of stable operation of
the motor in Fig. 7 in terms OI ~ orque . Speed decrease in
the prior art motor is 57~0 f o- the sarne point anci 50iio for
the motor according to the invention. II` the speed decrease
is consi~ered for both rr,otors with a?plication of one and
the same external torque, the difference ~ill be much great- ¦
er. 'l'his is due to the fact that the motor having a flo~v re- ¦
gulator will be supplied upon an increase in the pressure
at the working members an increased amount ( 2S compared to
the prior art) of liquid each time so that not only -the s ta-
bility of the cnaracteristic is improved, but average values
o3` workina ~orque and speed are al~o increa~ed.
