Note: Descriptions are shown in the official language in which they were submitted.
Lawrence Che-Keung Lee; Lee Stanley Kobylinski;
Mukul Kumar Tyagi; Michael Wesley Furnas; and
Francis Theodore Traylor
LIQUID-GAS SEPARATOR APPARATUS
SPECIFICATION
Background of the Invention
This invention relates to separator apparatus and
more particularly to downhole liquid-gas separators
used in conjunction with submergible pumps.
Liquid-gas separators are used downhole in oil-
producing wells to separate gas from crude oil be-
fore the oil enters the downhole pump. Any gas
present in the oil supplied to the pump tends to re-
duce the volume~ric efficiency of the pump. I
excessive quantities of gas are present in the oil,
"gas lock" can occur which completely restricts the
flow of the oil through the pump. ~hen "gas lock"
occurs, the pump must be shut down for later restart.
An effective liquid-gas se~parator reduces the occur-
rence of "gas lock" and enables the pump to operatecontinuously and efficiently to pump more oil.
'
. -
The prior art is replete with liquid-gas
separators for downhole use. ~.S. Patent No.
3,~87,3~2 to Bunnelle, issued June 3, L975, and U.S.
Patent No. ~,088,~59 to Tuzson, issued May 9, 1978
disclose centrifugal-type liquid-gas separators.
U.S. Patent No. 2,969,742 to Arutunoff, issued
January 31, 1961, and assigned to the same assignee
as the present invention, discloses a reverse flow-
type liquid-gas separator. U.S. Patent No. 4,231,767
to Acker, issued November 4, 1980, also assigned to
the same assignee as the present invention, discloses
a screen-type liquid-gas separator. Although known
centrifugal-type separators perform satisfactorily at
low to moderate flow rates, they do not.operate
well at high flow rates, particularly as the volu-
metric ratio of gas to liquid increases, and they are
unable to match the requirements of many high-capacity
submergible pumps, resulting in the pump being
"starved" and its output being reduced. Reverse
flow-type separators also suffer from the same dis-
advantages. Screen-type separators perform well at
high flow rates. However, over a period of time,
their screens tend to become clogged, which reduces
the capacity of the separator,
It is desirable to provide liquid-gas separators
which overcome these and other disadvantages of kno~n
separators, and it is to this end that the present
invention is directed.
Summary of he Invention
The present invention provides liquid-gas
separators which are capable of operating at high
flow rates, even with a relatively large volumetric
~ 3'~
ratio of gas to liquid, and which are exceptionally
effective ~o separate the liqtlid and the gas compon~
ents of a dowrlhole well fluid. :[n acldition, the
separators are smaller, less complicated, and less
expensive to produce than known separator apparatus
Briefly stated, a liquid-gas separator apparatus
in accordance with the invention may comprise an
elongated hub having means for connecting the hub to
a rotary shaft, helical blade means defining a
screw-type inducer disposed on a first longitudinal
portion of the hub, vane means defining a centrifugal
separator disposed on a second longitudinal portion
of the hub, and curved bl.ade segment means connecting
the blade means and the vane means and shaped to
provide a smoothly curved transition between the
blade means and the vane means.
Brief Description of the Drawings
Figure 1 is a longitudinal sectional view
illustrating a liquid-gas separator apparatus in
accordance with the invention;
Figure 2 is a perspective view of a separator
unit of the apparatus of Figure l;
Figure 3 i5 a top view of the separator unit
of Figure 2;
Figure 4 is a bottom view of the separator unit
of Figure 2;
Figure 5 is a diagram illustrating the operation
of a known reverse flow-type separator at different
volumetric ratios; and
Figure 6 is a diagram illustrating the operation
of a liquid-gas separator appara~us in accordance
with the invention at different volumetric ratios.
Detailed Description of the Preferred Embodi~lent
Fig~lre 1 lllustrates a liquid-gas separator
apparatus 10 in accordance with the inventi.on, The
apparatus comprises a tubular (preferably cylindrical)
housing 12 adapted to ex~end longitudinally within
and spaced from a well casing (not illustrated), The
upper end of the housing is threaded onto a discharge
head 14, which may be connected to the housing of
a submergible pump 16 (illustrated diagrammatically),
and the lower end of the housing may be threaded onto
an intake head 18, which may be connected to the
housing of an electric motor 20 (also illustrated
diagrammatically~, Pump 16 and motor 20 may be a
conventional submergible centrigugal pump and drive
motor adapted for operation downhole in an oil well,
A drive shaft 22 extends from the motor to the pump
along the axis of the housing and through the intake
head and the discharge head, Shaft 22 may be sup-
ported within the housing by sleeves 24 mounted in
the discharge head and the intake head, and by a
bearing assembly 26 mounted in the intake head,
The invention employs a separator unit 28 (shown
in more detail in Figures 2-4) located within the
housing between the intake head 18 and the discharge
head 14. Separator unit 28 comprises an elongated
tubular hub 30 having an axial bore 32 to enable
the hub to be mounted coaxially on shaft 22 for ro-
tation therewith. The hub may be connected to the
shaft by a key (not illustrated) received in a keyway
34 (see Figures 2 and 4~ within bore 32 and a corres-
ponding keyway (not illustrated) in the shaft, As
shown in Figure 1, the hub may be located axially
on the shaft by bushings 36 at opposlte ends of the
7~
hub and by sleeves 38, 40 mo~mted on the shaE~ by
snap rings 42 received :in circumferential grooves ~4
in the sha~. Sleeve ~IO, at the upper end of the
hub, may be the inner sleeve portion of a flow
divider 46, to be described hereinafter.
As shown in Figures 1 and 2, disposed at
dlfferent longitudinal posi-tions on the periphery of
hub 30 are pluralities of vanes and blades having
different shapes. The vanes and blades are shaped
to perform different functions, and they divide the
separator unit into three distinct regions or stages,
As will be described in detail hereinafter, the lower
portion of the separator unit comprises a screw-
type i.nducer 48; the upper portion of the separator
unit comprises a centrifugal separator 50; and the
portion between the inducer and the centrifugal separ-
ator comprises a transition region 52. The inducer
pressurizes the liquid-gas fluid mixture entering
intake ports 54 of intake head 18 sufficiently to
force the fluid mixture through the separator appar-
atus. The centrifugal separator 50 communicates with
the inducer via transition region 52 and imparts
rotary or circular motion to the fluid mixture to
separa~e the liquid and gas components thereof through
centrifuge action. The transition region 52 provides
a smooth transitîon between the inducer and the
centrifugal separator and is shaped to minimize
losses.
As shown in Figures l and 2, inducer 48 of
separator unit 28 comprises a pair of helical blades
60, ~2 disposed symmetrically about the lower por-
tion of hub 30 to define a double helix screw-type
~ 3~
inducer. Each blade has a radlally extending leading
edge 64, 66, respectlvely, located near the lower
end of ~he hub adjacent to the intake heacl. As
shown in Figure 2, blades 60, 62 are tapered (cir-
cumferentially) toward their leading edges so thatthe leadlng edges form sharp cutting blades. This
reduces turbulence and CaVitatiOIl in the fluid
mixture entering the inducer. As shown in Figure 4,
leading edges 64, 66 are symmetrically disposed 180
apart on opposite sides of hub 30 and they lie in an
axially extending plane indicated by the line A-A.
From their respective leading edges, blades
60, 62 extend helically upwardly about hub 30 for a
di.stance approximately equal to one-third the length
of the hub. Preferably, each blade makes approxi-
mately two complete revolutions (720 degrees) about
the hub with a relatlvely smal]. blade angle, 0, with
respect to a plane normal to the hub axis. In a
preferred form, the blades have a two-inch lead
or pitch1 i.e., they traverse 360 in two inches of
axial length. The blade angle 0 varies as a function
of radius; r, in accordance with the equation
tan ~ = p/2~r,
where p = pitch, i. e ., 2 inches in the above example.
At the inner radius of the blades (at the hub), the
blade angle is preferably approximately 29.6. At
the outer radius of the blades, the blade angle is
preferably approximately l0.6. For a given radius,
the blade angle of each blade 60, 62 is preferably
constant as the blade extends hellcally upwardly about
the hub.
~ '7~
In tlle transltion region 52, the blade angle
o~ each blade 60, 62 varies as a linear funct:ion of
ax:ial leng~h :Erom the constan~ blade angle in the
lower portion of the hub to a blade angle of 90,
i.e., vertical, in a circumferential distance of
approximately 90 (one-quarter turn about the hub).
The blades then extend vertically upwardly Eor
approximately the remaining length of the hub (in the
centrifugal separator portion) forming substantially
straight radially directed axially extending vanes
60', 62'.
As best shown in Figure 3, vanes 60', 62' are
symmetrically disposed 180~ apart on opposite sides
of hub 30, and lie in an axially extending plane
indicated by the line B-B, which is normal to axial
plane A-A. The one-quarter turn blade segments 60'',
62'' in transition region 52 provide a smoothly
curved transition between helical blades 60, 62 and
their corresponding axial vanes 60', 62', respec-
tively. (It should be noted that fluid transitionregions, in pumps for example, are conventionally
shaped to provide a change in fluid velocity which
is a linear function of distance, rather than shaped
to provide a change in blade angle which is a linear
function of distance, as in the invention. Design-
ing transition region 52 in a conventional manner
would result in an abrupt change in blade angle,
which would produce undesirable losses.)
In order to distribute the fluid mixture more
evenly in the centrifugal separator portion of the
apparatus, it is desirable to form the centrifugal
separator S0 with another pair of axially extending
vanes 70', 72', symmetrically disposed 180 apart on
7~
opposite sicles oE hub 30 and positioned at right
angles to vanes 60', 62'. As shown in ~igure 3,
vanes 70', 72' are pre:Eerably located in axial plane
A-~. Each vane 70', 72' is connected to an associ-
ated helical bl.ade 70, 72, respectively, by anassociated smoothly curved blade segment 70'', 72'',
respectively, in transition region 52. Blade seg-
ments 70'', 72'' preferably have the same shape as
blade segments 60'', 62'', and function in the same
manner to provide a smooth transition between vanes
70', 72' and their associated blades.
Unlike blades 60, 62, however, blades 70, 72 do
not extend to the lower end of hub 30. Rather, as
shown in Figures 1 and 2, blades 70, 72 terminate in
tapered leading edges 74, 76, respectively, just
below the transition region 52. As best illustrated
in Figure l, each associated blade, blade segment
and vane 70-70''-70', 72-72''-72' preferably traverses
approximately 180 (one-half turn) about hub 30 so
that leading edges 74, 76 lie in axial plane A-A.
Each blade segment 70'', 72'' may traverse approxi-
mately one-quarter turn about the hub and its associ-
ated blade 70, 72 may traverse another one-quarter
turn. As is also shown in Figures 1 and 2, leading
edges 74, 76 of blades 70, 72, respectively, are
located midway between adjacent blades 60, 62. Blades
70, 72 serve to divide the fluid mixture flowing
between blades 60, 62 into two different paths to dis-
tribute ~he fluid mixture evenly between adjacent
vanes of the centrifugal separator. Blades 70, 72
do not extend to the lower end of hub 30 since
this would unduly restrict the intake to the inducer.
3ti1~
As shown in Figures 1-4, the vanes, the blades,
and the blade segments all have the same radial
dimension, and extend to slightly less than the
inner surface of tubular housing 12. Representative
approximate dimensions for the separator unit may
be: outer diameter 3.4 inches, length 11 inches,
inducer length 4 inches, centrifugal separator length
3.75 inches, and transition region length 3.25 inches.
As previously mentioned, inducer 48 pressurizes
the fluid mixture sufficiently to force it through
the separator apparatus 10, and the centrifugal
separator 50 acts as a centrifuge to separate the
liquid and the gas components of the fluid mixture.
The centri~ugal separator is designed to impart the
maximum tangential velocity to the liquid-gas mixture.
Because of its greater densityj the liquid is centri-
fuged away from shaft 22 due to the rotary motion
imparted to the fluid mixture by the vanes of the
centrifugal separator, while the lower density gas
tends to conform itself to the region about the shaft.
Discharge head 14 may be formed with a plurality
of channels 80 symmetrically disposed about its
periphery (only one channel being illustrated in
Figure 1) which in cooperation with a tubular sleeve
82 lining the interior surface of houslng 12 form
passageways for the liquid. ~ach channel may be
connected to an upper chamber 84 in the discharge
head, which cornrnunicates with the pump impeller in-
take, by an upwardly angled~passageway 86. Discharge
head 14 may also have a lower chamber 88-formed
about shaft 22 for receiving the gas, and may have
a plurality of gas vents 90 symmetrically disposed
about the discharge head (only one such gas vent
being illustrated in Figure 1) which comrnunicate with
charnber 88.
k~
~.o
Flow divicler 46, which in the forln illustra~ed
comprises a spider assembly connected to shaf~ 22
for rotation therewith, aids in direc~:ing the separ-
ated liquid into channels 80 and in d:i.rec~ing the
separated gas into chamber 88. As shown, f].ow
divider 46 may comprise an inner sleeve 40 having
a bore through which shaft 22 passes, and an outer
concentric cylindrical member 92 connected to sleeve
40 by spokes 94. The openings 96 between cylindrical
member 92 and sleeve 40 provide passageways to chamber
88 for the gas, and the inner surface of the lower
end of cylindrical member 92 is curved, as shown, to
aid in collecting the gas leaving the centrifugal
separator. The flow divider is spaced slightly above
the centrifugal separator, as opposed to being formed
on the centrifugal separator itself, to provide a
settling time for the fluids leaving the centrifugal
separator. This enables better separation of the
liquid and the gas. Although, in the form shown, the
flow divider is a separate member which is connected
to the shaft 22 and which rotates with the shaft, if
desired, the lower end of discharge head 14 may be
configured to perform flo~ division.
In operation, pump 16, separator apparatus lO,
and motor 20 are submerged downhole within the
liquid-gas well fluid mixture. The liquid-gas
mixture enters the intake ports 54 of intake head 18
through a perforated or slotted member 100 which
assists in filtering debris from the fluid mixture.
From the intake ports, the fluid mixture enters
inducer 48 which pressurizes the fluid mixture and
supplies it to the centrifugal separator 50 via trans-
ition region 52. As previously described, the
ll
centrifugal separator separa~es the liquid from the
gas and supplies the liquid to the impeller intake
of the pump. The separated gas is vented via gas
vents 90 into the space between the well casing (not
illustrated) an~ the outer surfaces o~ the housings
of the discharge head and pump.
Although a screw-type inducer has a smaller
suction than a standard pump impeller and does not
provide as high an output as a pump, a screw-type
inducer has a number of advantages. To prevent pump
cavitation and possible "gas lock", it is desirable
to gradually increase the pressure of the fluid
mixture entering the inducer. This is accomplished
by maintaining the blade angle of the screw rela-
tively small, as previously descri.bed. In addition,the tapered leading edges of the blades reduce turbu-
lence in the fluid mixture and provide a smoother
flow through the inducer. The smoothly curved transi-
tion region between the inducer and the centrifugal
separator also contributes to a smooth fluid flow
through the apparatus and minimizes undesirable
losses. The flow rate through the separator apparatus
is primarily a function of the blade angle and the
length of the inducer. Since it is desirable to
maintain a relatively small blade angle to prevent
pump cavitation, the length of the inducer may be
selected appropriately to provide a desired output
flow and pressure.
Figures 5 and 6 contrast the perfonnance of a
liquid-gas separator apparatus in accordance with the
invention (Figure 6) with the performance of a con-
ventional reverse flow liquid-gas separator (Figure 5).
~ 7
12
~s shown in ~igure S, the flow rate through the
reverse Elow separator decreases dramatically as the
volumetr:ic ratio of vapor (gas) to liqui~ increases
Ior example, at V/L = 0.20, the flow rate is ~pproxi-
mately one-half of ~he flow rate of V/L = 0. In con~
trast, the curves of Figure 6, which were derived
from tests performed on a liquid-gas separator
apparatus in accordance with the invention, show that
the flow rate through the separator apparatus of the
invention changes very little with changes in volu-
metric ratio, and that even with a relatively large
volumetric ratio V/L = 0.60, the flow rate is not
substantially different from the flow rate at
V/L = 0. The curves of Figure 6 demonstrate that a
liquid-gas se-parator apparatus in accordance with the
invention is able to maintain a relatively constant
flow rate over widely varying volumetric ratios,
thereby ensuring that the submergible pump operates
at close to its maximum efficiency. Remarkably, the
invention achieves such improved results with a
relatively simple and inexpensive construction.
While a preferred embodiment of the invention
has been shown and described, it will be apparent
to those skilled in the art that changes can be made
in this embodiment without departing from the
principles and spirit of the invention, the scope
of which is defined in the appended claims.
