Note: Descriptions are shown in the official language in which they were submitted.
21 94801
FIELD OF THE INVENTION
2 The invention relates to a pressure vessel separator for continuously
3 separating the liquid, solid and gas components of pressurized drilling fluid returns,
4 produced from a well undergoing drilling. The separator utilizes a mechanical device,
that creates centrifugal action to firstly separate the gas and solids from the liquid,
6 followed by gravity separation under quiescent conditions to separate liquid
7 hydrocarbons from watèr. The solids, gases, liquid hydrocarbons and water are
8 independently removed from the separator. The invention also relates to the method
9 practised.
BACKGROUND OF THE INVENTION
11 The invention is an improvement of a prior art separator and method
12 described in United States Patent No. 5,415,776 (Homan).
13 This prior art separator is used to separate the components of
14 pressurized drilling fluids returning from a well undergoing drilling, usually
"underbalanced" or "multiphase flow" drilling.
16 Underbalanced drilling involves lightening drilling fluid (such as water or
17 diesel oil) with a gas (typically nitrogen). This is done so that the column of lightened
18 drilling fluid in the wellbore exerts a bottom hole pressure that is less than the pressure
19 in the formation being drilled. As a result, the drilling fluid does not invade the
formation. If it were to do so, the well productivity could be adversely affected.
21 Underbalanced drilling of a well may cause reservoir liquids and gas to enter the
22 circulating drilling fluid. Furthermore, the drilling fluid is circulated under pressure. As
23 a result, the drilling fluid returns, leaving the wellbore, are under pressure and typically
2 1 ~48 0 1
comprise a mixture of solids, liquids and gases. The solids commonly comprise coarse
2 bit cuttings and "fines". The liquids can comprise the original drilling liquid as well as
3 formation or reservoir fluids. And the gases can include the lightening gas and
4 formation gas.
The drilling fluid returns, therefore, need to be handled with pressure-
6 containing equipment. It is also necessary to separate the gases, liquids and solids
7 so that they are recovered as separate streams. The solids are removed. The gases
8 may be re-used or vented. And finally it is desirable to separate the hydrocarbons from
9 the balance of the liquid.
Pressure vessel separators for separating liquid/gas/solids components
11 of a stream have long been common in the oilfield equipment art. However, these prior
12 art separators are not adapted to process drilling fluid returns, which contain large
13 quantities of coarse bit cuttings and experience severe fluid slugging. Instead, drilling
14 fluid returns have almost entirely been processed using shale shakers and open mud
tank systems, which would not be environmentally safe or sound especially in the16 presence of H2S gas. These systems are not capable of handling pressurized returns.
17 The previously mentioned Homan patent discloses a separator for
18 separating the components of pressurized drilling fluid returns. The separator involves:
19 ~ An elongate, horizontal, cylindrical pressure vessel having
elliptical heads closing its ends. The commercial embodiment of
21 this vessel has a typical diameter of 8 feet and a length of 30
22 feet;
23 ~ A returns feed pipe extends into the vessel at its first end. The
24 feed pipe connects with an involute structure designed to reduce
the velocity of the incoming feed before discharging it;
21 94~01
~ A hopper-like compartment is located beneath the involute
2 structure, for receiving the incoming returns. The compartment3 is defined by the head, the vessel's curved sidewalls and a
4 slanted weir forming the downstream end of the compartment;
~ An outlet, at the base of the compartment, is connected with a
6 pump, for withdrawing of a solids slurry while drilling fluid
7 continues to enter the separator;
8 ~ The chamber downstream of the slanted weir is provided with
9 outlets at different elevations for removing gravity-separated water and liquid hydrocarbons; and
11 ~ The vessel has an overhead outlet for removing gases.
12 In operation, the coarse bit cuttings settle out by gravity in the inlet compartment and
13 are concentrated as they are funnelled down to the pump. Solids are removed from
14 the vessel without interfering with ongoing drilling and continuous production of drilling
fluid returns. The gas breaks out and is removed for venting, flaring or re-using. The
16 liquid overflows the compartment weir and separates by gravity separation into
17 hydrocarbon and water layers. These liquids are individually removed through suitable
1 8 outlets.
19 The patented separator (developed by the present assignee) has been
commercially successful. However there is on-going need to reduce the size of the
21 separator, both to reduce the vessel cost and transportability for smaller wellsites
22 and/or off-shore drilling platforms.
23 The present invention is directed to achieving these ends.
~! 9~801
SUMMARY OF THE INVENTION
2 In accordance with the preferred form of the present invention, there is
3 provided a separator comprising:
4 ~ A vertical cylindrical pressure vessel forming an internal chamber;
~ A tapered feed pipe extending into the upper end of the chamber,
6 for introducing pressurized drilling fluid returns;
7 ~ A cluster of vertical, cylindrical vortex tubes connected with the
8 feed pipe, with each tube having an inlet at its upper end. The
9 inlet is arranged so that returns are tangentially introduced into
each tube. The tube has transverse top and bottom walls, the
11 top wall having a central opening for gas oufflow, the tube
12 sidewall having peripheral bottom openings for liquid and solids
1 3 oufflow;
14 ~ A vortex breaker plate is situated below the vortex tubes for
stopping the gas vortex from reaching the fluid section;
16 ~ The vessel sidewall section, that extends down from the bottom
17 of the vortex tubes, and the curved bottom head together form a
18 lower chamber section;
19 ~ The solids settle out in the lower chamber section and are
concentrated as they move to a central bottom outlet formed by
21 the head, the outlet being connected with a solids slurry
22 withdrawal pump. The liquid migrates upward; forming a liquid
23 layer in the vessel chamber;
2 1 9480 1
~ The vessel sidewall has water and hydrocarbon outlets situated
2 above the bottom of the vortex tubes at different elevations.
3 These outlets serve to individually discharge oil and water into
4 discharge lines;
~ A transverse baffle is located above the vortex cluster tubes - the
6 gas flows upwardly and contacts the baffle, for removal of
7 entrained liquid in the gas;
8 ~ The vessel has an outlet, at its upper end, for discharging gases
9 into a gas line; and
~ The vessel has means, such as floats, for controlling the
11 discharge of water and hydrocarbons through their discharge
12 outlets, as well as to maintain pre-determined fluid levels.
13 In operation, the feed pipe delivers equal amounts of drilling fluid returns
14 at about the same velocity into each of the several vortex tubes forming the cluster.
15 The incoming fluid enters tangentially into each tube. A central gas vortex is formed,
16 which discharges upwardly out of the tube into the upper reaches of the vessel
17 chamber, impinging on a baffle. The gases are discharged through the gas outlet and
18 gas line. The solids concentrate as a downwardly moving, rotating layer pressing
19 against the inside surface of the tube. The liquid concentrates as a downward moving,
20 rotating layer between the solids and the gas. The solids and liquids contained inside
21 each vortex tube are forced downward to the bottom of the tube and are discharged
22 through the peripheral bottom openings. The bottom section of the tubes may have
23 a vortex breaker plate or a series of elbows to eliminate the vortex. In the lower
24 chamber section, the solids settle downward, concentrated by the curved head, and
25 are subsequently withdrawn by the slurry pump through the bottom outlet. The liquid
21 ~4~01
leaving the tubes collects and forms a separate layer external to the vortex cluster in
2 the chamber. This layer submerges the bottom of the vortex tubes and keeps the gas
3 vortex from reaching the discharged liquid. As a result, the solids and the liquid in the
4 vessel chamber remain relatively quiescent. This enables efficient separation of the
liquid and solids. The liquid in the layer further separates into water and hydrocarbon
6 layers, which are individually removed.
7 It has been found that a much smaller sized vessel, in accordance with
8 the invention, will provide efficient separation comparable to the prior art horizontal
9 vessel.
In one broad aspect, the invention comprises a separator for separating
11 the liquid, solids and gas components of pressurized drilling fluid returns from a well
12 undergoing drilling, comprising: a vertical cylindrical pressure vessel having top and
13 bottom end walls and a side wall, said walls forming an internal chamber; a cluster of
14 vertical vortex tubes positioned within the chamber and located above the vessel's
bottom end wall, so that a chamber bottom section extends below the bottom ends of
16 the vortex tubes; each vortex tube having a side wall forming a bore, said side wall
17 having an inlet at its upper end for tangentially introducing the returns into the bore, the
18 vortex tube being open at its upper end and closed by a transverse plate at its lower
19 end and having at least one peripheral opening at its lower end for discharging the
liquid and solids; means for feeding returns to each vortex tube through its inlet; the
21 vessel bottom wall being elliptical and having a central outlet; means for withdrawing
22 solids through the vessel bottom wall outlet; outlet means for discharging gas from the
23 upper end of the vessel; and outlet means, located above the bottom ends of the
24 vortex tubes, for discharging hydrocarbons and water separately through the vessel
side wall.
21 ~4801
In another broad aspect, the invention comprises a method for separating
2 the components of pressurized drilling fluid returns produced from a well undergoing
3 drilling, said fluid comprising bit cuttings, liquid, which may include produced oil, and
4 gas, comprising: providing a vertical pressure vessel having top, bottom and side
5 walls which form an internal chamber, said vessel containing at least one vertical
6 vortex tube having a top opening, a closed bottom end and a peripheral side opening
7 at its bottom end, said vessel having a returns feed pipe connected with the upper end
8 of the vortex tube for feeding returns tangentially to the inner surface of the vortex
9 tube, the bottom end of the vortex tube being spaced above the vessel bottom wall so
10 that the vessel chamber includes a bottom section between the vessel bottom wall and
11 the bottom end of the vortex tube, the vessel bottom wall having a central outlet at the
12 base thereof for solids removal, the vessel side wall having liquid discharge outlets
13 spaced above the bottom end of the vortex tube, the vessel having a gas outlet at its
14 upper end, said method comprising: feeding returns tangentially into the upper end of
15 the vortex tube so that they rotate downward through the tube bore and form a central
16 gas vortex, an outer layer of solids and an inner layer of liquid; discharging the gas
17 out of the upper end of the vortex tube and through the gas outlet; discharging liquid
18 and solids from the vortex tube through its peripheral opening into the chamber bottom
19 section and temporarily retaining them in the chamber so that they separate by gravity
20 separation under quiescent conditions to form a bottom layer of solids and an upper
21 layer of liquid; withdrawing solids through the vessel's bottom wall outlet while
22 maintaining the inflow of returns into the vessel; and discharging liquid through the
23 liquid discharge outlets at restricted rates so that the bottom outlet of the vortex tube
24 remains submerged.
21 94801
DESCRIPTION OF THE DRAWING
2 Figure 1 is a side view of the separator, showing the internals in shadow
3 lines;
4 Figure 2 is a top view of the separator;
Figure 3 is a process schematic of the separator assembly, showing the
6 flow directions and discharge lines;
7 Figure 4 is a top plan view of the separator showing its discharge lines;
8 Figure 5 is a side view of the liquid discharge lines; and
9 Figure 6 is a bottom view showing the solids slurry removal assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENT
11 The separator 1 comprises a vertical cylindrical pressure vessel 2 having
12 a side wall 3 and elliptical top and bottom heads 4,5. The vessel forms an internal
13 chamber 6.
14 A known vortex tube cluster assembly 7 is mounted in the chamber 6.
This assembly is available from Porta-Test International Inc., Edmonton, Alberta.
16 The assembly 7 comprises a tapered feed pipe 8 and one or more
17 vertical vortex tubes 9 connected thereto. Each vortex tube has an inlet 10 at its upper
18 end which communicates with the bore 30 of the feed pipe 8. The connection of the
19 feed pipe 8 with each vortex tube inlet 10 is such that incoming returns are fed
tangentially relative to the inner surface 11 of the vortex tube. The vortex tube 9 has
21 a transverse top wall 12 forming a central opening 13 for the release of the gas
22 component. The vortex tube also has a transverse bottom wall 14 closing its bottom
23 end. The vortex tube side wall 15 forms peripheral openings 16 at its bottom end for
24 the discharge of liquid and solids. T he tapered feed pipe 8 is designed to supply
21~4801
approximately equal amounts of returns to each vortex tube at about the same fluid
2 velocity.
3 A horizontal vortex breaker plate 14 is suspended from the bottom ends
4 of the vortex tubes 9 in close proximity to the peripheral openings 16. The breaker
plate 14 extends laterally beyond the vortex tubes but is inwardly spaced from the
6 vessel side wall 3.
7 The bottoms of the vortex tubes 9 are spaced above the bottom head 5,
8 so as to form a lower section 20 of the chamber 6. The tops of the vortex tubes 9 are
9 spaced below the top head 4 to form an upper section 50 of the chamber 6.
A pair of liquid outlets 21, 22 extend through the vessel side wall 3 at
11 positions above the bottoms of the vortex tubes 9. The outlets 21, 22 are vertically
12 spaced apart whereby the lower outlet 21 is used to discharge water and the upper
13 outlet 22 discharges oil. A pair of openings 23, 24 are positioned above the liquid
14 outlets 21, 22 respectively. Conventional float assemblies 25, 26 are mounted in the
openings 23, 24 to actuate conventional dump valves 27, 28 to maintain pre-
16 determined liquid levels as well as to control the discharge of water and oil through
17 lines 29, 31 respectively.
18 The bottom head 5 forms a central outlet 32 which is connected to a
19 slurry pump 33 by a solids discharge line 34. The pump 33 is used to withdraw solids
form the base of the separator under pressure while the inflow of the returns is21 continued.
22 Installed in the top head 4 is a central baffle deflector 38, against which
23 the gas impinges, to trap residual liquid droplets in the gas. The deflector 38 is
24 inwardly spaced from the vessel side wall 3. The gas discharges through outlet 36
which connects with a gas discharge line 37.
2 1 94801
In operation, the incoming returns are tangentially introduced through
2 feed pipe 8 and inlets 10 into the bores 35 of the vortex tubes 9. Each vortex tube
3 receives about the same amount of returns moving at about the same velocity. In each
4 vortex tube, the returns stream components separate under the influence of centrifugal
force to form: a central gas vortex, which reverses itself and exits upwardly through
6 the opening 13, across the baffle 38 and exits through outlet 36 and gas discharge line
7 37; an outer layer of solids which rotates downward through the vortex tube bore 35
8 and discharges through the vortex tube bottom peripheral openings 16; and an
9 intermediate layer of liquid located between the gas vortex and the solids layer, which
also rotates downward through the vortex tube bore 35 and also discharges through
11 the bottom peripheral openings 16. In the chamber lower section 20, the solid bit
12 cuttings settle and separate from the liquid. The cuttings are concentrated as they
13 funnel through the diminishing cross-sectional area defined by the bottom head 5 and
14 are withdrawn from the chamber 6 by the pump 33 and are discharged through the line
37. The liquid collects as a separate layer in the chamber 6 above the solids layer.
16 Oil and water separate in this layer by gravity separation. The water and oil are
17 individually dumped through lines 29, 31 under the control of float assemblies 25, 26
18 and dump valves 27, 28. The layer or level of liquid in chamber 6 covers the vortex
19 tube peripheral openings 16 to provide an effective seal that prevents gas from
escaping or blowing out of the vortex tube bottom openings.
21 The separation process in the separator is characterized by the following
22 advantages:
23 ~ the gas is efficiently separated in the vortex tubes, and is
24 removed as an upwardly moving stream, so that it does not
create a turbulence that would disturb liquid and solids;
21 ~4801
~ the solids and liquids separate efficiently in the chamber outside
2 the vortex tubes, under quiescent conditions;3 ~ there is improved efficiency of the separation process utilizing a
4 mechanical device (vortex cluster); and
~ due to these improved efficiencies, a smaller sized vessel can be
6 used.
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