Continuous mixing device, method and use in an installation for pumping a high viscosity fluid

The invention concerns a continuous mixing device (1) having a rotating shaft (4) fitted with blades (7, 7a). The mixture obtained at the outlet from the mixer results from admitting to the mixer a high-viscosity fluid (22) and at least one fluid of a lower viscosity. The mixing device is suitable for providing a mixture of lower viscosity compared with the most viscous fluid admitted at the inlet (2, 38) of the mixer. The invention provides a method of pumping a viscous fluid and use of the mixing device in an installation for pumping a high viscosity crude oil. FIG. 1 to be published.

The invention concerns a continuous mixing device intended for mixing in 
particular high-viscosity crude oil with at least one other less viscous 
fluid in order to obtain a mixture with a much lower viscosity than the 
said crude oil, the mixture being more efficiently moved by pumping by 
conventional systems. 
Current developments in petroleum production result in the exploitation of 
deposits of viscous oil, notably from wells having parts which are 
horizontal or steeply inclined with respect to the vertical passing 
through the deposit. 
Where pumping by pipe is technically impossible or economically 
unprofitable, the use of rotary pumps, either centrifugal or positive 
displacement, has to be considered. But these pumps cannot function 
properly with high viscosity fluids. 
Through the document U.S. Pat. No. 4,721,436, a method and installation for 
pumping viscous oil are known. This document describes the use of a 
centrifugal pump driven in rotation by a hydraulic turbine operated by 
injecting, from the surface, a driving fluid which is partly injected at 
the pump inlet in order to decrease the viscosity of the oil in the pump. 
This installation does not have any mixing device upstream of the pump. In 
this system the mixing takes place internally to the pump. 
Through the patent application FR-2656035 a device is known for pumping a 
high-viscosity liquid, but the entire volume of the driving fluid is mixed 
with the crude oil. Moreover, this installation does not disclose any 
dynamic and continuous mixing device located upstream of the pump. 
Advantageously the invention improves the prior art notably by the use of a 
mixing device separate from the pump and allowing suitable adjustment of 
the physical characteristics of the mixture conveyed to the pump inlet. 
The object of the present invention therefore concerns a continuous mixing 
device including a body in which fluids flow between an inlet and outlet 
of the said body and at least two fluids with different viscosities 
entering through the said inlet. The device includes a rotating shaft 
having at least two blades and it is suitable for supplying, at the outlet 
from the body, a mixture of the said two fluids, the said mixture having a 
viscosity less than that of the most viscous fluid entering. 
The profile of the blades can be such that, without any flow, the rotation 
of the blades produces a reaction force substantially parallel to the axis 
of rotation and directed in the same direction as the flow when the latter 
is established. 
In another variant, the profile of the blades can be such that, without any 
flow, the rotation of the blades does not produce a reaction force of any 
notable magnitude parallel to the axis of rotation. 
The device can include at least one assembly of three stages of blades, 
where each stage can consist of at least two blades having the same 
cylindrical volume generated by revolution. The stages can be offset by 
120.degree. with respect to the axis of the shaft and the cylindrical 
volumes generated by the revolution of each stage can be approximately 
adjacent. 
The device can include four assemblies and the stage can have two blades 
disposed at 180.degree.. 
The shaft can be connected with respect to rotation to the shaft of a 
hydraulic pump and the outlet from the body can open into the inlet to the 
pump. 
The pump can be rotated by a hydraulic motor, which can itself be rotated 
by the injection of a fluid under pressure. 
Some of the pressurised fluid injected into the motor can be conveyed to 
the inlet of the said body. 
The body of the device can advantageously include deflectors, the inner 
edges of which are approximately tangent to the volume of revolution of 
the blades. 
The invention also concerns a method for pumping a high-viscosity fluid in 
which the fluid and at least one other fluid of lower viscosity are 
conveyed to the inlet of a mixing device according to the invention, the 
mixture at the outlet from the body being conveyed to the inlet of a pump. 
In the method, some of the driving fluid can be conveyed to the inlet of 
the body, the said driving fluid being injected under pressure in order to 
rotate the hydraulic motor for driving the pump and device in rotation. 
The invention also concerns the use of the mixing device according to the 
invention in an installation for pumping a high viscosity crude oil in a 
well incorporating a casing. The installation has a pipe for feeding the 
crude to the inlet of the device, a pipe connecting the outlet from the 
device to the inlet of a pump, a hydraulic motor for rotating the pump and 
the device, a pipe for injecting driving fluid connecting an injection 
installation on the surface to the motor, an outlet pipe from the pump 
conveying the mixture to the surface again and an outlet pipe from the 
motor conveying some of the driving fluid to the surface again, the 
remainder being conveyed to the inlet of the device through another pipe. 
In a first variant of the use, a sealing means can be positioned between 
the crude feed pipe and the walls of the well defining an annular pipe 
communicating as far as the surface and the pumped mixture can travel to 
the surface through the annular pipe. 
In a second variant, a single pipe can convey the part of the driving fluid 
and the mixture upwards and at the surface this pipe can communicate with 
an installation for separating notably the crude oil and the driving 
fluid.

In FIG. 1, the mixer 1 is incorporated in a housing 12 secured to the body 
of the pump, which is not shown in this figure. The pipe 8 connects the 
reserve of crude oil to the inlet 2 of the body 17 of the mixer 1. An 
orifice 9 connects the duct 10 to the inlet 2 of the mixer. The duct 10 is 
notably located in the wall of the housing 12. 
The outlet 3 from the body 17 of the mixer 1 communicates with the inlet 13 
of the centrifugal pump, the first wheel of which is given the reference 
number 14. 
A cylindrical shaft 4 is guided at both ends by the bearing 6 and a means 5 
of connection to the shaft of the centrifugal pump. 
The shaft 4 has pairs of blades 7 and 7a, symmetrical with respect to the 
axis of the shaft 4 and located in the same cross section. In this 
embodiment, the shaft is fitted with twelve pairs of blades disposed over 
the length of the shaft so that the top edge of a blade is substantially 
in the same cross section as the bottom edge of the adjacent blade. Thus 
each revolution volume generated by the rotation of a pair of blades is 
substantially adjacent to the following one. 
The blades are inclined at an acute angle i with respect to the axis of the 
shaft oriented in the direction of flow, that is to say in the direction 
of the arrow 15, the direction of rotation of the shaft being indicated by 
the arrow 16. This mode of orientation of the blades relative to the 
direction of rotation of the shaft and in the direction of flow of the 
fluids in the mixer produces a reaction force on the shaft in the same 
direction as the flow. This force is the axial component of the resultant 
of the reaction forces on each blade. In fact, the rotation of these 
helixes formed by all the blades has a tendency to repel the fluid in the 
opposite direction to its flow. In this profile arrangement, the mixer can 
be compared to a repulsion screw. This arrangement assists the action of 
stirring the fluids in the mixer in order to obtain a homogeneous mixture. 
It would not be a departure from the scope of this invention if the cross 
section of the blades were not inclined as above. In certain cases of 
simplified use, the blades can in particular be flat and their width 
disposed parallel to the axis of the shaft, that is to say the angle i is 
zero. The blades can also have a substantially cylindrical shape. In a 
more general sense, it could be said that in this embodiment the mixer 
will neither repel nor attract with respect to the flow. The mode of 
action is then close to an action of shearing the fluid stream flowing 
through. 
In none of the embodiments can the blades of the continuous mixer have an 
action bringing about an acceleration of the flow, like an attraction 
screw or a centrifugal pump wheel. In other words, the mixer of our 
invention is completely different from a compression element, whether this 
is a pump element, a booster element or a priming element. On the 
contrary, the mixer of our invention brings about a pressure drop, 
generally minimal but nevertheless perceptible. 
The pairs of blades are distributed on the circumference of the shaft with 
an angular offset of 120.degree.. Thus the fourth blade has the same 
angular position as the first one, thus defining an assembly of three 
pairs of blades. The embodiment shown therefore has four of these 
assemblies. 
Without departing from the scope of this invention, the number or 
arrangement of the blades could be different. In fact, depending on the 
nature of the fluids and their flow rate in the mixer, the number of 
blades could be increased or decreased, and more than two blades could 
even be disposed in the same cross section. In this case, they will be 
distributed evenly on the circumference of the shaft. Moreover, the value 
of the angle i can be variable but equal to or less than 90.degree., 
having regard to the references indicated above. 
FIG. 2 shows in partial perspective view the arrangement thus obtained in 
the preferred embodiment. 
The body 17 of the mixer has deflectors 11 disposed in accordance with the 
generatrices of the internal cylindrical volume of the body. This 
embodiment has four deflectors distributed at 90.degree.. The deflectors 
can be produced in many diverse ways, their principal role being to 
redirect the fluid stream by assisting the turbulences created by the 
blades whilst allowing the fluid to flow between the inlet and outlet. 
In FIG. 3, three curves A, B and C have been traced, giving the viscosity 
variation in centipoise against temperature in degrees celsius. 
Curve A relates to an anhydrous heavy crude oil. 
Curve B gives the viscosity of an emulsion, 60% of which is the heavy oil 
of curve A and 40% water, the whole having passed through the mixing 
device of the invention at a flow rate of 2500 l/hour and at a speed of 
rotation of the mixer of 3000 rev/min. 
Curve C shows the viscosity of a mixture obtained in a receptacle from the 
same proportion of crude oil and water. 
The efficiency of the dynamic mixer compared with a static mixer (curve C) 
will be noted. 
FIG. 4 shows a pumping installation lowered into a well 20, in general 
lined with a casing 21. The well is in communication with a deposit of 
viscous oil. This oil flows into the well. The installation pump is 
immersed in the oil 22 at a suitable depth depending in particular on the 
characteristics of the deposit, the configuration of the completion and 
the static and dynamic level of the effluent. 
The bottom part of the installation is broken down as follows: 
23 indicates the crude oil feed pipe, 
24 indicates the continuous mixer, 
25 indicates the pump, 
26 indicates the hydraulic motor driving the pump and mixer. 
The top part 27 consists of concentric tubes, assembled as far as the 
surface, where there are located in particular an installation 28 for 
injecting the driving fluid, an outlet from a conduit 29 for collecting 
some of the driving fluid, an outlet from a conduit 30 for collecting the 
compressed mixture, an outlet from a degassing conduit 31 and the start of 
the conduit 35 for injecting the driving fluid. 
The conduit 35 connects the injection installation 28 to the inlet 33 of 
the hydraulic motor. 
The conduit 31 is an annular conduit defined by the well and the outside of 
the tubes and of the housings of the pumping installation. This conduit 
directly connects the crude oil reserve to the surface and makes it 
possible to collect the gas at the surface whilst allowing the oil to 
degas naturally. The more the fluid 22 is degassed, the better will be the 
efficiency of the pumping installation. 
The conduit 30 connects the outlet from the pump 34 to the surface. 
The conduit 29 connects the outlet 32 of the hydraulic motor. 
A conduit 37 connects the outlet 32 from the motor to the inlet 32 of the 
mixer 24. 
The feed conduit 23 has two concentric tubes 40 and 41 forming baffles in 
order to assist the degassing of the crude. The latter enters the conduit 
through the perforations 39, passes into the annulus of the tubes 40 and 
41 and then goes up the tube 41 to arrive at the inlet 38 to the mixer. 
The rotating shafts 42, 43 and 44 respectively of the mixer, pump and motor 
are connected with respect to rotation, that is to say the rotation of the 
motor shaft causes the rotation of the pump shaft and of the mixer shaft. 
It would not be departing from the scope of this invention if these three 
shafts were not identical and if their speeds were not identical. 
The motor 26 can be of the turbine or positive displacement type, for 
example according to the Moineau principle. The driving fluid can flow in 
the motor from bottom to top or vice versa. 
The pump can be of the single or multi-stage centrifuge type or of the 
positive displacement type, for example according to the Moineau 
principle. 
As an illustration, the dimensions of the triple concentric completion 
lowered into the lining 21 made from 95/8" casing can be: 7" casing or 
tubing for the conduit 30, 41/2" or 5" tubing for the conduit 29 and 2" or 
27/8" tubing for the conduit 35. 
In a first variant shown in FIG. 5, the installation is simplified from the 
point of view of the number of conduits compared with the preferred 
embodiment of FIG. 4, in which three concentric conduits 30, 29, 35 are 
used in the well 20, that is to say a triple completion. In fact, in cases 
where the crude oil does not degas, it is possible to install, on the 
lower body of the pumping assembly, a packer type sealing element 45 
between the oil supply conduit and the walls of the well. This packer 
isolates the reservoir zone and allows the use of the annular conduit 46 
above the said packer for raising the mixture from the outlet 34 of the 
pump as far as the surface. The completion then has two tubes 29 and 35 
for respectively raising some of the driving fluid and injecting driving 
fluid. 
A second variant of the pumping installation is shown in FIG. 6. In this 
case the pumped mixture and the portion of the driving fluid are pumped up 
together. The outlets 32 and 34 respectively from the motor and pump 
communicate in a single conduit 47. This conduit is connected at the 
surface to an installation 48 suitable for separating the crude oil, 
driving fluid and other fluids in the mixture if these are not the driving 
fluid. At the outlet from the separation installation, a conduit 49 
recovers the driving fluid so that it can be recycled in the injection 
installation 28. 
The conduits 29, 30 and 35 can be other than concentric, and indeed the 
prior art included multiple non-concentric completions, ie using parallel 
tubes in the well 20. 
Without departing from the scope of this invention, the lower-viscosity 
fluid admitted to the mixer inlet through the orifice 9 could be different 
from the driving fluid used for driving the pumping installation. In 
addition this lower viscosity fluid may have several constituents suitable 
for assisting the mixing. In this case another separate feed line 
connected to the surface could be used. 
The fluid or fluids mixed with the high-viscosity fluid can be of mineral 
or organic origin. The mixture obtained by the mixer according to the 
invention will be an emulsion and/or dilution. 
The proportions of the constituents of the mixture can be variable 
according to the characteristics of the deposit and the nature of the 
fluids in situ. In the case of the installation of FIG. 4 and its variants 
in FIGS. 5 and 6, means for regulating the flow of fluid injected at the 
inlet to the mixer are notably located between the outlet from the motor 
and the conduit 10 or 37. 
Without departing from the scope of the invention, the well could have an 
inclined portion and could even be close to the horizontal. The pumping 
installation is then in general lowered into a highly inclined part of the 
well.