Polymer flow control apparatus

Flow control of diluted polymer solutions is effected by utilizing positive-displacement flow devices such as gear pumps to withdraw flow energy in the form of shaft work. Control is obtained by varying the nature and amount of shaft work withdrawn, such as by operation of an electrical generating system, and the work so created may be used to provide operating power to a control system.

TECHNICAL FIELD 
The present invention relates to apparatus for controlling the flow of 
polymer solutions while minimizing degradation of the polymer and, in 
particular, to apparatus utilizable for the on-site flow control of 
diluted solutions of a partially hydrolyzed polyacrylamide for use in the 
secondary and tertiary recovery of oil from subterranean rock formations. 
BACKGROUND OF THE PRIOR ART 
Use of aqueous solutions of polymers such as a partially hydrolyzed 
polyacrylamide (PHPA) to recover residual oil from oil-bearing 
subterranean rock formations is well known. In secondary recovery 
operations, after normal drilling and pumping operations, the subterranean 
rock formation is flooded through an input well with a polymer solution 
and the resulting admixture of polymer solution and oil is forced to an 
output well head where it is pumped from the ground. In tertiary 
operations, recovery of residual oil is first accomplished by flooding the 
rock formation with water and, thereafter, flooding with a polymer 
solution. 
Through extensive research in the use of polymer solutions in secondary and 
tertiary oil recovery operations, it has been discovered that a polymer 
solution can be tailor-made, so to speak, to meet the performance demands 
of substantially any oil-bearing subterranean formation. More specifically 
in this connection, it has been found that such considerations as the 
average molecular weight and the molecular weight distribution properties 
of a polymer comprising the polymer solution can significantly augment and 
enhance oil recovery thereby resulting in important reductions in recovery 
costs. 
In the case of solutions of PHPA, care must be taken in formulating, 
diluting, and handling the solutions in order to limit the breaking up or 
"degrading" of the polymer and thus to preserve to the greatest extent 
possible its preselected average molecular weight and molecular weight 
distribution properties. The on-site and on-demand production and use of 
PHPA accentuates the problem of polymer degradation. 
Apparatus for the production and dilution of PHPA may be maintained on a 
continuous basis. The direction and control of flow of the aqueous PHPA as 
it is transported to the point of injection into an oil-bearing formation 
are critical in maintaining the integrity of the polymer. Mechanical 
stress, such as that induced by abrupt changes in flow direction, 
turbulent flow, and travel through partially closed valves or other flow 
control devices contribute to the degradation of the polymer solution, and 
adversely affect such properties as the polymer's mobility, injectivity, 
brine tolerance, and resistance to further thinning induced by shear 
forces. 
The systems presently used to prepare and inject aqueous PHPA solutions for 
oil recovery purposes can be preassembled and mounted on skids, for 
example, for ready transport to and from a site where recovery is to take 
place. Such a system may include a monomer supply, a source of water, 
polymerization apparatus, catalyst feed and monitoring equipment, 
hydrolyzation apparatus including means for feeding a controlled amount of 
a hydrolyzing agent into the polymer stream, and apparatus for diluting 
the hydrolyzed polymer and injecting it into an input well penetrating a 
reservoir of interest. 
A system of this type is capable of producing a broad spectrum of polymers 
of varying average molecular weight and molecular weight distribution to 
meet the permeability demands of substantially any oil-bearing formation 
being worked. Once the parameters are determined, the system can produce a 
polymer having the desired properties. The present invention, in one of 
its aspects, is intended to maintain the preselected characteristics of 
the polymer solution as the solution is moved through a system to the 
input well, while enabling the rate of solution flow to be properly 
controlled. 
In the past, flow control expedients have included varying the length of 
pipe through which the polymer solution is transported or the use of sand 
packs. These techniques are unsatisfactory because they are cumbersome, 
and require much time and labor to effect flow changes. 
Other prior art efforts involving the manufacture and transport of polymer 
solutions have not addressed the particular problems solved by the present 
invention. 
U.S. Pat. No. 3,034,526, for example, describes a three-dimensional 
T-shaped cascade system intended to prevent the degrading of molten, 
highly viscous linear polymers such as nylon, but does not teach a simple 
and efficacious manner to vary polymer flow rates while avoiding 
degradation. 
U.S. Pat. No. 3,128,794 describes apparatus for moving molten polymers 
through pipe lines and using inverters positioned in the flow path of the 
polymer to equalize residence time between the polymer flow segment at the 
outer periphery of the pipe line and the flow segment at the center of the 
pipe line. The patent merely teaches the diversion of polymer flowing 
along the conduit walls toward the conduit center, and vice versa, without 
controlling the rate of flow. A similar consideration, pipeline residence 
time, is addressed in U.S. Pat. No. 3,353,564, which uses a plurality of 
screens spaced apart one from the other and placed in the material flow 
path. The positioning of such screens is intended to prevent thermal 
degradation of the polymer by flattening the velocity profile of the 
polymer to equalize flow rates rather than to set flow rates. 
U.S. Pat. No. 3,945,402 teaches a pipe system incorporating turbulence 
control apparatus which includes spaced-apart screens positioned within a 
tapered pipe run. The internal wall roughness of the '402 apparatus is 
selected to achieve laminar flow at Reynolds numbers in excess of 2200. 
Although use of valves and pumps in the system is described, no teaching 
is found concerning use of a system to control the transport of 
mechanically degradable polymer solutions. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
In accordance with the present invention, apparatus is provided to control 
the flow of aqueous polymer solutions, such as PHPA, in a manner to 
effectively minimize polymer degradation. The apparatus employed allows 
for efficient and effective flow control without requiring time-consuming 
changes in pipeline length, or the use of inefficient sand packs. In 
addition, the apparatus finds particular application in on-site liquid 
transport systems which can be set up in the field, and easily moved or 
rearranged. The improved results in flow control moreover are achieved 
while simultaneously generating significant amounts of energy which can be 
utilized for automatically controlling the flow rate of the polymer 
stream, as well as for the energization of other equipment at the input 
well site. 
To this end, the apparatus described herein employs positive-displacement 
fluid flow control means positioned strategically along the path of flow 
of the polymer solution. Examples of such flow control means are flow 
meters, such as oval gear meters, birotor meters, or oscillating piston 
meters, piston-type pumps, vane pumps, gear pumps, and hydraulic motors. 
Flow control is obtained by varying the rate at which energy is removed 
from the polymer stream by the flow control means. Control of such energy 
removal can occur in many forms, such as by transforming the energy 
created by the polymer stream to a different form of energy. In accordance 
with one embodiment of the invention, an electrical generator, coupled to 
the flow control means, provides a field current or electrical load 
capable of varying the amount of work performed by the flow control means. 
In accordance with another aspect of the invention, the energy output of 
the generator coupled to the flow-control means can be used as a source of 
power for an automatic control system. Controls may be provided to set a 
desired flow rate, to measure the actual flow rate, and to adjust the flow 
rate to approximate the set rate by varying the resistance of the flow 
control means. Any excess power from this arrangement can be utilized to 
energize a lighting system, for example, at the input well site. 
Mechanical loads may also be coupled to the output of the flow control 
device, and thus used to absorb the work extracted from the flowing 
polymer stream. 
The foregoing, and other features and advantages of the present invention 
will become more apparent upon consideration of the following description 
and the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
While the present invention finds utility in the flow control of various 
polymer solutions, generally, the embodiments shown and described herein 
have special utility for controlling the flow of aqueous solutions of PHPA 
in conjunction with secondary and tertiary oil-recovery procedures. 
The on-site preparation of aqueous PHPA solutions involves the steps of 
polymerizing an acrylamide monomer in the presence of a suitable initiator 
or catalyst, preferably a co-mixture of ammonium persulfate and sodium 
bisulfite. After polymerization is complete, partial hydrolysis is carried 
out by adding to the polymer an amount of monovalent base, such as sodium 
hydroxide or potassium hydroxide, sufficient to hydrolyze about 20 to 
about 40 mole percent of the amide groups. Following hydrolyzation, the 
solution is diluted to about 1% or about 2% for temporary storage or for 
immediate injection into an input well. Careful regulation of the 
polymerization process produces aqueous PHPA solutions of predetermined 
properties which are matched to the performance demands of an oil-bearing 
formation of interest. Eventual transport to the well site for injection 
must then be accomplished in such a manner as to minimize any polymer 
degradation. 
Referring now to FIG. 1 of the drawing, the numeral 10 indicates generally 
a schematic representation of one embodiment of a flow control system of 
the present invention. An aqueous polymer solution diluted as described 
hereinabove, to a concentration of about 1-2%, flows through polymer 
stream inlet 11 to a hydraulic gear pump 12, and thence to polymer stream 
outlet 13. Thereafter, the polymer stream is directed to a well head 14 
for injection into an oil-bearing reservoir. 
Gear pump 12 may be of the type having two or more meshing gears, and is 
designed to be actuated by the passage of fluid therethrough. Other 
hydraulic motors, such as those of the piston type, or vane type, may also 
be employed. An important consideration is to have the internal structure 
and geometry of the pump such that passage therethrough of the PHPA 
solution does not induce polymer degradation. 
In order to control the rate of flow of the polymer solution, and to effect 
a pressure drop across the pump 12, means are provided to extract energy 
from the polymer stream as it passes through pump 12. In more conventional 
flow systems, flow control is accomplished through use of control valves, 
the closing of which presents progressively increased physical resistance. 
Such techniques are not suited for use with polymer solutions of the type 
and for the use hereinabove described, because such resistance can result 
in excessive degradation of the polymer. 
As shown in FIG. 1, the output shaft 15 of gear pump 12 is coupled to a 
drive shaft 16 of an electrical generator 17 by a coupling 18. A flywheel 
40 desirably may be positioned between the pump 12 and the generator 17 to 
store mechanical energy. This will help maintain a steady speed and flow 
rates. The electrical output of the generator 17 may be absorbed by a 
selectively variable load depicted at 19 via transmission lines 20 and 21. 
Load 19 may, of course, take whatever form is most useful, given the 
character of the output of the generator 17, and may even be used to power 
an automatic control system of the type described hereinbelow, to operate 
electric lights, to recharge electrical equipment, or to perform other 
useful applications. 
In FIG. 2, the embodiment of the present invention illustrated incorporates 
an automatic flow measurement and control system powered by a portion of 
the output of generator 17. 
A comparator 22 is provided to receive flow rate data via a detector 
connection 23 which, in turn, is connected to a flow detector capable of 
providing an electrical signal which varies as the rate of flow varies. As 
an example, a magnetic pickup may be mounted to pump 12 to measure rpm, 
and the resulting output converted to an electrical signal. Comparator 22 
includes means to set a flow rate, or range of rates, to which the actual 
flow rate may be compared. When the actual flow rate varies sufficiently 
from the set value, comparator 22 will detect this difference, or "error", 
and will activate means to vary the resistance to rotation of generator 
17. In the system shown in FIG. 2, means are provided to alter variable 
resistance 19 responsive to an electrical signal transmitted via a control 
line 24. Another means for accomplishing this result would be to vary the 
field current responsive to the error detected by the comparator 22. 
The above-described control system is powered by a portion of the 
electrical output of the generator 17 via power lines 25 and 26. It should 
be understood that well-known expedients may readily be interposed between 
generator 17 and comparator 22 to ensure that the resulting voltage is in 
a form appropriate for use by the comparator 22. A backup source of 
electrical power may also be employed should the output of generator 17 
fall to a level wherein comparator 22 cannot operate. 
Generator 17 may also power alternative control systems, such as those 
powered by compressed air, by providing the power to operate a compressor 
which, in turn, provides power for compressed-air control devices. Use of 
such a hybrid system may be desirable where flammable process components 
are involved, calling for minimum use of electrical apparatus. 
The above-described systems may be readily adapted for manual operation to 
allow adjustment of the flow rate by manual adjustment of load 19. 
Referring now to FIG. 3, there is depicted a schematic representation of a 
hydraulic gear pump 27 found suitable for use with the present invention. 
Incoming PHPA solution is directed to inlet 28, and enters pump inlet 
chamber 29. Upper gear 30 and lower gear 31 are rotatably mounted within 
pump housing 32, with upper gear 30 keyed to output shaft 33. 
In the embodiment depicted, upper gear 30 rotates in a clockwise direction, 
while lower gear 31 moves in a counter clockwise direction when contacted 
by incoming polymer solution. Individual increments or "bites" of solution 
are trapped between adjacent gear teeth, as in space 34 between teeth 35 
and 36, and are carried along as said teeth are "wiped" along the inner 
periphery of pump housing 32. As the solution reaches pump outlet chamber 
37, the meshing of gears 30 and 31, at 36, forces the solution to outlet 
39. Rotation of shaft 33 provides motive force for the generator 17. 
Exemplary of a pump which can be used effectively as part of the present 
invention is a fixed-displacement hydraulic gear pump manufactured by the 
Viking Pump Division of Houdaille Industries, Cedar Falls, Iowa, under the 
model designation GP-0514 and having a capacity measured at 3.22 
gallons/minute at 1,000 rpm. 
By way of illustrating the power generating capabilities of the flow 
control system of the present invention, the mechanical energy balance of 
the pumping process is: 
dWs=VdP-dF where 
Ws=shaft work realized 
V=Volume 
P=Pressure 
F=Friction work 
If it is assumed that friction losses are negligible, then the foregoing 
equation reduces to: 
EQU Ws=6.9.times.10.sup.-3 Q.DELTA.P=watts 
where Q=BPD (barrels per day) 
.DELTA.P=psi 
Assuming that a solution having a concentration of 1000 ppm of PHPA is 
available from a supply manifold at 600 psi, and it is desired to inject 
the solution into an input well at the rate of 100 BPD at 150 psi, the 
energy extracted by a system such as those illustrated in FIGS. 1 and 2 
would be equivalent to 310 watts. This energy, as indicated, could be 
utilized to energize light bulbs, or the like. If the differential 
pressure, .DELTA.P, changed for some reason, the light wattage could be 
changed to compensate in the following way: 
______________________________________ 
.DELTA.P, psi 
Ws, watts 
______________________________________ 
100 69 
200 138 
300 207 
400 276 
500 345 
______________________________________ 
It should be understood that the substantial drops in pressure across the 
gear pump, and the concomitant extraction of appreciable energy, are 
achieved with no, or minimal, polymer degradation. 
Where additional degrees of control are required, more than one 
positive-displacement flow element, such as gear pump 12, may be used in 
flow lines carrying diluted polymer solutions. 
It should also be understood that variations in concentration in the 
aqueous PHPA solution, and external factors such as ambient temperature, 
may affect the limits to which flow resistance may be applied without 
causing an undue amount of polymer degradation. Use of the 
before-described apparatus may be varied to take such factors into 
account, and it may be more efficacious under such circumstances to 
utilize several such flow devices simultaneously, rather than a single 
device. 
While the foregoing description has presented specific aspects of preferred 
embodiments of the present invention, it is to be understood that these 
embodiments have been presented by way of illustration only and not by way 
of limitation. It is expected that others skilled in the art will perceive 
differences which, while varying from the foregoing, do not depart from 
the spirit and scope of the invention as herein described and claimed.