U.S. patent number 3,889,579 [Application Number 05/431,124] was granted by the patent office on 1975-06-17 for oil well pumping system having reinforced plastic sucker rod.
This patent grant is currently assigned to Poly-Trusions, Inc.. Invention is credited to Richard C. Kostner, Delmar S. Miller, Joseph W. Wiechowski.
United States Patent |
3,889,579 |
Wiechowski , et al. |
June 17, 1975 |
Oil well pumping system having reinforced plastic sucker rod
Abstract
A system for pumping oil and a method for constructing a system
in which a pump, disposed at the bottom of the well, is connected
to the pump drive, at the top of the well, by a single length of
reinforced plastic sucker rod having specific constructions and
characteristics is disclosed.
Inventors: |
Wiechowski; Joseph W. (San
Clemente, CA), Miller; Delmar S. (Newport Beach, CA),
Kostner; Richard C. (Orange, CA) |
Assignee: |
Poly-Trusions, Inc. (Santa Ana,
CA)
|
Family
ID: |
23710577 |
Appl.
No.: |
05/431,124 |
Filed: |
January 7, 1974 |
Current U.S.
Class: |
92/3; 166/68;
417/545; 92/222; 166/72 |
Current CPC
Class: |
F04B
53/144 (20130101) |
Current International
Class: |
F04B
53/14 (20060101); F04B 53/00 (20060101); F04B
017/00 (); F04B 047/02 () |
Field of
Search: |
;417/545-554,437,572
;156/73,441 ;403/275,404 ;92/248,249,3,222 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Freeh; William L.
Attorney, Agent or Firm: Knobbe, Martens, Olson, Hubbard
& Bear
Claims
What is claimed is:
1. A pumping system for oil wells and the like which comprises a
pump in a well near the bottom thereof, a pump drive near the top
of the well, and a sucker rod drive connecting the drive to the
pump, the improvement wherein:
the sucker rod is of sufficient length to reach from the drive to
the pump, said rod being constructed of a multiplicity of glass
fibers bonded together into a semi-rigid rod by a set organic
resin; and
fittings affixed at the respective ends of the sucker rod for
connection to the pump and to the drive respectively.
2. The system defined in claim 1 wherein the sucker rod comprises a
single, continuous, semi-rigid rod consisting essentially of
generally parallel elongate glass fibers running lengthwise of the
rod and resin bonding the fibers together.
3. The system defined in claim 2 wherein the sucker rod comprises a
single, continuous, semi-rigid rod consisting essentially of
generally parallel elongate glass fibers running longitudinally of
the rod, thermoset resin bonding the fibers together, and a high
density filler, said rod having a density of at least about 1 pound
per foot and less than 4 pounds per foot sufficient to transmit
energy from the drive to the pump.
4. The system defined in claim 2 wherein the sucker rod comprises a
single, continuous, semi-rigid rod consisting essentially of
generally parallel glass fibers running lengthwise of the rod and
thermoset resin bonding the fibers together in a rod configuration
having a passageway extending along the length of the rod.
5. The system defined in claim 4 wherein the sucker rod comprises a
dense filler material in said passageway for at least a portion of
the length of the rod of give the rod an average density of greater
than 1 pound per foot and less than about 4 pounds per foot
sufficient to transmit pumping force efficiently to the pump.
6. The system defined in claim 4 wherein the sucker rod comprises
means in the passageway for permitting communication of sensing
signals or control signals between the pump and a station outside
the well.
7. The system defined in claim 2 wherein the sucker rod further
comprises at least one sheath enclosing the rod.
8. The system defined in claim 7 wherein the sheath comprises a
multiplicity of glass fibers having a substantial transverse
directional component bonded together to enclose the rod to thereby
increase the delamination resistance and abrasion resistance of the
sucker rod.
9. The system defined in claim 8 wherein the sheath comprises a
multiplicity of glass fibers running helically around the rod along
the length thereof, and thermoset resin bonding said helically
extending fibers together in at least one continuous sheath
enclosing the rod.
10. The system defined in claim 8 including a sheath which is an
extruded, flexible polymer layer having greater abrasion resistance
than the resin bonded glass fiber material.
11. The system defined in claim 8 wherein the sheath comprises a
multiplicity of glass fibers woven to form a fabric sheath around
the rod along the length thereof, and thermoset resin bonding said
fiber sheath together in at least one continuous sheath enclosing
the rod.
12. The system defined in claim 11 including a sheath which is an
extruded, flexible polymer layer having greater abrasion resistance
than the resin bonded glass fiber material.
Description
This invention relates to petroleum engineering and production, and
more specifically to systems and methods for pumping petroleum to
the surface in oil wells.
More particularly, this invention relates to the construction of a
system for pumping oil in which a single, continuous sucker rod
ranging from several hundred to several thousand feet in length is
run down the well and connected at the bottom to a pump and at the
top to a drive for the pump. A particular sucker rod comprising
glass fibers extending longitudinally of the rod bonded together
with a thermoset resin, which may have a passageway therethrough,
may be filled to give a desired density, and may be protected with
wrapped sheathing or extruded coating to give greater strength and
resistance to abrasion is disclosed.
Conventionally, sucker rods for oil well pumping systems have been
made of steel sections. These sections are carried to the oil well
site and individually extended down into the well and joined
together using special or conventional thread connections.
Typically, each of the connections is larger than the rod and,
therefore constitutes an obstruction to the flow of oil out of the
well. Steel rod weighs about 4 pounds per foot and, consequently, a
long sucker rod becomes so heavy that most of the energy input is
required simply to move the rod up and down. As a result, much
energy is wasted and only a minor part of the energy is available
for actually pumping oil.
Other disadvantages of the conventional steel sucker rods include
the tendency of connections to collect paraffin, which increases
the obstruction to the flow of oil, thus reducing production and
increasing pumping energy requirements. Also, the practical length
of conventional steel sucker rods is limited by the high density
inherent in such constructions. Depending upon the particular type
of rod involved, there exists a length beyond which it is not
practical, for a given installation, to extend the rod. When all of
the pumping power available is expended in simply raising and
lowering the rod, or when the weight of the rod itself approaches
the tensil strength of the rod at the upper end, no further
extension of the rod is feasible.
In many oil fields, for example in the Midland-Odessa oil field
area, corrosion of the steel sucker rods is an extremely serious
problem, requiring that the sucker rods be replaced as often as
every few weeks.
Cables, made of steel strands in the form of a wire rope, have been
suggested in lieu of sucker rods. This suggestion permits the use
of a continuous length without connections but does not solve the
problem of corrosion and is not entirely satisfactory inasmuch as
the cable is flexible and does not efficiently transmit the pumping
energy from the pump drive to the pump. A sucker rod comprising a
plurality of straight, longitudinally extended, spaced, flexible
steel rod wires embedded in plastic, produced by extrusion of the
plastic around the wires has been proposed; however, to the extent
that this proposal would tend to overcome the density and weight
limitations inherent in the use of steel rods, it fails in loss of
tensil strength. In addition, any small crack, pinhole, or other
defect in the plastic surrounding the wires, would subject the
wires to corrosive action which would be even more severe than
would be expected in the case of the conventional sucker rod
because of the small amount of load bearing material. No successful
application of either of these proposed constructions is known.
The simple substitution of resin bonded glass fiber sucker rod
sections for the conventional steel rod has also been proposed.
According to this proposal, each length of the resin bonded glass
structure is fitted at each end with a connector, typically made of
steel and having a much larger diameter than the rod, to permit the
lengths of the rod to be connected together in the manner typical
of the conventional rod structure. While this structure may reduce
the weight of the sucker rod to some extent, much of the weight
improvement is lost by the necessity for numerous heavy, bulky
steel connection fittings at the ends of each section of sucker
rod. The obstruction of the oil flow channel typical of the
conventional sucker rod, is retained and perhaps even aggravated by
the necessity for the bulky connections. In addition, the
connections are subject to corrosion.
All efforts to use resin bonded fiberglass connectors, by machining
the rod, using threaded connections, etc., which are known, have
not succeeded. One of the principle problems appears to be that the
machining of resin bonded fiberglass structure cuts the
longitudinal fibers and weakens the rod and/or the connector. The
use of numerous connectors which weaken the rod or which are bulky
and not easily connected and disconnected has proven
unsatisfactory.
This invention overcomes many of the problems and disadvantages
inherent in the prior art devices. Chemical resistance is provided,
overcoming the corrosion problem. Lightness coupled with high
tensil strength overcomes the weight problems of the prior art, and
the oil flow channel is left free of obstruction. These and other
improved features of the present invention will become apparent
upon consideration of the following.
A pumping system for oil wells and the like is constructed by
placing a pump in an oil well near the bottom in a reservoir of
petroleum to be pumped to the surface. A pump drive is placed at
the top of the oil well and the pump drive is connected to the pump
by a sucker rod. In this invention, the sucker rod is of sufficient
length to reach from the drive to the pump and is constructed of a
mulitplicity of glass fibers bonded together to form a semi-rigid
rod. The bonding material is a thermosetting organic resin.
Fittings are fixed at respective ends of the sucker rod for
connection to the pump and to the drive. The sucker rod is run into
the well and connected at the lower end to the pump and at the
upper end to the drive to complete the pumping system. The sucker
rod is fabricated by pulling a plurality of rovings of glass
fibers, each comprising a multiplicity of fibers, through a coating
vat or other resin application means to coat the fiber with a
liquid thermosetting resin. The rovings coated with the resin are
pulled through a forming die and the formed rod is pulled through a
curing station where the thermosetting resin is cured to form a
single, semi-rigid continuous rod having a length sufficient to
extend from the drive to the pump.
The rod may be made in many configurations. For example, the rod
may be hollow having a passage through the length thereof. The
passage may be filled, fully or partially, with a weighting
material, e.g. lead, particulate matter, beads, etc., and may
include cables or conductors to communicate conditions in the well
to the surface or to give control signals to devices in the well.
The rod may be covered with one or more layers of bonded glass
fibers helically wound or woven around the rod and may be protected
from abrasion by an extruded or otherwise applied covering of
abrasion resistant material.
The system is illustrated schematically in
FIG. 1 and FIGS. 2, 3, 4, 5 and 6 illustrate various alternative
configuration for the sucker rod.
FIG. 7 and FIG. 8 show examples of connector designs which can be
used to connect the rod to the pump or to the drive.
The method of constructing the oil pumping system of the invention
is illustrated schematically in FIG. 1 in which the well is
indicated at 1. The sucker rod 2 is carried to the well site in one
continuous piece, or is fabricated on site. In the exemplary
embodiment illustrated, the sucker rod is reeled on very large
diameter reels, indicated at 3, and run down the well 1 and
connected to the pump 4 which is disposed near the bottom of the
well. Once the rod has been run down the proper length into the
well, the upper end is connected to a pump drive 5.
One embodiment of the sucker rod construction, absent the end
connectors, is illustrated in FIG. 2. The rod 10 is made up of a
multiplicity of glass fibers running generally parallel to each
other longitudinally of the rod. The glass fibers are indicated by
numeral 12 in FIG. 2 and are bonded together by a thermosetting
resin 14.
The glass fibers may all be straight and unidirectional extending
longitudinally of the rod. This gives great tensil strength to the
rod, but such a rod is not highly resistant to longitudinal
delamination; i.e. splitting along the longitudinal axis of the
rod. Resistance to longitudinal splitting can be improved
substantially by using all spun glass fiber roving or a mixture of
spun roving glass fibers and straight unidirectional glass fibers,
the latter giving a higher tensil strength than the former. The
spun glass fiber roving tends to give greater transverse strength
and resistance to longitudinal splitting at very modest sacrifice
in longitudinal tensil strength.
While this specification speaks mainly in terms of glass fibers,
which are a preferred fiber for the purposes of this invention
because of their high tensil strength, the invention is not limited
to glass fiber usage, but would include inorganic fibers of various
types, e.g. graphite fibers, as well as natural and synthetic
organic fibers such as polyester fibers. Combinations of inorganic
and organic fibers of the various types may be used to provide a
proper balance of tensil strength, weight, resistance to abrasion,
chemical resistance and transverse resistance to splitting. Glass
fibers, other inorganic glass fibers and organic fibers, as well as
various blends and mixtures of the same may be used in the various
structures comprising bonded fibers disclosed hereinafter and
discussed throughout this specification.
Polyester and epoxy organic resins are the preferred bonding
materials for forming a rigid rod by bonding the fibers together.
Polyester bonding of glass fibers, as a fabrication technique, is
well known. While less commonly used, epoxy is also well known as a
bonding material for forming glass fiber reinforced articles. The
techniques of formulation and application of these resins to
produce various types of structures is well known in the art and
abundant descriptive information is available. Methods for forming
elongate glass fiber reinforced structures generally of the type
described herein are also well known. The pultrusion method, for
example, is quite well known and various techniques for using this
method in the fabrication of elongate articles has been described,
see, for example, U.S. Pat. Nos. 3,556,888 and 3,674,601, and the
method has been described in various technical publications; see,
e.g. 1973-74 "Modern Plastics Encyclopedia", page 428. Fibers,
bonding resins, techniques and equipment generally suitable for
producing the sucker rod constructions described herein are
described in 1973-74 "Modern Plastics Encyclopedia" and in
technical literature cited therein, and generally in the
literature.
Fibers such as carbon, graphite, boron, polyamides, polyesters, and
other equivalents as well as glass may be bonded with polyesters,
epoxies, thermoset acrylics, polycarbonates, vinyl esters,
polyamides, ABS acrylonitrile-butadiene-styrene, and other
equivalents as well as the better polyester bonding resins.
The sucker rod 10 is described here as being semi-rigid. A
semi-rigid rod, within the meaning of the present invention, is one
which is sufficiently flexible to be wound on a very large reel or
equivalent carrier or capable of being bent without permanent
deformation in a curve having a large radius of curvature.
Generally speaking, the semi-rigid rod referred to in this
invention has a diameter of from about 3/4 inches to about 2
inches, or more, and its capability of being bent is limited to a
radius of curvature of at least about five feet and typically of
greater than 6.5 or 7 feet, but is must be capable of bending on a
radius of curvature of about 15 feet to 20 feet. Another
characteristic contemplated within the meaning of semi-rigid, as
used here, is that the rod is sufficiently rigid to transmit
compression force down the rod from the pump drive to the pump
without being forced against the walls of the casing in such a
manner as to cause severe abrasion and frictional resistance to
movement. This characteristic is to be distinguished from a wire
cable or plastic coated wire cable, suggested previously, which did
not permit compressive forces to be transmitted downwardly through
the rod. The semi-rigid sucker rod contemplated by this invention
does not substantially reduce the pump stroke at the bottom of the
well by reason of slack in the rod, but rather transmits the
majority of the downward movement of the pump drive to the
pump.
In many instances no downward force is applied directly from the
pump drive, the downward force being derived from the weight of the
sucker rod in the well. The semi-rigid sucker rod of this invention
transmits the weight of the rod to the pump, a characteristic which
distinguishes it from the flexible cable like rods previously
proposed which tend to sag, coil and fold rather than transmit the
downward compressive force.
The downward force resulting from the weight of the rod is an
important factor in the design of sucker rods for oil well pumping.
The steel rod, having a density of about 4 pounds per foot, is
excessively heavy and transmits an undesirable and unneccessary
downward force to the pump and the lower portions of the rod. A
simple resin bonded glass fiber rod having a diameter of about 1
inch may be too light for some oil well pumping systems. The
density of such a rod will be in the range of about 0.6 to about
0.8 of a pound per foot, depending upon the particular resin used
and the ratio of resin to glass fiber in the rod.
Generally, a weight of at least about 1 pound per foot is desirable
for proper operation of an oil well pumping system. One of the
particularly advantageous features of this invention is that the
density of the sucker rod can be varied uniformly along the length
of the rod by adding filler materials to the resin formulation. For
example, in formulating the bonding resin, high density fillers,
such as lead phosphate, or other heavy metal salts or high density
powders are added to the bonding resin. When the bonding resin is
applied to the glass fiber roving, the filler is bonded as an
integral part of the rod, increasing the density of the rod. By
selecting an appropriate ratio of resin to glass to filler, a great
variety of rod densities can be achieved.
Another method of achieving variable rod densites is illustrated in
FIG. 3 in which the rod 20 is constructed in the manner previously
described of fibers 22 bonded together with a resin, filled or
unfilled, 24, but the rod has a central core 26 of lead or other
high density material. The core may be non-load bearing, as in the
case of lead, or it may be load bearing material such as a steel
wire, which would contribute to the tensil strength of the rod as
well as increasing its density. The core may extend the full length
of the rod or only part of the length, where variable density is
desired. The high density portion of the rod may be placed at the
bottom, at the top, or otherwise along the length of the rod. This
rod is formed in the same manner except that in fabrication the
glass fiber roving is positioned by the die around the central core
element before the resin is cured.
A hollow center rod 30 made up of fibers 32 bonded together with a
resin 34, in the manner previously described, but constructed so as
to provide a hollow center 36 is illustrated in FIG. 4 as an
alternative to the embodiment illustrated in FIG. 3. A pair of
insulated wires, an electrical cable, or other means of
communicating sensing or control signals between the bottom of the
well and the top may be included in the hollow passageway through
the center. Likewise, the density of the rod may be varied by
adding granular high density material, such as lead shot, after the
rod is in position.
FIG. 5 illustrates a rod of the type illustrated in FIG. 3 with
additional structure; however, any of the preceeding rod
constructions and other rod constructions can be used in the
embodiment used in FIG. 5. The rod 40, of FIG. 5, is, in the
particular rod illustrated, made up of fibers 42 bonded by resin 44
surrounding a high density core 46 which, together, form the
central rod construction 48. The rod 40 also includes a first
sheath 50 and a second sheath 52 and an outer sheath 54. In the
illustrative embodiment of FIG. 5, the sheath 50 is constructed of
fibers wound around the central rod structure 48 helically so as to
have a substantial transverse directional component and bonded
together to form an integral sheath enclosing the entire central
rod structure. Organic or inorganic fibers may be used but for this
application, the organic polyamide (nylon), polyester (Dacron),
acrylic, polyvinyl alcohol, polypropylene and other organic fibers
being preferred.
Sheath 52 is similarly constructed but, in the exemplary embodiment
of FIG. 5, the sheath fibers are wound helically in the opposite
direction. The purpose of the sheaths 50 and 52 is to protect the
central load bearing and load transmitting rod 48 from abrasion and
corrosion and to give the overall rod 40 greater resistance to
longitudinal splitting resulting from delamination or separation of
the fibers in the central rod structure 48. The density of the rod
is increased by the addition of the sheath 50 and 52 and the tensil
strength is also increased, but the increase in tensil strength is
secondary to the accomplishment of the principal purposes of
sheathing the central structure and this increase in tensil
strength is not equivalent to that which would be accomplished by
merely increasing the diameter of the central structure.
The sheath 54 is an additional protective sheating extruded about
the underlying structure. Typically, this sheathing would be made
of polyamide (nylon), ultra high density polyethylene,
polypropylene, Teflon (polytetrofluoroethylene), or other synthetic
extrudable material. This material preferably has a higher
resistance to abrasion than the underlying structure and may be
self lubricating as is typical of the polymers mentioned.
FIG. 6 illustrates another variation in which the rod 60 has a
central structure made up of a multiplicity of fibers 62 bonded by
resin 64 in a hollow configuration having a passage 66 extending
longitudinally of the rod. This passageway may be used in the
manner previously discussed in connection with the illustrative
configuration shown in FIG. 4. The central core structure 68 is
protected by a sheath 70 made up of a multiplicity of fibers,
organic or inorganic as previously discussed, which are woven about
the central structure to form a fabric sheath which is bonded
together by a resin of the type previously discussed and which has
a substantially transverse directional component. The central
structure 68 is constructed in the manner previously discussed and
the sheath is constructed by providing a weaving device at the
point of fabrication, either before or after setting the resin, to
weave the fibers around the central structure. The sheath is then
saturated with a bonding resin and the sheath bonding resin is
cured, as described in the patent and literature references
included herein by reference previously.
Sheaths of the type described with respect to the illustrative
embodiment of FIG. 6 may be used in constructions such as
illustrated in FIG. 5, alone or in combination with other sheaths.
Likewise, the rod 60 illustrated in FIG. 6 can be further protected
by the addition of a sheath of the type referred to at 54 in FIG.
5. Also, the central structure may be of any of the types
heretofore described or referred to.
Any of the rod structures previously discussed can be given greater
transverse strength, resistance to splitting, by incorporating, in
the resin, short fibers to improve the lateral strength of the
construction as well as by the use of spun glass fiber roving.
The advantages of the continuous reinforced plastic sucker rod in
an oil well pumping system include the following: The sucker rod is
chemically inert and the resin bonding and the fiber system can be
varied to meet various environments. Chemical inertness can also be
varied to meet particular requirements by appropriate sheathing
materials. The rod is free of joints and consequently the sucker
rod is considerably less expensive to manufacture, to install in
the well and to remove from the well, and obviates the extreme
disadvantage of the rod connectors interfering with flow through
the casing and the collection of paraffin about these connections.
The weight and linear density can be regulated to fall through the
fluid column, i.e., apply gravitational force of the proper
magnitude to the pump, without slack, thus permitting efficient
operation of the pump. The weight of the rod and the downward force
on the pump can be varied to meet particular conditions of fluid
viscosity, depth, etc. The longitudinal tensil strength, the
transverse strength and the circumferential integrity of the rod
can be tailored to meet particular strength requirements as
required for handling and operation. The outer surface can be
protected against abrasion as well as environment factors such as
particularly severe corrosion. The rod can be constructed with a
passage through its center and, therefore, can be used for
instrumentation and for venting of gasses or lighter fluids from
the bottom of the well or the injection of fluids down into the
well.
Any connector suitable for securing the ends of the rod to the pump
and to the pump drive, respectively, may be used.
Unlike the segmented rods of the prior art, the single connector at
either end of this rod may be tapered to meet specific conditions
and may be protected from corrosion by appropriate coating, or
other protective measures, since the position of the connector is
fixed by being connected to the pump at one end and to the pump
drive at the other. Joints as required to connect the sucker rod to
the pump and to the drive may be of the type described in National
Bureau of Standards Report No. NBSIR 73-129 "Evaluation of GRP Rod
and Rope Materials and Associated End Fittings", December 1972,
Final Report.
The fittings illustrated in FIGS. 7 and 8 are intended as merely
illustrative of the types which may be used and selection of a
particular design depends on the environment and circumstances of
use. In FIG. 7, the rod 80 extends into a cylindrical connector 82
which is threaded at one end and tapered at the other. The rod is
held in the connector by a plurality of wedges illustrated at 84
and 86 which are pressed against the rod by the conical
configuration of the cylinder 82. A potting compound, such as an
epoxy thermosetting resin, indicated at 88 bonds the end of the rod
in the cylinder and bonds the wedges in the cylinder to the
cylinder and to the rod.
In FIG. 8, the rod 90 is held in the cylinder 92 simply by a
potting compound 94. The potting compound would typically be an
epoxy or other thermosetting adhesive resin. The thickness of the
potting compound in 94 is exaggerated in FIG. 8 for illustrative
purposes.
In FIGS. 7 and 8, thread connectors are illustrated but it will be
apparent that bayonet connectors, hook connectors, or connectors of
any other desired configuration may be utilized. These connectors
may be of substantial length to extend along the rod a sufficient
distance to distribute the stress in the rod throughout the entire
rod construction, thus obviating one of the difficulties faced in
providing a multiplicity of connectors for fiberglass rods. Where
many connectors are required, the connectors must, to be of useable
weight and to minimize construction time, be comparatively short
and such connectors often tend to concentrate stresses in the skin
portions of the rod.
It will be apparent that one or more of the protective sheaths may
be peeled back or removed at the entry point into the connector to
provide direct fastening of the load bearing central structure to
the connector.
In the illustrated embodiments, the rods are shown as being
generally circular; however, other cross sectional shapes, such as
eliptical to aid in reducing the diameter of the core and giving
the rod greater flexibility in one dimension than in the other may
be fabricated, as might be required for particular systems.
The embodiments illustrated in the drawings are intended to
illustrate the various constructions which may be used in the oil
well pumping system of the invention and are not intended to limit
the invention to the structures specifically illustrated. Likewise,
while the preferred materials and embodiments have been principally
discussed, and other illustrative materials have been referred to,
the itemization of various specific materials is not intended to be
exhaustive of equivalent materials and equivalent steps. For
example, while this invention generally contemplates a single rod
in a well, an equivalent construction can be found, in appropriate
circumstances, where two or perhaps more long lengths of rod were
so joined as, in effect, to be one length or equivalent to one
length within the system under consideration. Finally, while the
invention and many of its facets have been described in
considerable detail, it is contemplated that the scope of the
invention will be according to the definitions in the claims and is
not limited to the specific illustrative examples set forth in the
body of the specification.
* * * * *