Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE BATTERY CASE
FIELD OF INVENTION
In order to gather information relating to the conditions existing at
some depth below the surface of an oil or gas well, the well operator
frequently lowers electronic sensing equipment into the well which by its
nature requires an electrical energy source (battery pack) to provide the
energy for sensing, recording and the remote transmission of the various
parameters being measured at the location of equipment in the well. The
battery pack must be of a particular size and configuration to be
accommodated by the drilling or servicing apparatus. Typically, such
battery packs have been in the shape of elongated cylinders having
electrical terminals at one or both ends of the battery pack for connection
to the electronic equipment. The battery pack must operate in conditions
which could be best described as being extremely hostile. Wide variations
in temperature and pressure of the medium surrounding the battery pack
can be expected. At times, the battery pack must withstand severe
vibrations which can cause the premature failure of the battery pack by
rupture etc. with the consequent loss of the capability to monitor and
transmit the well parameters being sensed. It is an expensive and time
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consuming operation to retrieve the electronic monitoring equipment just
to replace a failed battery pack.
BACKGROUND OF THE INVENTION
Oil and gas well drilling and servicing equipment, in the past, has
made successful use of elongated cylindrically shaped battery packs which
may be used with well tools to provide the power necessary for the
operation of the downhole equipment.
Prior art battery packs may contain a plurality of cylindrically
io shaped energy cells which are physically arranged in an end to end
relationship and are individually wired to suit the energy requirements of
the equipment with which the battery pack is being used. Usually, the
energy cells are connected by insulated conductive straps which are
connected to each cell by welding or soldering and the individual cells are
connected to a pair of bus conductors extending down the side of the
battery pack. These connecting straps are usually insulated from the string
of energy cells except where connections are being made. The energy
cells and the strap connections are usually encased in some kind of tubular
enclosure, such as paper or similar substance, in which the internal
diameter of the enclosure is slightly greater than the diameter of the string
of connected energy cells and the thickness of the bus connecting straps
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which pass along the side of the energy cells. The tubular enclosure is
provided with a coating of an impervious material such as plastic and a
sealed terminal structure is formed at one or both ends of the tubular
enclosure.
Failure of prior art battery packs in the hostile environment in which
they are forced to operate is usually due to fracture and leakage of the
tubular enclosure securing the individual cells together. At times, the
vibration in the medium surrounding the battery pack may cause the
abrasion and fracture of the flat strap type bus conductors which connect
io the individual cells together, leading to open circuiting of the bus
conductors and in some instances, short circuiting of the bus conductors
and the resultant premature discharge of the battery pack. At times the
failure of the bus conductors can produce an arc which may cause the
battery pack to explode.
Although every attempt is made to seal the prior art battery packs
against leakage of the surrounding medium into the interior thereof, when
severe operating conditions are encountered, some of the corrosive
components (i.e. hydrogen sulfide) of the surrounding medium may
penetrate into the interior of the battery pack causing components of the
battery pack not only to fail prematurely but also to corrode and swell so
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that removal of such a failed battery pack from its housing is often difficult
if not impossible to do.
SUMMARY OF THE INVENTION
This invention seeks to provide a self contained somewhat flexible
battery pack for downhole equipment which is robust and resistant to
failure in the modes of the prior art battery packs previously described.
The battery pack of this invention is composed of individual cells
which may be interconnected by insulated strap type conductors which are
io welded in a predetermined manner to the positive and negative surfaces of
the individual cells of the battery pack to produce the desired output
potential. A set of bus conductors extend up the side of the individual
cells and are connected into an external terminal structure of the battery
pack (usually at the top).
The individual cells, so connected, are encased in a pair of half
cylindrical (clam shell) containment members which are assembled to fit
together to hold the individual cells in the cavity formed in the interior
thereof as well as any bus type strap connectors which are required to
connect the interconnected cells to the terminals of the battery pack.
Damage to the battery pack caused by vibration and other shocks is largely
eliminated. The clam shells are preferably formed from a suitable plastic
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material or reinforced high impact plastic material such as a glass fiber
reinforced polymeric material which is capable of securing the individual
cells firmly in place in their predetermined locations in the stack of cells
forming the battery pack. One or both of the shells is provided with a
5 longitudinal grooved recess formed in the interior surface of the half shell
extending the length of the clam shell. This recess provides space and
support for the necessary connecting bus conductors (wires or straps) for
the individual cells and at the same time prevents the direct application of
external pressure and vibrating forces to the conductors which over a
io period of time can lead to failure of the conductor by abrasion and
fracture.
The clam shells are provided with a pair of end plugs which are
secured to the half shells in any desired manner and one or both of the end
plugs may be fitted with end terminals which are connected to the bus
connectors of the battery pack to energize downhole equipment.
The two clam shells containing individual energy cells, bus
conductors and end terminal structure is now inserted and sealed into an
outer metallic jacket (in the form of a tube) so as to inhibit the ingress of
foreign material into the battery pack to complete the assembly process.
PERTINENT PRIOR ART
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U.S. Pat. No. 4,675,259 Jun. 23. 1989
This patent describes a downhole battery package comprising a
linear array of interconnected battery cells in a tubular case. The tubular
case is preferably composed of a paper or Nomex paper. No provision is
made for the protection or stowage of the electrical lead conductors. This
battery pack is not robust; the entire case may fracture if severe bending of
the battery pack is experienced. Even if this battery package does not
rupture during use, it is subject to leakage of the surrounding medium into
the interior of the battery pack because of its fragile nature.
U.S. Pat. No. 4,970,073
This patent describes a battery pack composed of serially connected cells
which are enclosed in reinforcing members which are typically glass fiber
sleeves surrounded by binding tape. Standard insulated wire conductors
serve to connect terminals of the terminals of the battery pack to the
serially connected cells. The interconnected cells and the conductors are
inserted into a metal or epoxy tube where a thermosetting encapsulating
compound is introduced. The resulting battery pack is a very rugged piece
of equipment which is very strong physically and is very resistant to
bending. The encapsulating material used in the manufacture of this
battery pack takes up precious volume which in most battery packs
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would be put to better use by increasing the size of the cells used to power
the battery pack. The rugged construction of this battery pack renders it
incapable of undergoing distortion such as bending, thus, the above battery
pack is entirely unsuitable for the downhole application to which
applicant's invention is suited.
U.S. Patent 5,516,603 May 14, 1996
This patent describes a flexible battery pack which is used in
downhole electronic equipment. Several battery staves (containing serially
connected cells) are attached to flexible printed circuits to provide power
io to downhole apparatus. Little description is given to the encapsulation of
the serially connected cells and thus is believed to be not pertinent to
applicant's invention.
U.S. Patent 5,392,856 February 28, 1992
This patent describes a setting tool which includes a downhole
battery pack. The battery pack comprises a plurality of serially connected
cells which are housed in a steel tube which is provided with a fiberglass,
phenolic, or ceramic tube type liner. The cell stack is mounted between
spring terminals and the steel casing serves as a return lead for the battery
pack. This is a very rugged battery pack enclosure which is not easily
adapted for applicant's downhole application because of its complete lack
of flexibility.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an exploded perspective view of the battery pack of this
invention.
Figure 2 is a sectional elevational view of the battery pack of
Figure 1.
Figure 3 is a partial sectional view of the battery pack of Figure 1.
Figure 4 is a representative perspective illustration of the
arrangement of an eight cell pack.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figures 1 to 4, battery pack 10 comprises a plurality
of cells 12 in a stacked relationship which are serially connected by C
shaped conductive straps 14. Top terminal 16 of the battery cells 12 is
connected via strap conductor 18 to central pin 20 of top terminal 22, and
lower terminal 24 is connected via strap 26 to the outer threaded ring 28 of
terminal 22.
The interconnected cells 12 are separated by resilient washer rings
30 and in this instance a cylindrically shaped plug 50 having a connecting
pin 52 is shown in the middle of the battery string. The entire battery
string, plus conductors 18 and 26 are sandwiched between two elongated
semi-cylindrical clam shells 32 and 34. Shells 32 and 34 comprise a pair
of insulating members formed from a reinforced plastic insulating material
preferably a polyester plastic material reinforced with glass fibers (which
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must be capable of providing continuous service whilst undergoing some
distortion such as longitudinal bending without fracture or permanent
distortion during a downhole operation).
Members 32 and 34 are provided with at least one longitudinal
inner recess such as 36 to allow for the accommodation of strap
conductors 26 therein in the final assembly of the battery pack.
The shells 32 and 34 are fastened to end plugs 38 and 40 by screws
42 to form a solid unit. Plug 50 may also be fastened to shells 32 and 34
by means of screws 42.
Finally, the assembled unit is inserted into a containment tube 44
which comprises a top member 46 and a lower portion 48. The portions 46
and 48 are sealed together by welding or threading as shown at 54 to
ensure the integrity of the battery pack and seal the components against
the unwanted ingress of substances from the surrounding medium and yet
provide an element of flexibility for the battery pack. In this instance,
components 46 and 48 have rolled lips 56 and 58 to secure the inner
components in a working relationship. The sleeved components may be
fitted to the interior components by means of a polymerizing resin to form
a unitary structure if desired.
The battery pack of this invention is quite rugged and is easily
manufactured. It provides accommodation for housing and supporting the
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individual energy cells in a confined containment which is rugged and yet
flexible enough to travel around curves in a drilling pipe for direction
drilling.
The recess provided in the inside surface of the clam shell for
5 receiving and protecting the connecting conductor strap assures adequate
support and positive location of the conducting strap 26 as to provide
continuing operation of the battery pack, especially during periods where
the pack is exposed to intense vibrations which can lead to fretting
corrosion and the ultimate fracture of such conductors in prior art battery
10 packs.
Those skilled in the art will immediately be aware of alternative
constructions for this battery pack which may be applied to applicant's
disclosed construction. Applicant prefers to limit the ambit of protection
for this device as set out in the following claims.
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