Method for Preventing High Temperature Self Discharge in Primary Battery

Abstract

A discharge prevention system for a primary battery comprises an energy harvesting module that produces energy from an environment and a control circuit for applying electrical current to the primary battery from the energy harvesting module to prevent or reduce self-discharge. This system will prevent or reduce rapid self-discharge at high temperatures in lithium-based primary batteries, for example. It can significantly extend the operating lifetime of such batteries operating at high temperature, particularly in applications where battery power is used intermittently. Specifically, a very low current is supplied to the primary battery at high temperature, significantly extending its storage lifetime. In some cases, depending on the current characteristics of the battery, the energy associated with the bias current can be in the same order of magnitude as the energy that would be lost by self-discharge, but in many cases it is much lower. This bias current “biases” the battery in such a way that self-discharge current of the primary battery is minimized.

Claims

1. A discharge prevention system for a primary battery, comprising: an energy harvesting module that produces energy from an environment; and a control circuit for applying electrical bias current to the primary battery from the energy harvesting module to prevent or reduce self-discharge.

2. A system as claimed in claim 1, wherein the primary battery is a Lithium Sulfuryl Chloride battery.

3. A system as claimed in claim 1, wherein the primary battery is a Lithium Thionyl Chloride battery.

4. A system as claimed in claim 1, wherein the discharge prevention system is implemented in a downhole device in a well.

5. A system as claimed in claim 1, wherein the downhole device comprises a wake-up module for periodically activating a controller powered by the primary battery.

6. A system as claimed in claim 1, wherein the discharge prevention system is utilized in a spacecraft.

7. A system as claimed in claim 1, wherein the control circuit applies less than 1 milliAmpere bias current to the primary battery.

8. A system as claimed in claim 1, wherein the control circuit applies a bias current that is 500 times less than a rated maximum continuous current of the primary battery.

9. A system as claimed in claim 1, wherein the control circuit applies a constant current to the primary battery from the energy harvesting module.

10. A method for preventing self-discharge of a primary battery, comprising: producing electrical energy from an environment; and applying an electrical bias current to the primary battery to prevent or reduce self-discharge.

11. A method as claimed in claim 10, wherein the primary battery is a Lithium Sulfuryl Chloride battery.

12. A method as claimed in claim 10, wherein the primary battery is a Lithium Thionyl Chloride battery.

13. A method as claimed in claim 10, further wherein the discharge prevention system is utilized in a downhole device in a well.

14. A method as claimed in claim 10, further comprising applying less than 1 milliAmpere to the primary battery.

15. A method as claimed in claim 10, further comprising applying a bias current that is 500 times less than a rated maximum continuous current of the primary battery.

16. A method as claimed in claim 10, further comprising applying a constant current to the primary battery from the energy harvesting module when the device is dormant.

17. A downhole device for a well, comprising: a device controller; a primary battery for powering the controller; an energy harvesting module that produces energy from an environment; and a control circuit for applying an electrical bias current to the primary battery from the energy harvesting module to prevent or reduce self-discharge.

18. A device as claimed in claim 17, wherein the primary battery is a Lithium Sulfuryl Chloride battery.

19. A device as claimed in claim 17, wherein the primary battery is a Lithium Thionyl Chloride battery.

20. A device as claimed in claim 17, further comprising a wake-up module for periodically activating a device controller powered by the primary battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:

[0020] FIG. 1 is a circuit diagram for modeling the primary battery;

[0021] FIG. 2 is a plot of a self-discharge compensation circuit as a function of temperature for an exemplary battery;

[0022] FIG. 3 is a schematic diagram showing a well drilling operation;

[0023] FIG. 4 is a block diagram of an exemplary downhole communications device; and

[0024] FIG. 5 is a block diagram of an exemplary downhole sensor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0026] As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

[0027] It is not immediately obvious how a small compensation current delivered to a primary battery would result in a significant operating life extension. However, the voltage-current characteristic of these (and most) batteries is highly non-linear, i.e. in certain regions of the battery I-V characteristic, a very small change in battery current results in a very large change in battery voltage, while a small change in battery current will mean a very small change in voltage in other regions of the battery characteristic.

[0028] This non-linear behavior can be modeled with an equivalent circuit consisting of an ideal voltage source (zero internal impedance), a resistor R.sub.teak, in parallel with the ideal voltage source, representing a thermally activated current leakage path of self-discharge, and a series resistor R.sub.internal, representing the output impedance of the battery (see FIG. 1). From inspection of this equivalent circuit, it is apparent that a low current (applied with the same polarity as the ideal battery, but at the real battery terminals) can entirely shut off the internal leakage current coming from the ideal voltage source. For a AA Li Sulfuryl Chloride battery, typical values at 72° C. are R.sub.teak=50,000-60,000 Ohms (Ω), and R.sub.internal=1.6 Ω.

[0029] In FIG. 2, the calculated compensation current for this battery is plotted over one year of storage at 72° C., where the open circuit voltage of the battery is 3.35 V. The required bias current levels are relatively small, in the range of 60 microAmperes (μA)−70 μA or less, meaning that the supplied power per module is about 235 microwatts (μW) or less.

[0030] This bias current much lower than the rated maximum continuous current for the battery. In one example, for a AA battery, the rated maximum continuous current was 150 mA, yet the required bias current was only about 70 μA. Thus, in most cases, the bias current will be over 500 times less than the rated maximum continuous current, and is typically 1000 times or 2000 times less.

[0031] A number of advantages arise from this approach. It does not require any changes or adaptations to the battery design, but may allow for nearly indefinite storage life at high temperature for high temperature batteries. Thus, the batteries can be maintained for powering sensing and acoustic transmit/receive units placed within a downhole hydrocarbon recovery well at various depths. They can also maintain batteries for supplying power to sensing and acoustic transmit/receive units placed within environmental monitoring wells, looking for trace pollutants or maintaining readiness in batteries used intermittently in high temperature conditions found in aircraft or automobiles.

[0032] The approach is compatible with energy scavenging/harvesting systems (such as photovoltaic cells, thermoelectric elements, acoustic or vibration energy or inductive collection) which typically have very low power output which is nevertheless enough to reduce the self-discharge.

[0033] FIG. 3 shows an example of a well drilling rig. A derrick 20 is located above the well. It is used to lift drill pipe and well casing sections over the well. A turntable 32 is used to drive the drill pipe 26 that extends down the well. Typically, for at least a portion of the well, it is lined with the well casing 24.

[0034] Toward the end of the drill pipe 26, there is typically a drill collar 28 that the pipe to the drill bit 30, which cuts through the earth and rock.

[0035] Relevant to the invention is the use of downhole devices 100 that are typically located at different depths within the well and typically near the drill bit. In the illustrated example, sensor devices 100-1 include transducers that detect physical properties within the well. Communication devices 100-2 collect the data from the sensor devices 100-1 and encode the data so that it can be transmitted to the wellhead telemetry system 22 at the surface. Typically, these communication devices 100-2 might comprise modems for modulating the data and repeater devices that may line the well reaching to the surface to relay the data until it can be input into the telemetry system 22. Some of these devices 100 might be located in the collar and relatively accessible. Other devices 100, however, might be located along or even outside the casing 24.

[0036] FIG. 4 shows an example of a downhole communication device 100-2. In the illustrated example, it comprises a data receiver 112 for receiving data, such as from another communication device or a sensor device 100-1. Often, this data is transmitted by modulating acoustic waves. However, in other examples, it can be transmitted electrically. This data is received and interpreted by the controller 116 and then transmitted from the communications device 100-2 via the data transmitter 110.

[0037] FIG. 5 shows the example of a sensor device 100-1. It also comprises a controller 116 that monitors a sensor transducer 114. In various examples, the sensor transducer can be, for example, a thermistor for detecting temperature. In other examples, transducer 114 is a pressure sensor or flow sensor for detecting a fluid such as gas or petroleum flowing through the casing. In other examples, it can be an acoustic sensor for detecting vibration associated with the drilling operation. Different acoustic sensors may be used, e.g. accelerometer, measurement microphone, contact microphone, and hydrophone.

[0038] According to the exemplary configuration, at least one, but more typically each acoustic sensor either has a built-in amplifier or is connected to an amplifier (not shown) directly. The drilling acoustic signals picked up by the acoustic transducer 114 are amplified first by the amplifier and are then transmitted to the controller 116.

[0039] Most relevant to the invention in both FIGS. 4 and 5 is the inclusion of the primary battery 102 for powering the downhole devices 100. Further, energy harvesting module 118 provides power to a control circuit 120 that applies electrical current from the energy harvesting module 118 to the primary battery 102 to prevent its self-discharge.

[0040] As described previously, often the battery 102 is a Lithium Sulfuryl Chloride or Lithium Thionyl Chloride battery.

[0041] A number of different examples exist for the energy harvesting module 118. For example, energy harvesting module 118 is powered from an electrical current supplied from the wellhead. In other examples, it includes a piezo electric transducer for converting the vibration associated with the drilling operation into a small current. In other examples, the energy harvesting module is powered by a turbine that is rotated by the movement of fluid within the casing or drill pipe 26. If a thermal gradient is available, then a thermoelectric power source or Stirling engine could be used as the energy harvesting module 118.

[0042] In any event, the energy harvesting module 118 provides a low current that is applied by the control circuit 122 to the primary battery 102. In general, this current is less than 1 milliAmpere. Typically, however, it is less than 100 μA.

[0043] In a typical implementation, the downhole device 100 is mostly dormant or inactive. A wake-up module 122, however, periodically switches the control circuit 120 from supplying the small bias current from the energy harvesting module 118 to supplying power to the controller 116. In one example, the duty cycle of the device is less than 5%, between active and dormant states.

[0044] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.