The goal of this project is to develop prototype rechargeable batteries capable of operating in a high-temperature environment to power a variety of emerging measurement-while-drilling (MWD) and other logging equipment in deep wells.
Electrochemical Systems, Inc. (ESI), Knoxville, TN
MWD and logging-while-drilling (LWD) tools are powered by an autonomous power source that is most often a battery. Present tools operate at temperatures below 150 degrees Celsius (ºC) mainly because their components, including the battery, cannot withstand higher temperatures. Drilling and logging services need batteries that can safely operate at high temperatures, thus increasing the temperature limits of the tools they power.
Geothermal and deep oil and natural gas fields require high-temperature drilling systems that can reliably operate at 150–230 ºC and can survive to 250 ºC. Reaching the targets in these fields is a challenge (the majority of new, deep wells are highly deviated) and typically requires the use of MWD tools during drilling, which in turn require high-temperature-capable battery power. The cells to be developed during this project should be capable of providing power in such deviated wells where conventional wireline logging is difficult.
The lithium-magnesium/thionyl chloride battery, which was developed under a Halliburton-DOE Battery Engineering collaboration, offers the best high-temperature, gas-compatible, lithium-based chemistry for the oilfield. However, safe use of this battery chemistry has been limited to 200 ºC, and there is little likelihood of increasing the operating temperature or of increasing cell safety beyond this temperature. Polymer-based battery chemistries were considered to be an option but subsequently rejected as an alternative to existing chemistries because they tend to fail when soaked at high temperature. Also, the lithium-based batteries are primary batteries and rechargeable cells are preferred to primary cells because they have the potential to complete more jobs per cell, which in turn lowers life cycle costs, reduces environmental problems related to disposal, and open the door to new applications.
By offering a reliable and rechargeable battery for operation in extreme temperature environments, this project will support development of the kinds of durable MWD tools seen as essential to cutting costs and reducing risks in drilling deep natural gas wells.
This project was initiated in October 2006. Phase I had already been successfully completed via an earlier project supported by Sandia National Laboratories and performed from July 2005 to January 2006. DD size test cells were built and their electrical performance tested over a temperature range from 125 ºC to 250 ºC. Test results demonstrated the feasibility of the high-temperature cell for deep drilling applications.
The original project included the development of a prototype, high-temperature, rechargeable battery to power electronics which operate in drilling and logging systems in hot wells (>200 degrees C). The project also includes the development of critical cell components robust enough to sustain vibrations in the down-hole environment. A prototype cell will be built and tested for proper electronic operation, including recharge capability, when subjected to vibrations at high temperatures.
The add-on phase comprises building commercial-type DD cells based on the Phase II results and evaluating them for the intended application i.e., using them to power the tool in a hot well. DD cells with capacities from 3 to 5 amp hours (Ah) will be assembled, employing methods and components defined during the original phase of the project. Safety tests will be performed. The cells’ electrical performance will be determined once they are judged ready for commercial application. Fully qualified cells (known capacity, energy efficiency, cell resistance, vibration behavior) will be tested in a tool in a high-temperature well. Results of the tests will be reported as the final deliverable for this project.
The DD cell employs several hermetic seals in order to operate. There is a seal which closes the cathode compartment where an alumina plate is glass sealed to an alumina header, and the alumina header is also sealed to beta-alumina electrolyte, thus closing the cathode compartment.
Compatibility of these seals was tested under the most stringent conditions, such as exposure to cathode composition of a fully charged cell at 250ºC, for one month. The results obtained showed no leakage. The compatibility of the tungsten/glass seal was also determined when in direct contact with cathode liquid and when in contact with vapor. It was observed that the former was less affected than the latter; however, both showed long lifetimes.
The designed seals were submitted for FEM (Finite Element Model) analysis. Excessive compressive stress for the top alumina seal (alumina plate/alumina header) was estimated. The geometry of one of the components was changed to produce less stress, thus decreasing the likelihood of a leak.
The prototype cell design is comprised of a metal case employed as an anode compartment, an alumina top sealed to an alumina header-beta” alumina assembly serving as cathode compartment, and a seal. The cathode compartment is installed in the metal case. The alumina top, with a protruded metal current collector, seals the cathode compartment. A metal collar attached to the alumina is welded to the case, thus sealing the anode compartment.
The dummy cell was built and tested for vibration and shock resistance.. The cell design was comprised of the cathode compartment installed into a metal case which served as the anode compartment. The cathode compartment consisted of an alumina plate sealed to the alumina header-ß” alumina tube assembly. The two compartments were hermetically sealed by welding a metal collar to the cathode compartment and cell case. Anode and cathode compartments were filled with liquids simulating anode and cathode materials in an actual cell during operation. The cell passed the test; there was no indication that vibrations and shock had any effect on the cell components and its electrical properties during or after completion of testing. If there were any structural changes in the cell that would cause changes in the cell electrical properties, they were not shown by visual inspection.
The final cell design was completed—it is identical to the design of the dummy cell except that it contains sodium in the anode compartment and a cathode mixture in the cathode compartment.
A special welding technique was developed to hermetically seal the cathode compartment. Several DD cells with 2Ah and 3Ah capacities were assembled. The cells were submitted for electrical performance testing at 200ºC. The initial results of cycling at constant current showed some loss in capacity and it was observed that the loss was caused by a leak in the welded area of the cathode compartment. This problem was caused by constraints imposed by the environment and welding equipment used in developing the cell. The leak has been addressed, allowing completion of electrical performance and safety testing.
The period of project performance has ended and the project is complete.