Battery packs provide power to downhole devices. An understanding of battery technology is critical to maintaining a high level of success.

DataCan’s high temperature battery packs use Lithium Sulfuryl Chloride or Lithium Thionyl Chloride cells. There are numerous battery sizes, temperature ratings, and rate capacities. In most cases, the customer tool type and maximum downhole temperature will dictate the battery pack required. Refer to DataCan’s battery brochure page to match your tool with its correct battery pack.

Battery pack life is critical. Measuring the voltage of a lithium battery pack will not help you determine its remaining life. The voltage discharge curve of a Lithium cell is very flat. Hence, when you measure the voltage of a lithium battery pack, you are not confident in knowing how much life remains in the battery cells.

The voltage of a lithium battery pack will be “acceptable” until the very end of its life. At the end of its life, a lithium battery cell suddenly loses its available energy.

The battery tester is used to:
Depassify the battery cell.
Check to make sure the battery pack fuse has not blown
Check to make sure the battery pack is wired correctly
Check to make sure the battery pack is working correctly

The most common question DataCan receives is, “How long, will the battery pack last downhole?” To correctly answer this question you need to know the following:

What battery pack are you using, or more specifically, how much energy do you have available? Different battery packs have different amounts of available energy. All of DataCan’s new battery packs have their available energy printed on the label.

For used battery packs, the customer must manually record how much energy has been used during previous jobs. Alternatively, DataCan has a “Smart Battery” pack design which saves its own energy usage and its remaining energy can be downloaded by the customer.

What type of tool? Different tools use different amounts of energy as they sleep and sample.

What sample rate? DataCan’s tools use more battery energy while they are recording samples. In the case of the downhole shut in tool, relatively no energy is being used unless the motor is on.

What is the expected downhole temperature? This is critical as battery packs have significant levels of self discharge at temperature.

Once the above criteria are known, users can input this information in DataCan’s “Battery Calculator”. The Battery Calculator program can be found in DataCan’s program and download software under the Utilities tab.

It is important for users to also understand the concept of battery pack passivation. Battery cells contain two main chemicals: the anode, and the cathode. To increase shelf life, a thin layer of corrosion builds up between the anode and cathode. This thin layer is called the “passivation” layer. The passivation layer prevents the anode and cathode from reacting prematurely.

However, in some cases (especially in higher temperature cells) the passivation layer grows too large and can prevent the battery from operating correctly. The passivation can restrict the chemical reaction between the anode and cathode to the point where the cells appears to be dead. The solution, is to depassivate the cell (remove the passivation layer). To depassivate the cell you can:

Put a large current draw on the battery. A large current draw, will act to erode the passivation layer.
Vibrate the cell, physical shock will help to displace the passivation layer.
Heating the cell, will also help to melt the passivation layer (heat is a common catalyst to any reaction).

O-Rings, Back-Ups Redress Kits

If your job is critical, DataCan recommends using an Aflas 7182B® material. This material is great for H2S, CO2, and high pressure conditions. The cost of a failure due to a poor o-ring selection is too great.

For an o-ring to seal properly, it must have chemical and mechanical strength. The material must be chemically compatible with the sealing fluid. The gland and o-ring must be tough enough to maintain the seal during high pressures and high temperatures.

Chemical strength means matching the material to the environment. DataCan has a simplified o-ring selection guide that helps operators choose the correct material. In general, Viton 90 o-rings work most of the time. For critical wells, long term surveys, and unknown environments, DataCan recommends using Aflas 7182B® seals.

The physical strength of a seal is dependent on the o-ring strength and the gland design. Commonly, an o-ring will have an extrusion failure at high pressures and temperatures. This is because the high pressure squeezes the o-ring through the gap in the seal joint. An easy solution to this problem is to reduce the gap size. The smaller the gap, the higher pressure the seal can withstand before extruding. However, it becomes difficult to machine small gaps. Another solution, is to use a high strength back-up, such as a PEEK® back-up. The back-up must extrude through the seal gap. Since the back-up material is stronger than the o-ring, higher pressures can be withstood. The final solution is to use a face seal joint design, as seen in DataCan’s super seal. In the super seal design, a metal to metal face seal behind the o-ring gland prevents the o-ring from extrusion failures.

The premature failure of an o-ring can usually be attributed to a combination of causes and not merely a single failure mode. It is important to maximize sealing life and reliability by reducing the probability of seal failure at the onset with propercompound selection, installation and continued education of personnel.

Compression Set - The seal exhibits a flat-sided cross-section, the flat sides correspond to the mating seal surfaces. Excessive pressure and temperature, excessive volume swell in chemical, and specific elastomers with high compression set lead to this failure mode. Once an o-ring has compression set, it is no longer elastic and will not form a seal.

Chemical Degradation - The seal may exhibit many signs of degradation including blisters, cracks, voids or discoloration. In some cases, the degradation is observable only by measurement of physical properties. The selection of a more chemically resilient elastomer such as Aflas 7182B will prevent degradation.

Explosive Decompression - The seal exhibits blisters, pits, or pockets on its surface. Absorption of gas at high pressure and the subsequent rapid decrease in pressure results is gas that was once trapped inside the elastomer to explosively decompress and exit the seal. The absorbed gas blisters and ruptures the surface as the pressure is rapidly removed. High modulus or a harder elastomer, as well as a slower decompression rate will prevent this mode of failure. Aflas 7182B is explosion decompression resistant. It is an effective seal material for high CO2 gas wells.

Extrusion - The seal develops ragged edges (generally on the low pressure side) which appear tattered. Excessive seal clearances, excessive pressure, low modulus or hardness elastomers, or improper sizing will lead to an extruded seal. Decreasing gland clearances, use of a high strength back-up ring, or DataCan’s metal to metal super seal will prevent extrusion.
O-Rings, Back-Ups Redress Kits