Geology Reference
In-Depth Information
10.4.3 Batteries.
Discussions related to power are not complete without some mention of
batteries. We need not dwell on well known limitations: toxicity, explosiveness
and impractical handling. These negatives must be balanced with needs for
turbine maintenance and repair, which introduce inefficiencies of their own.
New to the market are rechargeable batteries, whose implications are discussed
in a recent article of Pitt (2010). Quoting from the article -
“MWD is a highly demanding application that creates a challenging
environment for the batteries. They must be able to operate over a wide
temperature range - from well below 0°C at the surface in Arctic oil and gas
exploration projects to well over 100°C during drilling - while enduring very
high vibrations (20 g rms). Another requirement is complete reliability and long
life time, typically from a few hours to more than 20 hours. Each time the
bottom-hole assembly has to return to the surface it costs tens of thousands of
dollars in downtime, so premature withdrawal to replace a failed MWD battery
adds significant costs to the operation.
During drilling operations, there is continuous mud flow and the battery
delivers a low idle current to the MWD tool. Drilling is often stopped and then
restarted, resulting in frequent battery replacement. If, for any reason, the
drilling operation has to be stopped early to replace a drill bit, the MWD tool
must return to the surface and the battery must be replaced to ensure there will
be a sufficient safety margin of battery power to maintain operation of the
MWD tool through to completion. Often, a primary battery might have to be
discarded with much of its capacity unused.
Until recently, specialized primary lithium batteries were the only product
capable of providing reliable, cost effective operation in harsh MWD conditions.
Saft offers primary lithium batteries for the oil & gas market and also recently
launched the world's first rechargeable lithium-ion (Li-ion) cell capable of
operating at temperatures up to 125°C under drilling conditions. This is a
significant increase in the previous Li-ion operating temperature - 65°C -
opening new horizons for MWD tool manufacturers. For the first time, MWD
tool developers can incorporate a high performance rechargeable battery into
their designs. This development eliminates the need to withdraw a MWD tool
for replacement of a spent battery, with the benefit of improved continuity for
the drilling operation.
Saft's VL 25500-125 C-size and new VL 32600-125 D-size cells are
intended for use in constructing batteries to be integrated into sophisticated
MWD tools that incorporate onboard alternator technology, driven by the mud
flow, to power their electronic systems. When the mud is flowing, the battery
will be charged. When the flow stops, such as when drilling is halted, the battery
will be discharged to provide power for the MWD electronics. When the mud
flow restarts, the battery is recharged.
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