China’s Xian University is developing an exploding wire fracking technique
A team at Xian University led by Professor Zhang Yongming is expecting to trial an exploding wire plasma generator as a fracking technique in April 2019.
An “exploding wire” setup feeds a large and steeply rising current (released from capacitors) down a 0.5-mm thick wire. A current rise of above 100 amps per microsecond is needed to vaporise the wire, releasing the energy needed to create the explosion.
The current melts the wire into spheroidal droplets (unduloids), but the current rise is fast enough then to vaporise the unduloids before they can move. As the current continues to increase resistance also rises, until the vapour becomes a plasma. As this expands it creates a powerful shock wave, disrupting the plasma and so cutting the current.
Prof Zhang’s theory is that the shock wave can be used to fracture deep and dense rock formations. While details are sketchy, it appears that the plan involves extracting the “energy rod” after each shot and pumping high-pressure water (and presumably proppants) into the fractured formation before the next “shot” is fired.
Reports seem to suggest that the device can deliver pressures of 200 megapascals (29,000 psi), and has created fracture zones of around 50 metres. The system has already been reportedly used to release coal-mine methane – a significant problem in China’s coal mines, and also now a significant source of energy. Coal-mine methane (distinct from coal-bed methane, CBM) is widely used in China to power mine power plant and to generate heat for mine services. The device also appears very similar to the plasma well-stimulation process developed in Russia by Novas Energy and now licensed in the US by Propell.
The Novas system is designed for re-stimulation of stripper wells rather than fracking new ones, and Novas claims that its effects on reservoir rock extend out to 1,500 metres from the well bore. Novas has conducted numerous stimulation jobs and the resulting data appears to corroborate that effect, though InnovOil could not find any recent test results or progress announcements either from Novas or Propell.
Novas appears to place its exploding bridge wire (EBW) inside a fluid container, which looks like a means of moderating the pressure pulse from an intense/short-range pulse to a less intense/longer-range combination of pulses with a very wide frequency range.
As it seems likely that the Xian device will be completely destroyed by its own detonation, its use in fracking looks problematic. Again, details are not in the public domain but presumably the capacitors are kept on the surface, with new detonators being dropped at intervals into the well-bore. There is no hard data on how proppants are to be deployed into the fractured rock between shots.
The same “exploding wire” approach is used in the detonators for implosion-based nuclear weapons, as it provides an almost instant and precisely timed set of triggers for the detonators that fire the explosive lens.
However, while the EBW is common to both solutions, Prof Zhang’s work is completely detached from nuclear weapons development. EBWs operate 1,000-10,000 times faster than a conventional heating wire. Because of their use as triggers for nuclear weapons EBWs are heavily regulated in the US, and cannot easily be exported. US attitudes to the proliferation of EBW technology are likely to obstruct the use of Prof Zhang’s solution outside China, if indeed it is successful anyway.