Effects of earthquakes

[Segilla]

Since drilling can cause oil to gush out of the ground under pressure, are there any occurrences of earthquakes causing fractures in oilfields and quantities of oil to be released?

[brachiopod]

I wouldn't like to comment on oil fields per se, since, by their nature, (ie, oil takes just a little bit of time to form), that any seismic movement would mean that no oil would collect in the first place - although it may be diplaced to some separate form of trap / reservoir over time.

HOWEVER, there are frequent and well documented instances of floods being caused by earthquakes. This is caused by rapid changes in lithostatic pressures (as a result of the earthquake) causing groundwaters to 'gush out' along the fault fracture, in a similar way that oil is forced out of an 'oil reservoir' when it is 'pierced' by the drill bit.

To clarify, earthquakes are 'frequent events' over geological time, whereas oil takes a fairly long time (geologically speaking) to form. So any oil that would potentially form in a seismically active area, would not accumulate (to form an 'oilfield') precisely because of the 'constant' seismic activity.

[brachiopod]

I'm sure Clanad would help clarify this one aswell, but being on the other side of the pond, he's probably just finishing work right now.

[qapmoc]

I would expect that even if an earthquake occured right in the middle of an oil field that no oil would get to the surface. You are thinking of a oil well which sends oil into the air when the well is opened to the atmsophere, but this works because the pressure in the oil reservoir will push the oil up the small hole drilled like a jet at speed, In an earthquake the ground would just split open in a large area at once and release the pressure underground.