ThatDamnedPanda
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quote:
ORIGINAL: Aneirin
But what makes me wonder when all this under pressure oil is removed from deep underground, what may it lead to in terms of earth plate movement, the stuff that leads to earth quakes and people dying, is there a relationship in this ?
Hi, Aneirin,
Yes and no. First of all, if you remove millions of cubic feet of oil from a geological formation, you're causing at least two physical changes - you're changing the volume, and the mass. Reducing the volume will often cause a small degree of settlement, depending on the nature of the formation. This settlement will typically be steady, but can sometimes be incremental. Slight, sudden adjustments in the settlement can be measured as seismic events, but they're typically very minor. In most cases, not even detectable except by seismic instruments.
But when you remove mass from a geological formation, you can have a secondary effect on the geology of the region. If you're drilling very close to an unstable fault boundary, removing enough mass can cause one of the tectonic plates to shift slightly in relation to the other, which is exactly what an earthquake is. Picture two canoes, side by side in the water, each with two people in it. One of the people gets out of one of the canoes, and that canoe suddenly floats a little higher in the water than the canoe that still has two people in it. If the canoes are actually touching, they'll slide against each other, and the friction will cause a slight scraping and shuddering as they readjust. Pretty much the same thing.
However, any quakes that might be triggered by this displacement are likely to be very small, and in any case are not actually caused by the removal of the weight of the oil - only triggered by it. In every case, the quake would have happened anyway; maybe a month later, maybe a year later, maybe ten years later, but it would still have happened as the plates tried to move past each other. Readjusting the mass just causes it to happen a little bit sooner.
Now, having said all of that, there is another way in which oil and natural gas exploration/extraction can cause earthquakes, but it doesn't actually have to do with the removal of the resource. Some geological formations need to be broken up in order to free the gas and/or oil they contain. They typically do this by pumping water into the formation at very high pressure to fracture the rock, and this activity has been linked to earthquakes with a fairly high degree of reliability. There was a town in Texas a few years ago where a credible link was established between gas exploration and a series of local earthquakes, and there was a geothermal project in Switzerland that (I believe) had to be halted because it was apparently causing some significant earthquakes in an area that had never been geologically active. And I think there was something similar to that near San Francisco sometime fairly recently, but I'm not entirely certain and don't recall the details. Just have a vague memory of hearing something about it on NPR.
So. To answer the question as asked, is there a relationship? Yes. A tenuous and occasional one. A direct cause and effect relationship? Possibly, to a limited extent, in some very limited instances. Does extracting oil actually cause earthquakes that would not otherwise have happened? Almost certainly not. Hope this answers the question.
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