Dear Editor,
I heard a lot of people in the country mutter sotto voce that the oil caused the earthquake, so I decided to float the hypothesis that it did. Here is a summary of my conversations with two oil people, written so that high school physics students can understand.
Me: The oil in the Takutu basin is a little higher than the offshore oil, of similar quality, and connected under the 2 km thick Guiana Shield. So when we extract oil and gas from offshore and don’t refill with something to replace those fluids, the porous rock and hollows that no longer hold the oil & gas crumble, hence the rumble. The earthquake happened when a large set of hollows collapsed.
Oil 1: This is incorrect. Any earthquakes here have nothing to do with drilling for oil.
Me: It’s a hypothesis. Please give an alternative and not a mere assertion.
Oil 2: Oil deposits are very rarely connected. They are in pockets and that is why we drill so many wells.
Oil 1: Earthquakes occur due to plate movements and movement of rocks along fault planes. The depth of this one was 10 km. Oil wells are drilled less than 6 km down. Be careful of spreading misinformation. Quite a lot of people, especially in Guyana, think that drilling results in earthquakes. I am a qualified person.
Me: And you know what is under the Guiana shield?
Oil 1: It is well studied as one of the oldest areas in the world. Plate tectonics is across the entire planet. The earth is ever changing. The porous rock also does not crumble when oil or gas is removed, so don’t worry about that. These rocks are under tremendous pressure. When oil or gas is removed the spaces are filled up with water moving up from surrounding rocks.
Me: Where does the pressure come from?
Oil 1: From the weight of rocks above.
Me: Agreed. So what is the source of the energy that causes the subterranean pressure to send oil and gas up a drill pipe?
Oil 1: I don’t understand the question.
He then opts out of the conversation and does not accept an invitation to a private discussion.
So I will answer my last question. The oil well pressure has to do work to raise the oil. Let us use what I think is a simple approximation of the situation: the oil is 3 km below, half of which is Atlantic Ocean (5,000 ft) and the other half below the ocean floor. Every million barrels of oil will therefore require 4 TJ (terajoule) of energy to be raised by the underground pressure, reckoned in this model as 523 atm.
This energy must come from the falling of sufficient mass under gravity, i.e., subsidence. If the average density of the Earth’s crust is 2 600 kg/m3, then it can be calculated that every million barrels of oil extracted creates the potential for 42 surface acres of earth 3 km deep to fall 1 foot. No one but God knows when, or over what time, the equivalent of this subsidence takes place.
Everyone assumes that subsidence takes place in the vicinity of the oil drilling, but in fact again only God knows where. Oil companies, especially after the BP disaster in the Gulf of Mexico, know it is preferable to drill through sealable rock, which is a bulwark against upward leaks and downward subsidence, to keep their operations from that kind of harm.
We are supposed to be protected by the Guyana shield, which is about 2 km thick. But the Takutu Basin where the earthquake occurred occupies a suture zone in the Guiana shield. This hypothesis proposes there is a fluid connection under the Guiana shield to oilfields elsewhere, like in the offshore oil blocks. The hypothesis under which the oil companies, and hence the Government and EPA, are operating is that there is no connection. Theirs should be the null hypothesis, quod erat demonstrandum, not mine, especially after the recent relatively shallow continental earthquake.
Gas escaping from the wells without reinjection is a bigger problem. Reinjec-tion would help considerably with maintaining subterranean pressures to prevent subsidence anywhere. Using the same model, every billion cubic feet of gas allowed to escape can cause the equivalent of 303 acres of land 3 km deep to subside one foot! Better check to see if the Guyana coast and seawalls are really on the Guiana shield.
That is why it is necessary to have qualified inspectors (with armed guard to prevent ‘accidents’) 24/7 on the FPSOs and oil rigs, who can check on the pressures and variations over time, and on the true amounts being reinjected. Reinjection of sea water alone will not have the permeation reach of gas fast enough. If the powers persist in taking blind risks, they must learn to build to withstand earthquakes, and do the decent thing by using the oil money to build such structures pronto for the poor victims of Sunday’s quake, who still have to live with the rumbles.
Sincerely,
Alfred Bhulai
