Also, I’ve seen signage mentioning “seismic survey work” in areas where traffic restrictions are occurring due to large trucks with some sorta huge blocks in their undercarriage.
Also, this past weekend a helicopter was flying around, trailing a cable that looked like it was 50 or so yards long and had a box on the end.
My guess is something having to do with fracking. AmIright?
And, as an aside: at work we were discussing this and someone wondered aloud about taking one of the roadside bundles for further inspection. Would it be “illegal” to take something left alongside the road?
Seismic surveys use artificially-generated sound waves to map subsurface geologic structures that may serve as traps for oil and gas. This helps identify potential drilling sites. This has nothing directly to do with fracking, which is a technique for enhancing production from wells drilled into formations with relatively low porosity (meaning that it is difficult to otherwise extract the oil or gas on the pore spaces of the rocks).
The orange devices are most likely receiving stations for the seismic signals. The vehicles you saw are equipped with hydraulic ‘thumpers’ which generate the sonic signals picked up by the receivers.
Not sure what the device towed by the helicopter was, but it is most likely some other (non-seismic) type of survey instrument.
Please don’t steal the receivers; they cost money and have no particular use other than what they were intended for.
I never intended (or even thought about) taking one. I was curious though about what the legal ramifications were, once someone else brought up the idea.
The fracking idea was a guess, as it has been in the local news the past few years.
My guess for the helicopter-towed device would be that it’s some sort of gravitometer. Very precise measurements of the gravitational field can also reveal some information about rock formations under the surface.
Seismic work is only indirectly associated with fracking. Seismic surveys are about measurement, most typically before drilling a well (though sometimes after a well has been drilled). Fracking is typically involved after you’ve drilled.
The trucks with giant blocks underneath are almost certainly some kind of vibroseis truck.
Why a vibrating block?
Seismic work is a lot like trying to figure out the contents of the next room over. You basically knock on the wall and listen to the echos, which tell you things based on when you hear the reverberations.
The ideal source for this is an impulsive source. Something as close to a prototypical Dirac-delta spike as you can get. The louder the better. On land, this means dynamite, if you can manage it.
But you can’t go around setting off thousands of dynamite charges in populated areas. If you are somewhat familiar with Fourier analysis, it turns out that a “chirp” signal is a reasonable alternative to an instantaneous pulse. You can sort of “invert” it. To do this, you want to introduce vibrations with controlled and steadily varying frequency into the ground. That’s what the giant truck does.
As for the helicopter, Chronos is probably right that it’s some kind of gravimetrics device. These are typically performed using helicopters or small airplanes.
The picture you showed seems to be more along the lines of wiring for geophones, rather than geophones themselves. You generally want to plant the measuring devices in the earth, rather than lying on top.
In my area they were using the helicopter to deliver big bags of sensors to workers in areas away from roads, and to pick them up after testing. Saved the guys from having to lug them out through the woods.
Unless you have really good evidence that the bundle was intentionally abandoned by the owner who had no intention of ever returning for it then yes, taking it would be illegal.
Helicopter is likely doing a potential field survey. Either gravity or magnetic, possibly both. The big deal at the moment is gravimetrics - which is a fancy word for measuring the gravity tensor. (Whilst I know it works, I still don’t, deep in my heart, believe a flown gravimeter can work. The engineering problems in making it do so are insane. But work they do.)
It is pretty astounding what can be detected below the ground with a carefully flown potential field survey. Density contrasts and magnetic susceptibility contrasts can be mapped, and it is possible to estimate depths for these using a range of mathematical techniques. It is possible to estimate the stress field in the rocks, which significantly helps guide the fracking operation. Can also map faults - which can be important for avoiding issues during fracking, especially shallow ones that could lead to leakage of fracking fluid.
IANAL, are you? I’m just having a hard time figuring out how people can pick up bottles, cans, tires, assorted refuse, etc from the roadside but be expected to realize that this isn’t trash.
El Kabong, no problem! My curiosity is just that, curiosity.
It surprises me, too. I’d have thought that you could get better data from telemetry of satellites. But if it helps, gravitational data along are insufficient to solve for the full density profile: You need to combine them with other forms of data and/or some assumptions about the shape and composition of formations (probably both) to get any solution at all, and even then it’s going to be at least somewhat a guess.
Even among industry folks, gravimetrics is a hard sell. When it appears to work at all, it’s in the shallow subsurface.
As for “guesses”, that describes most subsurface imaging. All the really challenging and interesting exploration targets require some element of educated guessing. No matter what the academics claim, nobody really has a good way of getting density or velocity information from the indirect sensing methods we use.
Depends upon how deep you want too see. Helicopter surveys can fly at 50m and take samples every few metres, and can thus resolve very shallow features. Satellite gravity data comes in two forms. Satellites that directly measure their acceleration are exquisitely sensitive, but the attenuation of high spatial frequencies due to their orbital height limits them to very deep crustal features. Over oceans satellite data uses sea height, which once processed to eliminate all the other issues (tides and weather) is a good proxy for gravity. But you are measuring at sea level, which can be a long way away from sea floor, and the radar spot on the sea surface is a few km in diameter, so again, attenuation of high spatial frequencies limits the ability to see shallow stuff. Shipborne surveys are OK. You put the gravimeter at the centre of buoyancy and try to process out the rest of the noise. Magnetics has to be towed well behind the ship. Both are usually done when a seismic survey is done.
The whole problem of working out what is down there is a classic underconstrained inversion problem. There are an infinite number of solutions, but if you make some reasonable assumptions, and have other data to help (like nearby seismic, wells, both mag and grav) you can start to piece it together. Geological processes can only produce a limited set of possible scenarios, so a large fraction of the infinite number of solutions can be ignored. The propensity of geology to create layers, and to then fold and fault them gives you a big clue about what you are seeing. You can make some useful assumptions about the statistical distribution of bodies, which turn out to be mostly good, and that allows work in the frequency domain as well.
I once worked in a factory that made and repaired geophones and seismic cable. The red and blue plugs in the photo are exactly what we made. The wire coming out of them would lead to a series of geophones plugged into the ground.
