Heliportable equipment

From Wikimarcellus

In some of the more rugged areas of the Appalachian Basin, such as parts of West Virginia, despite their greater expense, seismic studies are conducted using heliportable equipment in more challenging terrains. Mountain hollows and steep ridges often do not provide a stable footing for vibroseis trucks to carry out seismic surveys. Drills are surgically dropped from helicopter without having to move in heavy equipment on the ground. Seismic by helicopter is considered to be cost effective and less damaging to the environment.

How it works: A helicopter drops a diminutive shothole drilling rig tethered to a 160-foot cable. The 12' by 4' rig is gently lowered into the mountain location where it will be used and is unleashed from the helicopter hovering overhead.

Then, a 20-40 foot hole is drilled and a small explosive charge is detonated in the bore hole. The drilling rig is retrieved by the awaiting helicopter and transported to its next location. This same operation is repeated over and over until a grid of holes has been laid down often 50 or more to an acre.

Similarly a grid of geophone receivers are positioned so that they can hear and record reflected sound waves bounced back from the underground rock formations.

Each explosive charge is detonated by radio to send sound waves into the underground formations these echo back and are measured and recorded.

Once the sound data is acquired, it is processed in much the same way as that from vibroseis. The cost is roughly four times greater when collected by helicopter than by thumper truck, but in certain kinds of prospective terrain, this cost can be justified.