For the longest time, salt domes were unknown to us humans. It wasn’t until 1900 while drilling near Beaumont, Texas, that we first discovered massive bulges of salt curiously ascending through layers of the earth’s crust. What exactly are these structures? And why do they matter so much in the world of Petroleum exploration? Allow me to explain.
Remember lava lamps? My sister used to have one in her room, and I was always fascinated with them. Think of the blobs floating up and down inside the lamp–in this example, they’re the salt. Two kinds of pressure can produce a salt dome–tectonic movement upwards, and the downward pressure of overlying sediment. If there’s a weak spot in the rock above (a thrust fault, a valley), the salt can intrude up into it. As long as the pressure on the salt remains high, it’ll keep intruding upwards.
And when salt is found so far beneath the earth’s crust (2,500 to 10,000 feet), pressure forces it into a highly viscous material that flows like oil. When it reaches this state, it slowly floats up to the surface, and traps layers of oil found in the rock layers above it along the way.
These deposits are quite literally trapped–they have nowhere to go until they’re drilled.
Finding a salt dome is like finding the jackpot in oil and gas. Typically they’re right near the earth’s surface and their oil reservoirs are quite substantial. Because they’re so close to the earth’s surface, the cost of drilling them are super low.
To conclude the story from above, after the workers found the first salt dome oil well, they extracted nearly 100,000 barrels of crude oil per day–a greater yield than any previous oil well.