The Hunt for Hydrocarbons
Last time, we learned that four things are necessary to create and capture oil. Those four are, an organic carbon-rich source that gets “cooked” deep underground; a reservoir rock layer with bazillions of tiny empty spaces to hold liquid petroleum and water; a shape to the underground rocks that will trap the fluids in a confined space; and non-reservoir (impermeable) rocks to seal the hydrocarbons inside the trap. Now that we know which puzzle pieces have to join to create an oil field, to find oil we have to look for places where all four pieces are present.
Scientists who work for oil companies will tell you, “There is no direct hydrocarbon indicator.” That’s a fancy way of saying that there is nothing we can see or measure that lets us just point to a spot and say, “Drill here!” and know that we’ll strike oil. Instead, we have to study blurry images of the rocks deep beneath the surface and use training and experience to interpret them. That’s how we hunt for places where source, reservoir, trap, and seal all come together in the right relationships.
The first people to use oil found puddles where it had leaked out on the ground’s surface, like at La Brea Tar Pits in California, USA. Oil found at the surface, however, is usually gummy and thick because it’s been exposed to air and water; so early use was often as salves and medicines (not a good idea, really, since petroleum is an organic poison). Not only that, but the amount available in these leaks, or "seeps," is small. Early entrepreneurs dug wells by hand near seeps looking for larger deposits and, when they were successful, also noticed that the oil was higher quality – it was lighter and thinner, and could be burned in a lamp, for instance. The first successful drilled oil well in North America, the Drake #1 in Pennsylvania, was located near a surface seep. The presence of a seep is the closest thing there is to a direct hydrocarbon indicator, but we still have to figure out which direction to go if we want to find the good stuff!
As we entered the age of oil, demand grew faster than wells drilled or dug near a few surface seeps could supply it. Short supply means higher prices, and this bigger payback for the work ushered in an era of surface mapping to hunt for oil. By studying the shapes and order of rocks exposed at the surface, early oil-company geologists (scientists who study the earth) could identify possible traps in the crumpled layers around basin edges. Drilling holes in geological structures – bent or broken sedimentary rocks - caused a boom in oil exploration in the early twentieth century. This method also introduced the oil-seekers to risk: even though a trap is visible, that doesn’t mean that the other three pieces of the puzzle are present. If there’s no reservoir rock, there can be no oil accumulation. If there’s no source, there is nothing to put in a reservoir. And if there is no seal, anything that does enter a trap simply leaks out. Early “wildcatters,” as oil-drillers were called, either learned how to identify which structures had the best chance of all four components being present, or they went broke drilling “dry holes.”
Just before World War II, there was second forward leap in exploration. Research scientists devised a way to bounce sound waves off underground layers, and record the waves that return to the surface. By carefully measuring the time it takes for that sound to return, scientists can create a sort of “sound image” similar to the layering of the rocks underground. This method, called seismic exploration, created a new field for scientists who called themselves geophysicists. The new tool came along just in time: geologists doing surface mapping had found most of the fields visible on the ground. With seismic tools, the two groups of scientists – geologists and geophysicists – could work as a team to identify traps that aren’t visible from the surface.
Today, geologists and geophysicists work together exploring for oil fields using powerful computers and special software. Exploration geologists and geophysicists are like detectives: they spend their days following subtle clues, putting together complex puzzles for which there are never enough pieces – and when they’re done, the ultimate test of their puzzle-solving skill is an exploration well. As a famous geologist said more than fifty years ago, “All the easy oil has been found.” These days, the hunt for oil involves months and years of painstaking work by highly-trained professionals using state-of-the-art technology. Even with all that power brought to bear on the problem, only about one of every eight exploration wells drilled finds enough oil to pay the cost of the well.
And here you thought all they had to do was stick a pipe in the ground…
This is the third of a series of minilectures on the petroleum industry from the ground up
1) Where Does Oil Come From?
2) Where Do Oil Companies Find Oil?
3) How Do Oil Companies Find Oil? <== You are here. Future installments include:
4) The Economics of Petroleum Exploration and Production
5) Refining
6) The Economics of Big Oil
7) The Future of Oil
Scientists who work for oil companies will tell you, “There is no direct hydrocarbon indicator.” That’s a fancy way of saying that there is nothing we can see or measure that lets us just point to a spot and say, “Drill here!” and know that we’ll strike oil. Instead, we have to study blurry images of the rocks deep beneath the surface and use training and experience to interpret them. That’s how we hunt for places where source, reservoir, trap, and seal all come together in the right relationships.
The first people to use oil found puddles where it had leaked out on the ground’s surface, like at La Brea Tar Pits in California, USA. Oil found at the surface, however, is usually gummy and thick because it’s been exposed to air and water; so early use was often as salves and medicines (not a good idea, really, since petroleum is an organic poison). Not only that, but the amount available in these leaks, or "seeps," is small. Early entrepreneurs dug wells by hand near seeps looking for larger deposits and, when they were successful, also noticed that the oil was higher quality – it was lighter and thinner, and could be burned in a lamp, for instance. The first successful drilled oil well in North America, the Drake #1 in Pennsylvania, was located near a surface seep. The presence of a seep is the closest thing there is to a direct hydrocarbon indicator, but we still have to figure out which direction to go if we want to find the good stuff!
As we entered the age of oil, demand grew faster than wells drilled or dug near a few surface seeps could supply it. Short supply means higher prices, and this bigger payback for the work ushered in an era of surface mapping to hunt for oil. By studying the shapes and order of rocks exposed at the surface, early oil-company geologists (scientists who study the earth) could identify possible traps in the crumpled layers around basin edges. Drilling holes in geological structures – bent or broken sedimentary rocks - caused a boom in oil exploration in the early twentieth century. This method also introduced the oil-seekers to risk: even though a trap is visible, that doesn’t mean that the other three pieces of the puzzle are present. If there’s no reservoir rock, there can be no oil accumulation. If there’s no source, there is nothing to put in a reservoir. And if there is no seal, anything that does enter a trap simply leaks out. Early “wildcatters,” as oil-drillers were called, either learned how to identify which structures had the best chance of all four components being present, or they went broke drilling “dry holes.”
| Where there’s money to be made, technology soon comes along to make it easier (or not as hard) to earn it. This has happened in the “oil patch” many times. The first big leap in exploration came soon after World War I began, when French scientists developed a way to record the order and thickness of rock layers encountered in a well, and well logging was born. Well log measurements were soon invented that helped scientists figure out which deeply buried rocks are sources, reservoirs, or seals. Almost a century later, well logs are still used to help geologists understand the rocks in the subsurface, though the sorts of information collected today are much more complex than the first logs. |
Just before World War II, there was second forward leap in exploration. Research scientists devised a way to bounce sound waves off underground layers, and record the waves that return to the surface. By carefully measuring the time it takes for that sound to return, scientists can create a sort of “sound image” similar to the layering of the rocks underground. This method, called seismic exploration, created a new field for scientists who called themselves geophysicists. The new tool came along just in time: geologists doing surface mapping had found most of the fields visible on the ground. With seismic tools, the two groups of scientists – geologists and geophysicists – could work as a team to identify traps that aren’t visible from the surface.
Today, geologists and geophysicists work together exploring for oil fields using powerful computers and special software. Exploration geologists and geophysicists are like detectives: they spend their days following subtle clues, putting together complex puzzles for which there are never enough pieces – and when they’re done, the ultimate test of their puzzle-solving skill is an exploration well. As a famous geologist said more than fifty years ago, “All the easy oil has been found.” These days, the hunt for oil involves months and years of painstaking work by highly-trained professionals using state-of-the-art technology. Even with all that power brought to bear on the problem, only about one of every eight exploration wells drilled finds enough oil to pay the cost of the well.
And here you thought all they had to do was stick a pipe in the ground…
This is the third of a series of minilectures on the petroleum industry from the ground up
1) Where Does Oil Come From?
2) Where Do Oil Companies Find Oil?
3) How Do Oil Companies Find Oil? <== You are here. Future installments include:
4) The Economics of Petroleum Exploration and Production
5) Refining
6) The Economics of Big Oil
7) The Future of Oil
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