Bitumen is the scientific name for the heavy oil in what is known as oil sands or, more colloquially as, tar sands.
As Dr. Jim Lacefield has shared at recent public presentations in Florence and Hatton, the presence of oil sands in Alabama has been known for centuries. According to Dr. Lacefield, our native ancestors used the tar-like substance from the sands to seal canoes and for medicinal purposes.
Aside: I’ve known about the oil sands on my family’s land since I was a child in the 1970s. When I was growing up, state and university geologists occasionally paid a visit to do core drilling on family land since we have a surface level outcropping. We even had a few industry speculators visit. Oil and gas investors might recognize one gentleman’s name if I mentioned it.
Back in those days, the vision or goal was to find a way to “drill for oil.” It wasn’t economical to “develop” oil sands, then, because the costs of extracting oil from the sandstone far exceeded the revenue that could be generated.
As several geologists and petroleum engineers have confirmed in recent public meetings, the industry generally acknowledges that we’re beyond the “peak oil” stage, when easily-obtainable oil can be reached through conventionally drilling. And the bitumen in Alabama is trapped inside water molecules, surrounded by sand and clay. No one is likely to get a gusher of bubbling crude when out hunting critters like Uncle Jed.
Since the bitumen trapped inside the sand, clay and water won’t simply flow from the ground, what techniques have the geologists and petroleum engineers devised to economically extract the bitumen from the earth today?
Basic Geology: 101
We’re looking at a multi-step process that begins with a determination of the depth of the oil sands deposits. In Alabama, bitumen lies within the Hartselle Sandstone geological formation.
As Dr. Lacefield told us, the hydrocarbon deposits in the Hartselle sandstone were formed when a vast ocean covered the area we know today as the Shoals area of north Alabama.
As the continents moved and shifted a body of water that once was an ocean became landlocked. The sand that once washed in and out with the tides settled to the bottom and the water began to evaporate. Little ocean critters were trapped. The lack of oxygen in these waters as the microscopic ocean critters died off left hydrocarbon deposits trapped in the sand and clay that today comprise the formation we call Hartselle sandstone. I think that’s basically what he said.
These hydrocarbon deposits in the sandstone are the bitumen that the oil and gas industry is eager to “recover” today and process into crude oil and then petroleum-based products that “fuel our economy.”
(Aside: We could insist that our industries use other technologies to fuel our economy but, so far, no one seems willing to seriously pursue that approach in the United States. In other words, most of us have no choice except to drive gasoline-fueled vehicles because that’s the only option that’s economically available to us. And most all of us have to drive if we want to go to work or to the doctor or grocery store or wherever. So it’s disingenuous to suggest that we suddenly stop driving. Many of us can drive less. But few of us can avoid driving gas or diesel-fueled vehicles, as much as some of us might wish we could).
Back to geology:
As the water evaporated and left the hydrocarbons exposed, some of the oil and gas evaporated or eroded away, Dr. Lacefield told us. That’s why there’s no bitumen in Alabama north of the Tennessee River.
In the area just south of the Tennessee River, from the Moulton Valley over to Cherokee in west Alabama, the Hartselle sandstone formation appears at or near the surface. That’s how we have “outcroppings” in places like Wolf Springs, Shine’s Spring, and elsewhere.
An outcropping is where you see the oil sands at the surface. Sometimes, when it’s hot, the oily bitumen will seem to ooze out of rocks. But in Alabama, Hartselle sandstone is hard, with the bitumen trapped between a molecules of water and layers of sand and clay. So there’s not much oozing.
As we travel south down highway 43, the Hartselle sandstone formation is farther below the surface. I believe Joel Mize said it’s about 50-feet-per-mile drop as you travel south. But I might be wrong about that, so I’ll check. In any event, the father south you go, the deeper the Hartselle sandstone.
Removal Option 1: Surface Mining
When the Hartselle sandstone is relatively near the surface, such as less than maybe a few hundred feet deep, the technology requires removal of the “overburden” to get to the Hartselle sandstone formation.
“Removal of the overburden” is the industry’s way of saying: Remove the trees, grass and other flora, remove the top soil, then excavate down to the level of the desired mineral or geological formation.
Ordinary folks call this surface mining or strip mining. Some might call it a quarry if it’s in a small space, like a few hundred square feet, but it still requires digging out the surface to get to the Hartselle sandstone.
FYI: If you remove all the flora, you’ll also remove all the flauna. Flora and fauna go together like cornbread and buttermilk. If you like to hunt or listen to birds or frogs (like my grandmother), you probably like fauna.
Removal Option 2: Drilling
When the Hartselle sandstone formation is below a certain depth, another method of extraction is necessary. The industry now has a technology that makes it possible to use drilling to “extract” the bitumen that is trapped in the sand and clay soil.
Currently, there are two drilling methods used to “extract” deep-level bitumen from the earth:
A. Cycling steam stimulation
B. Steam-assisted gravity drainage (SAGD)
The Centre for Industry in Canada has prepared this nifty graphic to explain the two different drilling techniques used to extract bitumen deposits that are too deep to “extract” by surface mining.
It all sounds so clinical, doesn’t it? I don’t know about you, but I am suddenly reminded of neti pots, steam humidifiers, and having my wisdom teeth removed. If only …..
If you know anything at all about physical science, steam is what is produced when water is heated to a high temperature.
So, from that, we can rest assured that lots of water is needed to produce the steam to liquify the bitumen to a flowable level.
The other thing that’s required to produce steam is heat. And heat requires energy to produce. And energy, in the United States, largely comes from four sources: Natural gas, coal, hydroelectric or nuclear. Unfortunately, energy suppliers in the US don’t seem to put much stock in the energy produced by our good friend, the sun.
Based on my research, it appears that natural gas is the primary source of energy used to produce the steam needed in deep-level bitumen extraction.
To recap: Oil sands “development” first requires that bitumen be removed from the earth. The industry has two ways to do this: Surface mining or steam-drilling.
Surface mining requires the mechanical removal of the “overburden.” Non-scientists call this strip mining. Not pretty. Not good for flora and fauna. Not friendly to top-soil (which we need to grow food). Can also cause problems with air and water quality.
Two methods of steam drilling are currently in use: Cycling steam stimulation and steam-assisted gravity drainage. Both require lots of water and energy to heat the water to produce the steam. Both cause the oil to flow enough to remove it from the earth. Both produce side effects.
That’s probably enough for this lesson.
This post is intended to provide a simple overview of the 3 methods used to get TO the oil sands to extract the bitumen. Future posts will address each approach in more detail. In other words, the details are more complicated than this.
Stay tuned. In the meantime, you can watch the first episode of The Beverly Hillbillies, which is now apparently in the public domain. But first, contact your state legislators and tell them how you feel about the proposal to develop oil sands in the Shoals area of Alabama.