Fracking & The Forces That Create Petroleum
SciWorks Radio is a production of 88.5 WFDD and SciWorks, the Science Center and Environmental Park of Forsyth County, located in Winston-Salem.
Fracking, or hydraulic fracturing, is a method of extracting petroleum trapped in solid rock layers that were previously inaccessible. But how do they do it and how is it different from standard drilling? The politics and environmental planning involved in fracking are beyond the scope of this show, but we will explore what fracking is, and how the petroleum resources got there in the first place.
Over 200 million years ago, most of the land on Earth was part of one giant supercontinent called Pangea. That wasn’t the first supercontinent, however, because the Earth’s crust is always in motion (see here also). Even now tectonic forces are shifting continents around; merging them together and rifting them apart. When Pangea split, it opened the Atlantic ocean. You can even see on a map that South America fits against Africa like matching puzzle pieces! Along the East coast of the United States there are several rift valleys where the crust was stretched out and the weakened rock fell in. In North Carolina there are three of these. Two have been identified as containing petroleum resources. You’ve probably visited at least one of these ancient rift valleys. On a drive east toward the Raleigh-Durham area, you’ll notice a downhill slope into the the Deep River basin, starting east of Hillsboro. If things had worked out differently, this could have been where the continents separated, and everything east of Raleigh would now be part of Africa! So, how did these rift valleys come to hold oil and gas? I spoke with Tyler Clark, the former chief geologist for the North Carolina Geological Survey, and current Geology Instructor at Wake Technical Community College, to find out.
Rain water started to fill up the low spot in the basin. Much like the rift basin we see today in East Africa there’s this long series of lakes. These freshwater lakes were very deep, and anything that died, this organic material would sink down to the bottom. Plants, ferns, we find the fossil evidence of these.
Throughout millions of years the basin was filled with thousands of feet of material. Imagine the weight of a bucket of dirt and rock. Now imagine that bucket is more than seven thousand feet tall! That’s a lot of pressure, which caused the underlying material to compress and turn to rock. The layer of thick, organic lake-mud became the shale rock.
It’s that process of burying and compressing and the natural decay that gives off these petroleum products. It gets trapped in these layers of rock. There are small cracks in the rocks that allow gas to accumulate.
Shale is tightly packed, with no space between the grains for gasses and liquids to flow. This is the challenge of extracting gas and oil from shale. It can’t pass through the rock and into a gas well, so you need a way to open up those cracks and get the gas out.
The method is called horizontal drilling. We can drill down until we get to where the shale layer is, and then turn the drill bit and drill horizontally along that layer of shale for a long distance, maximizing the amount of contact you have with that particular unit.
That’s the first step. The next part is hydraulic fracturing, or “fracking.”
Sand, water and a mixture of chemicals then pumps down the well. They put it under so much pressure that the rock shatters. The sand then holds these fractures open and acts as a very porous material that the water and gas can escape through. The proprietary mixture of chemicals helps liberate that natural gas, and helps bring it up to the surface in the most efficient way possible.