Unlocking Fossil Fuels: The Inner Workings of Fracking
How a Fracking Oil Rig Works
Hydraulic fracturing, or fracking, has enabled oil and natural gas companies to tap pockets of fossil fuels tightly trapped in rock formations deep underground. The technology is responsible for surging oil and gas production in the United States.
Once the well is drilled, cased and cemented, a special tool called a perforating gun is lowered into the rock layer. It creates holes that connect the rock holding oil and gas to the well bore.
How It Works
A fracking site has the same surface equipment as a conventional well rig (including the rig itself, drill stem, casing and crew), but instead of drilling vertically toward a gas or oil deposit, these wells go down to the deposits and then run horizontally. They can also be much deeper than a vertical well, going down thousands of feet and needing tens of millions of gallons of water for each one [source: EarthWorks].
That water, which contains used fracking fluid, chemicals, heavy metals and other pollutants, is then pumped back to the surface and trucked off for treatment. It’s also injected into disposal wells thousands of feet underground.
Proponents of fracking argue that the process is an essential part of our energy future, providing us with abundant new fossil fuels. But critics say fracking is dangerous and destructive to the environment, and that its profits aren’t worth the price. Both sides have valid points. So, where does the truth lie?
Well drilling is the process of creating a hole in bedrock that can extend to hundreds of feet. A steel pipe called a casing fits inside the well and is protected by cement, and then perforated in small holes. Fracking fluid (more on that below) is then pumped down the hole and through these holes at high pressure to create new fissures in the rock. These fissures allow natural gas, if present, and if oil is found, to flow through pipes to the surface and into storage tanks.
A fear raised by critics of fracking is that these fissures could migrate up through aquifers and contaminate groundwater. But regulations protect the water table by requiring independent lab tests to ensure that all drill and frack fluids meet quality standards. Additionally, the wells themselves are bailed or pumped after drilling to develop them and determine their yield. This can be done using a conventional rig or with UBD or MPD techniques.
Once the well has been drilled and cased, it needs to be perforated for fluid communication between the reservoir and the borehole. The perforation process is done by shooting explosive charges into the casing and cement sheath using either expendable guns or retrievable gun systems.
The effectiveness of a perforation shot is determined by the size of the charge and the amount of pressure it creates in the formation, as well as the geometry and quality of the surrounding rock. A shaped charge with the appropriate geometry and pressure generates a perforation tunnel that effectively connects the wellbore to the reservoir.
Impaired connections between the wellbore and the formation can hinder the productivity of fracture stimulated intervals. Achieving a clean connection requires that the well be test flowed and pumped to clear the debris from the newly formed perforation tunnels. Alternatively, it may require extensive and costly secondary cleanup techniques. Oriented perforating minimizes damage to unstimulated inflow potential, reducing the amount of debris that must be cleaned and the number of unproductive days required for effective testing and treatment distribution.
A mixture of water and sand is pumped down the well through the perforations at high pressure, creating tiny fractures in the rock. The sand props open the cracks and enables gas (or other resources) to flow through them. The fracturing fluid is then pumped back up to the surface, and separated. It is either pumped into injection wells or recycled, but it can also be used as mud for lubricating drilling tools.
The precise formulations of fracturing fluids are closely-guarded company secrets, but most contain more than 99 percent water and less than 10 percent sand. The other one to two percent consists of chemical additives that may include gelling agents, borehole-cleaning acids and corrosion-preventing stabilizers.
Fracking is credited with enabling natural gas producers to access vast new energy supplies trapped in tight rock formations. This has led to lower prices for consumers and a manufacturing renaissance. But it is not without its challenges. Millions of gallons of water are required for fracking, and sometimes must be trucked in from distant locations, diverting it from other uses. Also, spills and leaks can contaminate water tables.