Hydraulic fracturing

Hydraulic fracturing, or fracking, is a drilling technique used to extract natural gas and other hydrocarbons trapped in low-permeability, low-porosity rock formations. The process is straightforward: fluids are pumped under high pressure into a rock formation to fracture the rock containing the hydrocarbons. This creates cracks and factures in the rock, allowing hydrocarbons to flow more easily into the well for extraction. As a result, hydrocarbons deposits that were previously uneconomical to develop became economically viable (this increases the reserve).

Figure 1. A map of shale gas and shale oil deposits. Hydraulic fracturing can aid in the extraction of the fuels from these deposits.

Fracturing Process

Hydraulic fracturing is used to enhance the extraction of oil and natural gas by stimulating the flow of hydrocarbons through porous and permeable rock formations. Since unconventional oil and natural gas are often trapped within low-permeability rock formations, such as shale, pathways must be created to allow the hydrocarbons to flow through the rock and into the well. Before the widespread use of hydraulic fracturing, drilling companies often drilled multiple wells into a formation in an attempt to increase production from oil and gas reservoirs. However, this approach is relatively inefficient because each well can only access a limited volume of the reservoir. Hydraulic fracturing addresses this limitation and is typically performed after the well has been drilled.

Figure 2. Diagram of a fractured well.

To fracture the rock, a fluid known as fracturing fluid (or fracking fluid) is pumped into the wellbore at high pressure, creating fractures in the surrounding rock. Because hydraulic fracturing is performed after a well has been drilled, it can be used either shortly after drilling or later to help increase production from an existing well. These wells are often drilled directionally or horizontally to increase the contact area between the wellbore and the oil- or gas-bearing rock formation. The fracking fluid consists of primarily water containing chemicals and sand, along with small amounts of chemical additives that vary depending on the geology and operational requirements of the well. The sand, known as a proppant, helps keep the newly created fractures open, allowing oil or natural gas to flow into the well.

Injecting the fracturing fluid creates a network of small fractures in the rock surrounding the well. These fractures increase the volume of the reservoir that can contribute oil or natural gas to the well, improving production.

Environmental Impacts

Hydraulic fracturing is an efficient technique that improves the extraction of natural gas and oil from low-permeability rock formations. The largest environmental impact associated with natural gas production is the combustion of gas, which releases carbon dioxide into the atmosphere. By enabling access to previously uneconomical oil and natural gas resources, hydraulic fracturing has contributed to increased fossil fuel production and the associated greenhouse gas emissions that drive climate change.

As with any resource extraction method, hydraulic fracturing has several associated environmental concerns. These concerns primarily include the large volumes of water required for fracturing, the management of wastewater, and the potential for groundwater or surface water contamination if fluids are improperly handled. Hydraulic fracturing can also induce small earthquakes, although larger induced seismic events are more commonly associated with the underground disposal of wastewater from oil and gas operations. In addition to these environmental concerns, fracking also offers several operational advantages. One advantage is that fewer well pads may be required to access a reservoir, reducing the surface footprint of oil and natural gas extraction. Before the widespread use of hydraulic fracturing and horizontal drilling, more wells were often required to access the same resource.

Water Use

Hydraulic fracturing requires a significant amount of water. Water use varies depending on the geology and well design, but a single hydraulically fractured well may require between 7 million and 38 million litres (2 to 10 million gallons) of water. Additionally, in some locations, the water must be transported by large fleets of trucks, contributing to greenhouse gas emissions and increased traffic.

Fracking Chemicals

Another environmental concern associated with hydraulic fracturing is the use of chemicals additives in the fracturing fluid. Fracturing fluids contain a variety of chemical additives, while naturally occurring substances such as radium, uranium, lead, and mercury may be present in the flowback and produced water that returns to the surface after hydraulic fracturing. One concern is that fluids from fracturing operations could contaminate groundwater or drinking water if spills occur at the surface or if wells are improperly constructed or maintained. Although many companies disclose much of the composition of their fracturing fluids, some chemical formulations remain proprietary. Critics argue that proprietary chemical formulations can limit transparency regarding potential environmental and health risks, while industry representatives maintain that protecting specific formulations preserves trade secrets and competitive advantages.

Drinking Water Contamination

Another issue related with hydraulic fracturing is the potential for groundwater contamination. Images and videos have shown homeowners igniting methane that is present in water flowing from household taps. When the tap is turned on, dissolved methane can be released from the water. Although methane occurs naturally is some groundwater systems, there have been documented cases where methane contamination of drinking water has been linked to oil and gas operations, typically because of inadequate well construction or faulty well casing rather than the hydraulic fracturing process itself. In these cases, methane typically migrates because of failures in well integrity rather than from the hydraulic fractures themselves. Poorly constructed or damaged well casings and cement barriers can allow methane to migrate into surrounding groundwater. Proper site characterization and well design help minimize the risk of unintended migration of fluids or gases during oil and gas development.

Overall, proper well casing construction are critical for reducing the risk of methane, hydrocarbons, and hydraulic fracturing fluids entering groundwater supplies. However, spills, improper wastewater storage, or leaks from wastewater holding ponds may also pose risks to groundwater and surface water quality.

Seismic Disruption

Hydraulic fracturing and wastewater disposal have both been associated with induced seismic activity. Although hydraulic fracturing has been linked to some induced earthquakes, most larger induced seismic events are associated with the underground disposal of wastewater rather than the hydraulic fracturing process itself. Most induced seismic events linked with oil and gas operations are related to the underground disposal of wastewater into deep injection wells. To dispose of non-potable wastewater, companies may inject it into deep, porous, and permeable rock formations underground. Injecting wastewater increases fluid pressure within the rock formation, allowing the water to move through interconnected pore spaces. The increased pore pressure can reduce friction along existing faults, potentially triggering earthquakes if the faults are already close to failure. Wastewater disposal typically occurs at lower pressures but over much longer periods and with much larger fluid volumes than hydraulic fracturing, making it more likely to induce felt earthquakes.

For Further Reading

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• Wellbore
• Horizontal drilling
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