Oil and gas operations, like all large-scale industrial operations, are inherently dangerous and sometimes interact with human populations in confusing or concerning ways. Fluids including hydrocarbons, wastewater and other chemicals might spill or leak. The groundwater through which wells are drilled could be contaminated. Equipment for drilling operations create noise and light pollution. Trucks carrying materials to and from drilling sites make mobile noise, pollute the air and strain local roadways. Energy development sites take up physical space on the surface. Most worrying to many are emerging links between wastewater injection and seismic activity.
Naturally, these negative consequences of oil and gas operations do not sit well with many people, particularly those who live near extraction operations.
First let’s look at the possibility of contaminating groundwater. Best management practices for drilling and completion, combined with careful engineering, help mitigate the risk of produced hydrocarbons or associated chemicals and fluids ever interacting with groundwater. Oil and gas operations occur in stratigraphic layers far below underground sources of drinking water. This distance ensures there are layers upon layers of rock—often including low-permeability shale—between the groundwater and operational activites, such as hydraulic fracturing or an injection point.
Of course, this doesn’t provide an ironclad defense against contamination or hydrocarbon migration. Damage to wells themselves from structural or chemical interference might introduce paths for fluid migration anywhere along the length of a wellbore. In order to guard against such hazards, operators must install wells with utmost care and adherence to regulations. Well technology—casing, liners, cement, and extra isolation of wells from freshwater zones—is tremendously important.
Another environmental issue is that of disruption to nearby communities. Noise, dust, light and traffic increase as operations increase in an area. High walls enclose some drilling sites to mitigate the light and noise issues. For example, the operators of the Beverly Hills Oil Field in Beverly Hills and Los Angeles, California, have the unique challenge of producing in the middle of a completely urban and affluent community. Large buildings hide almost 100 active producing wells at four different production sites around the city.¹
The video clips below demonstrate how operators are moving toward a more neighbor-friendly sound management strategy with sound abatement walls and new hydraulic fracturing trucks. These trucks are quieter than previous models, as shown by sound level readings 3 feet from the trucks, 450 feet from the trucks outside the wall, and 650 feet from the trucks in a residential area near the production site. There is a difference between the A-scale and the C-scale readings because the A-scale measures loudness only from about 500 hertz (Hz) to 10,000 Hz, but the C-scale measures loudness at all frequencies from 30 Hz to 10,000 Hz.
Sound Reading 3 Feet from Pump Truck
Sound Reading Right Outside Sound Wall
Sound Reading 650 Feet from Pump Trucks Near a House
Public Concerns About Hydraulic Fracturing and Horizontal Drilling – Azra N. Tutuncu – Colorado School of Mines
Hydraulic fracturing in the US has unlocked vast low permeability tight gas and shale gas and tight oil reservoirs that were previously uneconomic to produce. That has increased production and created jobs. Yet, it has also raised environmental concerns about these operations. Let’s look at the roles that education and regulation can play in keeping the public informed and safe.
Hydraulic fracturing involves injecting a mixture of water, sand and chemicals down into the tight reservoirs. The pressurized fluid causes the reservoir formation to fracture. During this process and a few days to weeks afterwards when production starts, this fluid returns as flowback water. Produced water along with the natural gas and oil released from the reservoir rock travels through the fractures into the well and to the surface. Produced water continues to accompany oil and gas production throughout the life cycle of the well.
Like many other engineering operations, hydraulic fracturing has raised concerns about noise, dust, bright lights, heavy traffic and environmental impacts. Moreover, there are additional concerns unique to hydraulic fracturing operations. These include wastewater disposal, induced seismicity and the possible contamination of water supplies. Like any production operation, hydraulic fracturing is disruptive to those living nearby. High walls around the sites are common to mitigate noise and light pollution, and hours of operation are often restricted in wells close to populated residential areas.
Truck traffic is a concern at many phases of the process. Operators truck in millions of gallons of water for fracturing. Trucks may congest or increase the wear and tear on roadways. Trucks also introduce noise and air pollution. Later, trucks carry wastewater and hydrocarbons away from the sites, introducing risk of potential spills along the roadways away from production sites. However, there are safeguards in place to protect against spills and also programs to properly train drivers.
Outside of trucks, emissions from equipment and storage remain a concern in the oil and gas industry. Once hydrocarbons have been brought to the surface, they are stored on site prior to being transported. Poorly maintained tanks can leak methane and other gases. Venting and flaring of natural gas releases carbon into the atmosphere as methane and CO2. Therefore, these emissions must be monitored as well.
Another concern for all oil and gas production is footprint of the pad sites and wells. This is an area where hydraulic fracturing has significant advantages. Let’s look at a simple example. Most oil and gas operations are drilled and produced from vertical wells. Let’s assume we want to produce from a 100 foot thick reservoir. If instead of drilling 100 feet vertically across the formation, we drill 2,000 feet into the reservoir horizontally, the wellbore will have much larger exposure to the reservoir, allowing it to produce more than the vertical well.
Imagine what happens when we introduce several hydraulic fractures along the horizontal well. The fractures induced will allow us to reach deeper into the reservoir, and we can produce even more. Hence, we can replace many vertical wells and many horizontal wells with a single horizontal well if you hydraulically fracture it. This way, we produce much more oil and gas with fewer wells and ultimately reduce the footprint of the operations. A reduced footprint makes the reclamation process simpler as well.
One of the greatest concerns voiced by the public is about water. How much is used and how is it disposed of? Fracturing a single well can use from one to 15 million gallons of water, depending on the fracture design. This is obviously a concern in areas of the country experiencing drought. On the other hand, both flowback and produced water must be treated, possibly recycled and then disposed of. Treating the wastewater may be most desirable from an environmental point of view, but the wastewater typically has a high TDS content, making the treatment process far more complicated. The recovered wastewater may also contain small amounts of chemicals or naturally occurring radioactive materials, such as uranium. These components present challenges to safely treating water before returning it to the environment.
After multiple treatments and recycling, the last step for wastewater management is disposal. When we review the disposal process, we must investigate where the wastewater ends up and how it gets there. Typically, wastewater is temporarily stored in tanks or pits at the well site. Tanks and pits must be properly constructed and maintained, and a risk management plan must be in place to deal with the accidents or equipment failures. Most commonly, trucks transport wastewater to its final destination, the disposal wells.
Disposal sites where wastewater is injected into wells must be properly identified, constructed and regularly inspected. If there is an aquifer nearby, we need to ensure that no contamination will occur. Disposal wells are in high permeability formations, and injection is done at high rates for many years. Without proper well construction and monitoring, migration of fluids might occur, and the wastewater could contaminate a nearby aquifer. There is much smaller risk of this type of migration and contamination in hydraulic fracturing operations because of the short duration at lower injection rates and the depth at which fluids are injected in the hydraulic fracturing operations.
In most US large shale plays, like the Marcellus and the Eagle Ford, the distance between the shallowest hydraulic fracture induced in the wells and the deepest aquifer above the wells is typically between one and two miles. Because the various formations between the aquifer and the hydraulic fracture will each serve as a barrier, it is almost impossible for a fracture to propagate across such a distance.
One of the most common concerns we hear from the public is about earthquakes. To clarify, microseismic activity created during hydraulic fracturing operations is much smaller in magnitude than the seismicity related to underground injection. Since the wastewater injection sites are the main sources of induced seismicity risk, these disposal sites must be carefully chosen, and all stakeholders need to better understand the real sources of their concerns and how these are prevented and mitigated.
We have seen that hydraulic fracturing is a multi-step process that involves large-scale operations. We need to understand what these steps are, what risks they entail, and we must have clear and fair regulations that allow efficient production while keeping the public safe and well-informed.
1. Alan Taylor, 2014, “The Urban Oil Fields of Los Angeles,” The Atlantic, https://www.theatlantic.com/photo/2014/08/the-urban-oil-fields-of-los-angeles/100799/ (accessed March 9, 2017).
2. Dave Feeling, March 19, 2012, “Roads Killed: Texas Adds Up Damages from Drilling,” StateImpact Texas, https://stateimpact.npr.org/texas/2012/03/19/roads-killed-texas-adds-up-damages-from-drilling/ (accessed March 9, 2017).
Sound Reading Videos: Courtesy Azra N. Tutuncu
Images: “Fracking Operations” by Joshua Doubek licensed under CC BY SA 3.0