Hydraulic fracturing is an often-misunderstood technique. Here are answers to some common questions.
Can the fractures allow natural gas to seep up into the water table?
Typically, North American gas formations that require fracturing are located a mile (1.6 kilometers) or more below the water table, trapped below many layers of impermeable rock. These thousands of feet of rock overlying the tight gas formations, combined with the low permeability of the tight gas formations themselves, keep the natural gas and other hydrocarbons contained within the target formation, and also help prevent migration of any hydraulic fracturing fluids that may be pumped into such formations.
Can fracturing fluid seep from the gas formation into the groundwater supply?
Shell’s drilling, casing, and cementing procedures, which meet or exceed regulatory requirements, are designed to protect groundwater by isolating the well from any groundwater supplies.
We pump the fracturing fluid through the well into the rock or shale zone containing the gas, which has very low porosity and is typically trapped far below the deepest source of potable water and underneath many layers of impermeable rock. Consequently, the fracturing fluid should either stay within the target formation or be forced back out through the well, but in either case it remains isolated from groundwater zones.
Can fracturing fluid get into the water supply from the well?
We design and test the integrity of our wells to meet strict specifications based on the local environment. The upper portions of the well, where the wellbore passes through the water table, are extensively reinforced to prevent either gas or fluids from escaping into the surrounding ground. Wells are made of steel pipes and sealed in place with cement from the surface to below the level of drinking water supplies, typically to a depth of 1,000 feet (about 300 meters) or more.
These barriers help to contain the fracturing fluid and, along with the depth at which fracturing takes place, prevent the fluid from mingling with drinking water close to the surface.
During and after hydraulic fracturing, wells are monitored with pressure sensors to check that they are firmly sealed. Shell also periodically monitors the fractures and the fluids using micro-seismic technology to map the formation, which helps to make production as efficient as possible and protects the environment.
Are the chemicals used in hydraulic fracturing dangerous?
Most of the fluid used in hydraulic fracturing is water. We add chemicals, typically 1 percent of fracturing fluids, to keep the pipes cool by reducing friction and to prevent scale build-up and bacterial growth. Many of these additives are compounds that are used in other applications you encounter in your daily life, from citric acid and guar gum, commonly used as food additives, to ethylene glycol, commonly used in household cleansers and automotive antifreeze.
Some of the chemical additives can be hazardous if not handled carefully. We take great care when using all the compounds added to fracturing fluid, and meet or exceed all regulatory requirements related to handling hazardous materials.
The formulas for fracturing fluids vary, partly depending on the composition of the gas field and partly on the expert opinion of the operator or fluid supplier as to what works best. These formulas are owned by the supplier and some are considered proprietary. Shell is transparent about our operational methods. This includes releasing information about the chemicals we use in our hydraulic fracturing operations to the extent we are permitted by suppliers to release their proprietary information. We support regulatory efforts that require our suppliers to release such information.
Find data at fracfocus.org for any of our wells in the U.S. that have been hydraulically fractured since January 1, 2011.
Can the chemicals stored on the site affect groundwater?
Safe handling of all water and fluids on site, including chemicals used for hydraulic fracturing, is a high priority for Shell. We comply with all regulations regarding containment, transport and spill handling. To protect groundwater, we keep chemical containers and all fluid handling equipment located on site within secondary containment barriers that could capture a spill in the unlikely event that one would occur. The containers must pass regular integrity checks and certification.
We check water storage tanks for integrity before we use them and check them visually each day. Single-use containers that are used to transport small volumes of chemicals are returned and disposed of offsite. Any spill that were to occur on a well pad would be immediately cleaned up, reported and documented according to both our own and regulatory requirements.
What happens to the fracturing fluid after it is used?
We take multiple steps to properly handle hydraulic fracturing fluid. First, when possible, we reuse it for additional wells in a single field. This both reduces our overall use of fresh water and reduces the amount of recovered water and chemicals that must be disposed of. Second, we keep the recovered water in storage tanks or lined storage pits until it is disposed of in a permitted saltwater injection disposal well or taken to a treatment plant for processing.
All treatment and disposal facilities used by Shell undergo extensive on-site environmental assessments to ensure they meet regulatory standards and Company-established specifications prior to use.
All of our Shell-operated injection wells are designed to meet federal regulations set by the Environmental Protection Agency to protect groundwater. Our geologists and engineers work together to design, drill and test injection wells for integrity and compliance. We isolate the wells in three ways:
- We choose zones that have multiple confining layers above the zone to keep the injected fluids within the target formation
- We use multiple layers of well casing and cement (similar to our production wells) and periodically run mechanical integrity tests to verify that the casing and cement are holding the liquids
- We control how much fluid we inject and at what pressure (specified in each well permit) to help keep the fluids in the target zone, and we monitor the pressure in the injection well and the spaces between the casing layers (also called the annuluses) to check and verify the integrity of the injection well
We also screen any non-Shell-operated injection wells that we use to verify that they comply with all regulatory requirements.