The hydraulic fracturing work site is often full of various basins, pits, and ponds to hold fluids and other materials close to the active well pads. Most of these pits and ponds qualify as frac pits since they’re designed to hold some kind of liquid necessary for hydraulic fracturing. Since the term frac pits is a broad one, that encompasses various types of in-ground containment and storage, it’s important to distinguish between the various designs. A pit built for holding produced water will need slightly different features than one built for fresh water only. Yet, they all share common characteristics and demands that guide how they should be designed and installed.
The High Demand for Water
Hydraulic fracturing is a powerful technique that has allowed for a new oil boom in areas there were previously believed to be inaccessible or already tapped out. However, it does rely on large volumes of water to send the fracturing materials and fluids deep into the gas deposits trapped in porous shale below ground. Up to 9 million gallons may be needed per well, although 4 to 5 million gallons is a more accurate average for most facilities. Even just 1 to 2 million gallons per well is a massive amount of water to pump, transport, and store when an operation may have dozens of wells running at once. While much of the water remains in the ground after fracturing, hundreds of thousands of gallons of produced water mixed with gas and oil do return to the surface. All that liquid must go somewhere, and it can’t be allowed to leak out into the surrounding environment where it could cause damage.
Risky Byproducts of Fracturing
While produced water obviously creates environmental risks due to its oil content and radioactive contamination in many cases, even the fresh water supplies held in frac pits can be risky. Any supply of millions of gallons of water in one location poses a risk of serious erosion and property damage if there is a dam collapse or overfilling from rainfall. All frac pits are at risk of liner breakdown due to exposure to hydrocarbons, even if they’re designed for fresh water only, since there’s a constant chance of contamination if a well malfunctions. Frac pits must be designed for the challenges of storing and being exposed to the byproducts of the fracturing process even when they’re not explicitly built to hold them.
In-Ground Storage Solutions
Ponds and pits offer in-ground, rather than above-ground, storage for large volumes of water; which has many benefits despite the amount of space they take up. First, it’s possible to build frac pits large enough to hold all of the produced water coming from the well or the fresh water needed for fracturing. Most well sites, relying on tanks, can only hold part of what’s needed for the full operation at once. Thus, resulting in higher transportation or pumping costs. Second, in-ground pits are also far less expensive to build in most cases, even after accounting for the cost of premium flexible liners. Large tanks with appropriate hydrocarbon and corrosion resistance are expensive not only to fabricate, but they’re also hard to transport, even in pieces. Finally, in-ground ponds and pits are just as easy as tanks to check for leaks when designed with double-layered liners and sump monitoring that immediately sets off sensors when liquid breeches the first liner layer. These sump sensor designs are often even more sensitive than other types of level detection, allowing for the discovery of pit and pond leaks as soon as possible.
The Issues of Seepage
The main reason that fresh water frac pits shouldn’t go unlined is due to losses, not contamination like with produced water and sludge storage. Unlined storage pits and ponds will steadily lose water due to seepage. This is because even well-compacted clay soils have microscopic openings between the particles that allow water to escape. Even if seepage doesn’t significantly reduce water holding capacity, it can lead to a sudden collapse of the banks or dam of the pond after years of underground erosion. All frac pits, regardless of the type of liquids they hold, must be lined to prevent seepage. The liner must be impermeable enough to stop liquids, not just designed to slow down water loss. This means that only flexible polymer liners will work for most frac pit designs.
Basic Design Components of Frac Pits
Each frac pit is different because it must be designed with both the local regulations and the challenges of the site in mind. Since the federal regulatory bodies leave the handling of frac pit regulations to the states, a pit in Texas often needs different features than the same one built in Oklahoma. However, there are common components that many frac pits share, such as:
- Pipes and trenches for transporting both fresh and produced water between tanks and pits, including those made from aluminum, HDPE, and woven materials
- Extensive freeboard above any emergency drainage spillages to ensure that wind blowing across large surface areas won’t allow waves to damage the banks of frac pits and ponds
- Freeze controls to prevent ice from damaging the liner and pumping equipment
- Oil reclamation and control to prevent wildlife from accidentally coming in contact with it
- Overflow and spillway protection so that unexpected rainfall or sudden surges in the water supply won’t cause damaging flooding
- Gentle slopes on the banks so that it’s easy to access the bottom to remove sludge and solids and to allow workers to get out safely if they slide or fall in.
Despite having all these common features, frac pits can vary greatly depending on their purpose and location. A pit designed to permanently hold waste will be deep and relatively small on the surface, while evaporation ponds need exactly the opposite design. All frac pits operate best when lined, so turn to BTL Liners for the RPE products you need to handle the challenges of the oil field.
