Pad Construction

Why build a pad?

After a permit has been obtained for a well site, the next step is to begin construction of the well pad. The construction of the pad is the first phase of oil and gas exploration that has the potential to impact the environment.

What function do well pads serve? Among other things, they:

  • Provide a level, packed, well-drained surface for drilling operations and equipment.
  • Support infrastructure necessary for completions operations.
  • House the wellhead and associated production equipment over the producing lifetime of the well.
  • Serve as a staging area for drilling, completion, production equipment, and associated vehicle traffic.
  • Serve as an initial spill prevention and control countermeasure.
  • Minimizes the environmental impact footprint of drilling and stimulation operations.

The construction of an effective, low-impact pad sets the stage for safe and environmentally responsible site activities.

Building the Pad

Surveying the Site

During the permitting process, company representatives work with landowners, regulators, and government officials to select the location of the well pad.

Once the location has been decided upon and the required permits have been obtained, the site will need to be surveyed.  The sides and corners of the pad are staked out first, followed by the location of the future borehole.

A typical well pad covers a square area 250-400 feet to a side.

Building the Road

Before any work can be done on the pad itself, construction vehicles need to be able to get to the site. The first stage of building a well pad is to construct an access road.

Several factors are taken into account when building a site access road:

Site restrictions

Depending on the state of the land around the drill site, roads may be subject to restrictions, either spelled out in the lease, related to local environmental regulations, and/or local municipal permitting requirements.

For example, a farmer may stipulate that due effort must be made to construct roads along the edges of fields rather than through them. In low-lying areas, the road should avoid disturbing sensitive wetlands if possible. In ranching areas, landowners may require the construction of a fence to keep livestock off the road or a corridor to pass over or under the road.

Construction Regulations:

As with most roads, well pad access roads must be built according to local construction regulations, which normally require that the road be constructed using best management practices for erosion control and stormwater management. We’ll learn more about these practices later on.

Expected Road Traffic:

The size and quality of the road depends on the total expected truck traffic. Since a typical unconventional well often requires over 1,000 trips by heavy trucks, the road is probably going to get a lot of use. A recent study in Colorado found that the average fracturing job in the state required about 1,400 truck trips. If all those trucks were lined up end to end, they would stretch 17 miles. In addition to building the access road, companies may reinforce local, municipal roads that will be used during well operations. Additional bonding, route identification and potentially a road-use maintenance agreement may be required for the use of a municipal road.

Clearing the Pad Area

Depending on where drilling is taking place, clearing the pad can be a day’s work (in the desert or grazing land) or a major undertaking (such as in a forest or near bedrock outcrops).

When clearing a pad, companies are often required to conserve as many site resources as possible.

Topsoil

Topsoil is a valuable resource for agriculture and healthy ecosystems. Usually, companies are required to remove all topsoil from the pad and store it on site so that it can be used for site restoration in the future. Since excavated soil is easily eroded, proper selection of the storage location is key (more about that in the erosion control section below).

Vegetation:

Landowners often stipulate what will happen to trees that need to be cleared from a site in their lease agreements. Some landowners take care of the trees themselves or hire a contractor to remove and sell them. In other cases, the oil or gas company pays the landowner for the trees and sells them itself. In either case, both the oil company and the landowner may hire foresters to assess the value of the timber in order to gain a stronger bargaining position.

Of course, many types of vegetation have very little economic value. This vegetation must be removed and dealt with according to local construction regulations.

Building a pad not only entails removing plant material but controlling the introduction of potentially invasive species of plants. Invasive species are generally not native to the area, a characteristic that may give them a competitive advantage over local plants. So, in addition to removing plant material to build a pad, weed control after a pad is built may be equally important to help protect the local environment.

Building the Pad

Once the site is staked out and cleared of rocks, topsoil, and vegetation, the real work begins. Construction contractors with bulldozers work to create a level surface for the pad. Often, this is accomplished with cut-and-fill techniques: materials from the higher parts of the pad site are used to fill in low points until a level surface is created.

A pad typically consists of several layers of dirt and gravel, which are graded to form a level surface. Once the surface is level, it is coated with a thick layer of gravel. This provides support for pad equipment.  The amount of stone used can vary from area to area but may require a few truckloads of aggregate to literally thousands of loads to complete the pad and access road.

By way of example, if you wanted to cover a 4-acre well pad with 24 inches of stone, it would require about 12,900 cubic yards of stone or roughly 700 triaxle truck trips.

Stormwater Management

During the construction of the pad and access road, it is critical that operations are conducted in a way that minimizes soil erosion during rain events. Increased sediment loads in streams can cause environmental problems such as fish and aquatic plant die-offs and drinking water quality reduction.

To reduce erosion and runoff, access roads should follow natural contour lines rather than cutting across them. This will prevent the road from becoming a new stream bed.

Gullies should be avoided during road construction; if the road must cross one, a culvert should be built to carry water and sediments under the road. Drainage ditches should be built on the uphill side of the road in order to conduct water to under-road culverts.

When topsoil is stockpiled after removal from a site, it should stored in a place where it does not block natural drainages, or else it may be lost to erosion. Topsoil stored at a location should also have a vegetative cover to minimize both wind and water erosion.

The well pad itself should be sited in a location where it does not block major water flow paths. If this is unavoidable, a system will need to be constructed to conduct water around the pad, while addressing the water needs of plants and animals located on the downslope side of the well pad.

Well pads should be designed and constructed to prevent contaminants from entering the soil and/or nearby waterways. Any stormwater that enters the pad locations should be captured so that it does not carry any materials used in the drilling, completion, or production process to groundwater or surface water supplies. Stormwater pathways near the pad may need to be rerouted to prevent contamination by potential spills.

Storage Pits

Although the primary goal of pad construction is to provide a foundation for the drilling rig and future site activities, one additional component of drilling operations may be built before drilling contractors move onto the site: water storage pits.

As we’ll learn over the course of this module, storage pits, also known as impoundments, are essential to waste management operations during drilling and completion operations. Several types of pits can be constructed on or near the drilling pad during pad construction. In some locations, metal tanks are used instead of pits.

Mud Pits

These pits are used to circulate drilling mud during drilling operations. In some places, closed-loop drilling (called Zero-Discharge systems) are used to mix and circulate the mud in metal tanks instead of in pits.  The solids generated by these systems are disposed of in an environmentally benign manner such as land farming.

Completion Pits

These pits are built to receive flowback or produced fluids removed from the well during the completion and flowback phase of development.

Emergency Pits

These pits are kept empty during drilling so that they can be used to capture fluids produced during an emergency such as an unexpected well shutdown, overflow of another pit, or cementing operations.

Reserve Pits

These pits capture fluids retrieved from the well after hydraulic fracturing or other well stimulation operations. Since these fluids contain more hazardous chemicals than other fluids used in drilling, construction regulations for reserve pits are typically more stringent than those for the other pit types.

Water impoundments

These pits contain fresh water for use in water-intensive operations such as hydraulic fracturing. Sometimes metal tanks are used instead.

There are three primary considerations when designing a pit:

  1. Pit location: Obviously, pits need to be located near the source of fluids. There are often environmental constraints on pit location as well:
    • Regulations often require that pits be a minimum distance from surface waters.
    • Approval or alternate construction methods may be required if the pit is to be located within a floodplain.
    • Pits cannot be built in wetland areas without regulatory approval.
    • Pits built in areas with shallow water tables may be subject to additional construction rules.
  2. Pit Design: Typically a pit is excavated below ground level by construction equipment. However, pits are often required to have above-ground berms to prevent surface waters from entering. In addition, pits need to be designed to handle floods of a certain intensity, usually defined by state or local regulations.
  3. Pit Liner: Pit liners prevent fluids from escaping from the pits into the groundwater system below. Pits can be lined with plastic, clay, or cement. The liner type depends on the fluids stored in the pits, and is usually dictated by state or local regulations.

Containment Berms

State and federal laws often require that any storage tanks containing hazardous liquids be surrounded by containment berms capable of retaining the total volume of those liquids. These berms, which are typically built after the tanks have been brought on to the site, are lined with PVC or geomembrane materials. However, during pad construction it is critical that the site plan provides the space required for storage tanks and containment berms.

Finishing Touches

After the access road, well pad, and containment pits have been built, the pad is almost ready for drilling. One step remains – preparing the conductor hole, rathole, and mousehole.

The conductor hole is a large diameter hole that makes up the first section of the borehole. This roughly 16-36 inch diameter hole is generally drilled down to bedrock or a stable soil profile and lined with a conductor casing in order to stabilize the upper borehole.

The rat hole is used to store the kelly (part of the drill rig) during drilling. It’s typically around 30 feet deep and 12 inches in diameter.

The mouse hole is used to stage pieces of drilling pipe during drilling operations. It is about the same diameter as the rat hole but not as deep.

All three of these holes are usually drilled by a portable, truck-mounted or track-mounted rig. In areas where drilling passes through loose material near the surface, all three of these holes are lined with metal casings.

Multi-well Pads

The advent of horizontal drilling in unconventional reservoirs such as shale gas has brought about many changes in the industry. One of the most important is the ability to drill multiple wells from one well pad. This new technique has rapidly gained popularity. For example, in 2007, none of the well pads built in Pennsylvania contained more than one well. By 2011, over 80% of new pads were designed for more than one well.

Multi-well pads are usually only slightly larger than single well pads. Once the first well is drilled, the rig is simply moved a short distance (15-20 feet) to drill the second well. The process repeats until all the wells have been completed. Typically, the wells are largely parallel until they approach the depth of the producing formation, where they diverge and become horizontal.

Although multi-well pads can support 12 or more wells, current practice appears to average about 3-5 wells per pad.

Multi-well pads have several advantages:

  1. Decreased land disturbance: By placing multiple wells on a single pad, the total land disturbance required to produce oil and gas can be significantly reduced. This reduces the disruption of existing land use, the oil and gas operational footprint, and ecosystem services and makes it easier for companies to come to agreements with landowners.
  2. Increased operational efficiency: On a multi-well pad, only the drilling rig itself needs to be moved for each well. This eliminates the expensive and time consuming process of rigging up and rigging down the drilling rig multiple times and setting up and removing a variety of equipment and infrastructure used to support drilling operations at each new well (i.e. crew quarters, supply staging areas, environment, health and safety procedures, security, etc.).
  3. Reuse of pad facilities: On multi-well pads, surface pits used during drilling operations can be reused for each well. This reduces the risks of spills and environmental contamination.

As multi-well pads continue to increase in popularity, these advantages can significantly reduce the impact of oil and gas extraction on the landscape while saving the cost of developing multiple well locations.

Conclusion

A properly planned and constructed pad provides a safe, environmentally responsible base for all future operations on a site. Given the importance of pad design to the rest of the drilling operation, the pad design, permitting, and construction process typically takes several months.

As with any hydrocarbon exploration and production operation, one of the challenges of pad construction is the coordination of large numbers of contractors, including construction crews, drilling companies, forestry and environmental consultants, surveyors, and government officials.

After the pad is completed, even more contractors are brought in to “rig up” and start the drilling process itself. That’s where we’re heading in the next section.

Citations

1. EPA, 2011, Federal Requirements Under the Underground Injection Control (UIC) Program for Carbon Dioxide (CO2) Geologic Sequestration (GS) Wells Final Rule, https://www.epa.gov/uic/federal-requirements-under-underground-injection-control-uic-program-carbon-dioxide-co2-geologic (accessed March 9, 2017).

Images: “Wykoff Aerial” by Jim Ladlee for Top Energy Training; “Surveyor” by DIGITALproshots via iStock; “Grader resurfacing a narrow rural road” by Pi-Lens via iStock; “Machinery” by WillSelarep via iStock; “Soil Erosion Africa” by NeilBradfield via iStock; “Marcellus Shale containment pond” by Dwight Nadig via iStock; “Containment Berms” by Michael Black; “Multiwell Pad” by Marcellus Center for Outreach and Research for Top Energy Training