Horizontal Wells

BARRIER AIR SPARGING

Why Air Sparging?

Quick Refresher: air sparging (AS) is a proven groundwater remediation technique that removes volatile organic compounds (VOCs) from groundwater by injecting air into water-saturated formations. There are two common approaches to AS. The first involves injecting air through wells into the impacted area to remediate the plume. The second creates a transport barrier by sparging downstream from the impacted zone, VOCs are removed as the groundwater passes through the sparge barrier and aeration enhances natural attenuation.

How are Barrier Air Sparge Systems Usually Installed?

There are three principal methods: vertical wells, horizontal wells and horizontal trenches.

How Do Vertical Wells and Horizontal Trenches Fall Short? One must ensure there is appropriate overlap to account for radius of influence (ROI) limits with a vertical well network to avoid breakthrough. Vertical well networks require interconnecting piping which can be costly to install and cause expensive business interruptions in commercial areas. There are practical limits to the number of vertical wells that can be networked due to piping friction losses and blower sizing requirements. Horizontal trenches involve depth limitations related to readily available excavation equipment and the potential for expensive business interruptions.

 

Horizontal AS wells typically have 20-40' perpendicular ROI on each side of the well screen.



1,000 foot AS Barrier well

installed at a depth of 23'

to protect Lake Michigan.

HRW directionally drilled by

Directional Technologies, Inc.

 

How Can Horizontal Wells Enhance The Barrier Sparging Process?

Horizontal wells typically have a robust radius of influence if properly designed. Directional Technologies uses a proprietary screen design methodology to ensure uniform air flow across the screen length. Horizontal wells can be designed to effectively protect extensive areas. For example, Directional Technologies recently installed a 1,000-foot long horizontal well to serve as an AS barrier at a site adjacent to Lake Michigan in Waukegan, IL. Horizontal wells do not involve complicated interconnecting piping networks – connect your surface equipment at one location. In addition, horizontal wells can be “stacked”, if required, to provide a deeper barrier. In other words, two horizontal wells could be installed one on top of the other (appropriately spaced to ensure overlapping ROI) from essentially one drilling location. Finally, horizontal wells can be configured to avoid expensive business disruptions in commercial locations typically associated with vertical technologies.

Directional Technologies Installs Horizontal Wells!

 

Directional Technologies has been successfully installing horizontal wells since 1984! The companies' experience in the oil field, environmental remediation industry and utility industry allows us to complete projects that were previously considered unfeasible. Give us a call to discuss your next AS system project.

For additional information

contact Kathy Sequino

203-294-9200

A multiple product plume under an active paint facility includes No. 6 Oil, No. 4 Oil, mineral spirits and lube oil. Contrasting viscosities can cause preferential flow, complicating LNAPL recovery efforts that are required by the state environmental agency. The plume is under a building, and installation of vertical wells would be costly, not only because of the large number of concrete pad penetrations and conveyance pipe installation, but also because it would interrupt operations of the active business. Six horizontal wells were installed instead, radiating from a central drilling location in the shipping department. The central drilling location kept the footprint of drilling operations to a minimum, and the six horizontal wells were installed as blind wells, like spokes of a wheel. All six wellbores were drilled through a 20-by-10-foot, decommissioned underground storage tank beneath the central drilling location, and the wellheads were completed within this tank, conveniently placing surface equipment for all six wells, including piping and oil-water separation, inside the tank. Since the wells were drilled blind, there was no need to exit at ground surface at the far end of the wells. Instead, each well terminated in the target zone at the distal endpoint of the well screen, eliminating unnecessary drilling and surface construction.

The wells were completed with 6-inch, schedule 80 PVC pipe, with conventional slots appropriate for LNAPL recovery. Each well was equipped with a down-hole pump that can easily be moved to the optimal location for efficient LNAPL recovery. The ability to adjust the pump location along the horizontal screen allows continuous optimization of recovery in response to changing positions of the multiple LNAPL phases with contrasting viscosities. This flexibility avoids or greatly delays the need for installing new well points that are often required in vertical LNAPL recovery well fields as the LNAPL distribution changes.

Directional Technologies, Inc. (DTI) installed the 6 wells, with over 200 feet total of screen, in less than two weeks. Forklifts moved unimpeded during those two weeks, allowing the shipping department to continue business as usual. Operation and maintenance of the LNAPL recovery system will likewise not impede operations at the paint facility. The centralized location of surface equipment in the underground tank at the center of the “wheel” of horizontal recovery wells will cut the time required for O&M activities to a fraction of what would have been required for an equivalent vertical well LNAPL recovery system dispersed within the building.

• A dense network of subsurface utilities, tanks and monitoring wells at the gasoline retail station that required narrow tolerance along the planned wellbore paths

• Drilling and locating through a high-density neighborhood, with many homes and fenced yards

• Drilling and locating across multiple highway lanes, with traffic and strong subsurface interference to the locating system

• Drilling and locating under the gasoline retail facility and fast-food restaurant with drive-through lanes, with zero interruption of the flow of business at either location.

Wells are wells are wells, right? Both conventional vertical wells and directionally drilled horizontal wells have a screened casing that is connected to solid riser casing which leads to the ground surface. Groundwater or soil vapor is drawn through a well screen to remove contaminants. Remediation agents such as air, bioamendmnents or potassium permanganate are injected through a well screen to treat contaminants in situ. This is where the similarities end.

There are some important practical benefits of horizontal wells, independent of the remediation strategy.

• Horizontal wells can be installed in areas with subsurface obstructions such as utilities and under buildings, lagoons, wetlands, railroad tracks, etc. Directional drilling makes it possible to install wells where vertical drill rigs have no access.

   

• Natural flow patterns in typical soil strata tend to create plumes that are much longer and wider than they are thick.  Horizontal wells can therefore be favorably oriented to take advantage of plume geometry and flow direction.  This allows horizontal wells to achieve greater efficiency of delivery or recovery than vertical wells in many hydrogeologic settings.

   

• Accurate installation with respect to elevation and location allows for efficient recovery of LNAPLs, but the well placement must take into account fluctuations in the water table.  Installation along the base of aquifer allows efficient recovery of DNAPLs and prevents further downward migration through the confining layers.

   

• Because of the larger screen area in contact with the impacted media, fewer wells may be needed, and therefore fewer pumps, less piping, and lower operation and maintenance costs.  Horizontal wells can be drilled and completed while normal site business continues without interruptions. 

   

• Horizontal wells have a longer screen interval in contact with a larger mass of contaminated media. This results in a greater zone of influence and more efficient remediation. The table below describes the typical zones of influence for common subsurface conditions and this generally results in shorter time of operation and quicker cleanup.  

Horizontal well technology can be adapted to many in situ remediation techniques.

 

Groundwater Pump and Treat

A horizontal well is in contact with a larger area of soil or groundwater and therefore can treat a larger mass of contaminates.    Since only one submersible pump is needed in a horizontal well system compared to typically 5 or more pumps in a comparable system of vertical wells, savings can be realized in both up-front capital costs and long-term operation and maintenance costs

See Illustrations Below

Enhanced Bioremediation

This technology injects air, nutrients or other amendments into the contaminated zone, to stimulate microbial growth and promote the degradation of contaminants. The increased surface area provided by horizontal wells allows for more efficient delivery and distribution of amendments as compared to vertical wells. Increased surface area is of particular advantage in diffusion-driven delivery of some bioamendment materials.

Air Sparging and Soil Vapor Extraction (SVE)

In this technology air is introduced below the water table to enhance not only bioremediation but also volatilization of contaminants. It will remove dissolved and adsorbed contaminants from the saturated and vadose zones. Groundwater is not removed to the surface for treatment.

In general, this technology employs two parallel wells—one below the water table to inject air and one above the water table to extract vapors. Due to the long screened interval (increased surface area) and linear configuration horizontal wells more effectively distribute air into and extract vapors from the contaminated area.

Success stories using this approach have been reported for releases at airports impacted with jet fuel, petroleum terminals, refineries and pipelines. In all of these cases the impacted media consisted of soils and groundwater with dissolved and adsorbed constituents, and with free product. This approach can successfully mitigate a plume of contamination flowing off-site, protecting down-gradient neighbors.

In an article entitled “Horizontal Biosparge Wells Treat Petroleum Free Product (Horizontal News Volume 8/Number 1, Fall 2005) Louis B. Fournier, PhD reported that a typical vertical sparge well will have a radius of influence of less than 20’ around the well. Whereas, horizontal sparge wells will typically have a radius of influence of 100’ on each side of the well. For this reason a horizontal well will introduce far more air into the subsurface than a vertical sparge well. Similarly, this results in greater removal of contaminants via SVE.

Additionally, according to Dr. Fournier, if free product is present, the use of vertical sparge wells can “push” the separate phase product away from the wells. EPA guidance suggests that the presence of separate phase petroleum may prevent vertical sparge wells from cleaning up a contaminated site due to the migration of product away from the vertical well. While there is migration of free product away from a horizontal well it must travel much further to get out of the treatment zone due to the much larger zone of influence. Horizontal biosparge wells can be designed to minimize mounding and keep migration under control.

In many cases, the cost of environmental cleanup is lower if the system takes advantage of horizontal well technology, not only because of lower annual operation and maintenance costs, but because cleanup goals are met in less time than with a traditional vertical well system.

In summary horizontal wells have functional differences that result in improved remediation efficiencies. This can result in total project savings of 50% or more.

The company has experience in the oil field, environmental remediation industry and utility industry which allows us to complete projects that were previously considered unfeasible. The company’s personnel have been directional drilling horizontal wells since 1984! Please give us a call to further discuss the key elements of successful horizontal remediation systems.