Natural Gas Exploration Carries Water Management Challenges
From the Marcellus Shale to the Eagle Ford Shale, developers across the country are looking to access ...
By Alan Robinson and Doug Henderer
Barnett Shale flowback/PW (left) and recycled distilled water (right) from Devon operations near Justin, TX. NOMAD units shown in background.
From the Marcellus Shale to the Eagle Ford Shale, developers across the country are looking to access vast quantities of natural gas beneath U.S. soil.
Marcellus, located under the Appalachian Basin of the northeastern United States, is the second largest natural gas basin in the world and holds an estimated 500 trillion cubic feet of natural gas. Eagle Ford, which spans more than 40 miles by 400 miles in southern Texas, is considered the sixth largest oilfield discovered in the U.S. and the biggest discovery during the past 40 years. It is projected that Eagle Ford holds billions of barrels of recoverable oil and trillions of cubic feet of natural gas.
These resource development programs have the potential to transform regional economies and the nation. Considering the Marcellus alone, it is estimated that the formation holds enough natural gas to meet the United State's natural gas requirements for the next 23 years at the current rate of consumption, or 25 percent over the next 100 years.
Successfully recovering this plentiful resource will require a delicate balance of environmental care, particularly water management, and innovative techniques.
Natural gas has the potential to replace petroleum to directly power vehicles and for power generation, including electricity for electric-powered vehicles. This makes Marcellus and the other gas and petroleum shales very valuable resources for the recovering U.S. economy, with the potential to substantially reduce the nation's dependence on importing petroleum and natural gas from the Middle East.
Much of the new drilling interest that is taking place in northeastern Pennsylvania and southern New York is targeted at reaching the natural gas found in the Marcellus Shale formation. The Marcellus Shale underlies about 36 percent of the Delaware River Basin.
The natural gas in the Marcellus Shale is located some 9,000 ft below the surface, which requires the application of a technology called hydraulic fracturing. Hydraulic fracturing uses high-pressure liquid to crack the shale and form a series of interconnected pathways leading from the rock to the well screen.
More than 1 million gallons of water can be required for each well. Many thousands of new wells will be needed to fully develop the Marcellus, Eagle Ford, and other gas and petroleum shales of value. Environmental regulators have begun to define the boundaries for moving forward.
Clearly, an operator's goal is to design and implement the best approach to facilitate gas field development in compliance with and in full support of environmental requirements and values.
Current issues surrounding natural gas exploration water management include:
- Recycling: Because of the quantities of water used in hydraulic fracturing, recycling is of utmost importance. Chemicals are added to the fracturing fluid, and current technologies – reverse osmosis and distillation – are expensive considering how much water is involved. New technologies must be developed to remove dissolved solids cheaply and effectively.
- Contamination: There is a general public concern for drinking water and groundwater contamination. Great care is taken to properly drill and complete wells so that water resources are protected. The industry is working diligently to prevent these negative outcomes via engineering controls, well construction quality control and implementing best management practices to prevent accidental releases and the unwanted displacement of fracturing fluid.
- Land/water management: Managing natural hydrologic relationships to maintain streamflow and aquatic and terrestrial habitats will be a challenge, but this can be accomplished with proper planning and management of the resource.
Often time, the decision to drill is based on land ownership, the desires of the landowner, the avoidance of steep topography, or the easiest for road access. Environmental experts can help by developing early environmental siting studies that help developers select sites that minimize potential environmental impact. These studies involve mapping wetlands and threatened and endangered species habitats, and optimizing well pad locations to avoid sensitive resources, minimize surface impacts, and prevent habitat fragmentation. Environmental experts can help guide developers through the permitting process associated with getting approval for the necessary water appropriation, and the management of frac water and produced water reuse, recycling and disposal.
Delaware River Basin
The Delaware River Basin Commission, a federal-interstate compact government agency, defined several areas of concern. Specifically they noted that gas drilling projects in the Marcellus Shale or other formations may have a substantial effect on the water resources of the basin by reducing the flow in streams and/or aquifers used to supply the significant amounts of fresh water needed in the natural gas mining process. In addition, the on-site drilling operations may potentially add, discharge or cause the release of pollutants into the ground water or surface water.
Photo of skid interconnections on a typical NOMAD (Fountain Quail - Texas Operation).
In December 2010, the Delaware River Basin Commission proposed regulations that would require a natural gas development plan (NGDP) for lease holdings over 3,200 acres or for those who intend to construct more than five natural gas well pads.
Designed to foster protection of water resources and encourage development only in areas that minimally impact sensitive water resource features, an NGDP would identify the project sponsor's foreseeable natural gas development in a defined geographic area. It would also demonstrate that the well and pipeline locations they choose have the least impact to the environment (i.e., shortest roads, fewest streams, the appropriate setbacks from habitats and streams). The plans would identify geographic and hydrological constraints, flood hazard areas, and critical habitats for threatened and endangered species and identify measures to minimize those impacts
Drilling thousands of feet below the surface is not new in the U.S. In the West, operators have implemented water management strategies to reduce operating costs.
In 1997, the first slick water frac (or light sand frac) was performed on the Barnett Formation shale in Fort Worth, TX. According to a January 2011 Railroad Commission of Texas report, Fountain Quail Water Management of Fort Worth uses a recycling process that allows reuse of approximately 80 percent of the returned fracture fluids processed through its commercial mobile recycling unit.
When water injected to fracture formations returns to the surface, it becomes unsuitable for reuse due to its high salt content. The recycling process involves on-site distilling units to separate the brine into a relatively small volume of concentrate that is reused when possible or disposed of in a disposal well, and a large volume of distilled water that can be reused to drill and fracture additional wells.
Further, the report stated that instead of hauling unusable return fracture fluids to a disposal well, the fracture flow-back fluid is stored in tanks on location and piped into treatment equipment. Natural gas produced on location is used to fire the distilling units that in turn treat the returned fracture fluid and produce distilled water. The distilled water can then be used to fracture treat another Barnett Shale well.
As of October 2010, Fountain Quail has processed over 12.7 million barrels of returned fracture fluid to recover over 9.9 million barrels of reusable distilled water.
The report also noted that Fountain Quail Water Management received authorization for a commercial stationary recycling facility in Parker County (RRC District 7B) in November 2009. The stationary facility will use the same technology as Fountain Quail's mobile water recycling process. While the facility has yet to begin operations, Fountain Quail's submitted plans indicate the stationary facility would initially be able to process 7,000 barrels per day of returned fracture fluid and an additional 7,000 barrels per day of produced water. Like Fountain Quail's mobile recycling units, the stationary facility will allow for reuse of approximately 80 percent of the fluids it processes.
The lessons learned during the drilling of Barnett Shale and other sites will most certainly provide developers with valuable insight as they proceed to drill in other areas across the country. Operators have implemented water management strategies to reduce operating costs. These may include the construction of large central lined pits to store frac flow back and produced water for reuse. In some cases, operators have treated the recovered water using vacuum evaporation treatment units that make the water suitable for reuse, or they have implemented central water collection infrastructure to minimize truck traffic and provide for more economic treatment. At least one operator is pursuing water treatment with a reverse osmosis system so that they may surface discharge under NPDES permit, thus returning the water for other beneficial uses.
Successful developers will look to team environmental experts with engineers and geologists from the start of a project with the goal to get the gas out while meeting the drilling requirements with the least environmental impact.
About the Authors: Doug Henderer, PE, is a senior principal professional with Kleinfelder. He may be contacted at email@example.com. Alan M. Robinson, P.G., is an environmental group manager with Kleinfelder. He can be contacted at firstname.lastname@example.org
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