Features - May 2011
NETL Technologies Turn Shale Gas into a Reliable, Domestic Star Energy Resource
The Setting: Devonian Period swamps, 360 - 415 million years ago, a warm, humid climate.
The Players: Flourishing marine life. Testing out their new lungs, some of the first creatures to crawl out of the water and the beginnings of great forests colonize the land.
The Action: Exploration, survival, and finally death. As these primitive land dwellers died, their remains ended up in the water and were pressed down within the forming rock layers.
And why is NETL so interested in this never-to-be-Hollywood-blockbuster?
|Geologists believe the land looked like this during the Middle Devonian period when shale gas was forming. Today's states are shown in outline. (Photo courtesy of Prof. Ron Blakey, Northern Arizona University)
During the Devonian Period, today’s thick shales were being deposited as fine silt and clay particles in these swamps, and with time and pressure, organic matter (plants and animals) buried with the sediments created methane, one of today’s energy sources. Some of this methane escaped into sandy rock layers adjacent to the shales, forming accumulations of natural gas, which were relatively easy to extract. But most of it, which we now call “shale gas,” remained locked in the shale layers. Has this shale gas so quickly become a has-been? Not so.
After lying dormant for hundreds of millions of years, this shale gas resurfaced in the first well producing natural gas from shale in 1821. Since that day, industry professionals have been searching for ways to make the extraction process more efficient. For 30 years now, NETL has helped lead the development of novel technologies for shale gas production.
In the 1970s and ‘80s, fear of dwindling U.S. natural gas resources prompted research to develop methods to estimate the volume of gas in “unconventional natural gas reservoirs” such as gas shales, tight sandstones, and coal seams, as well as research in extraction methods. The research led to the first, publically available estimates of technically recoverable gas for gas shales in West Virginia, Ohio, and Kentucky. Because petroleum and natural gas that come from these reservoirs were challenging to extract, their recovery in the ‘70s and ‘80s was largely uneconomical. Thanks to improved extraction methods, the recoverable shale gas resources in the United States - nearly half of which lie in the Marcellus shale, a vast, 1 to 2 mile-deep rock formation stretching from southern New York through Pennsylvania, western Maryland, eastern Ohio, and West Virginia - are now being tapped to provide much-needed domestic energy.
NETL collaborated with industry to advance horizontal drilling techniques - which reduce the environmental footprint - by drilling the first directional and the first horizontal shale wells. NETL also worked with industry to introduce hydraulic fracturing and other shale well stimulation methods and spearheaded fracture mapping, which uses sound waves to identify the orientation and extent of hydraulically created fractures. Industry has optimized and advanced the use of these technologies to extract large volumes of shale gas economically.
Today’s shale gas wells are drilled vertically down to the shale formation, between 6,000 and 14,000 feet deep. Once the shale is reached, the drillers bore
|Steel casing lines the well to prevent any communication up the wellbore during fracturing or production. Shallow formations holding fresh water that may be useful for farming or public consumption are separated from the fractured shale by thousands of feet of rock (USDW = underground source of drinking water).
horizontally through the shale layer, creating a well several thousand feet long. Wells can be targeted toward natural fractures in the shale, which provide pathways for gas in the rock matrix to flow into the well. Then, segments of the well are isolated, the casing is perforated, and water is pumped under high pressure through the perforations, creating fractures that extend into the surrounding rock hundreds of feet, until the pumping ceases. Sand in the water props the fractures open after pumping stops and the pressure is relieved. The propped fracture is only a fraction of an inch wide. Once the fracture is in place, shale gas can be extracted.
Although shale gas is now being produced routinely using these techniques, research will continue to enhance extraction methods for efficiency and environmental safety.
Environmental concerns with shale gas wells are being addressed alongside the advances in drilling and extraction techniques. NETL conducts research to monitor air emissions from Marcellus Shale gas wells using a mobile laboratory, and to determine the impact of access road and drill pad construction on sensitive indicator species. Other NETL research projects focus on improving the characterization of shale gas resources, determining the possible weathering products of shale drill cuttings, and assessing the potential of depleted gas shales to store CO2.
|Gas from a Marcellus Shale well in Greene County, PA is flared prior to a workover in the winter of 2010. (Photo courtesy of Tom Mroz, DOE)
Our Strategic Center for Natural Gas and Oil has been addressing shale gas water management issues through a number of active shale gas research projects. Working with industry and academia, these projects have and are expected to provide solutions to some of the most vexing shale gas water problems.
Altela Inc.’s AltelaRain® 4000 water desalination system, part of a recent NETL-sponsored demonstration, was tested at BLX, Inc.’s Sleppy well site in Indiana County, Pa. for its ability to turn wastewater from shale gas production into distilled water. All of the clean water produced at the demonstration site was suitable for beneficial re-use by well operators for additional simulations and was suitable to be discharged to surface waterways. The system also significantly reduced the need for trucking wastewater from the site. As a result of the project, the AltelaRain® 600 modules are already being sold and installed to treat produced and flowback water from hydraulic fracturing.
Osorb® is another NETL project which will improve management of water resources, water usage, and water treatment during oil and gas exploration and production. This novel technology uses swelling glass to remove impurities from water and has been shown to clean produced water and flow-back waters from hydraulically fractured oil and gas wells. ABSMaterial’s Osorb has the potential to significantly reduce the environmental impact of producing natural gas from the Marcellus shale and other geologic formations. In independent testing, the system was found to remove more than 99 percent of oil and grease, more than 90 percent of dissolved BTEX (benzene, toluene, ethylbenzene, and xylenes), and significant amounts of production chemicals.
|Acid mine drainage from abandoned mine openings is an environmental concern that may be reduced through use of this water to react with impurities in water from drilling operations, so the combined waters can be reused.
In the Marcellus Shale play, NETL and partners are examining ways of blending acid mine drainage water with flowback water from drilling for re-use in the hydraulic fracturing process. The team believes that sulfate in the mine water will react with the barium and strontium in the flowback water, eliminating one of the barriers to simply reusing the water to hydraulically fracture the shale elsewhere. The project responds to growing concerns over flowback water management in the Marcellus shale, particularly in Pennsylvania where drilling has expanded dramatically in the last year. A technically and economically feasible approach for the reuse of flowback water could reduce the amount of freshwater needed for Marcellus Shale development, minimize disposal liability and costs, and find a practical use for an existing wastewater product from past mining activity in the Appalachian Basin.
NETL’s research in shale gas technologies has come a long way, but promises to go even further. With new techniques for extraction, monitoring, and protecting the environment, NETL has played a leading role in developing a large suite of technologies to make shale gas a resource that could reduce our dependence on foreign oil, create domestic jobs, provide energy for our homes and businesses, as well as keep the Earth green. Production from the Barnett Shale has leveled off, but volumes of gas from the Marcellus, Haynesville, Fayetteville, and Woodford shales are growing as more wells are drilled in these plays and as other emerging plays are developed. The United States is already the world’s largest producer of natural gas, and the Marcellus Shale, with its 100s of trillion cubic feet of shale gas, is becoming a star in that bright energy future. To find out more about the Marcellus Shale, please visit http://marcelluscoalition.org/home/.
Other Department of Energy Efforts in Shale Gas Development
- The Ground Water Protection Council (GWPC) and the Interstate Oil and Gas Compact Commission (IOGCC), through an NETL-managed project funded through the Oil & Natural Gas Program, developed a landmark web-based national registry (http://www.fracfocus.org) disclosing the chemical additives used in the hydraulic fracturing process on a well-by-well basis. Information covers wells drilled starting in 2011. Participating energy companies voluntarily upload information about the chemical additives and the proportion used in each hydraulic fracturing job.
- DOE is exploring creation of a Shale Gas Initiative, in cooperation with public, private, and non-governmental stakeholders, to build on current shale gas efforts and identify best practices that could be used by both operators and regulatory agencies to raise the bar on safety and environmental sustainability during shale gas development.
- DOE has worked with states through the GWPC to develop and maintain the Risk-Based Data Management System (RBDMS). DOE has recently enhanced the RBDMS to track and record data related to hydraulic fracturing treatments.
- The flow of gases and liquids through the sediments in fractures can be studied to determine best methods for injecting carbon dioxide, a means for both increasing production from the well and for sequestering this greenhouse gas. Injection of carbon dioxide near the end of natural gas production could help maintain reservoir pressures, keeping channels for extraction open and displacing the remaining shale gas to ease recovery. A series of laboratory experiments with carbon dioxide and black shales, like the Marcellus Shale, are planned at NETL to examine these ideas.
- In 2009, DOE teamed with IOGCC to form a Shale Gas Directors Task Force to serve as a forum for states to share insights on issues and innovations related to shale gas development at the local, state, and federal levels. More information is available at http://www.iogcc.org and http://groundwork.iogcc.org.