Casing Gets Early Blame in Fracturing Studies

A wise adage states that anything worth having is not easily obtainable – and it just so happens that the most promising source of cleaner, domestic, cost-effective energy of the near future also is incredibly controversial.

Shale gas, due to extensive resource availability and low fuel prices, is expected to provide the United States with 46 percent of its domestic energy needs by 2035, according to the Energy Information Administration.

Additionally, a 2009 Department of Energy report estimates the United States has over 900 trillion cubic feet of technically recoverable shale gas resources, which could provide up to a century of energy for the nation.

Concerns have been raised, however, regarding the production of shale gas using hydraulic fracturing that include: potential groundwater contamination, induced seismicity, “fugitive” air emissions, composition and treatment of produced waters, water use, soil erosion and state versus federal regulation.

Given the urgent need for this cheap, local fuel, it is imperative that the risks are properly investigated using quality science in order to develop best practices, improve technology and write effective policy so public health and the environment are not compromised and this energy opportunity is not overlooked.

In the United States, federal agencies, academic institutions and private research firms all are taking the initiative to fund studies on various hydraulic fracturing topics. Below are a few scientific studies already completed or currently in the works, along with what they already have found or what questions they hope to answer.

Last May, Secretary of Energy Stephen Chu organized a Subcommittee on Shale Gas Production to identify ways that hydraulic fracturing can be executed safely without environmental or health impacts. The subcommittee, composed of seven experts from industry, environmental groups and state regulatory agencies, compiled a list of 20 recommendations in its first 90-day report, released in August.

The report’s take-away message is that fracturing itself does not cause gas leakage into groundwater sources; rather, insufficient well casings and other human errors cause the problem.

The Environmental Protection Agency, under the direction of Congress, has begun a review according to its “Plan to Study the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources.” The study will be conducted by EPA scientists who have consulted with experts in the field, hosted technical workshops and facilitated public meetings with stakeholders.

Initial results will be released at the end of 2012, and the final report is expected in 2014.

The University of Texas at Austin released in early November preliminary results from its study on the use of hydraulic fracturing in the Barnett, Marcellus, and Haynesville shale plays (see October EXPLORER ). Like the Secretary of Energy’s Shale Gas Subcommittee, UT has found no direct link from fracturing to drinking water contamination. Accidents have instead been linked to above-ground spills, mishandlings and poor cementation of well casings.

The university’s final report, which is addressing groundwater contamination, fugitive air emissions, regulation and public perceptions, will be released in early 2012.

UT also intends to conduct two additional projects that will tackle more specific hydraulic fracturing issues.

A Duke University study published in May (Methane Contamination of Drinking Water Accompanying Gas-Well Drilling and Hydraulic Fracturing) found gas signatures in groundwater that matched those of deep shale methane where fracturing is taking place. While the researchers believe the seepage is a result of poor casings and not migrating cracks in the rock, they advocate for additional studies on the matter.

The study confirmed that distance from drill wells does have an effect on leak accidents, but there is no evidence of hydraulic fracturing fluid contamination in groundwater sources.

Duke also recently published a study that proposes seven safeguards to minimize negative impacts from hydraulic fracturing, including baseline data, safety requirements, mandated disclosure of chemical data and regulatory programs.

Resources for the Future, an independent, non-partisan research organization, received a grant to investigate its study, titled “Managing the Risks of Shale Gas: Identifying a Pathway Toward Responsible Development.”

The 18-month review will survey experts and the public, analyze risk drivers, assess federal and state regulations and make recommendations to reduce risks.

Internationally, hydraulic fracturing for shale gas already has been banned in France, Australia’s New South Wales province and in the Karoo region of South Africa. The United Kingdom and New Zealand are continuing the practice but taking careful steps along the way.

With clear, thorough scientific research, implementation of best practices and effective communication to the public, the United States can lead by example during this controversial time.

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Washington Watch

Washington Watch - Erin Riley Camp

Erin Riley Camp is the AAPG Government Affairs intern at the American Geological Institute.

Policy Watch

Policy Watch is a monthly column of the EXPLORER written by the director of AAPG's  Geoscience and Energy Office in Washington, D.C. *The first article appeared in February 2006 under the name "Washington Watch" and the column name was changed to "Policy Watch" in January 2013 to broaden the subject matter to a more global view.

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In prospective basins affected by exhumation, uncertainty commonly exists regarding the maximum burial depths of source, reservoir, and seal horizons. One such basin is the Otway Basin, an important gas province in southeastern Australia, which has witnessed several exhumation events. Here, we present estimates of net exhumation magnitudes for 110 onshore and offshore petroleum wells based on the sonic transit time analyses of Lower Cretaceous fluvial shales. Our results show significant post-Albian net exhumation in the eastern onshore Otway Basin (gt1500 m [sim4920 ft]) and a generally minor net exhumation (lt200 m [sim655 ft]) elsewhere in the Otway Basin, consistent with estimates based on thermal history data. The distribution of net exhumation magnitudes in relation to mid-Cretaceous and Neogene compressional structures indicates that exhumation was dominantly controlled by short-wavelength basin inversion driven by plate-boundary forces.

Deeper burial coupled with high geothermal gradients in the onshore eastern Otway Basin and along the northern basin margin during the early Cretaceous have rendered Lower Cretaceous source rocks mostly overmature, with any remaining hydrocarbons from the initial charge likely to be trapped in tightly compacted reservoirs and/or secondary (fracture-related) porosity. However, the embrittlement of these reservoirs during their deeper burial may present opportunities for the development of low-permeability plays through hydraulic fracturing where smectite clay minerals are illitized. Source rocks at near-maximum burial at present day are at temperatures suitable for gas generation, with key controls on prospectivity in these areas including the sealing potential of faulted traps and the relationship between charge and trap development.

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