The strategic placement of shale gas infrastructure could reduce environment impacts for a reasonable additional cost, but doing so would require commitments from planners and regulators and would be a departure from current practices, according to researchers.
In the 25-page study "The costs of avoiding environmental impacts from shale gas infrastructure" published in Conservation Biology, researchers used new software and developed a spatial optimization algorithm to plan well pad locations, access roads and pipeline routes at 84 sites in the Marcellus Shale in five counties in Pennsylvania.
The researchers found that on average up to 38% of aggregate environmental impacts from shale gas infrastructure could be avoided for a 20% increase in development costs.
The study was performed by Austin Milt of the Center for Limnology at the University of Wisconsin; Tamara Gagnolet, Appalachian Energy Program Manager at The Nature Conservancy; and Paul Armsworth of the Department of Ecology & Evolutionary Biology at the University of Tennessee at Knoxville.
According to the researchers, shale gas developers usually plan infrastructure configurations by hand. Since the industry's current practice is to minimize costs, the researchers said developers often equate conservation-oriented planning as being more expensive.
"To change industry practice, it is vital to quantify the costs of avoiding additional environmental impacts beyond regulatory requirements," the researchers said, adding that the oil and gas industry "lacks software that simultaneously plans multiple types of infrastructure with environmental avoidance as a primary objective."
Although numerous studies have previously quantified the environmental impacts of shale gas infrastructure, the researchers said theirs was the first to quantify the tradeoffs between the costs of development and the resulting environmental impacts. They added that "existing software could not adequately serve our study," and so they developed new planning software called Bungee, which stands for "Balancing Unconventional Natural Gas Extraction and the Environment."
Bungee uses a three-step process to plan infrastructure. The program first determines where and how much infrastructure may be placed, taking into consideration planning constraints such as regulatory setbacks and construction practices. It then prepares the collected data to assess the environmental impact of the proposed infrastructure and creates an aggregate environmental impact score. In the final step, Bungee plans infrastructure layouts using a generic algorithm.
The researchers analyzed 84 developed sites in Pennsylvania's portion of the Marcellus Shale with grouped unconventional, horizontal, "active" or "regulatory inactive" wells drilled from 2008-2013. The sites ranged in size from 465-7,297 hectares. Each well pad point was then overlaid with a six-well production unit measuring 3,000-by-11,000 feet and rotated 27-degrees counterclockwise to imitate local gas operations.
The impact score took into account five metrics: forest acreage lost, total edge-to-area ratio; wetland encroachment; potential sedimentation in water bodies; and expected impact on rare species.
"On average across our study sites, avoiding 38% of the aggregate environmental impact of development would increase development costs by 20%," or between $800,000 and $3.8 million per well pad, the researchers said. "Further avoidance quickly becomes cost prohibitive." They added that large, low-cost reductions were possible at some sites, but the results varied widely -- one site could avoid 75% of environmental impacts for an additional 15% in cost ($4.1 million total, or $1 million per well pad), but another site could avoid only 2% of impacts for an additional 14% in cost ($7.7 million total, or $1.1 million per well pad).
According to the researchers, most of the sites (75 of 84, or 89%) have tradeoff curves that indicate "it is relatively cheap to avoid impacts [there]."
For sites without planning, the researchers found that in most cases a visual inspection -- where overlaid layouts on a raster approximation of the impact score are then visually compared to the locations of high-impact layouts to lower-impact layouts relative to the underlying raster -- could differentiate between sites that could avoid much impact for little cost (25 of 84, or 29%) and those sites which could do very little (17 of 84, or 20%).
"Those 25 sites of the first group tended to have more planned roads or pipelines in high-impact areas," the researchers said. "Much less often planned well pads, but not roads or pipelines, were in high-impact areas.
"Those 17 sites of the second group, which achieved either no large or very costly impact avoidance, tended to be constrained by impacts. Many sites lacked low-impact alternatives for pipelines and pads. Often, sparse existing pipelines and/or feasible well-pad locations forced gathering pipelines through high-impact areas. In other sites, reductions in some impacts led to increases in others, such that the aggregate environmental impacts did not change much."