What are the risks?

Due to the low permeability of shales, gas production from shales applies hydraulic fracturing of the rocks. A high demand for freshwater, the production of large amounts of waste water, induced seismicity, greenhouse gas emissions, and groundwater contamination have all been linked to hydraulic fracturing technology in the past. Dense well-spacing, noise from operations and increased truck traffic are further concerns for the environment and the public. Economic risks apply to shale gas operators.

The development of technology within shale gas operations has been rapid within the last few years and is still ongoing. Some environmental impacts have already been effectively reduced using these new technological developments. The reduction of greenhouse gas emissions during shale gas production and the reduction of freshwater demands by increased recycling and re-use of wastewater are prominent examples. Other issues still need more attention from research and development, e.g. the prevention of induced seismicity.

Water contamination

Groundwater contamination can happen through spillage via the surface route or by  leakage from the wellbore. Leakage of fluids through the rock formations between the targeted shale and shallow freshwater aquifers is in principle also possible, but much less likely.

Wastewater is produced in shale gas operations mainly during the flowback phase, when a portion of the fracturing fluid returns to the surface after hydraulic fracturing. Additional to proppant and chemicals initially present in the fracturing fluid, the returned water will have picked up a variety of elements from contact with the shale rocks, including NORM. This water needs proper treatment for recycling or disposal.

This can be achieved with available technologies, which are currently being developed further to be more efficient and less costly. However, discharge of contaminated waters into rivers, delivery to unsuitable publicly owned treatment works, and spills due to improper surface handling of wastewater have all occurred and need to be investigated, remediated and, importantly, learned from.

Induced seismicity

Hydraulic fracturing causes millions of very small and localized seismic events when the fractures are actually produced in the shale. Recorded by special equipment, operators benefit strongly from this seismic response by pinpointing the spatial and temporal distribution of produced fractures in the underground. 

On the other hand, the stress applied to the rocks by hydraulic fracturing interacts with the pre-existing stress field underground and might induce further seismic events that can be larger than the deliberately produced microseismicity. Seismic events apparently connected to shale gas hydraulic fracturing have been documented, and although of small magnitude, have prompted much attention and thorough investigation.

Operational best practices to reduce the risk of induced seismicity have been developed in geothermal energy production, where similar hydraulic fracturing techniques are applied to stimulate flow. These best practices can be applied in much the same way to shale gas production. However, since precise knowledge of the prevailing underground stress field and mechanical properties of the rocks present is always limited, induced seismicity risk-reduction is a complex and challenging task.

Greenhouse gas emissions

Methane, the main component of natural gas, may act as a potent greenhouse gas that contributes to global warming when released into the atmosphere. Large quantities of methane may be released into the atmosphere during the flowback-phase of a shale gas well: when the fracturing fluid is returning to the surface, it brings along natural gas that is released from the freshly-fractured shale. 

It was common practice in shale gas developments to release the gas produced during flowback into the atmosphere or to flare it. Flaring (burning) the gas results in the conversion of methane to carbon dioxide, which is also a greenhouse gas. Available technologies, so-called Reduced Emission Completions (REC), can capture the emerging gas at the wellhead. RECs are increasingly applied by shale gas operators for various reasons, one of them being the revenue from selling the captured natural gas.

Water demands

Variable, but large amounts of water are used for hydraulic fracturing. This water may come from natural sources such as rivers or groundwater but increasingly, hydraulic fracturing fluids are recycled and reused. The shale gas industry´s water demands usually make up only a small share of total water usage in a given region. However, this demand must be properly managed in a collaborative effort by industry and regional water planning agencies. In general, the availability of water for shale gas operations should only pose a problem in the world´s arid regions.

Economy

A holistic view of shale gas development must include economic factors alongside the ecological risks and societal issues. The economic risk with shale gas wells is that they require horizontal drilling and hydraulic fracturing, which significantly increases capital costs. Major factors in calculating economic risk and uncertainty include 1) poorly constrained, eventual long-term gas production of shale gas plays, and 2) long-standing and possibly long-term low world market natural gas prices. The economic success of shale gas developments, which has been reported recently, may continue in the future, but is no self-seller.