Total makes environmental criteria a central concern when deciding about the feasibility of future shale gas developments. We make no exceptions to our commitment to produce energy sources sustainably and in a manner compatible with environmental stewardship, regulatory requirements and local residents. Shale gas recovery must address three major challenges: reducing water use, managing pollution risks and limiting visual and noise intrusions at and around production sites.
Hydraulic fracturing requires more water than conventional wellbores: the fracs for a single well use 10,000 to 20,000 cubic meter of water. Therefore, substantial water resources must be available for the duration of the fracking operations – which typically last about three weeks. Diminishing the water requirement is among the goals of current research by oil companies.
Depending on the type of reservoir, 20 to 80% of the water injected flows back in the early years of production.
That makes it critical to treat flowback water from the wells to remove the various pollutants - solid particles, hydrocarbon molecules, salts - that it picks up as it flows through the source rock. Total has developed a range of effective treatment processes to remove these contaminants and fracking additives, allowing up to 90% of the water to be recycled. Seawater can also be used, which avoids the use of fresh water.
Oil companies are looking at the possibility of using deep saline aquifers, whose water is unsuitable for human consumption, as a new source of supply.
Treated effluents can then be recycled for another hydraulic fracturing operation.
As for any oil or gas well, shale gas well integrity must be perfect to protect the aquifers intercepted by the drilling from contamination. This is achieved by cementing the wells in the annular space between the rock and the casing (lining of the borehole wall).
Total has leading-edge expertise in designing effective barriers, able to withstand extreme temperature and pressure conditions.
What About Additives?
The chemical compounds used inhydraulic fracturing amount to 0.5% of the total injection volume (water + sand). They are ordinary compounds, such as those found in household products or food. Moreover, they are used more than 1,000 meters below aquifers. We are also working to facilitate the use of alternative compounds, including additives sourced from the food industry.
Reducing Surface Intrusions
Because the output from a shale gas well is less than from a conventional gas well, more wells are needed. To minimize the visual impact of these developments, the wells are grouped together in 10- to 15-well clusters - sometimes more - drilled from a single pad. This technique is used for offshore oil platforms.
Once all the wells have been drilled, the derrick (35 meters high) is removed. During the production phase, only the wellhead is visible (about 1.80 meters high).
Drilling and fracturing operations are also a source of noise and other construction disamenities. However, these nuisances only last a few days for each well. In urban areas, noise barriers can be built to mitigate the problem. New drilling and hydraulic fracturing units are also being developed to reduce the associated noise.
Furthermore, the logistics related to hydraulic fracking generates significant truck traffic to bring in the drilling equipment and subsequently take away produced water on completion of the operations. Again though, traffic nuisances last only a limited period of time, confined to the well developed phase.
Hydraulic Fracturing and Microseismic Events
Using hydraulic fracturing to open fractures triggers minute tremors within the source rock. These movements are termed "microseismic events." Although significant enough to induce fracturing within the rock, they can be detected only by the most sensitive instruments because of their extremely low magnitude: typically -3 to -2 on the Richter scale, or even at most +0.5. Humans can only detect earthquakes with a magnitude of at least +3 (which is a million times higher than the -3 induced by fracking). And every day, seismographs record several thousand quakes with a magnitude of less than +2.
It is true that slightly stronger tremors indirectly linked to hydraulic fracturing have been reported, for example in the United Kingdom. Studies have shown that these phenomena are due to the unusual combination of two factors: the pressure exerted on the rock by water injection and the presence of a naturally fractured, seismically unstable zone. Prior geological surveys and continuous monitoring of rock behavior during fracturing operations should prevent this type of incident, by enabling operations to be halted immediately.