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GSA Critical Issue: Hydraulic Fracturing

Table of Contents

Introduction

Hydraulic Fracturing Defined

Hydraulic Fracturing’s History
and Role in Energy Development

Potential Environmental Issues
Associated with Hydraulic Fracturing

Water Quality

Water Use

Triggered or Induced Seismicity

Regulation Issues

Staying Informed

References

Glossary

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POTENTIAL TRIGGERED OR INDUCED SEISMICITY

Seismic Expression from Hydraulic Fracturing Figure 15:

Seismic Expression from Hydraulic Fracturing; Warpinski et al, 2005. Reproduced with permission of SPE; further reproduction prohibited without permission.

Injection of fluids deep into the earth can trigger a small or moderate earthquake. There are two types of fluid injections that may occur with oil and gas development: (1) injection of hydraulic fracturing fluids into the reservoir rock; and (2) disposal of waste fluids through deep well injection. Hydraulic fracturing imparts pressures of several thousand pounds per square inch on reservoir rocks. The fractures created in these rocks may extend several hundred feet away from the borehole (Fig. 15) but generally no more than that due to physical and technological limitations on the hydraulic fracturing process[38]. As small cracks are induced in rock formations, the hydraulic fracturing process creates very small seismic events or earthquakes. This microseismic activity is generally too small for humans to feel or to cause surface damage [14]. It can be detected by instruments at the surface that monitor the fracturing process and can precisely determine where the fractures have propagated. A number of studies, including one by the National Academy of Sciences, have determined that hydraulic fracturing does not create a high risk for creating seismicity strong enough to be destructive or for people to feel [33].

Disposal of large volumes of waste fluids produced from hydraulically fractured rocks through deep-well injection has been documented to produce small earthquakes, generally less than magnitude 2.0 [33]. Wells that have been hydraulically fractured produce large volumes of waster fluids (produced and flowback water). Deep disposal of any fluids, whether or not they are associated with oil and gas production, can trigger earthquakes [33, 39]. Most, although not all, of these earthquakes have occurred in areas of long-term or continuous injection of wastewater into the subsurface. Fluids injected near a subsurface fault can reduce the frictional resistance that keeps faults from slipping. These small movements allow energy already stored in brittle rock formations to be released in earthquakes. In some situations, sites of slowly accumulating forces in the earth resulting from natural geologic processes are already susceptible to seismic events (which is why this is often referred to as “triggered seismicity”). Deep well injection of fluids has been suspected as the likely cause of seismicity in excess of magnitude 2.0 over the past several decades, including a magnitude 5.7 earthquake in 2011 in Oklahoma[40]. The potential for triggered seismicity with the increasing volume of wastewater disposal is unknown [33, 40, 45].

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