Research on Induced Seismicity Presented at EWRI International Congress
Energy of tectonic forces relentlessly reshaping the Earth’s crust can impart stresses in geologic formations that may build over time, perhaps suddenly released in a seismic event such as an earthquake. Earthquakes occur when rock formations along geological faults move in response to stress, sometimes violently, causing damage that can be severe and widespread. Seismic events can also be induced from stresses caused by human activity such as underground explosions, filling or draining of reservoirs, or when fluid is injected into subsurface formations. It is this last cause of induced seismicity that has raised concern in areas of intensive oil and gas activity.
Oil and gas are produced from rock formations which often also bear water containing a high level of salts and other substances as Total Dissolved Solids (TDS). This “produced water” flows to the surface along with the oil and gas as it is produced. In recent years, hydraulic fracturing has enabled robust development of domestic oil and gas from low-permeability rock such as shale, bringing with it large volumes of produced water. While treatment and reuse of produced water is an area of intensive research and technology development, it remains difficult and costly to sufficiently remove TDS so that the water can be used for other purposes. Because of this, most produced water is transported from production sites to permitted underground injection disposal wells, sometimes known as saltwater disposal wells, or Underground Injection Control (UIC) wells. Large numbers of these wells are located in Texas, as well as Oklahoma, Kansas, Ohio, and other states where there is active, ongoing oil and gas production.
Post-Doctoral Researcher Dr. Nelka Wijesinghe addressed this topic in her whitepaper entitled "Induced Seismicity Associated with Oil & Gas Development.” This work was presented by HARC Research Scientist Carolyn LaFleur, P.E. at the American Society of Civil Engineers Environmental and Water Resources Institute 2018 International Congress held in Minneapolis last month.
Areas of the central and eastern United States have experienced an elevated level of earthquake clusters over the past several years. Particularly in areas where tectonic seismic activity is uncommon and energy development is ongoing, induced seismicity can be disturbing and raises concern. Scientists have compelling evidence that the seismicity in many of these locations is correlated with the deep injection of produced water from nearby oil and gas operations. UIC disposal wells operate over a long period of time and throughout large areas, resulting in prolonged elevated fluid pressure in the receiving rock formations. A small percentage of disposal wells seem to be associated with clusters of earthquakes, typically small to moderate in strength. Earthquakes associated with disposal wells are not necessarily limited in time and space to injection operations. The area of potential influence from injection wells may extend over several square miles, with earthquakes triggered more than ten miles away, and continue for months after injection ceases. Therefore, quickly and accurately detecting seismicity associated with produced water injection for oil and gas operations is key to avoiding costly shutdowns and damage to nearby property. Tools for hazard assessment are improving, so that this can be done before or after operations begin.
Additional Resources, including a Primer on management of risks associated with potential injection-induced earthquakes can be found at StatesFirst, an initiative of the Interstate Oil and Gas Compact Commission and the Groundwater Protection Council. Additional information can be found at the Stanford University Center for Induced and Triggered Seismicity.