Induced seismicity is commonly defined as earthquakes that are caused by a variety of human activities. The U.S. Department of Energy defines it as: “earthquake activity resulting from human activity that causes a rate of energy release, or seismicity, which would be expected beyond the normal level of historical seismic activity.”
Anadarko supports expanding the science, data and knowledge base around induced seismicity and how it may be related to human or industrial activity. We work with federal and state agencies on the development of appropriate regulations and guidance on the management of oil and natural gas operations, including the regulation of processes, materials and water management.
Hydraulic fracturing is an essential process in the modern development of unconventional oil and natural gas reservoirs. Hydraulic fracturing has been around since the 1940s and the associated technology has significantly evolved. The process has become more commonplace as the development of unconventional tight shale oil and natural gas reservoirs gained prominence in the mid-2000s. The hydraulic fracturing process occurs at great depth below the surface (5,000 to 10,000 feet or more) and impacts a relatively small area of rock immediately surrounding the wellbore.
Experts and regulators appear to agree that hydraulic fracturing, or fracking as it is more commonly referred to, is not a significant source of concern for induced seismicity for several reasons including:
- During the hydraulic fracturing process, only a limited volume of water is pumped into the formation for each stage of treatment; and
- Each pumping stage is a one-time event lasting 2-4 hours. The micro-seismic events that are generated from the fracking process are so small that, to be detected, requires sophisticated instruments that either have to be deployed in adjacent wells or on a very tight surface grid around the stimulated well.
Wastewater Injection Wells
Along with the oil and natural gas that are produced, potentially large amounts of natural saline brine water (formation water) may also be produced. This brine water is mainly a remnant of ancient oceans and contains high concentrations of salt and other dissolved minerals, as a result. The brine water must be separated from the oil and natural gas and, in some cases where recycling is not feasible, re-injected back into the Earth through the use of underground injection wells permitted in compliance with federal and state regulations. Such wells are common in oil and natural gas producing areas around the globe.
The relatively recent increase in seismic events in some isolated regions of the United States, including southern Kansas, Oklahoma and Texas, have led to numerous studies and increased deployment of seismic monitoring stations across the region. These stations increase data sampling and better enable independent researchers, regulatory bodies and industry partners in their ongoing efforts to study the possible correlation between wastewater disposal and increased seismic activity under unique geological conditions.
Although the seismic activity referenced above is generally occurring in areas where Anadarko has limited or no operations, the company is reviewing the data collected and monitoring the progress of the studies mentioned above, as well as engaging with various independent agencies and other experts to gain better scientific understanding. For instance, Anadarko has joined the Center for Integrated Seismicity Research (CISR) to further improve understanding of the mechanisms that may contribute to induced seismicity.
Anadarko continues to review the data pertaining to seismic activity associated with production operations, monitoring the progress of the studies mentioned above, as well as engaging with various independent agencies and other experts to gain better scientific understanding. We are aware of seismic activity across the Delaware Basin and continue to monitor any regional seismic events. Anadarko’s operations in the Delaware Basin only injects produced water into the shallower Delaware Mountain Group, the primary injection target for the majority of local operators, which is well understood and suitable to handle significant volumes of water. Furthermore, Anadarko has joined the leading academic research consortiums at Stanford University and the University of Texas at Austin to further improve our understanding of the mechanisms that may contribute to induced seismicity.
We use the results and findings of studies and research in this area to continually improve our procedures and processes to assess the potential risk of induced seismicity from new well completions, drilling and operation of disposal wells and associated wastewater disposal activities. Across all U.S. onshore operations, Anadarko works to position production wells geographically to avoid large faults and felt seismic events from hydraulic fracturing or production operations, including those operated by a third party. In addition, we screen all operated SWD wells for an association with induced seismicity and continuously monitor pressure and rates to ensure compliance with permit conditions.
For siting and development of injection wells at all assets, we have a review process to evaluate the potential for felt induced seismicity, including the following:
- Review of local and regional geology using 3D seismic datasets;
- Identification of all existing disposal and other wells in the vicinity of proposed operations and their associated wellbore integrity;
- Review of current and historic seismicity events with consideration of trends; and
- Assessment of local faults and potential for reactivation, including basement faults.
If Anadarko is alerted to a felt seismic event in an area of our operations, we would initiate a multidisciplinary investigative process to identify both operated and non-operated disposal wells in the vicinity of observed seismicity and review associated construction, operation history, and other well details. This process determines if any modifications to our efforts to manage the risk of induced seismicity need revision.