Seismicity Review

Information for Permitting Disposal Wells in Areas of Seismicity

RRC Seismicity Response Brief 
This document provides an overview of the Railroad Commission’s work mitigating earthquakes in Texas.

Application Information

The checklist below outlines the information required for disposal well applications that undergo a seismicity review. Applicants are encouraged to submit any additional information that will assist seismicity review.

Checklist

• Area of Interest (AOI) Map
• Geologic Information
• Fault hazard analysis if fault in AOI

Area Of Interest (AOI) Map

• An application for a new disposal well permit or an amendment of an existing disposal well permit for injection pressure, injection rate, or injection interval must include a survey of historical seismic events within the Area of Interest (AOI). The AOI is a circle centered on the disposal well location with a radius of 5.64 miles (9.08 km) for shallow wells and 15.53 miles (25 km) for deep wells. A disposal well is generally considered deep if the disposal interval includes geologic strata below the Wolfcamp formation or the bottom of the interval is deeper than 10,000 feet.
• For instructions on how to create a survey of historical seismic events see the Historical Seismic Events section of the Attachments for New Injection/Disposal Wells webpage.
• A seismic event of 2.0 Magnitude (M) or greater from the USGS earthquake catalog or the TexNet earthquake catalog triggers seismicity review and requires additional geologic information across the AOI. A Seismicity Review can be triggered by complex geology (for example, injection into basement or near basement strata with known faulting).

Geologic Information

• Structure maps on top and bottom of injection interval,
• Isopach map of the injection interval, and
• Cross-sections oriented along strike and dip of the formation(s) proposed for injection.

Fault Hazard Analysis

• If a fault exists within the AOI, a fault hazard analysis may be required. The Stanford Center for Induced and Triggered Seismicity (SCITS) provides a free tool, Fault Slip Potential, to screen a fault's likelihood to slip, using data on the nature of the fault and nearby injection.
• Applicants are encouraged to submit any additional information that would assist evaluation of seismic hazard.

Seismicity Review Score Sheet

Applications for disposal well permits in areas of seismicity should include additional information to assist the seismicity review. Seismicity reviews outside of the Permian Basin or with a score of C or C- will also be reviewed by RRC's Seismologist. You can see an example of the score sheet RRC staff will use to evaluate the seismic hazard near the proposed location.

Seismicity Review Factors

RRC staff will review at least the following factors to determine appropriate disposal well permit conditions in areas of seismicity:

• Maximum Seismic Event Magnitude in AOI
• Number of Seismic Events ≥ 3.0M in AOI
• Number of Seismic Events ≥ 2.0M in AOI
• Horizontal Distance to Seismic Event ≥ 2.0M
• Number of Mapped Faults in AOI
• Horizontal Distance to Nearest Mapped Fault
• Years Since Last Seismic Event in AOI
• Seismicity & Faulting Data Confidence
• Permitted Cumulative Injection Rate within 2.82 mi (4.54 km)

Permit Conditions

To ensure that disposal permits issued with a seismic event ≥ 2.0M in the AOI do not contribute to seismic activity, permit conditions may be applied for administrative approval, including:

• Lower permitted injection rate in accordance with seismicity review score,
• Lower injection pressure if disposal is into a formation with a low fracture gradient,
• Step-rate test(s),
• Bottom-hole pressure test(s),
• Daily recording of injection volumes and pressures, and
• Permitting conditions recommended by the RRC Seismologist.

Seismic Monitoring

Disposal well operators are encouraged to perform seismic monitoring. An operator may be permitted for a higher injection rate if an operator develops and implements an RRC-approved Seismic Monitoring Plan and an Earthquake Response Plan.

Seismic Monitoring Plan

The Seismic Monitoring Plan must contribute data to an existing public seismic network, for example The University of Texas, Bureau of Economic Geology's TexNet program. TexNet has specified seismic station requirements. Monitoring should contribute to the body of public knowledge to better resolve earthquake locations, especially depth. At a minimum, the Seismic Monitoring Plan must include:

• The method of monitoring,
• The location and type of instrumentation, and
• An archive of the data in a public seismic database.

Earthquake Response Plan

The Earthquake Response Plan must identify actions that will be taken to inspect for facility damage, mitigate risk by modifying operations, and establish thresholds for suspension of injection activity. At a minimum, the Earthquake Response Plan must include:

• Monitoring plan will be filed with the Commission before disposal activities begin.
• Operator will monitor TexNet and USGS catalogs.
• Response plan triggered when a 3.5M event is detected with a reported hypocenter location within the AOI.
• Operator will notify the Commission within 24 hours of an earthquake that triggers the response plan.
• Within 30 days of an earthquake trigger, the operator will file a report with the Commission documenting the event.