Injection Induced Seismicity Management Framework

ABSTRACT: Regardless of the operational causal type of induced seismicity, effective management is comprised of specific key elements. Here we focus on injection induced seismicity, associated with either subsurface injection or hydraulic fracturing. The key elements of a risk management framework associated with injection induced seismicity include the following: 1. Continuous risk assessment through operational life cycle, 2. Transparency and collaboration with stakeholders, 3. Mitigation plan if anomalous events occur, 4. High resolution monitoring, 5. Integrated interpretation of the subsurface system, 6. Mitigation and operational changes. Risk assessment should begin prior to the start of injection, during pre-operational planning stages. Risk is a combination of seismic hazard or probability of occurrence of an event of concern and associated consequences. Most operations are not associated with seismicity of concern and hence are low hazard/risk. In the limited sites where injection induced seismicity have been encountered, only a small fraction of operations is seismogenic. Therefore, an important element of risk assessment is screening for situations of concern which is typically reliant on evidence of historic seismicity associated with similar regional operations. In addition to historic seismicity, fault mapping from 3D seismic and associated slip analysis in the regional stress field. Depending on the risk level, pre-job decisions can potentially be made to mitigate the potential risk. Prior to drilling, for example, the actual location of the well could be adjusted to avoid potentially hazardous structures. Transparency and collaboration are key throughout the project, starting with pre-injection planning for risked projects. Preparing a mitigation plan is one of the most important elements of effective management and should include: 1. Roles and responsibilities within the organization, 2. Monitoring of operational status and seismicity, 3. Communication plans both internally and externally, 4. Operational responses/traffic light thresholds. Seismic monitoring should be realtime (at least at traffic light levels) and include public networks, which also provide access to public “did you feel it” reports. Generally proprietary monitoring is recommended with a minimum magnitude of completeness below the minimum traffic light thresholds. Background seismicity data can be integrated with other operational and subsurface data to regularly interpret the response of the subsurface. 3D seismic imaging of inferred structures can identify potentially seismogenic structures for geomechanical assessment for potential to slip with increased pressure. Integrating background seismicity with the structural interpretation and operational activities provides useful insights to update the risk assessment. Of particular importance is how background trends change with time, and in particular any spatial changes or migration of activity with time can be insightful to understand potential pore pressure diffusion or mechanical stress changes associated with slip can be insightful. Investigations of how seismicity changes during operational shut in or curtailments can also assist understanding associations with injection. The background seismicity can prove to be a rich dataset in terms of the geomechanical response of the reservoir. Finally, if any events exceed the traffic light levels and engage the operational protocols, changes should be made to reduce both the pressure changes at the seismogenic structure, and the area of structure over which slip is activated. The anomalous seismicity should lead to reviewing the risk assessment. What operational changes to make are dependent on numerous factors and risk tolerance, however in general smaller, early operational changes may be more impactful than waiting for extreme events that might require larger op