Microseismic monitoring is the passive observation of very small-scale earthquakes which occur in the ground as a result of human activities or industrial processes such as mining, hydraulic fracturing, enhanced oil recovery, geothermal operations or underground gas storage. Microseismic science grew out of earthquake seismology and focuses on micro-earthquakes (i.e. magnitude less than zero). These micro-earthquakes are too small to be felt on the surface, but they can be detected by sensitive equipment such as geophones and accelerometers.
Microseismic fracture mapping schematicUnlike traditional 3D seismic technologies which measure acoustic reflections from an energy source, microseismic monitoring is a passive method, meaning that it listens for seismic energy which is already occurring underground. Passive seismicity is also commonly referred to as "induced seismicity."
Passive methods provide a continuous 4D record of seismicity in the monitoring region, rather than individual snapshots in time obtained by conventional 3D seismic methods. Microseismic results are often delivered in real-time, and can literally offer a video recording of what is happening deep underground as a result of industrial operations.
What is a microseismic event?
Large-scale earthquakes are caused when energy is released as a result of rock failure along a fault. In contrast, microseismic events are caused when human activities such as mining or oil and gas production change the stress distribution or the volume of a rockmass.
When the rock attempts to redistribute the stress within the rockmass, it will suddenly slip or shear along pre-existing zones of weakness such as along faults or fracture networks.
What can microseismic monitoring tell us?
Basic microseismic monitoring aims to answer three fundamental questions about microseismic events:
1. When did the microseismic event occur?
2. Where did the microseismic event occur?
3. How big was the microseismic event?
Traditional microseismic mapping determines the location and magnitude of the event. When microseismicity is observed over time, operators may start to see patterns of seismicity related to production activities.
Advanced microseismic analysis performed by ESG can reveal more detailed information about the microseismicity of the area and how the rock is responding to mining or oil and gas production activities, leading to increased efficiency and optimized operations.
This small failure results in the release of energy in the form of seismic waves and is known as a microseismic event.