Surface Microseismic Monitoring

Automated Seismics provides services for surface-based microseismic analysis.  We can analyze data collected with our AS-Monitor real-time seismic data acquisition system or reprocess data collected from other systems.  We specialize in leveraging data from large arrays with 1000+ channels to detect and locate microseismic events in noisy environments.  Our aim is to provide high quality microseismic event catalogs ready to integrate with other field data and improve the understanding of your reservoir.

Applications

In any application where fluids are injected into the subsurface, imperceptible earthquakes called microseismic events result from slip on rock discontinuities such as faults, fractures, or bedding planes as the stress field changes. 

Microseismic monitoring is highly valuable in understanding:

• Geometry and evolution of fracture networks

• Location of faults

• Fluid flow pathways

• Stress state of a reservoir

• Potential for larger, hazardous induced earthquakes

Advantages

Despite the noisy character of surface-based microseismic data, it has several advantages compared to downhole geophone or fiber optic data.

• Cost-effectiveness: Surface array deployment requires less infrastructure and equipment compared to downhole sensors.

• Flexibility: The geometry and size of a surface array can be adapted based on the layout of wells, project budget, permitting requirements, and local noise sources such as roads and buildings (see right).

• Risk reduction: Surface arrays avoid the risks of deployment in harsh borehole conditions and may be quickly serviced when faults occur.

• Broad area coverage: A surface array has uniform coverage over many square kilometers, which is particularly important when monitoring a multi-well project and accurate epicenter locations are essential.  It also enables the focal mechanism (fault plane orientation and direction of slip) to be estimated from the radiation pattern of each event.

Processing

The most up-to-date data processing techniques and our own purpose-built software is used to extract the most out of noisy data.

• Source scanning event detection:  A source scanning algorithm is used to detect and locate events even when data is too noisy to see microseismic signals in individual traces (see right).

• Coherent noise attenuation:  When channels are densely spaced, spatial noise filters are available to reduce coherent noise from surface waves.

• Statics correction and velocity model calibration:  Perforation shots are utilized to reduce velocity model uncertainties and accurately locate the depth of all events.

• 3D Velocity Models:  In structurally complex areas, 3D velocity models beyond a layer cake approximation can be used to locate events more accurately.

• Moment tensor inversion: The focal mechanism is determined from the radiation pattern of each event (see below).

Left: Microseismic event data showing polarity flips in the radiation pattern caused by the focal mechanism. Middle: Beachball representation of the radiation pattern emitted by the microseismic event. Right: A fault plane orientation and slip vector obtained from the moment tensor inversion.

Data Products

The final product of microseismic monitoring is a catalog of properties for every detected microseismic event.

• Event Time: Correlate seismic activity with the fluid pumping schedule.

• Event XYZ Location: Constrain the shape of the stimulated rock volume, identify interference between wells, and locate natural faults.

• Moment Magnitude: Determine the rate of earthquakes by size and meet regulatory requirements.

• Moment Tensor and focal mechanism:  The orientation of fault planes and direction of slip can provide valuable information on natural or induced fractures.

• Stage and well attributes:  For hydraulic fracturing projects, events are tagged by well and stage number.  Attributes such as distance to the perforation cluster and time from pumping start calculated for well interference and stage performance studies.

All event data is collated into a 3D animation to visualize the spatial distribution of microseismic activity over time.  We can also work with you directly to integrate well log, pumping, 3D seismic, and fiber optic data to get the most out of your microseismic data.