Microseismic Acquisition and Survey Design
Microseismic acquisition involves continuous passive seismic monitoring, using sensors in a number of different possible configurations. Although some refer to shooting a microseismic survey, the expression incorrectly implies an active source, whereas the passive nature means that terms such as recording, acquiring, or listening are more appropriate. Sensors can be deployed permanently or temporarily (Figure 1) in either an observation well or on surface, depending on the scope of the monitoring. Borehole arrays are the most common deployment (Maxwell et al., 2010), installed via wireline (as used for VSP or crosswell), cemented geophone arrays in shallow or deep observation wells (Smith, 2010). Alternatively, arrays can be deployed on surface (Duncan and Eisner, 2010), as used for reflection surveys or earthquake monitoring. Wireline arrays can be deployed in a near vertical borehole or conveyed into a horizontal borehole using a wireline tractor that pulls the array along. Surface arrays can use broadband seismometers (as in earthquake monitoring) or similar sensors to reflection surveys (Eaton et al., 2013) deployed in crosslines (radial lines away from the treatment wellhead or following gridlines), or in 2D patches over the target area (Pandolfi et al., 2013).