Seismic method can be divided into active seismic and passive seismic. Active seismic or reflection seismic use controlled seismic source like dynamite, seismic vibrator, or air gun and make use of reflected wave to discern subsurface properties. Passive seismic, in other hand make use of background noise from naturally occurring event like earthquake, oceanic microseism, or from artificial noise such as urban traffic. Passive seismic usually focuses on a low frequency signals (0 – 20 Hz) and sometimes called low frequency seismology.

Typical spectra of ambient seismic vibrations recorded in a region with an oil reservoir (Lopes and Nunes, 2010)

Our main interest in passive seismic is in hydrocarbon microtremor, a low cost exploration method for for hydrocarbon indicator. Hydrocarbon microtremor method used spectrum analysis of recorded seismic data for creating map of hydrocarbon probability. If we have velocity information of subsurface, we can do Time Reverse Modeling to get 3D position information that create microtremor anomaly.

Time reverse modeling to get source position.

Currently we are doing joint research in hydrocarbon microtremor with Institut Teknologi Bandung and PT. Pertamina EP Asset 2. This research is done for validation of spectral anomaly and Time Reverse Modeling method of hydrocarbon microtremor.

Hydrocarbon Microtremor​

Hydrocarbon microtremor is low cost exploration method for direct hydrocarbon indicator. This Microtremor is caused by ocean background waves that go through porous reservoir containing oil and water, inducing resonant amplification in frequency around 3Hz. Result of this method is map and 3D volume of hydrocarbon probability.

Velocity Modeling​

Passive seismic acquisition using several sensor simultaneously can be used to infer subsurface velocity. Using method such as spatial autocorrelation (SPAC), or passive seismic tomography, we can get P-Wave Velocity and S-Wave velocity of subsurface.

Reservoir Monitoring​

Passive seismic monitoring uses existing geophones to monitor ongoing changes in reservoir, caused by injection or hydrocarbon extraction that alter state of stress in the host rock. Subsequent changes in either pore pressure or deformation-induced stresses can then cause seismic events. ​

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