Low frequency seismic - A new tool for exploration and development
Published in
DEW - The Complete Energy Journal
Date of publication
12 December 2009
Abstract
One of the most exciting developments in recent times for hydrocarbon exploration is the advances in Low Frequency (LF) Seismic as a tool for hydrocarbon detection.
This technology involves the spectral analysis of the ambient seismic wavefield between 0.1 and 6 Hz to extract hydrocarbon reservoir related anomalies. The method uses highly sensitive broadband seismometers – of the type used for earthquake monitoring – to directly record the earth’s ambient wavefield down to below 0.1 Hz. The sensors are chosen for their frequency range, low noise floor, and sensitivity. Each recording station consists of a three component broadband seismometer, battery pack, a GPS unit and hand-held controller.
The recorded LF data is analyzed to study amplitude variations or anomalies in the low frequency band range (<10 Hz). Low Frequency hydrocarbon-related spectral anomalies are an observed phenomenon and reported in the literature by Spectraseis and others. Empirical observations suggest that multiphase fluids in hydrocarbon reservoirs redirect energy from the earth’s ambient wavefield to cause small energy anomalies as recorded at the surface.
Current hypotheses state that these anomalies may be directly related to the fluids inside the reservoir structure. A preliminary model has been hypothesized to explain the potential source mechanism of the microtremors generating the spectral anomalies. Poroelastic effects, due to wave induced fluid flow and oscillations of different fluid phases, are significant processes in the low frequency range that can modify earth’s seismic background wavefield. The assumption here is that hydrocarbon reservoirs are partially saturated while the surrounding rocks are fully saturated (Saenger, 2009).
This technology involves the spectral analysis of the ambient seismic wavefield between 0.1 and 6 Hz to extract hydrocarbon reservoir related anomalies. The method uses highly sensitive broadband seismometers – of the type used for earthquake monitoring – to directly record the earth’s ambient wavefield down to below 0.1 Hz. The sensors are chosen for their frequency range, low noise floor, and sensitivity. Each recording station consists of a three component broadband seismometer, battery pack, a GPS unit and hand-held controller.
The recorded LF data is analyzed to study amplitude variations or anomalies in the low frequency band range (<10 Hz). Low Frequency hydrocarbon-related spectral anomalies are an observed phenomenon and reported in the literature by Spectraseis and others. Empirical observations suggest that multiphase fluids in hydrocarbon reservoirs redirect energy from the earth’s ambient wavefield to cause small energy anomalies as recorded at the surface.
Current hypotheses state that these anomalies may be directly related to the fluids inside the reservoir structure. A preliminary model has been hypothesized to explain the potential source mechanism of the microtremors generating the spectral anomalies. Poroelastic effects, due to wave induced fluid flow and oscillations of different fluid phases, are significant processes in the low frequency range that can modify earth’s seismic background wavefield. The assumption here is that hydrocarbon reservoirs are partially saturated while the surrounding rocks are fully saturated (Saenger, 2009).
