This technique is based on the principles that hydrocarbon reservoirs as a multi-fluids system in porous medium has an unconventional (non linear) transfer characteristics for acoustic waves. Hydrocarbon fluid in porous system can be detected as a characteristic deformation of the natural earth noise spectra in the acoustic low frequency range between 0.2 and 10 Hz. The anomalous absorption/emission of micro-seismic noise is used as source for direct detection of oil/gas accumulation (OGA) trapped in a porous matrix/reservoir.
In these conditions, the OGA passes in generation of its proper infra-acoustic waves. The mechanical energy of hydrodynamic nature is simply transforming in acoustic energy generating the IPDS waves/signals (downward conversion). The spectral amplitude of background micro-seismic emission above the OGA exceeds considerably that of outside the OGA in the frequency range of 0.1-30 Hz. Measuring and processing the characteristic spectral amplitude of this generated and amplified natural micro-seismic noise defines the presence or absence of OGA.
Applying this technology to three important fields in the North Caspian basin has shown that it provides a detailed spatial hydrocarbon distribution, reservoir delineation and monitoring and reliable estimation of hydrocarbon potential reserves or resting un-produced oils. Correlation of field production data with the passive seismic monitoring results shows an enough satisfactory output of the applied technology for reservoir monitoring. This technology could be also promising for EOR/IOR projects, as well as for horizontal and vertical well drilling projects.
However, in faulted disintegrated zones owing to increased heterogeneous stress as factor of both micro- and macro-seismic instability the IPDS signals are somewhat deformed. This fact implies some ambiguities, which have to be clarified and resolved.