Patent Document ID: 9279897
Application ID: 11608155
Patent Flag: 1

Claim One:
1. A qualitative method to locate and dimension a fluid saturated zone in the earth, said fluid consisting of oil, gas and water, by extracting characteristic resonance response of said zone in the range of 1-20 Hz to ambient noise, said method comprising the steps 1.1. perform seismic measurements, over a survey area, where oil, gas and water are suspected or searched for, with long period seismometers for certain time duration each, measuring done in successive manner or in arrays, said measuring seismic energy produces seismograms, spacing between seismometers chosen not larger than wave length of interest, performing a few reference seismic measurements where fluid is not present in the survey area, and performing a continuous seismic measurement to monitor signal variation in time, said seismometers placed away from local noise and buried to avoid wind, 1.2. while performing said seismic measurements, passively exciting said fluid saturated zone into resonance by seismic noise in the earth, the excited fluid saturated zone constituting fluid related oscillators, 1.3. correct said seismograms for local impedance changes, effect of topography and geological differences, regional noise patterns and possible tidal effects, 1.4. perform a main signal analysis of said seismograms in the frequency domain, by a computer executing computer programs, to (a) define behavior of average signal frequency and average signal phase of said seismic measurements over the entire duration of said seismic measurements, and also process said seismograms to obtain regional velocity correlation coefficients, to derive from said regional velocity correlation coefficients a corresponding velocity dispersion, under the assumption of random surface waves, to determine velocity as a function of depth by inverting said velocity dispersion, based on main mode surface wave dispersion, (b) use a horizontal/vertical component ratio test in said seismograms to exclude rock only oscillations, related to rock layering and rock structures alone and unrelated to said fluid saturated zone, said rock only oscillations are excluded from further consideration and optionally filtered out, (c) examine signal character of said seismograms within standard seismic noise with shifted time windows, 1.5-30 sec size, to determine signal frequency peaks in said frequency domain, characterizing said fluid related oscillators, with signal frequency peak characteristics signal frequency peak amplitude, signal frequency peak sharpness, signal frequency peak duration, optionally phase behavior of signal frequency peaks, signal frequency peak repetitiveness, identifying said signal frequency peaks within standard seismic noise by use of a frequency/time/strength plot and optionally filter said seismograms by using a signal frequency range based on said signal frequency peaks for further processing, and (d) use Sompi method on said seismograms, with or without said optionally filtering, to determine prevalent—if any—oscillator frequency f and oscillator quality Q of said fluid related oscillators, (e) correlate shape and amplitude of signal of said seismograms to a depth indicator; more smoothness in said shape and amplitude of signal indicates more depth, (f) map strong seismic signals said average signal frequency from (a), said signal frequency peaks from (c), said oscillator quality Q from (d), said depth indicator over said survey area, (g) set up and use statistics in time and space of said oscillator frequency f, said oscillator quality Q, said depth indicator, said signal frequency peaks for comparisons between different areas, where additional details are known: depth of said fluid saturated zone, fluid type, dimensions of said fluid saturated zone, to deduce additional physical or geometrical properties of said fluid saturated zone.