Method for absolute preserved amplitude processing of seismic well data
AssigneeInstitut Francais du Petrole
InventorsCharles Naville, Sylvain Serbutoviez
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Abstract
A method for absolute preserved amplitude processing of data obtained by seismic prospecting known as VSP. The method comprises reception, by seismic receivers (R) arranged in a well and coupled with the surrounding formations, of seismic waves generated by a source (S) and reaching directly the receivers (direct or downgoing waves DW) or after reflections on discontinuities (D) (upgoing waves UW). The method has an application of precise measurement of the amplitudes of reflected and diffracted seismic events on monocomponent or tricomponent VSP data, in addition to conventional seismic wave propagation time and velocity measurements.
Claims46
A seismic processing method for recovering, within a VSP type seismic prospecting method, of absolute amplitude ratios between, seismic signals corresponding to upgoing waves emitted by a seismic source coupled with a geologic formation and reflected from subsoil discontinuities, the seismic signals being received by separated seismic receivers coupled with a wall of a well through the geologic formation, in a depth zone of the well, and seismic signals corresponding to downgoing waves received by the seismic receivers coming directly from the seismic source, comprising:
- normalizing downgoing waves at the seismic receivers of a zero-phase amplitude pulse in a frequency band determined by a signal-to-noise ratio observed in the frequency band, which is carried out after deconvolution of a signature of a total field of the downgoing and upgoing waves by the downgoing waves, which compensates for the upgoing wave attenuation in a downgoing wave path between-the source and the receiver;
- separating the upgoing and downgoing waves with multitrace velocity filters including parameters adjusted to observed waves;
- compensating differences between amplitudes received by each seismic receiver, due to spherical divergence between a path of the upgoing waves and a path of the downgoing waves coming directly from the seismic source, and wherein
- the normalizing downgoing waves at seismic receivers in a form of zero-phase amplitude pulse is between a level of each seismic receiver and a level of each reflecting discontinuity, to normalize an amplitude of reflectors at a value measured by receivers located immediately above the reflectors.
A seismic processing method for recovering, within a VSP type seismic prospecting method, of absolute amplitude ratios between, seismic signals corresponding to upgoing waves emitted by a seismic source coupled with a geologic formation and reflected by subsoil discontinuities, the seismic signals being received by seismic receivers coupled with a wall of a well through the geologic formation at selected different positions, in a depth zone of the well, and seismic signals corresponding to downgoing waves received by the seismic receivers coming directly from the seismic source, comprising:
- deconvoluting a signature of a total wave field including downgoing and upgoing waves by the downgoing waves which compensates for the reflected waves for all physical attenuation causes concerning a downgoing wave path between the seismic source and the receivers;
- separating upgoing and downgoing waves by multitrace velocity filters with parameters adjusted to observed waves;
- normalizing the downgoing waves at the seismic receivers in a form of a zero-phase amplitude pulse in a frequency band determined by a signal-to-noise ratio;
- and
- compensating amplitudes of deconvoluted reflections accounting for a ratio between a spherical divergence on a path of the upgoing waves and a spherical divergence on a path of the downgoing waves at a position of each of the seismic receivers.
Dependencies are inferred from the claim text.