Objective
THE AIM OF THIS PROJECT IS TO DEVELOP A SERIES OF CORRECTION TECHNIQUES WHICH WOULD ALLOW A GREATLY IMPROVED AND MORE RELIABLE INTERPRETATION OF SEISMIC WAVE REFLECTIONS BY DEEPLY BURIED LAYERS.
Seismic wave propagation anomalies due to shallow and deep causes were studied.
The research improved the various links of the seismic prospecting sequence, as a preparation to seismic inversion (ie the determination of the lithology from seismic data).
The results were obtained from various lines of research.
Seismic elastic modelling programs were validated and a study was initiated into the response of random media (rugged interfaces) involving the conversions between P and S waves at the interfaces. Several case studies were considered, among which the effects of rapid lateral variations of velocity were prominent.
Modelling was also used to help the interpretation of deep reflection seismics.
The evaluation of the maximum resolution of classic velocity analyses was carried out using innovative nonlinear analyses of the peak of the response.
The limits of blind deconvolution (the determination of the transfer function of linear system given the output and only some statistical information on the input data) together with innovative techniques to initialize the search for the seismic wavelet were analyses.
In particular, attention was brought to the possibility of determination of the elastic absorption from the extracted wavelet.
A new theory has also been sketched for the case of non independent reflection coefficients.
Classical ray tomography was extended to finite bandwidth data and the limits of the lateral resolution of seismic transmission surveys were evaluated in order to valuate the lateral extent of velocity anomalies.
Finally, the seismic modelling program, originally developed on IBM machines and the seismic migration codes, based on Stolt and cascaded migration were developed on a Cray supercomputer.
WHEN APPLYING THE SEISMIC REFLECTION METHOD TO DEEPLY BURIED ROCKS ANOMALOUS WAVE PROPAGATION PHENOMENA OCCUR WHICH RENDER VERY IMPRECISE THE VELOCITY ANALYSIS AND GREATLY IMPAIR THE USEFULNESS OF THE REFLECTION WAVEFORM BY ALTERING THE RECEIVED SIGNALS.
ANELASTIC ABSORPTION, FAST LATERAL VELOCITY VARIATIONS - ESPECIALLY IN SHALLOW LAYERS -, REVERBERATIONS IN SHALLOW AND DEEP LAYERS, P TO S WAVE CONVERSION AND VICE VERSA ARE AMONG THE MOST IMPORTANT OF THESE PHENOMENA. COMPENSATION TECHNIQUES WILL BE DEVELOPED BY THE JOINT EFFORT OF SEVERAL UNIVERSITIES. THE RESULTS WILL BE VALIDATED AND COORDINATED BY OGS IN CLOSE COOPERATION. FIRST AN ANALYSIS OF THE FIELD TECHNIQUES FOR DATA ACQUISITION WILL BE CONDUCTED IN ORDER TO PRODUCE A SET OF PRACTICAL RULES FOR THE DESIGN OF FIELD WORK.
THIS WILL FIRST BE ACCOMPLISHED BY THE CHARACTERISATION OF THE MAIN OBJECTIVES, THEIR LITHOLOGIES AND THE EXPECTED STRUCTURAL BEHAVIOUR. A RAY-TRACING CHECK OF THE PROPOSED MODEL WILL BE EFFECTED TO CONSTRAIN THE POSSIBLE HETEROGENEOUS STRUCTURES AND TO RECOGNIZE THE INFLUENCES OF VARIOUS STRUCTURAL CAUSES ON THE FIELD DATA RECORDING PARAMETERS. THESE SHALL ACCOUNT FOR: THE VARIATIONS OF THE REFLECTION COEFFICIENT WITH THE INCIDENCE ANGLE, THE NEED FOR ACQUIRING SIMULTANEOUS SEISMIC INFORMATION ALONG DIRECTIONS NORMAL TO THE MAIN PROFILE, THE NEED FOR ACQUIRING P AND S VELOCITY VALUES FROM THE DEEPER LAYERS ETC. TO COMPENSATE FOR THE ANELASTIC ABSORPTION A Q DECONVOLUTION TECHNIQUE WILL BE DEVELOPED, BASED ON A QUALITY FACTOR Q LINEARLY INCREASING WITH FREQUENCY, DEPENDING UPON THE DEPTH AND DECREASING NEAR THE SURFACE.
COMPUTER PROGRAMMES WILL BE DEVELOPED WHICH SHOULD BE ABLE TO:
A) REMOVE THE EFFECT OF A Q FACTOR PROGRESSIVELY VARYING IN SPACE AND TIME, ONCE ASSIGNED (E.G. FROM VSP DATA);
B) IDENTIFY DIRECTLY THE ABSORPTION EFFECT IN THE FREQUENCY CONTENT OF THE SEISMIC TRACE. SUBSEQUENTLY THE ESTIMATION OF THE PROPAGATION WAVELET, TAKING INTO ACCOUNT THE SHALLOW REFLECTION STRUCTURES, WILL BE MADE BY BLIND DECONVOLUTION TECHNIQUES. THE TRADITIONAL TECHNIQUES MAY NOT BE SUITABLE, DUE TO PHASE CHANGES OF THE WAVELET AT THE REFLECTIVE BOUNDARY. COMPLEX BLIND DECONVOLUTION TECHNIQUES WILL BE DEVELOPED BASED ON SUITABLE HYPOTHESIS ABOUT COMPLEX SERIES. THESE ARE MODELLED AS SEQUENCES OF SPARSE LARGE REFLECTORS DISTRIBUTED ALONG SEQUENCES OF SMALL EVENTS WITH A PROPER AMPLITUDE DISTRIBUTION. THUS BAESIAN AND PSEUDO-BAESIAN ESTIMATORS CAN BE USED IN ITERATIVE METHODS.
THE RESULTS OF THE AFOREMENTIONED DATA PROCESSING TECHNIQUES WILL LEAD TO THE IDENTIFICATION OF THE COMPLEX REFLECTION COEFFICIENTS AS A FUNCTION OF THE INCIDENCE ANGLE ON THE REFLECTING INTERFACE. THE ELASTIC PROPERTIES OF THE REFLECTING LAYERS WILL THEN BE DETERMINED, NAMELY THE VARIATIONS OF THE POISSON MODULES WILL BE MODELLED, THUS DETERMINING: THE VARIATIONS OF THE FLUID CONTENT IN HTE ROCKS, THE FRACTURATION, THE LATERAL FACIES VARIATIONS.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- natural sciences earth and related environmental sciences geology lithology
- engineering and technology electrical engineering, electronic engineering, information engineering electronic engineering computer hardware supercomputers
- natural sciences computer and information sciences data science data processing
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Coordinator
SGONICO-TRIESTE
Italy
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