Presentation on theme: "Reflection Seismic Processing"— Presentation transcript:
1Reflection Seismic Processing ObjectiveGeneral concept of CMP processingProcessing steps and toolsReading:YilmazSeismic Un*x primer
2Reflection Seismic Processing Objective - transform redundant reflection seismic records in the time domain into an interpretable depth image.Data reduction and editing;Transformation into conveniently computer-manageable form;Removal of bad records;Gathering;CMP sorting;Filtering in time and space;Attenuation of noise;ImagingFinal velocity and reflectivity image.
3General CMP Processing Sequence Demultiplex, Vibroseis correlation, Gain recoveryConversion from file formats produced by field data loggers into processing-oriented formatsSEG-Y, SEG-2.ProMax, Focus, Omega, SU, Vista, etc., internal formats.Rarely required now (done in the field).Field GeometryAssignment of source-receiver coordinates, offsets, etc. in the trace headers.EditRemoval of bad traces (noisy channels, poorly planted geophones, channels contaminated by power line noise, etc.).
4General CMP Processing Sequence (continued) First arrival pickingMay be semi-automatic or manual;Required for generation of refraction statics; models and for designing the mutes.Elevation staticsBased on geometry information, compensates the travel-time variations caused by variations in source/receiver elevations.Transforms the records as if recorded at a common horizontal datum surface.Refraction staticsBuilds a model for the shallow, low-velocity subsurface;Compensates the travel-time variations caused by the shallow velocities.‘Top’, ‘bottom’, and ‘surgical’ muteEliminates (sets amplitude=0) the time intervals where strong non-reflection energy is present:First arrivals, ground roll, airwave.
5General CMP Processing Sequence (continued) Gain recoveryCompensates geometrical spreading;Based on a simple heuristic relation.Trace balanceEqualizes the variations in amplitudes caused by differences in coupling;In true-amplitude processing, replaced with ‘surface-consistent deconvolution’.DeconvolutionCompresses the wavelet in time, attenuates reverberations.Gather, CMP sortIn modern processing systems (ProMax, Omega, Vista) done by using trace lookup spreadsheets rather than by creating additional copies of the dataset.
6General CMP Processing Sequence (continued) Velocity analysisFor each of the CMP gathers, determines the optimal stacking velocity.Dip Moveout (DMO) correctionTransforms the records so that the subsequent NMO+stack work well even in the presence of dipping reflectors.Normal Moveout (NMO) correctionRemoves the effects of source-receiver separation from reflection records;Transforms the records as if recorded at normal incidence.Residual staticsRemoves the remaining small travel-time variations caused by inaccurate statics or velocity model
7General CMP Processing Sequence (continued) Steps above are usually iterated 3-5 times to produce accurate velocity and residual statics models.Success of velocity analysis depends on the quality of DMO/NMO and residual statics, and vice versa.StackProduces a zero-offset section;Utilizes CMP redundancy to increase the Signal/Noise ratio.MigrationTransforms the zero-offset time section into a depth image;Establishes correct extents and dips of the reflectors.
8ProMAX, Echos Processing organized around the database Area (project)LineProcessing Flows (perform specific processing tasks with the traces or databases)Datasets (traces, headers, lookup tables)Databases (most of them called OPF – Ordered Parameter Files)Tables (travel times, velocity models, etc.)A special area used for archiving and restoring other projects ('areas')
9ProMAX Key components Front-end GUI Flow builder Monitor Navigates within areas, lines, flows, datasets, databases, tables, etc.Flow builderAllows building processing flows from a library of modulesSend flows to executionMonitorMonitors running jobs, allows suspending and killing themDisplays job logsDatabase editorsDisplay/edit various databases
10VISTA Processing organized around a dataset in a SEGY file Processing operations are mostly modifications of this file
11Seismic Un*x and IGeoSProcessing organized by processing flows (shell scripts)Additional files (velocity model, picks, etc.) created and used by tools as neededInteractive displays also created by tools
12Processing Flow Seismic processing flow is a computer program Implemented as a 'script' (DISCO, SIA, SU), 'instruction list' (ProMAX), or visual 'graph' (Vista, Omega)User builds the processing sequence using a collection of tools for data manipulationResults in generation of a code customized to perform the specified task
13A More General Processing Flow (IGeoS/SIA) SIA Seismic processing logic is based on independent operation of the modulesEach module transforms an input gather of multicomponent traces into output oneSIA also maintains a system of database tables and inter-modular messaging mechanism