AVO and Shear Reflectivity in Geophysics

<p>Gradient inversion</p> Signup and view all the answers

<p>Due to class 4 AVO predominance</p> Signup and view all the answers

<p>To analyze amplitudes and their variation with offsets</p> Signup and view all the answers

<p>To form windows of different sizes based on data quality</p> Signup and view all the answers

<p>To avoid signal degradation</p> Signup and view all the answers

<p>Comparing near-offset, mid offset, and far offset stacks</p> Signup and view all the answers

<p>To display pre-stack information in a more compact way</p> Signup and view all the answers

<p>Angle gathers are generated from offset gathers using a transform that needs a velocity model</p> Signup and view all the answers

<p>Intercept and Gradient</p> Signup and view all the answers

<p>To locate anomalous amplitude behavior</p> Signup and view all the answers

<p>A linear relationship</p> Signup and view all the answers

<p>Low acoustic impedance</p> Signup and view all the answers

<p>Near-zero impedance contrast</p> Signup and view all the answers

<p>Multiplication of Intercept and Gradient</p> Signup and view all the answers

<p>Shuey’s equation</p> Signup and view all the answers

<p>Peak decreases and changes polarity</p> Signup and view all the answers

<p>Negative response at the top and positive response at the base</p> Signup and view all the answers

<p>Scaled Poisson’s Ratio Change</p> Signup and view all the answers

<p>AVO Difference (A-B)</p> Signup and view all the answers

<p>Fluid Factor</p> Signup and view all the answers

<p>Other lithologies and/or pore fluids</p> Signup and view all the answers

<p>NMO Correction = Correction of reflection arrival times to match those of the zero-offset trace Residual NMO = Common reason for distorted AVO response due to inaccurate velocity analysis or azimuthal velocity variations NMO Stretch = Stretching of individual events and broadening of wavelet shape at further offsets Migration = Corrects moveout and requires an accurate velocity model</p> Signup and view all the answers

<p>Reverberations = Cause interference of the primary wavefield by creating 'multiples' Tuning effects = Can cause interference with primary wavefield and tuning effects Processing Noise attenuation = Techniques to attenuate noise while preserving primary amplitudes Directivity of source wavefield = Effect related to orientation of directionally sensitive receivers</p> Signup and view all the answers

<p>AVO Analysis = Qualitative tool to detect anomalies by preserving relative amplitudes as a function of offset Intercept and Gradient = Parameters used to analyze the AVO response from seismic data Offset-dependent Reflectivity = Reflectivity that may be distorted by residual NMO or NMO stretch AVO Product = Result of mathematical operation used as a potential hydrocarbon indicator</p> Signup and view all the answers

<p>Attenuation, dispersion, transmission effects = Can contribute to changes in amplitude due to wave spreading or subsurface interactions Noise interference = Can obscure desired signal amplitudes and cause interference with primary wavefield Residual Moveout correction = Phenomenon that distorts offset-dependent reflectivity and should be addressed Correct focussing and positioning of primary signal = Important for processing techniques to achieve while correcting for noise</p> Signup and view all the answers

<p>Distorted offset-dependent reflectivity = Result of residual NMO or NMO stretch phenomena that need to be addressed Sparse velocity analysis = May lead to residual NMO distortion in AVO response and requires denser analysis Higher order corrections = Applied to reduce impact of residual NMO in AVO analysis AVO Attribute stacks = Primarily used in seismic data analysis for qualitative detection of anomalies</p> Signup and view all the answers

<p>Random noise = Uncorrelated spatially and cannot easily be modelled Coherent noise = Annotated by dashed lines indicating greater move out than flat primary events Ground roll = Linear noise energy affecting near offsets Multiples = Crosscutting primary signal and causing amplitude effects varying with offset</p> Signup and view all the answers

<p>NMO Correction = Addressing NMO stretch to prevent frequency distortion Noise Attenuation = Removing random noise and improving signal-to-noise ratio SuperGather Formation = Reducing random noise and preserving offset-dependent amplitude variations Post Imaging Processing = Preparing data for AVO analysis by attenuating multiples and distortions</p> Signup and view all the answers

<p>AVO gradients = Restricting range of angles and increasing error of estimated AVO attributes Multiple attenuation = Impacting AVO analysis by causing interference on amplitude effects varying with offset Ground roll attenuation = Affecting near offsets and impacting true primary AVO measurement Structural dip smoothing = Smoothing out structural variations in steep dip locations</p> Signup and view all the answers

<p>Gradient section anomalies = Method attempting to remove NMO stretch effects Flat seismic events obscured by noise = Forming SuperGathers to reduce random noise Multiple energy interference = Attenuating multiples before AVO analysis Ground roll amplitude distortion = Post imaging processing prior to AVO analysis</p> Signup and view all the answers

<p>Gradient section after NMO correction = Illustrating anomalous AVO gradients in red in shallow section Synthetic forward modelled gather = Showing predicted AVO response for comparison SuperGathers for noise reduction = Preserving offset-dependent amplitude variations Amplitude Vs incidence angle plots = Used for analyzing amplitude distortion before and after processing</p> Signup and view all the answers

<p>NMO correction = Correction for the velocity variation with offset Trace Muting = Elimination of noisy or unreliable traces Noise removal = Process to eliminate unwanted signal interference Amplitude-preserved processing = Technique that maintains the original amplitude values</p> Signup and view all the answers

<p>Wave propagation and geologic effects = Phenomena related to natural geological structures and wave behavior Acquisition and noise effects = Phenomena caused by data collection and external disturbances Processing artifacts = Issues introduced during data processing steps Energy losses during travel = Attenuation of seismic waves through subsurface materials</p> Signup and view all the answers

<p>Estimate and remove energy losses = Ensure accurate representation of subsurface properties Remove noise effects = Enhance data clarity by eliminating unwanted disturbances Avoid processing-related artifacts = Prevent artificial distortions in the data Preserve amplitude changes = Maintain the true amplitudes for reliable interpretation</p> Signup and view all the answers

<p>Factors affecting seismic amplitudes = Categorized by their primary causes Factors related to wave propagation = Influences from natural geological and wave phenomena Factors due to acquisition noise = Disturbances introduced during data collection Processing-induced factors = Artifacts introduced during data processing</p> Signup and view all the answers

<p>Amplitude-preserved processing = Approach to maintain original amplitude values True-amplitude processing = Technique ensuring accurate representation of subsurface properties AVO anomalies recognition = Identifying abnormal variations in seismic amplitudes Angle gathers creation = Generating seismic data grouped by reflection angles</p> Signup and view all the answers

<p>NMO correction = Compensate for velocity differences at various offsets Trace Muting = Eliminate noisy traces for cleaner data analysis Noise removal = Get rid of unwanted signal disturbances for clearer interpretation Processing artifacts removal = Eliminate distortions introduced during data processing</p> Signup and view all the answers

<p>AVO Analysis = Involves extracting amplitude and phase information from seismic data NMO Correction = Corrects for the differences in arrival times of seismic waves Trim Statics = Aligns traces within a time window using time shifts Super-gathers = Combine adjacent locations in both inline and crossline directions</p> Signup and view all the answers

<p>Gradient (B) = Measures the rate of change of amplitudes with offset Intercept (A) = Measures the zero-offset response Fluid Factor = Affected by changes in matrix or lithology AVO Sum (A+B) = Shows amplitude changes at top and base of reservoir</p> Signup and view all the answers

<p>Two term NMO = Application of the first 2 terms in the NMO equation Higher Order NMO = Includes terms raised to the 4th power of velocity Time-variant Trim Statics = Performs cross-correlation over smaller, overlapping windows Conventional Trim Statics = Calculates a single time shift for each trace in a gather</p> Signup and view all the answers

<p>Conventional Trim Statics = Limited by calculation windows, may not align separated events Time-Variant Trim Statics = Interpolates shifts over overlapping windows for consistent flattening NMO Correction = Requires correct velocity for flat gathers and peak amplitude extraction Super-gathers = Combine data from adjacent locations to create more comprehensive datasets</p> Signup and view all the answers

<p>Trim Statics - Conventional = Calculates single shifts for trace alignment within a time window Trim Statics - Time-variant = Performs cross-correlation over smaller, overlapping windows and interpolates shifts Super-gathers = Combine data from adjacent locations to improve overall alignment NMO Correction = Corrects for differences in arrival times to ensure flat gathers</p> Signup and view all the answers

<p>Residual moveout effects = Addressed to flatten events in seismic gathers Ground roll = Distorts near-offset traces and has high amplitude NMO stretching = Related to Normal Moveout, can distort offset-dependent reflectivity Trace Mute = Used to limit the influence of long offset traces in stack processing</p> Signup and view all the answers

<p>Aggressive ground roll removal = Causes decrease in primary amplitudes and false AVO interpretation Noise removal = Can lead to a distortion of the AVO response if not performed carefully Muting in traditional processing = May restrict the maximum range of angles for AVO analysis Unmuting data = Recommended before AVO analysis to keep the range of offsets wide</p> Signup and view all the answers

<p>Energy losses and noise effects = Should be estimated and removed during seismic-data processing Effects of the near surface = Should be removed to avoid processing-related artifacts Muting in traditional processing = Should be done separately from that used for generating stacks in AVO analysis Factors affecting amplitudes in pre-stack domain = Must be understood and considered before running an AVO analysis</p> Signup and view all the answers

<p>Pre-imaging processing = Shows great variability in amplitudes but matches general trend Post-imaging processing = Produces more consistent plots with better attenuation of noise and energy Class 3 AVO response = Does not match with synthetic response in near and middle angle range Class 4 AVO response = Performed poorly due to predominantly in the text</p> Signup and view all the answers

<p>Wave propagation and geologic effects = Category 1 Acquisition and noise effects = Category 2 Processing artifacts = Category 3 Energy losses during subsurface travel = Category 1</p> Signup and view all the answers

<p>NMO correction = Correct for wave propagation effects Trace muting = Remove noise effects Noise removal = Eliminate acquisition-related distortions Amplitude-preserved processing = Avoid processing artifacts</p> Signup and view all the answers

<p>Noise effects = Acquisition-related distortions Wave propagation effects = Energy losses during subsurface travel Geologic effects = Wave propagation and geologic effects Processing artifacts = Errors introduced during data processing</p> Signup and view all the answers

<p>Gradient (B) value = Indicator of fluid properties AVO sum (A+B) = Shows variations at top and base of reservoirs AVO product = Potential hydrocarbon indicator Scaled Poisson’s Ratio Change = Derived from rock properties changes</p> Signup and view all the answers

<p>Near/far stack operations = Aligns seismic events for better interpretation Intercept-gradient product = Attempts to align events using gradients Super-gathers formation = Combines adjacent locations for comprehensive analysis Angle gathers creation = Generates data for AVO analysis based on offsets</p> Signup and view all the answers

<p>Fluid Factor attribute = Highlights potential hydrocarbon zones Class 2 gas sands behavior with offset = Impacts impedance contrast understanding Class 1 gas sands behavior with offset = Influences AVO Sum (A+B) results Derived AVO attributes for anomaly recognition = Helps in identifying specific AVO anomalies</p> Signup and view all the answers

<p>Conventional Trim Statics = Calculating a single time shift for each trace in the gather to align traces within a time window Time-Variant Trim Statics = Performing cross-correlation calculation over smaller, overlapping windows and interpolating the shifts for a more consistent flattening</p> Signup and view all the answers

<p>Super-gathers = Combining adjacent locations in both inline and crossline directions for better analysis Trim Statics = Applying time shifts to align traces within a gather, constrained by the Normal Moveout equation</p> Signup and view all the answers

<p>AVO Sum (A+B) = Highlighting potential hydrocarbon zones by summing the intercept and gradient attributes AVO Product = Mathematical operation indicator for hydrocarbons, based on the intercept and gradient attributes</p> Signup and view all the answers

<p>Residual moveout effects = Distortion of near-offset traces High amplitude noise = Restriction of angle range NMO stretching = Removal of energy losses Noise removal = Distortion of AVO response</p> Signup and view all the answers

<p>Trace Mute = Optimum stack production Ground roll removal = Limit influence of long offset traces Energy loss estimation = Avoid processing-related artifacts Muting in traditional processing = Restrict maximum angle range</p> Signup and view all the answers

<p>Higher Order NMO = Applying corrections related to anisotropy and velocity heterogeneity using terms beyond the standard NMO equation Two Term NMO = Utilizing the first 2 terms of the NMO equation to correct for moveout, with an optional additional 4th order term</p> Signup and view all the answers

<p>Gather Flattening using NMO = Correcting non-flat gathers by applying NMO correction based on velocity models Cross-correlation = Calculating time shifts to align traces within a gather for improved data consistency</p> Signup and view all the answers

<p>AVO analysis = Estimate and remove energy losses Super-gathers formation = Remove noise effects Amplitude vs angle plot = Remove near-surface effects Wave propagation factors = Avoid processing-related artifacts</p> Signup and view all the answers

<p>Amplitude vs angle plot = Show impact on data quality AVO attribute stacks = Highlight hydrocarbon zones AVO Sum (A+B) = Examine amplitude variability Negative Gradient (B) value = Prospect reconnaissance of gas sands</p> Signup and view all the answers

<p>Trim Statics = Addressing residual non-flatness after NMO correction to improve alignment Higher Order NMO = Reducing deviations in seismic events across gathers, especially at far offsets</p> Signup and view all the answers

<p>Class 1 gas sands = Exhibiting behavior indicating gas presence as offset increases Class 2 gas sands = Showing typical impedance contrast characteristics related to gas presence</p> Signup and view all the answers

<p>Noise effects removal = False AVO interpretation Class 3 AVO response mismatch = Decrease in primary amplitudes Ground roll distortion = Great variability in amplitudes Structural dip adjustment = Residual moveout correction</p> Signup and view all the answers

<p>Class 1 gas sands behavior = Variability in amplitudes Fluid changes effect = Energy better attenuated Scaled Poisson’s Ratio Change = Random noise attenuation Intercept-gradient product result = Meaningful AVO interpretation</p> Signup and view all the answers

<p>AVO Intercept = Measures the zero-offset response of amplitudes AVO Gradient = Indicates the rate of change of amplitudes with offset</p> Signup and view all the answers

<p>NMO Correction = Aligning events by applying corrections based on velocity models Interpolated Shift Corrections = Applying time-variant series of shifts to traces for consistent flattening</p> Signup and view all the answers

<p>AVO Anomalies = Incorporate amplitude and phase changes, resembling time shifts in analysis Fluid Factor Deviations = Indicate variations from Castagna’s Mudrock line, highlighting potential hydrocarbon zones</p> Signup and view all the answers

<p>Random noise = Uncorrelated spatially and cannot easily be modelled Coherent noise = Causes interference affecting the amplitude of seismic events Linear noise energy = Represents seismic wave travelling in the very shallow sub-surface Ground roll = Affects just the near offsets and interferes with primary signal</p> Signup and view all the answers

<p>SuperGather formation = Reduces random noise and preserves offset-dependent amplitude variations NMO correction = Stretches traces as a function of time and offset, causing frequency distortion Far offset muting = Prevents lower frequency events from affecting stack resolution Multiple attenuation = Reduces amplitude effects caused by events with greater moveout than primary signals</p> Signup and view all the answers

<p>AVO anomaly = Anomalous AVO gradients observed in seismic sections AVO attribute = Quantitative measurement derived from amplitude variation with offset or angle AVO moveout = Variation in moveout time of seismic reflections due to changes in rock properties AVO product = Result of multiplying intercept and gradient values from AVO analysis</p> Signup and view all the answers

<p>NMO stretch = Shifts events to lower frequencies, affecting event amplitudes Amplitude effect from multiples = Interference affecting event amplitudes based on offset variations Linear noise energy (ground roll) = Affects near offsets and interferes with primary signal amplitudes Coherent noise interference = Crosscuts primary signals, causing amplitude variation</p> Signup and view all the answers

<p>Fluid factor attribute = Indicates deviations from Castagna’s Mudrock line related to fluid changes Impedance contrast attribute = Helpful in recognizing Class 2 gas sands based on impedance differences Poisson’s Ratio Change attribute = Derived from Scaled Poisson’s Ratio Change for AVO analysis AVO sum (A+B) attribute = Shows top and base reservoir characteristics in AVO analysis</p> Signup and view all the answers

<p>AVO attribute stacks = Primary use is for quantitative analysis of amplitude variations with offset or angle Angle gathers from offset gathers = Used to examine AVO response based on different angles of incidence Intercept-gradient product calculation = Results in AVO Product which is a potential hydrocarbon indicator Near/far stack operations = Do not yield meaningful results in AVO analysis due to various factors</p> Signup and view all the answers

<p>NMO correction stretch functions = Result in frequency distortion, shifting events to lower frequencies SuperGather formation on steep dips = Can smooth out structural variations by stacking adjacent locations Noise attenuation techniques = Reduce random and coherent noise to improve signal-to-noise ratio Ground roll amplitude distortion near offsets = Interferes with primary signal amplitudes, impacting measurements</p> Signup and view all the answers

<p>Class 1 gas sands behavior with increasing offset = 'Gas sands exhibit increasing negative intercept values as offset increases' AVO anomaly recognition using derived attributes = 'Helps recognize different types of AVO anomalies in seismic sections' AVO attribute impact on seismic data interpretation = 'Quantitative measurements provide insights into subsurface rock properties' AVO moveout term understanding for reflection patterns = 'Variation in moveout time helps understand rock property changes'</p> Signup and view all the answers

<p>Seismic flat events obscured by random noise = 'Partial stacking using SuperGathers can improve S/N ratio' Coherent noise crossing primary signals causing interference = 'Multiple attenuation techniques can reduce amplitude effects' Strong linear noise energy affecting near offsets interfering with signal amplitude = 'Ground roll removal methods can help improve data quality' Flat seismic events affected by NMO stretch shifting to lower frequencies = 'Post-imaging processing can correct amplitude distortion due to NMO stretch'</p> Signup and view all the answers

<p>Reverberations or 'multiples' = Causes interference with the primary wavefield Tuning effects = Can cause interference with the primary wavefield Residual NMO = Distorts offset-dependent reflectivity NMO Stretch = Broadens the shape of the wavelet at further offsets</p> Signup and view all the answers

<p>NMO Normal Moveout correction = Corrects reflection arrival times for amplitude analysis Migration or imaging = Corrects moveout and aligns events across a gather Residual Moveout correction = Addresses residual NMO effects Calculation of Intercept and Gradient = Quantifies the impact of residual NMO on AVO response</p> Signup and view all the answers

<p>Residual NMO = Distorts AVO response and requires higher order corrections NMO Stretch = Broadens wavelet shape and affects near offsets more Fluid Factor = Indicates deviations from Castagna's Mudrock line for hydrocarbon zones AVO Sum (A+B) = Shows potential hydrocarbon indicators at top and base of reservoir</p> Signup and view all the answers

<p>Noise interference = Obscures desired primary signal amplitudes Acquisition related effects = Can cause interference due to source wavefield directivity Processing Noise attenuation techniques = Attenuate noise while preserving primary amplitudes Understanding distortions in offset-dependent reflectivity = Essential for successful AVO analysis</p> Signup and view all the answers

<p>NMO Normal Moveout correction = Corrects reflection arrival times for amplitude analysis Residual Moveout correction = Addresses residual NMO effects for accurate velocity analysis Calculation of Intercept and Gradient = Quantifies the impact of residual NMO on AVO response AVO Sum (A+B) = Shows potential hydrocarbon indicators at top and base of reservoir</p> Signup and view all the answers

<p>Noise interference with primary wavefield = Obscures desired signal amplitudes Noise attenuation techniques = Preserve primary amplitudes while reducing noise Acquisition noise issues = Related to source wavefield directivity or receiver orientation Processing noise removal = Efficiently removes noise while maintaining primary signal</p> Signup and view all the answers

<p>Residual NMO correction = Improves AVO response by addressing velocity variations Migration or imaging step correction = Corrects moveout and aligns events for accurate imaging Calculation of Intercept and Gradient analysis = Quantifies impact of residual NMO on AVO attributes NMO Stretch correction = Reduces broadening of wavelets at far offsets</p> Signup and view all the answers

<p>Reverberations or 'multiples' = Causes interference with the primary wavefield Tuning effects = Can cause interference with the primary wavefield Residual NMO = Distorts offset-dependent reflectivity NMO Stretch = Broadens the shape of the wavelet at further offsets</p> Signup and view all the answers

<p>NMO Normal Moveout correction = Corrects reflection arrival times for amplitude analysis Migration or imaging = Corrects moveout and aligns events across a gather Residual Moveout correction = Addresses residual NMO effects Calculation of Intercept and Gradient = Quantifies the impact of residual NMO on AVO response</p> Signup and view all the answers

<p>Residual NMO = Distorts AVO response and requires higher order corrections NMO Stretch = Broadens wavelet shape and affects near offsets more Fluid Factor = Indicates deviations from Castagna's Mudrock line for hydrocarbon zones AVO Sum (A+B) = Shows potential hydrocarbon indicators at top and base of reservoir</p> Signup and view all the answers