Amplitude Distribution in Different Frequency Ranges

Reservoir oriented quality control (QC) and pre-conditioning = Ensure reliable interpretation of amplitude changes Different tools for Quality control = Detect and correct processing artefacts Wave propagation and geologic effects = Distort amplitudes in the pre-stack domain Acquisition and noise effects = Also distort amplitudes in the pre-stack domain

Estimating and compensating for energy losses = Critical for reliable analysis Removing noise effects from data = Essential for accurate interpretation Removing near surface effects = Improves the quality of interpretation Completely removing processing-related artifacts = Ensures true-amplitude processing

Amplitude-preserved or amplitude-controlled processing = Characterized by maintaining amplitude fidelity True-amplitude processing = Aims to completely remove processing-related artifacts Compensating for energy losses = Important for preserving amplitude information Removing noise effects from data = Enhances the clarity of seismic signals

Wave propagation effects = Can distort amplitude changes Acquisition artifacts = Pose challenges in interpreting rock and fluid properties Processing distortions = Can significantly affect the accuracy of AVO results Noise contamination in data = Hampers reliable interpretation of seismic amplitudes

Visual Analysis = Simplest way to QC data Deterministic wavelet analysis = Detailed review of wavelet consistency Amplitude distribution with offsets or angles = Checking amplitude distribution in pre-stack data Horizon interpretations = Calculating amplitude and frequency maps

Petrophysical logs = Include Caliper, Gamma ray, and Spontaneous Potential Seismic data = Should include full stacks and gathers Processing reports = Contain valuable information about processing workflows Wells with elastic properties = Measure VP, VS, and density over an interval

Purpose of seismic data usage = Determines level of QC needed Type of seismic data = Impacts choice of tools needed Stage of data processing = Determines extent of control required Data consistency requirements = Directs the need for amplitude and frequency control

Random noise = Detection through visual review or wavelet analysis Acquisition footprint = Spatial and vertical recovery control Migration artifacts = Identified during reservoir-oriented seismic conditioning Residual moveout = Can impact amplitudes if not removed during conditioning

Wavelet consistency is key for inversion success = Ensures accurate interpretation of results Pre-conditioning stage is essential for amplitude preservation = Removes noise and residual moveout issues Checking amplitude distribution with offsets in pre-stack data = Compares amplitudes with synthetic gathers Detection of alignment issues on gathers or angle stacks = Ensures accurate estimation of reservoir properties

Vertical amplitude anomalies = Visible in both stack section and amplitude map Acquisition footprints = Regular patterns in amplitudes not related to geological events Migration artefacts = Smiles or poorly collapsed diffractions on cross section Lateral amplitude variation = Strong amplitude variation due to overburden absorption effect

Reviewing dataset line by line = Identifying noise or unflatten horizons Using different colorbars = Detecting different effects better in various colors Applying additional amplitude correction = Addressing vertical anomalies for quantitative interpretation Calculating amplitudes across a wide time window = Effective method to review time slices

Grey scale seismic cross section = Migration artefacts more obvious Red/black scale seismic image = Vertical amplitude anomalies more visible Amplitude correction map extraction = Correcting lateral variation in seismic energy Frequency panels analysis = Useful tool to understand and analyze data

Amplitude Anomalies In this example we can observe vertical amplitude anomalies on the section after processing. = Presence of vertical ‘columns’ in amplitudes and frequencies Footprints in 2D Sections In this example we can see acquisition footprints: regular patterns in amplitudes that can hardly be related to geological events. = Regular patterns in amplitudes not related to geological events Migration Artefacts Sometimes migration artefacts such as smiles or poorly collapsed diffractions can be seen on the cross section as illustrated in these examples. = Problems with the velocity model used for migration or poorly attenuated noise trends Strong Lateral Amplitude Variation In this example from offshore Brazil we can see a strong amplitude variation due to an overburden absorption effect. = Absorption effect visible on sections, requiring amplitude correction

Amplitude Spectrum Analysis = Calculating spectra in various windows and locations to analyze amplitude-frequency distribution Frequency Range Expansion = Expanding the frequency content to minimize sidelobes and capture finer details in seismic images Before-After-Difference Control = Monitoring denoising effects by assessing what has been removed from the data for QC purposes Amplitude Correction = Ensuring consistency in amplitudes for successful inversion

Column-like Amplitudes = Caused by heterogeneity of near-surface Frequency-Dependent Anomalies = Anomalies differ in different frequency ranges Low-Frequency Energy = Some wavelets have more energy in low frequencies and less in high frequencies Inconsistent Amplitudes = Corrected through amplitude correction for successful inversion

Higher-Resolution Seismic Images = Capturing finer details and subtle features within subsurface geology with wider seismic signal Deeper Penetration into Subsurface = Achieved with increased low frequency bandwidth in the seismic signal More Accurate Reservoir Property Estimates = Constrained inversion algorithms due to wider range of frequencies Less Interference with Primary Reflections = Minimizing sidelobes by extending frequency range at lower end

Red and Green Wavelets = Consistent with each other Blue Wavelet = More energy in low frequencies and less in high frequencies Other Two Wavelets = Different energy distribution compared to red and green wavelets Amplitude Attenuation with Depth = Observed for both seismic cubes

Before-After-Difference Control = Monitor denoising effects and ensure no valuable signal is eliminated Amplitude Correction = Ensure consistency in amplitudes for successful inversion Frequency Range Expansion = Minimize sidelobes and capture finer details in seismic images Amplitude Spectrum Analysis = Analyze amplitude-frequency distribution by calculating spectra in various windows and locations

AVO = Amplitude versus offset analysis NMO = Normal moveout correction QC = Quality control Anisotropy = Property of materials having different physical properties when measured in different directions

Super gathers = Formation of larger seismic data subsets for analysis Q compensation = Adjustment made to account for attenuation effects in seismic data Trim-statics = Application of corrections to align seismic traces in gathers Angle Stack Generation = Creation of angle-dependent seismic data volumes

Under-recovery of amplitudes with offsets = Usage of angle-dependent wavelets High time-shifts in gathers = Application of trim-static corrections Random noise in seismic data = Additional denoising procedures Difference in near-offset amplitudes = Ground roll removal

Modelling-based methods = Utilize Rock Physics Modelling and Wave or Zoeppritz equations to calculate synthetic gathers Direct methods = Analyze partial stacks or AVO attributes like Intercept or Gradient

Frequency difference between full stack and partial stacks = The Processing workflow needs to be checked to understand the reasons for this Lateral amplitude and frequency variations = These should be investigated to understand the reasons behind them Amplitude variations between stacks = A Global decrease with increasing offset Well-tie in QC workflow = An essential tool to accurately identify target reflections

A high correlation coefficient (>0.6) between seismic and synthetic data = Symmetrical cross-correlation function with envelope's maximum close to 0 Utilization of a zero-phase deterministic wavelet = Consistency of wavelets across different wells Symmetrical cross-correlation function with envelope's maximum close to 0 = Absence of minor lobes Consistency of wavelets across different wells = High correlation coefficient (>0.6) between seismic and synthetic data

Before deconvolution in well tie example = Fair correspondence between synthetic and seismic traces with CC of 0.597 After deconvolution in well tie example = Better correspondence with CC=0.705 and more symmetrical cross-correlation function Wavelet control of amplitude correction - Lack of consistency among wavelets = Can lead to errors in impedance estimation Pre-stack data QC objective = Assess the accuracy of amplitude recovery with offsets and address alignment issues

Calculation of AVO product (Intercept * Gradient) = Rapid method to identify lateral and vertical variations in AVO Comparison of AVO effects in seismic and synthetic data = Critical for quality control to detect processing issues Visual control on pre-stack gathers = Performed on both full stack and pre-stack data Amplitude anomalies elimination after version 2 correction = Observed in target interval after amplitude correction