Common Mid Point (CMP) gathers = Generated from offset gathers and show anomalous amplitude behavior for AVO classes Angle gathers = Generated from offset gathers using a transform that requires velocity model and ray tracing Super-gathers = Formed by combining adjacent locations in both inline and crossline directions to improve signal-to-noise ratio Partial stacks = Display pre-stack information in a more compact way by limiting offset or angle range

Create super-gathers = With adjustments for structural dips to avoid signal degradation in case of steep dip horizons Use larger window for super-gathers = When individual gathers have poor signal-to-noise ratio Compare near-offset, mid offset, far offset stacks = To examine amplitude variation between them Avoid using individual gathers for large data volumes = As they are not suitable for examination of large data volumes

Ray tracing procedure = Used to generate angle gathers from offset gathers with the help of a velocity model Combining adjacent locations for super-gathers = Done to improve signal-to-noise ratio based on data quality Formation of partial stacks = Helps in displaying pre-stack information in a compact way by limiting offset or angle range Adjustments for structural dips in super-gathers = Recommended for steep dip horizons to avoid signal degradation

AVO Sum (A+B) = Negative response at the top of the reservoir and positive response at the base Shear Reflectivity = Derived from A-B, proportional to Shear Reflectivity AVO Difference (A-B) = Increase at the top of the reservoir, affected only by changes in matrix or lithology Fluid Factor = Highlights layers where Castagna's equation does not hold, indicating potential hydrocarbon zones

RP0 = P reflectivity at zero degrees RS0 = Shear reflectivity at zero degrees Fluid Factor = Attribute based on Castagna's Mudrock equation AVO Difference (A-B) = Derived from the Aki-Richards equation

Shear Reflectivity = Confirms hydrocarbon effect indicated by AVO Product and Scaled Poisson’s Ratio Change Fluid Factor = Identifies potential hydrocarbon zones or other lithologies AVO Sum (A+B) = Useful for prospect reconnaissance of Class 3 gas sands RP0 and RS0 = Transformed into Fluid Factor attribute for elastic property analysis

Gas-filled reservoir = Shows deviation from mudrock trend at both top and base in Colony reservoir Oil-bearing reservoir = Classifies as weak AVO class 2 near gas sand in Goliat field Carbonate under Paleozoic unconformity = Deviate from mudrock trend showing anomalies in Colony reservoir Stacked gas sands above Colony reservoir = Show fluid factor anomalies in Colony reservoir

Barents Sea = Tested amplitude/reflectivity derived and impedance-based fluid identification techniques by M.Fawad et al. Goliat oil and gas field = Located in the southeastern part of Hammerfest Basin within Norwegian Barents sea Colony reservoir = Showed strong deviation from mudrock trend at top and base using Fluid Factor attribute Major anticline in the crestal part with faulted structural closure = Location of Goliat field

Stack operations = Near/far stack operations do not yield meaningful results in class 4 AVO Intercept-gradient product = Does not yield meaningful results in class 4 AVO Fluid Factor attribute = Performs poorly in cases where inversion based methods provide better results AVO attributes = Include Intercept A and Gradient B as basic attributes

Inversion based methods = Provided better results compared to amplitude/reflectivity methods Derived AVO attributes = Combine attributes A and B to recognize class 3 AVO anomalies Impedance-derived methods = Give better results in hydrocarbon detection and mapping for complex cases Cross-plot of A and B attributes = A simple and intuitive way to examine the AVO response

Gathers = Analyze amplitudes and their variation with offsets Partial stacks = Analyze amplitudes and their variation with offsets AVO attribute volumes = Used to analyze amplitudes and their variation with offsets Amplitude/reflectivity methods = Not as effective as inversion based methods in providing good results

Basic AVO attributes (Intercept A and Gradient B) = Used for examining the AVO response by cross-plotting them Derived AVO attributes = Especially useful to recognize class 3 AVO anomalies Impedance-derived attributes = Give better results in hydrocarbon detection for complex cases Fluid Factor attribute = Performs poorly in comparison to inversion based methods

Inversion based methods = Provided better results compared to amplitude/reflectivity methods Impedance-derived methods = Give better results in hydrocarbon detection for complex cases Amplitude/reflectivity methods = Less effective compared to inversion based methods

Intercept (A) = Y-intercept of the linear fit equation Gradient (B) = Slope of the linear relationship AVO Product = Result of multiplying A times B Scaled Poisson’s = Derived from the sum of A and B

Class 1 = Higher impedance than encasing medium Class 2 = Near zero impedance contrast with encasing material Class 3 = Lower impedance than encasing medium Class 4 = Low impedance gas sands

Class 1 = Peak decreases with offset and can change polarity at far offsets Class 2 = Small amplitude response that becomes more negative with offset Class 3 = Strong trough at near offset, becomes more negative with offset Class 4 = Reflection coefficients decrease with increasing offset

Intercept A volume = Useful for analyzing acoustic impedance variations across layer boundaries Gradient B volume = Useful for analyzing variations in Vp/Vs ratio Product volume = Considered as a hydrocarbon indicator used for prospect reconnaissance Poisson’s Ratio Change volume = Derived from Shuey’s equation to solve for the change in Poisson’s ratio

Extracting amplitudes at target reflector and plotting against sin2θ = To calculate Intercept and Gradient values Multiplying Intercept and Gradient values = To obtain the AVO Product Summing Intercept and Gradient values = To derive Scaled Poisson’s Ratio Change Applying Shuey’s equation assuming background Poisson’s Ratio equal to 1/3 = To calculate Scaled Poisson’s Ratio Change

Cross-plotting Intercept and Gradient attributes = To understand AVO responses intuitively Mapping anomaly areas based on Intercept and Gradient values = To interpret and contour gas saturated reservoirs Using derived AVO attributes in various combinations = To enhance interpretation beyond basic Intercept and Gradient attributes Calculation of AVO Product for bright spot verification = To identify potential hydrocarbon indicators

Higher impedance than encasing medium, peak decreases with offset = Class 1 Near zero impedance contrast, small amplitude response becoming more negative with offset = Class 2 Lower impedance than encasing medium, strong trough near offset becoming more negative with offset = Class 3 Low impedance gas sands, reflection coefficients decrease with increasing offset = Class 4

High negative Intercept and negative Gradient values for Class 3 gas sands = "Bright" positive Product at top and base of sands Negative or near-zero Product for other gas sand classes = "Bright" positive Product indicating hydrocarbon potential Positive Product indicating hydrocarbon presence = "Bright" positive Product for Class 1 gas sands Zero Product suggesting absence of hydrocarbons = "Bright" positive Product for Class 4 gas sands

Combining Intercept and Gradient attributes in various ways to derive new attributes = 'Derived AVO attributes' useful for enhancing interpretation beyond basic attributes Summing up Intercept and Gradient values to calculate Scaled Poisson’s Ratio Change = 'Scaled Poisson’s Ratio Change' representing a scaled version of the sum of A and B values Multiplying Intercept and Gradient values to obtain a hydrocarbon indicator = 'AVO Product' used as a tool for prospect reconnaissance where Class 3 gas sands are anticipated

Analyzing acoustic impedance variations across layer boundaries = Utilizing Intercept A volume as a tool in large seismic datasets analysis. Analyzing variations in Vp/Vs ratio = Utilizing Gradient B volume as a tool in large seismic datasets analysis. Identifying potential hydrocarbon indicators = Utilizing Product volume derived from multiplying Intercept A and Gradient B. Calculating change in Poisson's ratio = Utilizing Poisson's Ratio Change volume derived from Shuey's equation.