#Hampson russell r2.2 full#
Assuming that VP/VS = 2 in the full Aki-Richards equation, it can be shown that:.A and B can be combined in variousways and displayed, or cross-plotted and interpreted. Intercept/Gradient Analysis Gathers AVO Processing Intercept Gradient Crossplot The Intercept (A) and Gradient (B)approach is the most common AVO method. Above: pseudo-gradient stack, or difference between near and far stacks.įaroe Shetlands Basin Line 99/116 AVOC (AVO Classification) = IVO x Pseudo-gradient Above: 0–10 degree inversion to relative acoustic impedance (RAI).įaroe Shetlands Basin Line 99/116 Below: Impedance vs Offset (IVO) amplitude stack, or difference between RAI stacks. Note that if =0o, EI reduces to Acoustic Impedance (AI), where:įaroe Shetlands Basin Line 99/116 Below: 10–20 degree inversion to relative acoustic impedance (RAI).Using the Aki-Richards equation, Connolly(1998) proposed the Elastic Impedance (EI) concept to physically explain range-limited stacks, where:.Inversion can be done using a standard inversion algorithm, or using an elastic impedance model.(b) Time slice showing amplitudes of far-trace stack for Alberta channel sand.įaroe Shetlands Basin Line 99/116 Below: 10–20 degree stack. Range-limited Stacking Gathers AVO Processing Near Stack Far Stack Invert (Optional) Invert (Optional) The near and far stacks can be created either from angle or offset gathers, and can be optionally inverted.ģD Channel Sand Example (a) Time slice showing amplitudes of near-trace stack for Alberta channel sand with known gas. Rutherford/Williams Classification Class 4 The Rutherford and Williams classification scheme as modified by Ross and Kinman (1995) and Castagna (1997). Rutherford/Williams Classification Rutherford and Williams (1989) derived the following classification scheme for AVO anomalies, with further modifications by Ross and Kinman (1995) and Castagna (1997): Class 1: High acoustic impedance contrast Class 2: Near-zero impedance contrast Class 2p: Same as 2, with polarity change Class 3: Low impedance contrast Class 4: Very low impedance contrast (b) Peak/trough picks vs sin2q,where A=intercept, and B=gradient. The Aki-Richards linearized approximation to the Zoeppritz equation can be written as the sum of 3 terms: where: or (using Shuey’s approximation):Ī real data example (b) Picks Zoeppritz Amplitudes (a) Gas Sand (c) (a) Common offset stack over a gas sand, where (b) represents model and picks over trough, and (c) represents model and picks over peak.Įstimating A and B from Seismic Data Offset +A +B sin2q -B Time -A (a) Small part of common offset stack.The Aki-Richards linearized approximation can be used to both understand the modeled results and to interpret the AVO response.The modeling can be done using the Zoeppritz equations for primaries only, or using the full elastic wave equation to include converted waves and multiples.Before performing an AVO analysis on seismic data, it is important to model the expected AVO response.The amplitudes can be modelled by the Zoeppritz equations. īasic Theory Incident P-wave Reflected S-wave Reflected P-wave = RP r i r VP1, VS1, r1 VP2, VS2, r2 t t Transmitted P-wave Transmitted S-wave If q > 0o, an incident P-wave will produce both P and S reflected and transmitted waves. Inversion of RP and RS to give ZP and ZS.Relative acoustic impedance (RAI) inversion.A number of different possibilities have been proposed, which can be grouped into three main categories:.But which two attributes will give us the best estimate of these reservoir parameters?.
Seismic Lithology Estimation Gathers Stack AVO Analysis Inversion Attribute 1 Estimate ZP= VP Attribute 2 Estimate VP, VS, and The AVO method allows us to use multiple attributes to simultaneously estimate VP, VS, and , thus inferring fluid and/or lithology. This allows only for the estimation of acoustic impedance, which is not sufficient for inferring fluid content. Seismic Lithology Estimation Gathers Stack Inversion Estimate ZP= VP Traditional methods of seismic lithology estimation involve stack followed by inversion. I will illustrate these ideas with examples taken from Canada, the Gulf Coast and the West of Shetlands, UK.These new trends involve alternate ways of extracting information about the fluid content and lithology of the reservoir.In this presentation, I will review the principles of the AVO (Amplitude Variations with Offset) method and then look at some of the new trends that are emerging.By Brian RussellHampson-Russell SoftwareCalgary, Alberta.
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