Multi-parameter inversion through offset dependent elastic FWI

Patent metadata

Field	Value
Publication number	US-9702993-B2
Application number	US-201414272020-A
Country	US
Kind code	B2
Filing date	May 7, 2014
Priority date	May 24, 2013
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

Abstract

Method for multi-parameter inversion using elastic inversion. This method decomposes data into offset/angle groups and performs inversion on them in sequential order. This method can significantly speed up convergence of the iterative inversion process, and is therefore most advantageous when used for full waveform inversion (FWI). The present inventive approach draws upon relationships between reflection energy and reflection angle, or equivalently, offset dependence in elastic FWI. The invention uses recognition that the amplitudes of small angle (near offset) reflections are largely determined by acoustic impedance alone ( 1 ), independent for the most part of Vp/Vs. Large angle (middle and far offset) reflections are affected by Ip, Vp/Vs ( 2 ) and other earth parameters such as density ( 3 ) and anisotropy. Therefore, the present inventive method decomposes data into angle or offset groups in performing multi-parameter FWI to reduce crosstalk between the different model parameters being determined in the inversion.

First claim

The invention claimed is:

1. A computer-implemented method for full wavefield inversion of seismic data to infer subsurface physical property parameters including P-wave (pressure wave) velocity, S-wave (shear wave) velocity, and density, comprising:
extracting only PP mode (P-wave down/P-wave up) from the seismic data, and inverting, with a full wavefield inversion algorithm, the PP mode data sequentially in two or more different offset ranges, each offset range full wavefield inversion determining at least one physical property parameter, wherein in a second and subsequent full wavefield inversions, parameters determined in a previous inversion are held fixed, and further wherein all full wavefield inversions are performed using a computer; and
generating, with a computer, a subsurface physical property model that includes the P-wave velocity, S-wave velocity, and the density from the full wavefield inversion algorithm, which transforms the seismic data into the subsurface physical property model, wherein the subsurface physical property model is a quantitative rock-property description of a hydrocarbon reservoir, and using the subsurface physical property model for geophysical prospecting.

2. The method of claim 1 , wherein a near offset range is sequentially first to be inverted, and said first full wavefield inversion infers P-wave acoustic impedance Ip, using a computer programmed with an acoustic full wavefield inversion algorithm.

3. The method of claim 2 , wherein a mid-offset range is sequentially second to be inverted, and said second full wavefield inversion infers S-wave acoustic impedance I S , or P-wave velocity V P divided by S-wave velocity V S , with I P fixed at its value from the first full wavefield inversion, said second full wavefield inversion using an elastic inversion algorithm.

4. The method of claim 3 , wherein a far-offset range is sequentially third to be inverted and said third full wavefield inversion infers density or V P , using an elastic full wavefield inversion algorithm, with I P fixed at its value from the first full wavefield inversion and V P /V S fixed at a value determined from the second full wavefield inversion.

5. The method of claim 4 , wherein V P and Vs are computed from I P and I S using definition of acoustic impedance, and using density as inferred in the third full wavefield inversion.

6. The method of claim 4 , wherein V P is inferred in the third full wavefield inversion, and density is computed from the relationship I P =ρV P and I P is as determined in the first full wavefield inversion.

7. The method of claim 4 , wherein one or both of the relationships I P =ρV P and I P =ρV s are used in performing the method.

8. The method of claim 4 , further comprising repeating the sequential full wavefield inversions at least one time to update the inferred physical property parameters.

9. A computer-implemented method for inversion of seismic data to infer at least P-wave (pressure wave) velocity, S-wave (shear wave) velocity, and density, comprising:
(a) taking only PP-mode (P-wave down/P-wave up) data from the seismic data, and dividing the seismic data into a near-offset range, a mid-offset range, and a far offset range, which ranges may or may not overlap;
(b) inverting the near offset range for P-wave acoustic impedance IP, using a computer programmed with an acoustic full wavefield inversion algorithm;
(c) inverting the mid-offset range for S-wave acoustic impedance Is, or for P-wave velocity V P divided by S-wave velocity V S , with I P fixed at its value from (b), using an elastic full wavefield inversion algorithm;
(d) inverting the far-offset range for density, using an elastic full wavefield inversion algorithm, with I P fixed at its value from (b) and V P /V S fixed at a value determined from the value of I S from (c);
(e) computing V P and V S from I P and I S using definition of acoustic impedance and density as determined in (d); and
(f) generating, with a computer, a subsurface physical property model that includes the P-wave velocity, S-wave velocity, and the density, wherein the steps (b), (c), and (d) transform the seismic data into the subsurface physical property model, wherein the subsurface physical property model is a quantitative rock-property description of a hydrocarbon reservoir, and using the subsurface physical property model for geophysical prospecting.

10. The method of claim 1 , wherein at least some of the two or more different offset ranges overlap.

11. The method of claim 1 , wherein at least some of the two or more different offset ranges do not overlap.

Assignees

• Wang Ke
• Lazaratos Spyridon
• Exxonmobil Upstream Res Co

Inventors

• Wang Ke
• Lazaratos Spyridon

Classifications

• G01V2210/622

  Velocity, density or impedance · CPC title

• G01V1/306

  for determining physical properties of the subsurface, e.g. impedance, porosity or attenuation profiles · CPC title

• G01V1/28 Primary

  Processing seismic data, e.g. for interpretation or for event detection (G01V1/48 takes precedence) · CPC title

• G01V2210/673

  Finite-element; Finite-difference · CPC title

• G01V1/303 Primary

  for determining velocity profiles or travel times · CPC title