Inversion, migration, and imaging related to isotropic wave-mode- independent attenuation

Patent metadata

Field	Value
Publication number	US-11360224-B2
Application number	US-202016806660-A
Country	US
Kind code	B2
Filing date	Mar 2, 2020
Priority date	May 3, 2019
Publication date	Jun 14, 2022
Grant date	Jun 14, 2022

Abstract

A method and apparatus for identifying features of a subsurface region, including: obtaining an initial physical property model and survey data for the subsurface region; identifying a current model to be the initial physical property model; and executing one or more iterations of: generating synthetic data and forward wavefields with the current model and the survey data by forward modeling with forward wave equations representing isotropic wave-mode-independent attenuation; generating adjoint wavefields with the synthetic data and the survey data by adjoint modeling with adjoint wave equations representing isotropic wave-mode-independent attenuation; computing an objective function gradient with the forward wavefields and the adjoint wavefields by solving gradient equations with the corresponding wave equations representing isotropic wave-mode-independent attenuation; computing a search direction of the objective function; searching for a possible improved model along the search direction; and updating the current model to be the possible improved model.

First claim

The invention claimed is:

1. A method for identifying features of a subsurface region, comprising:
obtaining an initial physical property model and survey data for the subsurface region;
identifying a current model to be the initial physical property model; and
executing one or more iterations of:
generating synthetic data and forward wavefields with the current model and the survey data by forward modeling with forward wave equations representing isotropic wave-mode-independent attenuation;
generating adjoint wavefields with the synthetic data and the survey data by adjoint modeling with adjoint wave equations representing isotropic wave-mode-independent attenuation;
computing an objective function gradient with the forward wavefields and the adjoint wavefields by solving gradient equations associated with the corresponding wave equations representing isotropic wave-mode-independent attenuation;
computing a search direction of the objective function;
searching for a possible improved model along the search direction;
if the possible improved model more closely matches the survey data than the current model, updating the current model to be the possible improved model; and
if a difference between the synthetic data and the survey data has not converged, executing another iteration; and
after the difference between the synthetic data and the survey data has converged:
identify a final model to be the last current model; and
generate an image of the subsurface region based on features of the final model.

2. The method of claim 1 , further comprising generating an image of the subsurface region with at least one of the current model and the possible improved model.

3. The method of claim 2 , wherein executing one or more iterations comprises at least one of Wave Equation Migration (WEM) and Reverse Time Migration (RTM).

4. The method of claim 1 , wherein at least two iterations are executed.

5. The method of claim 4 , wherein executing one or more iterations comprises at least one of Full Wavefield Inversion (FWI) and Least-Squares Reverse Time Migration (LSRTM).

6. The method of claim 1 , wherein the initial physical property model comprises a property representing arbitrary velocity anisotropy throughout at least a portion of the subsurface region.

7. The method of claim 1 , further comprising, after the difference between the synthetic data and the survey data has converged:
identifying a final model to be the last current model; and
managing hydrocarbons in the subsurface region based on features of the final model.

8. The method of claim 1 , wherein:
the forward wave equations comprise velocity-attenuation forward wave equations,
the adjoint wave equations comprise velocity-attenuation adjoint wave equations, and
the gradient equations comprise velocity-attenuation gradient equations.

9. The method of claim 8 , wherein:
the velocity-attenuation forward wave equations comprise:

ρ
⁢

∂

v
→

∂
t

=

Π
⁢

σ
→

-

∑

l
=
1

L

⁢

⁢

ω
l

⁢

m
→

l

+

S
→

v

,

⁢

∂

σ
→

∂
t

=

C
⁢

⁢

Π
T

⁢

v
→

+

S
→

σ

,
and

∂

m
→

l

∂
t

=

-

ω
l

⁢

m
→

l

+

(

a
l
T

⁢

Π
T

)

T

⁢

σ
→

,

where
{right arrow over (σ)}=(σ xx σ yy σ zz σ yz σ xz σ xy ) T is a stress vector,
{right arrow over (v)}=(v x v y v z ) T is a velocity vector,
C is a stiffness matrix representing the medium properties,
L represents a number of modeled attenuation mechanisms,
π a matrix of spatial derivatives,
p is density,
ω l is an l th relaxation frequency and l=1, 2, . . . , L,
α

Assignees

• Exxonmobil Upstream Res Co

Inventors

• Tan Sirui
• Anderson John E
• Lee Sunwoong

Classifications

• G01V1/306

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

• G01V2210/679

  Reverse-time modeling or coalescence modelling, i.e. starting from receivers · CPC title

• G01V2210/51

  Migration · CPC title

• G01V2210/614

  Synthetically generated data · CPC title

• G01V1/303

  for determining velocity profiles or travel times · CPC title