Domain freezing in joint inversion

Patent metadata

Field	Value
Publication number	US-9702995-B2
Application number	US-201214113103-A
Country	US
Kind code	B2
Filing date	May 9, 2012
Priority date	Jun 17, 2011
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

Abstract

Method for estimating geological properties in a subsurface region using multiple types of geophysical data ( 21 ). An initial physical properties model 22 is constructed. Some parameters in the model are frozen ( 23 ) and optionally portions of the model wave number and spatial domains ( 24 ) and the data frequency and data time domains ( 25 ), are also frozen. Then, a joint inversion ( 26 ) of the multiple data types is performed to calculate an update to the model only for the portions that are not frozen. The converged model ( 27 ) for this inversion is used as a new starting model, and the process is repeated ( 28 ), possibly several times, unfreezing more parameters and data each time until the desired spatial and parameter resolution ( 29 ) has been achieved.

First claim

The invention claimed is:

1. A computer-implemented method for estimating a physical properties model in a subsurface region using data comprising two or more geophysical data types, said model comprising numbers in a model parameter domain representing one or more physical properties, said method comprising:
using a computer to jointly invert the data in a plurality of sequential phases, wherein in each phase until a last phase, only a portion of the data is inverted in order to infer a subset of the model's parameter domain, said portion being determined at least partly based on relative frequency content of the two or more data types,
wherein in a first phase of the sequential phases, the portion of the data inverted is longer wavelength data from the data's frequency domain, and model parameters expected to vary at shorter wavelengths are frozen, further comprising, between said first phase and said last phase, one or more intermediate phases, each intermediate phase and the last phase progressively using more of the data frequency domain and inferring more of the model parameter domain, and
wherein a last of the plurality of sequential phases yields a final subsurface physical property model that provides reservoir properties for the subsurface region; and
prospecting for hydrocarbons with the reservoir properties of final subsurface physical property model.

2. The method of claim 1 , wherein a converged model from one phase is used as a starting model, or a damping model, or both, for a next phase.

3. The method of claim 1 , wherein the intermediate phases is topped when a pre-selected spatial and parameter resolution is reached.

4. The method of claim 1 , wherein the joint inversion takes place in an inversion domain comprising, in addition to the model parameter domain and the data frequency domain, one or more of a data time domain, model wave number domain, and a model spatial domain.

5. The method of claim 4 , further comprising, between said first phase and said last phase, one or more intermediate phases, each intermediate phase and the last phase progressively unfreezing more of:
the model parameter domain, the model spatial domain, or the model wave number domain; and
the data frequency domain or the data time domain.

6. The method of claim 5 , wherein as the sequential phases progress, one or more of the following occurs:
the model wave number domain moves from a coarser inversion grid to a finer inversion grid;
the data time domain moves from only earlier arrivals to including later arrivals;
the model spatial domain moves from freezing deeper portions of the model to solving for the deeper portions, or from freezing regions of the model expected to vary rapidly to solving for such rapidly varying regions;
the model parameter domain moves from freezing model parameters for a physical property expected to vary at shorter wavelengths to solving for model parameters for the physical property expected to vary at shorter wavelengths and four model parameters and for model parameters for any other of said one or more physical properties; and
the data frequency domain progresses from lower frequency data to include higher frequency data, which is accomplished by using a filter or by selecting from among the two or more data types by frequency content.

7. The method of claim 6 , wherein the selecting from among the two or more data types by frequency content is accomplished by adjusting weights in an objective function used in the joint inversion to measure misfit between measured data and model-predicted data, said objective function having a term for each of the two or more data types, each term containing an adjustable weight.

8. The method of claim 7 , wherein the two or more geophysical data types are selected from a group consisting of active seismic reflection data, a high-frequency data type; electromagnetic data, either controlled source or magneto-telluric, both low-frequency data types; and gravity measurements, also a low-frequency data type.

9. The method of claim 8 , wherein the weight for a low-frequency data type is progressively decreased at each successive phase of the joint inversion through said last phase.

10. The method of claim 9 , wherein the two or more geophysical data types are seismic data and either electromagnetic or magneto-telluric data, the physical properties are rock porosity, lithology, and water saturation, lithology being parameterized as shale volume fraction, and model parameters for water saturation are frozen through said last phase of the joint inversion, further comprising an additional phase after said last phase during which all model parameters except for water saturation are fixed, a strong damping is applied constraining the model to agree with a starting model obtained from the last phase of the joint inversion, and a large weight is given to the electromagnetic or magneto-telluric data compared to the seismic data.

11. The method of claim 1 , wherein the one or more physical properties are rock porosity, lithology, and water saturation, lithology being parameterized as shale volume fraction, and each sand layer or interval identified during the joint inversion is assigned a single value for water saturation.

12. The method of claim 1 , wherein the one or more physical properties include water saturation, and the model parameters for water saturation are frozen for at least a first phase of said plurality of sequential phases.

13. The method of claim 1 , wherein in each phase of the plurality of sequential phases, the portion of the data inverted corresponds to a selected frequency band.

Assignees

• Dicaprio Christopher
• Schmedes Jan
• Jing Charlie
• Leahy Garrett M
• Mullur Anoop A
• Saltzer Rebecca L
• Exxonmobil Upstream Res Co

Inventors

• Dicaprio Christopher
• Schmedes Jan
• Jing Charlie
• Leahy Garrett M
• Mullur Anoop A
• Saltzer Rebecca L

Classifications

• G01V2003/086

  Processing · CPC title

• G01V1/282 Primary

  Application of seismic models, synthetic seismograms · CPC title

• G01V11/00 Primary

  Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00 · CPC title