Iterative Inversion for EM Subterranean Characterization

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Solution Overview

Problem

Electromagnetic surveying techniques for characterizing earth subterranean structures are affected by wellbores lined with conductive casings and near-surface heterogeneities, leading to inaccurate measurements, which existing methods have not adequately addressed.

Innovation Solution

A method and system that use electromagnetic receivers and sources to collect data, with iterative inversion based on a cost function that computes the difference between measured voltage data and a product of predicted electromagnetic data and distortion parameters, accounting for distortion effects from casings and near-surface heterogeneities, to solve for model and distortion parameters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If electromagnetic surveying techniques are used to characterize subterranean structures, then information about reservoir properties can be obtained, but measurement accuracy deteriorates due to distortion effects from steel casings and near-surface heterogeneities

Engineering Contradiction:

Improvemeasurement accuracyVSAvoiddistortion effects from casings and heterogeneities

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies iterative inversion techniques that explicitly model and account for the distortion effects caused by steel casings and near-surface heterogeneities. Rather than attempting to eliminate these sources of distortion, the method incorporates them into the forward model and solves for both the subsurface properties and the distortion parameters simultaneously, converting the harmful distortion into a solvable component of the inverse problem.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces additional parameters to the inversion process to represent the distortion effects from casings and heterogeneities. By expanding the parameter space to include both subsurface properties and distortion parameters, the method can separately resolve the effects of the casing from the actual subsurface variations, thereby improving measurement accuracy despite the presence of distorting structures.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If iterative inversion based on cost function with distortion parameters is performed, then measurement accuracy is improved, but computational complexity increases

Engineering Contradiction:

Improvecharacterization accuracyVSAvoidinversion process complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the inversion process into distinct computational stages: forward modeling of EM responses, calculation of the cost function measuring data misfit, and iterative optimization to update subsurface and distortion parameters. This segmentation of the complex inversion process into manageable computational steps makes the overall procedure more tractable and implementable.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The iterative inversion process employs feedback mechanisms where the cost function continuously evaluates the difference between measured and modeled data, and this feedback drives the adjustment of inversion parameters in subsequent iterations. The process repeats until convergence criteria are met, providing a systematic approach to managing the computational complexity while achieving accurate results.

Inventive Principle:

Principle #23Feedback

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach improves the accuracy of subterranean structure characterization by iteratively removing distortion effects, leading to more precise determination of reservoir parameters and resistivity profiles, enhancing the detection of hydrocarbon reservoirs and groundwater aquifers.

Implementation Method 1

EM sources are placed in one wellbore and EM receivers are placed in a second wellbore... EM receivers measure electric and/or magnetic fields induced by EM sources

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS7756642B2Characterizing an earth subterranean structure by iteratively performing inversion based on a function

Publication Date: 2010.07.13 SCHLUMBERGER TECH CORP

AI summary

To characterize an earth subterranean structure using a measurement assembly including electromagnetic (EM) receivers and one or more EM sources, measured voltage data collected by EM receivers in response to transmission by one or more EM sources is received. Based on a model, predicted EM data is computed. Inversion is iteratively performed according to a function that computes a difference between the measured voltage data and a product of a term containing the predicted EM data and a term containing distortion data that accounts at least for distortion effect by an environment of the measurement assembly. The inversion is iteratively performed to solve for parameters of the model and the distortion data.