Spectral Ratio Log Extraction for Gas Detection

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Solution Overview

Problem

Current methods for predicting well logs before drilling a wellbore lack effectiveness in accurately determining the presence of gas in hydrocarbon reservoirs, as they fail to adequately utilize seismic data to differentiate between gas presence and other geological features.

Innovation Solution

A method involving the creation of a spectral ratio log using a time domain seismic image and a seismic velocity model, which transforms a time domain spectral ratio image into a depth domain spectral ratio image to define a wellbore path and extract a spectral ratio log, indicating the presence of gas along the wellbore path.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional well log prediction methods are used, then drilling decisions can be made before actual drilling, but the accuracy of gas presence detection is insufficient

Engineering Contradiction:

Improveaccuracy of gas presence detectionVSAvoiddifferentiation between gas presence and geological features

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The seismic data is segmented into multiple frequency components through spectral decomposition, creating mono-spectral seismic images at different frequencies. This segmentation allows the system to analyze specific frequency bands separately, improving the ability to detect gas presence by examining how different frequencies are attenuated, thereby resolving the contradiction between reliability and information loss.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transforms the conventional single-domain seismic analysis into a multi-dimensional spectral domain analysis by computing spectral ratios across different frequencies. This dimensional transformation from time-domain only to frequency-time domain enables better differentiation of gas presence from geological features, enhancing detection accuracy without losing critical information.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If spectral decomposition is applied to enhance gas detection accuracy, then the precision of well log prediction improves, but the complexity of the processing workflow increases

Engineering Contradiction:

Improveprecision of spectral ratio logVSAvoidcomplexity of seismic processing workflow

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent performs spectral decomposition and computes mono-spectral seismic images as preliminary processing steps before extracting the final spectral ratio log. By preparing the frequency-domain representations in advance, the system enables accurate gas detection while organizing the complex workflow into manageable sequential stages, reducing the perceived complexity for users.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces mono-spectral seismic images as intermediary products between the original seismic data and the final spectral ratio log. These intermediaries serve as computational bridges that facilitate the complex spectral analysis by breaking it down into frequency-specific components, making the overall process more systematic and manageable despite the increased precision requirements.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enhances the accuracy of predicting gas presence by providing a spectral ratio log that correlates with gas deposits, aiding in drilling decisions and reservoir development planning.

Implementation Method 1

transforming a time domain spectral ratio image into a depth domain spectral ratio image using the seismic velocity model

Methodology Applied

Scientific EffectSeismic velocity model transformation:

Implementation Method 2

The presence of gas in the pores of a geological formation are known to affect the attenuation of acoustic waves, whether at seismic or sonic frequencies. Attenuation is known to affect the amplitude of high frequency acoustic waves more than the amplitude of low frequency acoustic waves.

Methodology Applied

Scientific EffectAcoustic wave attenuation: Acoustic Absorption

Data Source

PatentUS11821307B21D mono frequency ratio log extraction workflow procedure from seismic attribute depth volume

Publication Date: 2023.11.21 SAUDI ARABIAN OIL CO

AI summary

Methods and systems for determining a spectral ratio log using a time domain seismic image and a seismic velocity model are disclosed. The method includes determining a first mono-spectral seismic image and a second mono-spectral seismic image from the time domain seismic image. The method further includes determining a time domain spectral ratio image from the first mono-spectral seismic image and the second mono-spectral seismic image and transforming the time domain spectral ratio image into a depth domain spectral ratio image using the seismic velocity model. The method still further includes defining a wellbore path through the depth domain spectral ratio image and determining a spectral ratio log along the wellbore path from the depth domain spectral ratio.