GC-MS Aromatic Ratio Analysis for Heavy Oil API Gravity

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Solution Overview

Problem

Existing methods for determining API gravity of crude oils, particularly in heavy and extra heavy oils, are inaccurate and require large sample volumes, making it challenging to classify oils reliably.

Innovation Solution

A method using gas chromatography mass spectrometry (GC-MS) to analyze the ratio of 4-methyldibenzothiophene to 1-methyldibenzothiophene isomers, establishing an empirical correlation for calculating API gravity, which is applicable to sulfur-rich marine Type II-S kerogen oils.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If hydrometers or digital density meters are used to measure API gravity, then measurement can be performed, but large uncertainties and high requirements for laboratory skills are incurred

Engineering Contradiction:

ImproveAPI gravity measurement accuracyVSAvoidmeasurement uncertainty

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces mechanical measurement systems (hydrometers, digital density meters) with a chemical analysis system using GC-MS. Instead of directly measuring density with mechanical instruments, the method analyzes the molecular composition of aromatic fractions, specifically the ratio of 4-MDBT to 1-MDBT isomers, and correlates this chemical signature to API gravity. This substitution eliminates the mechanical measurement uncertainties and operator skill dependencies while maintaining measurement capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an intermediary approach by using aromatic compound ratios as a proxy for API gravity measurement. Rather than directly measuring density, the method measures the ratio of specific dibenzothiophene isomers in the aromatic fraction, which serves as an intermediate chemical indicator that correlates to API gravity. This intermediary measurement bypasses the direct mechanical measurement problems while providing reliable classification data.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If digital density meters are used to measure API gravity, then better reproducibility is achieved, but large volumes of oil and meticulous laboratory skills are required

Engineering Contradiction:

ImproveAPI gravity reproducibilityVSAvoidoil sample volume

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent extracts and analyzes only the aromatic fraction of the crude oil, specifically isolating dibenzothiophene compounds for GC-MS analysis. This extraction approach requires minimal sample volume because the analysis focuses on specific molecular markers rather than requiring bulk density measurement. The method takes out the essential diagnostic components (aromatic isomers) from the complex crude oil matrix, enabling accurate API determination with small samples.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If digital density meters are used to measure API gravity, then measurement can be performed, but the method is not suitable for extra heavy and heavy crude oils

Engineering Contradiction:

ImproveAPI gravity measurement capabilityVSAvoidapplicability to heavy crude oils

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent applies local quality analysis by focusing on specific molecular components (aromatic dibenzothiophene isomers) within the crude oil rather than attempting to measure bulk properties. This localized chemical analysis of aromatic fractions provides consistent results across different oil types including extra heavy and heavy crudes, where bulk density measurement methods fail. The method adapts to heavy oils by analyzing the unique aromatic fingerprint rather than relying on overall density that varies problematically with oil weight.

Inventive Principle:

Principle #3Local quality

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

Provides accurate and reliable API gravity measurements with small sample sizes, suitable for heavy and extra heavy crude oils, and aids in assessing reservoir productivity.

Implementation Method 1

analyzing the aromatic fraction using a gas chromatography mass spectrometry (GC-MS) instrument

Methodology Applied

Scientific EffectGas chromatography: Chromatography

Implementation Method 2

analyzing the aromatic fraction using a gas chromatography mass spectrometry (GC-MS) instrument

Methodology Applied

Scientific EffectMass spectrometry:

Data Source

PatentUS12601731B2Method to determine API gravity of sulfur-rich marine oils using aromatic compound chemistry

Publication Date: 2026.04.14 SAUDI ARABIAN OIL CO

AI summary

A method of determining an API gravity of a crude oil includes obtaining a reservoir sample containing the crude oil, separating an aromatic fraction from the reservoir sample, analyzing the aromatic fraction using a gas chromatography mass spectrometry (GC-MS) instrument, determining peak areas and a ratio of 4-methyldibenzothiophene and 1-methyldibenzothiophene, and determining the API gravity of the crude oil in the reservoir sample using an empirical correlation between API gravity and the ratio of 4-methyldibenzothiophene to 1-methyldibenzothiophene. A method of determining productivity of a region of a reservoir includes determining an API gravity of a crude oil in the sample from the region of the reservoir using an empirical correlation between API gravity and the ratio of 4-methyldibenzothiophene to 1-methyldibenzothiophene, and based on the API gravity of the sample, determining the productivity of the region of the reservoir.