Investigating LHC Preservation in Core Samples

In the field of reservoir geochemistry, the preservation and analysis of light-end hydrocarbon (LHC) compounds in core samples play a crucial role in understanding the characteristics of oil reservoirs.

GeoMark delve into this topic of LHC preservation using various solvent extraction techniques. Traditional methods of solvent extraction have proven to be exhaustive and destructive towards LHCs, rendering any comparison to the fingerprint of produced oil invalid. However, the success of any extraction method relies heavily on adhering to proper core sampling and handling procedures. 

It is important to note that tight lithologies inherently retain the LHC organic compound better than more permeable lithologies, irrespective of the chosen sample handling and extraction protocol. Consequently, there are geological limitations that prevent complete LHC preservation, regardless of the laboratory process employed.

Limitations of Lab Procedures

Laboratory procedures for core extraction, whether utilizing:

• Solvents
• Thermal Processes
• Or Supercritical Gases

cannot precisely mimic the conditions and timescales of geologic processes responsible for oil expulsion. Therefore, it is unrealistic to expect a perfect correlation between core extracts and produced oils, even under ideal conditions. However, these two entities share common characteristics, making correlation work possible and emphasizing the importance of LHC preservation in core extracts. 

Hydrocarbon Core Extracts in Reservoir Geochemistry Studies

Hydrocarbon core extracts have played a vital role in reservoir geochemistry studies for correlation purposes, providing valuable insights into the composition and characteristics of oil reservoirs. 

Over time, the significance of maximizing sample integrity and utilizing the available data for comprehensive geochemical assessments has grown, especially in the realm of unconventional reservoir geochemistry and its link to production and source rocks.

The use of hydrocarbon core extracts has long been established in reservoir geochemistry studies for correlation purposes. 
Maximizing sample integrity and the available data for geochemical assessments has become increasingly important, particularly in unconventional reservoir geochemistry and the connection between production and source rocks. 

Hydrocarbon core extracts have played a crucial role in reservoir geochemistry studies, offering valuable insights and correlations. 

However, as the industry explores unconventional plays, specific challenges arise that require a dedicated focus on sample integrity and data analysis to effectively address the distinct characteristics of these reservoirs.

Challenges in Unconventional Plays

Unconventional plays present a unique set of challenges in reservoir geochemistry studies, particularly due to higher thermal maturity and the reduced presence of biomarkers. As a result, the focus shifts toward the preservation and analysis of light-end hydrocarbon (LHC) compounds. 

The significance of LHC preservation in unconventional plays lies in its importance in both high and lower-maturity samples and the impact of light-end peak loss on detailed allocation and production monitoring.

• In unconventional plays with higher thermal maturity, the presence of biomarkers is significantly reduced, shifting the focus to LHC compounds. 
• Preservation of LHC compounds is crucial in high thermal maturity samples and remains important in lower maturity samples that heavily rely on HRGC results.
• Loss of light-end peaks can alter the character of chromatography, impacting detailed allocation and production monitoring. 
• Light-end preservation becomes increasingly important in unconventional reservoirs where the analytical program predominantly relies on HRGC results. 

The challenges faced in unconventional plays underscore the criticality of preserving LHC compounds in reservoir chemistry studies. With higher thermal maturity and reduced biomarker presence, the reliance on LHC analysis becomes paramount, especially in unconventional reservoirs where the analytical program predominantly relies on high-resolution gas chromatography (HRGC) results. 

Recognizing the importance of light-end preservation and implementing effective strategies enhances the reliability and accuracy of reservoir characterization in unconventional plays, contributing to a more comprehensive understanding of these complex reservoir systems.

Solvent Extraction Methods

The extraction of a hydrocarbon organic molecule is a critical step in reservoir geochemistry studies, and the selection of solvent extraction methods plays a crucial role in preserving the integrity of the samples. 

In this study, eight different solvent extraction methods (A to H) were tested on frozen core samples from the Delaware Basin, utilizing various solvents and extraction techniques to optimize the analysis of hydrocarbon compounds.

Eight different solvent extraction methods (A to H) were tested on frozen core samples from the Delaware Basin.

• Three different solvents were utilized:

            - Dichloromethane (DCM) (A)
            - Carbon disulfide (CS2) (B-E, G, H)
            - Cyclohexane (C6H12) (F)

• Methods involved grinding the frozen core under solvent (B-C, F), using closed vials (D-E & G-H), or extraction using a Dionex ASE 350 (A).
• Closed vial methods utilized samples from powders [60 mesh sieve] (D-E) or chips [10-20 mesh sieve] (G-H).
• Some closed vial samples were concentrated on a cold plate (D,G), while others were analyzed without concentration (E,H).

The selection of solvent extraction methods for hydrocarbon core samples greatly influences the preservation and analysis of these samples in reservoir geochemistry studies. Through the testing of various techniques utilizing different liquid solvents and extraction approaches, valuable insights have been gained into the optimal practices for maximizing sample integrity. 

By considering factors such as grinding techniques, closed vial extraction, and concentration methods, researchers can effectively enhance the accuracy and reliability of hydrocarbon compound analysis in core samples, thereby improving the overall quality of reservoir geochemistry studies.

Evaluating Sample Integrity

The evaluation of sample integrity is a crucial aspect of reservoir geochemistry studies, particularly when analyzing hydrocarbon core samples. In this study, eight different extraction methods (Preparations A to H) were examined to assess the preservation of light-end hydrocarbon (LHC) peaks. Significant variability in LHC preservation was observed, and the findings shed light on the most effective extraction method for maximizing peak retention.

• Significant variability in LHC preservation was observed among the eight extraction methods (Preparations A to H).
• Preparation A (Quantitative Extraction) preserved almost no peaks lighter than nC-12, as it was the only method to evaporate to dryness.
• Preparation F (Cold Cyclohexane Extraction) exhibited better preservation than A, with some peak retention down to nC-7, but most LHC peaks were still missing. 
• Closed vial samples extracted from powders (Preparations D & E) and standard CS2 extraction (Preparation B) showed slightly better results than Cyclohexane solvent (Preparation F), with some peaks evident down to nC-6.
• Cold CS2 extraction (Preparation C) and closed vial samples extracted from chips and concentrated (Preparation G) demonstrated a significant improvement in LHC preservation compared to the previously discussed methods. 
• The best extraction method for retaining LHC peaks (down to nC-4) was closed vial samples extracted from chips that are not concentrated (Preparation H).

The evaluation of various extraction methods has provided valuable insights into optimizing sample integrity and LHC peak preservation in reservoir geochemistry studies. The results demonstrated that certain preparations, such as cold CS2 extraction and closed vial samples extracted from chips, showed a significant improvement in LHC preservation compared to other methods. 

Notably, the best organic chemistry extraction method for retaining LHC peaks was identified as closed vial samples extracted from chips without concentration. These findings emphasize the importance of selecting the appropriate extraction technique to ensure accurate and reliable analysis of hydrocarbon core samples in reservoir geochemistry studies.

Significance for Reservoir Geochemistry Program Design & Application

In the realm of reservoir geochemistry, the maximization of sample integrity holds significant importance. This consideration becomes particularly crucial when dealing with core extract fluids. Among various methods, closed vial CS2 solvent extraction on chips without concentration (Preparation H) has emerged as the most effective technique for maximizing the retention of larger hydrocarbons. 

To ensure the utmost reliability and confidence in organic chemistry programs, it is essential to incorporate a comprehensive analytical suite comprising bulk, isotopic, traditional biomarker (GC-MS), and non-traditional biomarker (GC-MS/MS QQQ) methods, alongside a solvent extraction and high-resolution gas chromatography (HRGC) approach designed to optimize sample integrity.

• Maximizing sample integrity is crucial for any geochemical study involving a core extract compound.
• The closed vial CS2 solvent extraction on chips with no concentration (Preparation H) emerged as the most effective method to maximize LHC retention of hydrocarbons.
• A well-designed reservoir geochemistry program should incorporate a robust analytical suite of geochemical methods, including bulk, isotopes, traditional biomarkers (GC-MS), and non-traditional biomarkers (GC-MS/MS QQQ).
• Combining these analyses with a solvent extraction and HRGC method designed to maximize sample integrity ensures the greatest reliability and confidence in any reservoir geochemistry program.

The significance of maximizing sample integrity resonates deeply in reservoir geochemistry programs involving core extract fluids. Through careful evaluation, the closed vial CS2 solvent extraction method on chips without concentration (Preparation H) has emerged as the optimal approach for maximizing the retention of hydrocarbons. For a robust reservoir geochemistry program, it is imperative to combine a range of analytical techniques, including bulk, isotopic, traditional biomarker (GC-MS), and non-traditional biomarker (GC-MS/MS QQQ) methods. 

Pairing these analyses with a solvent extraction and HRGC method specifically designed to enhance sample integrity guarantees the highest levels of reliability and confidence in reservoir geochemistry studies. By embracing these strategies, researchers can unlock deeper insights into the complexities of reservoir systems, thereby advancing our understanding of hydrocarbon resources.

Key Considerations for Reservoir Geochemistry Studies

Maximizing sample integrity should be a priority in any geochemical study in which core extract fluids will play a role. The best method to maximize LHC retention of hydrocarbons is closed vial CS2 solvent extraction on chips with no concentration. Assuming good sampling and handling procedures and favorable lithology, this method ensures the best preservation in the extracted fluid.

GeoMark Research specialize in providing state-of-the-art analytical services tailored to client specific needs. Their team of experienced scientists and technicians are equipped with advanced technologies and methodologies to ensure the highest accuracy and reliability in hydrocarbon analysis. Whether you require comprehensive geochemical assessments, isotopic analysis, traditional biomarker profiling, or non-traditional biomarker analysis, GeoMark can help.

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