Geochemical Trends Reflecting Hydrocarbon Generation, Migration and Accumulation in Unconventional Reservoirs Based on Pyrolysis Data (on the Example of the Bazhenov Formation)

Polina Maglevannaia,Evgeniya Leushina,Timur Bulatov,Mikhail Spasennykh,Elena Kozlova,Nikita Morozov

doi:10.3390/geosciences11080307

Polina Maglevannaia, Evgeniya Leushina + Show 4 more

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https://doi.org/10.3390/geosciences11080307

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Abstract

The current study is devoted to the determination and interpretation of geochemical trends reflecting hydrocarbon generation, migration and accumulation in unconventional reservoirs; the study is performed on the Bazhenov shale rock formation (Western Siberia, Russia). Results are based on more than 3000 Rock-Eval analyses of the samples from 34 wells drilled in the central part of the West Siberian petroleum basin, which is characterized by common marine sedimentation environments. Pyrolysis studies were carried out before and after the extraction of rocks by organic solvent. As a result, we have improved the accuracy of kerogen content and maturity determination and complemented the standard set of pyrolysis parameters with the content of heavy fraction of hydrocarbons. The data obtained for the wells from areas of different organic matter maturity was summarized in the form of cross-plots and diagrams reflecting geochemical evolution of the source rocks from the beginning to the end of the oil window. Interpretation of the obtained results revealed quantitative trends in the changes of generation potential, amount, and composition of generated hydrocarbons in rocks at different stages of oil generation process. The analysis of geochemical trends allowed us to improve approaches for the productivity evaluation of the formation and study the effect of organic matter maturity on distribution of productive intervals of different types.

Highlights

Source rocks with high organic matter content and related processes of hydrocarbon formation in petroleum basins have been studied for many decades [1,2,3,4,5]
One of the most widely used geochemical methods for the analysis of organic matter in unconventional reservoirs is Rock-Eval pyrolysis [6,7,9,11,12,13,14]. This highly informative method is applied for determination of the organic matter content, its source, maturity, oil and gas generation potential, mobile hydrocarbon content, and other characteristics which are necessary to assess the quality of source rock in exploration of conventional petroleum-geological systems, to estimate oil and gas reserves of unconventional fields, and to choose the methods for hydrocarbon recovery
The output pyrolysis parameters are S0, S1, and S2 measured in mg HC/g rock, as well as parameters S3, S4 and S5 measure and reported as mg CO2/g rock

Summary

Introduction

Source rocks with high organic matter content and related processes of hydrocarbon formation in petroleum basins have been studied for many decades [1,2,3,4,5]. Geochemical studies of organic matter are commonly used to establish the most important characteristics that reflect hydrocarbon forming processes and determine the current hydrocarbon potential of rocks [6,7,8,9,10]. One of the most widely used geochemical methods for the analysis of organic matter in unconventional reservoirs is Rock-Eval pyrolysis [6,7,9,11,12,13,14] This highly informative method is applied for determination of the organic matter content, its source (kerogen type), maturity, oil and gas generation potential, mobile hydrocarbon content, and other characteristics which are necessary to assess the quality of source rock in exploration of conventional petroleum-geological systems, to estimate oil and gas reserves of unconventional fields, and to choose the methods for hydrocarbon recovery. In case of the absence of vitrinite, the combination of pyrolysis and biomarker analysis of oils and rock extracts allows one to determine maturity using the data on kerogen and mobile hydrocarbons composition [7,15]

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