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Programmed pyrolysis (Rock-Eval) data and shale paleoenvironmental analyses; a review

B. S. Hart and A. S. Steen
Programmed pyrolysis (Rock-Eval) data and shale paleoenvironmental analyses; a review (in Shale paleoenvironments, Bruce Hart (prefacer), Gilles Hennenfent (prefacer), Joe Macquaker (prefacer) and Harry Rowe (prefacer))
Interpretation (Tulsa) (February 2015) 3 (1): SH41-SH58

Abstract

We use public-domain data from programmed pyrolysis, collected using Rock-Eval or similar apparatuses, to illustrate the utility and challenges of using this method for paleoenvironmental analyses. These data are widely available and commonly collected and analyzed for a variety of purposes in the petroleum industry in the fields of paleo-oceanography and paleoclimate research and elsewhere. We show how factors such as sample condition, mineralogy, organic content, and others can influence the results, leading to potential interpretational complications. We also evaluate ways that the data can be plotted to maximize their utility for interpretation purposes. Four types of organic matter are commonly identified based on programmed pyrolysis results. Type I organic matter has a high (e.g., >700) hydrogen index (HI), is oil-prone and is commonly assumed to represent lacustrine depositional settings. Type II organic matter is also oil-prone (i.e., having an HI between 350 and 700) but is commonly assumed to represent marine organic matter. Type III organic matter has a lower HI (<350), will tend to generate gas, and is commonly assumed to represent terrigenous (e.g., land plants) organic matter. Type IV organic matter has very low HI values and is associated with nongenerative (i.e., inert) organic matter. We show that these simple associations between organic matter type and paleoenvironment were not always valid. Preburial degradation of the organic matter and mixing of different organic matter types are two possibilities that can lead to erroneous paleoenvironmental interpretations. Furthermore, the programmed pyrolysis results characterize the present composition of the organic matter which, especially at high thermal maturities (e.g., dry gas window), can be significantly different to that of the original organic matter. Other types of advanced geochemical and sedimentologic analyses should be integrated with the programmed pyrolysis results during their interpretation.


ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 3
Serial Issue: 1
Title: Programmed pyrolysis (Rock-Eval) data and shale paleoenvironmental analyses; a review
Title: Shale paleoenvironments
Author(s): Hart, B. S.Steen, A. S.
Author(s): Hart, Bruceprefacer
Author(s): Hennenfent, Gillesprefacer
Author(s): Macquaker, Joeprefacer
Author(s): Rowe, Harryprefacer
Affiliation: Statoil, Stavanger, Norway
Affiliation: Statoil, Houston, TX, United States
Pages: SH41-SH58
Published: 201502
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 44
Accession Number: 2016-007500
Categories: Economic geology, geology of energy sourcesGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Chevron, USA, United StatesExxonMobil, USA, United StatesBureau of Economic Geology, USA, United States
Source Note: Online First
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201604
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