A combined integrated multi-method approach for the assessment of the thermal maturity of sedimentary basins
- Lea Di Paolo (Eni E&P) | Sveva Corrado (Roma Tre University) | Claudia Romano (Roma Tre University) | Luca Aldega (Sapienza University of Rome) | Danilo Di Genova (Ludwig-Maximilian-University of Munich) | Domenico Grigo (Eni E&P)
- Document ID
- Society of Petroleum Engineers
- Abu Dhabi International Petroleum Exhibition and Conference, 10-13 November, Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2014. Society of Petroleum Engineers
- Thermal Maturity, FTIR and Raman spectroscopy, optical analysis, organic and inorganic thermal maturity parameters, X-ray diffraction
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The reliable assessment of thermal maturity of sedimentary successions is crucial for the evaluation of hydrocarbon generation/expulsion. Uncertainties in thermal maturity assessment up to 0.2-0.3% of vitrinite reflectance values can occur according to commonly adopted parameters (eg., vitrinite reflectance, Tmax, etc.) especially when exploring Lower Paleozoic shale gas targets that are devoid of vitrinite macerals. This level of uncertainties is not acceptable in thermal modelling and can negatively influence decisions on the development of prospects.
This contribution provides a new methodological workflow to assess thermal maturity of organic matter dispersed in sediments and hosting sedimentary succession to largely reduce such uncertainties.
The multi-method approach consists in combining optical analysis and Raman and FTIR spectroscopy of organic matter dispersed in sediments with X-ray diffraction of the inorganic fine-grained fraction of sedimentary successions.
The four techniques have been systematically compared in diagenesis for the first time. Results are from an about 3000 m deep Cretaceous-Silurian section that shows a regular and highly resolved trend of increasing thermal maturity with depth on the base of spectroscopic and XRD data, and a general agreement among vitrinite reflectance, FTIR quantitative and qualitative indexes, pyrolysis and Raman indexes. Levels of thermal maturity of dispersed organic matter range from immature-early mature stages of hydrocarbon generation in the Cretaceous-Jurassic section to mid-late mature in the Triassic and Silurian units. Moreover, fine grained sedimentary rocks record an increasing trend of thermal maturity from early diagenesis in the Cretaceous-Jurassic section to late diagenesis for the Triassic and Silurian sections.
The problem of the reliable assessment of thermal maturity of sedimentary successions is crucial for the evaluation of hydrocarbons generation/expulsion. Uncertainties in thermal maturity assessment up to 0.2-0.3% (expressed as equivalent vitrinite reflectance) can occur according to common adopted methodologies. Nevertheless this degree of uncertainties can negatively influence decisions on the development of prospects, especially when aimed at exploring shale gas targets. This happens because either vitrinite is absent or because generation windows boundaries are not accurately defined.
Thus, the thermal parameters that should be used to constrain thermal models must be carefully chosen according to geological, thermal and stratigraphic evolution of the studied successions (e.g., lithology, paleo-heat flow, etc.).
As widely known from the existing literature, any method has its own advantages, pitfalls and fields of application. Thus, any step of application of each method must be carefully checked when adopted as a standard procedure in industry (e.g., sampling in the field, specimen preparation, lab analysis, elaboration, interpretation and modeling of data).
The practice of using more than one parameter of thermal evolution is getting more and more diffused in studies on diagenesis in order to (i) guarantee a cross check among thermal indicators prior to modelling (ii) adopt the parameters that fit stratigraphic, lithological, thermal and other features of the analysed intervals.
In this work, we investigated the thermal maturity of the A well integrating vitrinite reflectance data, infrared and raman spectroscopy analyses on organic matter and X-ray diffraction (XRD) data on clay minerals to:
- determine the most appropriate technique to be used depending on the lithology, organic facies and thermal maturity;
- determine the best correlation among parameters;
- define a standard workflow.
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