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First Break - Volume 43, Issue 3, 2025

Volume 43, Issue 3

Volume 43, Issue 3, 2025

  • Technical Article

      • Unsupervised Clustering as a Tool for Geomorphological Interpretation: A Case Study from a Sarmatian Delta in Romania’s Dacian Basin

        Authors Luca Fava
        https://doi.org/10.3997/1365-2397.fb2025019
        Abstract

        Seismic attributes are a valuable tool in identifying sedimentary facies. Machine learning (ML) techniques can be helpful in combining information coming from different attributes. The unsupervised clustering algorithm called self-organising map (SOM) has already been successfully applied in paleo deep-water settings in many basins defining seismic facies. To evaluate the applicability of this ML method to a paleo shallow-water setting the SOM workflow is applied to 3D seismic data acquired onshore Romania over the south Carpathian foredeep. Many attributes are extracted along an interpreted horizon. Principal Component Analysis (PCA) is performed on the list of attributes in two ways. Firstly, the main principal components are defined to use them as input for the first run of SOM clustering (SOM 1). Secondly, the most important attributes are identified and used as input for the second run of SOM clustering (SOM 2). The geomorphological interpretation of the SOM results is compared with the interpretation of conventional attributes. The results show that the SOM is a powerful tool in defining seismic facies as it allows the definition of details not discernible using other tools. This exercise shows also that ML techniques can be easily implemented by exploration geophysicists using standard interpretation software’s and open-source Python libraries.

    • Musings on the Golden Fault and the Front Range Zone of Flank Deformation

      Authors Tom Davis
      https://doi.org/10.3997/1365-2397.fb2025021
      Abstract

      The Golden Fault on the west side of Golden, Colorado has been the subject of debate in the geological community for several years. The source of the basalt that caps North and South Table Mountain is also of interest to the scientific community as the source of the basalt has never been identified. There may very well be a connection between these two major geological features. In addition, the structure of the Front Range Zone of Flank Deformation itself is of interest as it contains mineral resources that have helped to shape the economic development of the region. This natural resource setting also shaped the Colorado School of Mines from its creation in 1874 to become one of the most famous engineering universities in the world.

    • Ametista Block - An Unusual Prospect in Santos Basin - Albian Atoll Upon Exhumed Mantle

      https://doi.org/10.3997/1365-2397.fb2025022
      Abstract

      The authors present a new, distinctive prospect in the southern Santos Basin, constituted of a possible Albian atoll developed upon exhumed mantle. The prospect was identified due to the acquisition of new high-quality 3D with the latest processing techniques. The prospect shows great petroleum potential and has excellent analogs in the present Pacific atolls and on an island in the Red Sea. A large buildup composed of stratified seismic facies exhibiting basin-edge offlaps/clinoforms, and capped by a massive structureless construction, is developed upon a protrusion of exhumed mantle. This four-way closed structure is surrounded by Aptian salt bodies that onlap its flanks and by the lowermost strata of the Drift Sequence of the Santos Basin, known to be the ACT source rocks. Considering the nearby geology, this buildup is interpreted as an Albian carbonate platform capped by a reef (rudist?). An adjacent on-trend structure is constituted by volcanos developed upon the exhumed mantle. The overall structure resembles the well-known atolls of the Pacific Ocean.

    • Estimating Petrophysical Parameters from Acoustic Impedance and P to S Wave Velocity Ratio Using a Simple Rock Physics Model

      https://doi.org/10.3997/1365-2397.fb2025023
      Abstract

      In reservoir characterisation, rock physics analysis has been frequently used to describe petrophysical properties of rocks based on their elastic behaviour. Recently, a new rock physics model that facilitates direct estimation of porosity and fluid saturation from acoustic impedance (AI) and P to S wave velocity ratio (V/V) was introduced. The method has the flexibility to adapt the rock physics model to the data by simply adjusting two parameters without the need to consider the detailed elastic moduli. In this study, a slight modification is proposed by considering the influence of fluids on V/V ratio to better comply with the Gassmann equation. A workflow for obtaining optimal model parameters for the observed data by incorporating the curved pseudo elastic impedance (CPEI) approach is also demonstrated. The modified method successfully produces a model that fits the data. The proposed workflow effectively finds optimal model parameters, resulting in better estimation of petrophysical properties. However, a detailed examination of the results shows that variations in shale volume should be incorporated to obtain better petrophysical estimation results. This method offers a simple yet reliable way to estimate porosity and fluid saturation directly from AI and V/V ratio typically obtained from the pre-stack seismic inversion.

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