A graphic method for depicting basin evolution and changes in the dominant hydrodynamic process from paleocurrent data

Abstract Paleocurrent data measured on depositional elements and sedimentary structures (e.g., channels, cross-strata) are commonly utilized in the description of sedimentary strata. Paleocurrent data provide information about the depositional setting and in some cases can be useful for immediately detecting specific depositional processes (e.g., herringbone cross-strata for bimodal tidal currents). The typical graphical representation used to report paleocurrent data is the rose diagram. However, rose diagrams are not able to disclose all information contained in paleocurrent data, limiting the potentiality of such a representation method. In particular, there is presently no method to highlight changes in the paleogeographic configuration that can ultimately have an impact on the evolution of depositional processes and paleocurrent direction through time. Here, we present a graphic method that permits instant visualization of anomalies in paleocurrent distributions of the stratigraphic record that can be linked to changes in the paleogeography due to tectonic evolution or in the dominant hydrodynamic process. It is important to highlight that the proposed method does not aspire to replace rose diagrams but to provide an additional tool to be used before and in combination with rose diagrams in order to extrapolate as much information as possible from paleocurrent data

Tectono-stratigraphic architecture of the Ionian piedmont between the Arso Stream and Nicà River catchments (Calabria, Southern Italy)

Along the northern Ionian margin of Calabria, three Neogene basins comprise wedge-top depozones containing syntectonic deposits which cover the frontal part of the fold-thrust belt. One of the best exposed onshore allochthonous siliciclastic successions is represented by the Cariati Nappe, cropping out in the Cirò Basin. Field geological mapping and aerial interpretations were used to characterize the stratigraphy and tectonics of the area between the Arso Stream and Nicà River catchments (about 170 km2), including a Paleozoic metamorphic basement complex unconformably overlain by Upper Oligocene to Quaternary siliciclastic deposits and minor carbonates. This paper presents a 1:25,000 scale map of the Ionian study area, providing lithological and structural data towards reconstructing its tectono-sedimentary evolution

Permeability characterisation of sedimentological facies in the Bunter Sandstone Formation, Endurance CO2 storage site, offshore UK

Permeability variations due to sedimentological heterogeneity are important in controlling CO2 migration pathways, CO2 plume dynamics, and stratigraphic, capillary and dissolution trapping of CO2 in subsurface storage units and complexes. Thus, knowing these parameters is crucial to developing a CO2 injection strategy that maximizes storage and trapping efficiency. In this study we analyzed the sedimentological and permeability heterogeneity of the Bunter Sandstone Formation at the Endurance CO2 storage site, offshore UK, through integrated facies analysis, minipermeameter measurements, and thin section analysis. Detailed core logging and outcrop analysis were performed to identify facies and related heterogeneities. Twelve lithofacies have been identified in cores. By analyzing the stacking patterns of the facies, three facies associations and three architectural elements were identified in cores and outcrop analogues, respectively. Heterogeneities occur at all the scales ranging from mm-scale laminae to 10′s m-scale architectural elements.Permeability variations at outcrop and in core are closely related to sedimentological heterogeneities. Minipermeameter and core plug permeability data show up to three orders of magnitude variation across the facies. Cross-bedded (Sp, St, Sl, Spmc) and structureless (Sm) sandstones are the most permeable (4–5400 mD) facies, whereas pebbly conglomerates (Gmg) and laminated mudstones (Fl) are least permeable (0.18–89 mD) facies. Mottled and deformed sandstone (Smd) and crinkly laminated sandstone (Sc) have highly variable permeability (0.69–480 mD). Minipermeameter data reveal permeability varies by a factor of five at centimeter scale within planar cross-bedded (Sp), trough cross-bedded (St) and planar bedded sandstone (Sh) sandstone facies, while planar cross-bedded sandstone with mud clasts along foresets (Spmc) exhibit permeability variation up to a factor of four. Petrographic analysis of thin sections shows that these permeability variations are related to changes in grain size, clay content, and distribution of dolomite cements

Using legacy core material to assess subsurface carbon storage reservoir potentiality

The growing importance of subsurface carbon storage for tackling carbon emissions requires an accurate characterisation of potential reservoirs to understand their capabilities. In this context, the use of legacy data originally acquired in the last fifty years for scientific projects and petroleum exploration and production activities would represent a suitable cost-effective solution and help to maximise the value of this extended national asset. Core material represents the only direct observation of subsurface deposits and must be preserved from the current disposal process related to the decommissioning of hydrocarbon fields. In this contribution, a suite of samples from core material stored at national (i.e., British Geological Survey) and local (i.e., Department of Earth Sciences, Royal Holloway, University of London) core repositories, previously characterised at the micro scale using X-ray micro-computed tomographic (μCT) imaging are discussed. Using this technique it has been possible to investigate how pore and grain geometries control crucial features of a suitable reservoir such as porosity and permeability. The aim of this contribution is to describe the methodology behind digital image analysis (DIA) following μCT imaging applied to core material. We show how DIA can be used to provide significant measures of reservoir suitability when making initial assessments of storage reservoirs, without the need for expensive and time-consuming analyses

The upper percolation threshold and porosity–permeability relationship in sandstone reservoirs using digital image analysis

Subsurface sandstone deposits represent globally ubiquitous reservoirs which can potentially provide the characteristics necessary for the effective geological storage of CO2. Geological carbon storage is widely agreed to be a key asset in tackling anthropogenic emissions and climate change to reach a sustainable ‘net zero’, despite the present financial challenges associated with it. Therefore, improved understanding of the characteristics of the materials in which we plan to store many gigatons of CO2 is critical. Developing cheaper characterisation techniques is therefore crucial to support the global push for net zero. In this work we use digital analysis of 3D microscale X-ray images of a range of sandstone samples to constrain the porosity–permeability relationship and the upper percolation threshold; the point at which near full pore structure connectivity is achieved. This is one of the most significant controls on the viability of carbon storage as a practical solution to achieving net zero. We find that the upper percolation threshold in sandstone occurs at ca. 14% total porosity whilst the relationship between porosity (ϕ) and permeability (K) can be defined as K=105.68ϕ3.88. The investigation of the upper percolation threshold may allow a target criterion to be designated when assessing potential carbon storage reservoirs, whilst investigation of the porosity–permeability relationship allows for a greater understanding of the fluid flow regimes in the subsurface. By using a digital technique to assess carbon storage reservoir potentiality we show that initial characterisation of reservoirs can be carried out rapidly and relatively economically, prior to further full reservoir characterisation studies. This approach is also non-destructive, allowing samples to be reused and multiple analytical phases performed on the same materials

Types of mixing and heterogeneities in siliciclastic-carbonate sediments

Mixed siliciclastic-carbonate deposits consist of a suite of different types of mixing between the two components, from bed (core-plug) to stratigraphic (seismic) scales, producing a high vertical and lateral lithological variability. Mixed deposits results from the interaction of siliciclastic input and coeval carbonate production controlled by temporal and/or spatial factors. Although mixed deposits are very diffuse in the geological record, studies about these deposits are scrappy and not well encoded. Accordingly, mixed deposits represent a labyrinth for researchers who want to investigate them for the first time. In this paper, different types of mixing (compositional versus strata) controlled by different allocyclic (e.g. sea-level, climate) and/or autocyclic (e.g. depositional processes) factors that operate at different scale are documented. Mixing is recognized and described at three main scales of observation: bed/core-plug scale; lithofacies/well-log scale; and stratigraphic/seismic scale. (i) Compositional mixing reflects the contemporaneous accumulation of the two heterolithic fraction in space and time. This type of mixing is observable at lamina to bed scale, locally producing depositional structures diagnostic for particular depositional environments. (ii) Strata mixing results from the alternation of the two heterolithic fraction in time. This type of mixing is observable at lithofacies to stratigraphic scale and can be related to depositional processes, climatic variations and/or relative sea-level changes. A correct identification of these different types of mixing and the scale of their occurrence is crucial in revealing (i) physical processes that control the sedimentation, (ii) environmental factors that influence the carbonate factory related to the siliciclastic dispersal mechanisms, and (iii) internal heterogeneity of the resulting sedimentary deposit. Furthermore, the petroleum industry is interested to unravel new insights about internal properties of mixed siliciclastic-carbonate systems (e.g., porosity, permeability) and to reconstruct predictive 3D models for the related reservoirs. The correct prediction of internal heterogeneity and the recognition of lateral and vertical compartmentalization have an important impact on hydrocarbon exploration and exploitation