The Carboniferous Bowland Shale Formation (UK): Understanding the Sedimentological and Diagenetic Processes within a potential Shale Gas Exploration Play

University of Manchester

Sarah Newport (NERC funded PhD student)

The core aim of the project is to provide new data that documents the scale and nature of the microfacies, sedimentological and diagenetic variability within the Bowland Shale succession in the Bowland Basin (NW England). The sedimentological and diagenetic variability within the succession will likely play a major role in controlling reservoir quality, but current knowledge is limited, leading to significant uncertainty for exploration. This project will focus on how diagenetic alterations affect the relationships between mineralogy, organic matter and pore characteristics within source rock reservoirs, using the Bowland Shale as an example. A detailed paragenetic sequence for the Bowland Shale will be also be constructed and used to determine the burial evolution of the shales.

Current Work:

  • Sedimentary logging of 125m of previously undescribed core within a marginal to basinal succession from the Bowland Basin, containing both the upper and lower Bowland Shale Formations.
  • A detailed microfacies scheme constructed using scanned thin sections, optical microscopy and high resolution SEM images based on texture and composition, and refined through consideration of physical sedimentary structures, biogenic sedimentary features and diagenetic products.
  • Relate facies descriptions and vertical changes across the core with temporal variations due to changes in basinal inputs and eustatic sea level.
  • Determine the relationship between organic matter richness and facies type.
  • Relate diagenetic variability to facies to identify any facies control over diagenetic products.

Future Work:

  • Detailed SEM-CL to determine the various phases of calcite cementation present within samples; to allow more accurate determination of the clay cements; to provide a detailed qualitative paragenetic sequence for the Bowland Shale.
  • (Q)XRD analysis to allow definite mineral identification, and % level quantification; can differentiate chemically similar minerals and polymorphs excellent for clay mineral identification and to quantify the variations between facies.
  • Stable isotopes (δ18O and δ13C) analysis on cement generations to trace origin, temperature of growth and relative timing of generation.

The project will be expanded to include a more basinal succession within the Bowland Basin in order to compare and contrast the sedimentological and diagenetic variability observed within the two successions.

Controls on UK Lower Namurian Shale Gas Prospectivity: Understanding the Spatial and Temporal Distribution of Organic Matter in Siliciclastic Mudstones

University of Leicester

Joe Emmings (NERC funded PhD student)

We seek to understand the controls on the spatial and temporal distribution of organic matter (sedimentological, biological, preservation) and how this relates to the unconventional hydrocarbon prospectivity of the Upper Bowland Shale. This project will test and explore the hypothesis that the deposition of carbonate-bearing, organic rich mudstones is a basin wide phenomenon driven by the exchange with nutrient-rich oceanic waters during periods of high sea-level. This nutrient exchange led to an increase in water column productivity and the increased flux of organic matter to the basin-floor. An alternative hypothesis is that these mudstones are more localized and potentially controlled by distance from the shorelines and/or sediment transport mechanisms. A component of this project also investigates the styles of geochemical alteration of samples collected from outcrop due to modern weathering.

Above: Joe Emmings at an outcrop in the field with a hand-held core drill

Project Objectives:

  • Describe the variability of biological input to mudstones through sedimentological field logging, optical imaging of thin sections, macropalaeontological, palynological, geochemical (organic and inorganic) and isotopic methods.
  • Interpret lithofacies variability in terms of changing processes and palaeoenvironments.
  • Link palaeoenvironments to larger scale climate change and carbon cycle events.
  • Investigate types of organic matter and their potential for gas generation.
  • Develop a predictive model relating the temporal and spatial distribution to biological input to shale gas prospectivity a‌nd criteria for identifying these intervals in exploration wells.

Joe Emmings - Research Profile:

Characterization of the kerogen fraction of Arnsbergian (late Mississippian, Serpukhovian) mudstones in the UK Pennine Basin

British Geological Survey

Dr Jan Hennisen (PDRA)
  • Palynology: especially its uses in palaeoecological reconstructions.
  • Palynology-based proxy development: statistical analysis of palynological results.
  • Carboniferous palynofacies analysis

Current project:

The composition and amount of organic matter in shales and mudstones determines the quality and influences the quantity of hydrocarbons contained in shale reservoirs. The kerogen fraction in Serpukhovian-aged Carboniferous mudstones in the south-eastern part of the Pennine Basin includes up to 95% amorphous organic matter (AOM), mostly heterogeneous material of unknown origin lacking a distinct morphology. We aim to better understand the amount and origin of AOM so that predictions can be made regarding the hydrocarbon potential of these rocks. This is relevant to both industry and government in understanding this currently unexploited source of indigenous energy.

Figure 1 (Above): Palynological characterisation

In the current project (Figure 1) we design a palynological kerogen classification scheme that is relevant for Carboniferous mudstones in the UK with an emphasis on AOM. We characterise the kerogen fraction of samples from three different core locations (Carsington Dam Reconstruction C3, Karenight and Grange Hill) using a novel quantitative transmitted light microscopy technique. Based on these observations, each group we recognized is characterised by conducting scanning transmission electron microscopy (STEM) analysis on isolated kerogen fragments. To characterise samples geochemically (stable isotope analysis, Rock-Eval pyrolysis and pyrolysis gas chromatography) we used whole rock and kerogen fractions but also AOM isolates that were separated from the total kerogen fraction using a new technique consisting of sequential sonicating and centrifuging cycles of kerogen samples. Future work includes experimental taphonomy to see whether the observed classes of kerogen can be produced under controlled conditions in the laboratory.

Dr Jan Hennisen - Research Profile:

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