Organic Petrology and Thermal Maturity of Dispersed Organic Matter from the Ramalhal-1 Well (Lusitanian Basin, Portugal)

Organic petrology is an important tool used to characterize dispersed organic matter (DOM) in sediments and sedimentary rocks, and to assess its thermal maturity. This study was carried out on 33 cutting samples (Middle-Upper Jurassic) from the Ramalhal-1 well to characterize the particulate organic matter and to evaluate its thermal maturity. The samples were submitted to optical petrography analysis (reflected white and blue incident lights) and the mean random reflectance was measured. Microscopic observations revealed a low DOM content, characterized by the predominance of macerals of the inertinite group (including charcoal), followed by solid bitumen. Huminite/vitrinite is usually small in size and quantity. Liptinite macerals were also present, represented by sporinite, cutinite, liptodetrinite and rare bituminite. A type III-IV kerogen was defined for the Ramalhal-1 sequence. Huminite/vitrinite mean random reflectance varied between 0.38% and 0.75%, pointing to an immature-to-mature stage of the organic matter. Multi-populations of solid bitumen occurred in almost all the samples, filling voids and fractures in the inorganic materials (mainly carbonates). The bitumen populations were quite heterogeneous, concerning both the optical characteristics and distribution, displaying different thermal maturities. No relationship between vitrinite and bitumen reflectance was established, indicating that these bitumens were not generated in situ.

Direct signs of oil-generation in the rocks of Bazhenov Suite

Nowadays, the term “organic petrology” is widely used for the microscopic study of the organic matter (OM) of rocks. In the world, there are a large number of articles describing organic macerals in regions where shale oil and gas are produced. It is no coincidence that the new term “organic petrology” appeared instead of “coal petrography” since new macerals were found and described in the dispersed organic matter. So, along with alginites (previously the only term describing the oil-source sapropel-type OM), bituminite and bitumen appeared. Bituminite is heterogeneous, so it has varieties as “post-mature bituminite” and “atypical bituminite”. One of the typical components of the Bazhenov formation, along with described above, are the remains of soft radiolarians bodies. All of these organic macerals have a similar reflectance index with small differences. Long-term studies of the OM rocks of the West Siberian basin have revealed indications of oil generation, which are easily established by standard microscopic studies. These indications include a change in the colour of macerals, a different glow of oil-source components (all from the liptinite group), the appearance of bitumen films, the appearance of post-mature bituminite, the appearance of secondary porosity.

The influence of solid-phase organic carbon on the sorption of hydrophobic organic pollutants in landfill barriers, UK

The Oxford Clay from Bletchley, the Kimmeridge Clay from Kimmeridge Bay, Dorset, and Tertiary mud (Wittering Formation) from Whitecliff, Isle of Wight, United Kingdom were used as sorbent samples because of their distinctive organic material characteristics (Amorphous organic matter rich and/or phytoclast rich). Organic material was isolated for identification and analysis using a non-acid extraction method (heavy liquid) extraction and traditional methods involving HF digestion. These organic materials were then used to determine influences of extraction on hydrophobic organic contaminants, (toluene and naphthalene) sorption. Organic petrology classification was applied to identify the various types of isolated organic material. Amorphous organic matter from the Kimmeridge Clay displayed a higher sorption capacity (Sorption–desorption distribution coefficient (Kd), Kd = 6,481, 59, 670; for toluene and naphthalene, respectively) compared to literature values. Amorphous organic matter-rich sorbent extracts demonstrated a higher absorption capacity than the phytoclast-rich sorbents (e.g., Wittering Formation, Kd = 219, 10, 134; for toluene and naphthalene, respectively). Implications of results in landfill design/risk assessment and modelling are discussed.