Organic matter maturation

Dell Abate, M. T., Canali, S., Trinchera, A., Benedetti, A., and Sequi, P. (2000). Thermal methods of organic matter maturation monitoring during a composting process. J. Ther. Anal. Cal. 61, 389-396. 

Plant in slightiy acid, moist but well-drained soil rich in organic matter. Mature plants endure... 

Figure 3.16 Schematic representation of amount of hydrocarbons generated in, and expelled from a type II kerogen-bearing source rock as a function of organic matter maturity for the initial part of the oil window (after Leythaeuser et al., 1987. Reprinted with permission from the Proceedings 12th World Petroleum Congress, Houston, Vol. 2, Fig. 2a, p. 229).

Secondary porosity development as the main contributor to the present reservoir porosity in Hibernia Field is closely related to the former presence of early calcite cements. The fraction of total porosity which is secondary increases with depth, from 20% in Avalon/Ben Nevis Sandstone (Hauterivian-Albian), to 60% in Catalina Sandstone (Lower Hauterivian), and to >80% in Hibernia Formation (Berriasian to Mid-Valanginian). In the Avalon/Ben Nevis Sandstone the formation of secondary porosity may have been caused by meteoric water influx. In the deeper reservoirs it was caused by acidic pore fluids generated by organic-matter maturation. The present average geothermal gradient of 26°C/km suggests that the most deeply buried sandstone reservoirs in Hibernia (Tithonian Jeanne d Arc Formation) did not experience temperatures in excess of 130°C. 

The Devonian source shales, when compared with the Silurian, appear to be markedly less mature than the Silurian they have developed to the stage of a gas-and-conden-sate window only in certain locations of the area of their occurrence. This situation is most clearly observed in the Triassic Basin, where the Devonian thickness at depths greater than 3 km exceeds 1.0 km. Here the organic matter maturity in the Silurian and Devonian shales is markedly different. Indeed, in certain regions of the Devonian roof,... 

Determining the activation energy spectrum from Rock-Eval pyrolysis data is an inverse task of mathematical statistics having multiple solutions. Some problems are related to the restoration of chemical-kinetic parameters of effective reactions for organic matter maturation in source rocks. For example, reactions with activation energies of less than 50 Kcal moD do not contribute to the Rock-Eval pyrolysis Sj curve because these reactions can occur during the burial stage and would not contribute to S. ... 

Slow, continuous sedimentation during the period beginning in the Permian resulted in minimal variation in isotherm depths and in the depths of isolines (Fig. 6.17) in the Mereksen area. Our calculations of temperature and organic matter maturity in Ordovician, Silurian, and Devonian rocks at the close of the Carboniferous (approximately 288 Ma) are shown in Table 6.7. These calculations show that at the beginning of the Permian, organic matter in Ordovician and Silurian shales was in the lower part of the oil window (Fig. 6.17). 

Measured TOC ranges from 2 to 8% in the Middle Devonian shales, and from 1 to 5% in the Late Devonian shales, but with maximum decreasing concentrations westward from 1.5 to 5.0% in the Illizi Basin, 1.0 to 3.5% in the Mouydir basin, and 1.0 to 1.8% in the Timimoune basin. These variations are likely linked to changes in transport direction and in the provenances of detritus as compared to Silurian shales. The level of organic matter maturation in the Devonian sources in these basins is higher (Ro = 1-4%) than it is in the equivalent sources of the Triassic province (Oued el-Mya, Ghadames, and Trias basins) due to differing sedimentation, burial, and tectonic histories. 

Roksandic M. M. (1986) Dynamic interpretation of organic-matter maturation and evolution of oil-generative window discussion. Am. Assoc. Petrol. Geol. Bull. 70, 1008-1010. 

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