Data-driven elastic modeling of organic-rich marl during maturation

The elastic modeling of source-rock reservoirs during maturation must incorporate microstructural and geochemical alterations. The common challenge is calibrating the volumetric proportion between each form of organic porosity along with the changes in the bulk and shear moduli of kerogen as a function of maturity. Two forms of organic porosity have generally been observed: (1) spongy and bubble pores inside kerogen and (2) low-aspect-ratio pores or gaps at the interface between shrinking kerogen bodies and the matrix. We have constructed a rock-physics model of organic-rich marl during maturation and calibrated it using rock-physics data sets from controlled pyrolysis experiments of organic-rich marl under stress. We chose these pyrolysis data because the samples provide subsequent changes in porosity and P- and S-wave velocities as a function of maturity, while evidencing minimal grain sliding and mechanical compaction due to their stiff matrix. Our calibration results indicate that spongy and bubble pores should be used as the predominant form in the model regardless of maturity. Our results also indicate a competing effect between increasing kerogen porosity and the increasing moduli of solid kerogen. Kerogen porosity mainly develops throughout the oil windows. Whereas the moduli of solid kerogen increase by a factor of two in the early-peak oil window and remain relatively constant afterward. Consequently, the effective moduli of kerogen experience minimal changes in the early-peak oil window and rapidly decrease to half of the immature values in the late oil window. These calibration results are consistent with several petrophysical and nanoindentation studies on kerogen. Finally, we used the calibrated model to build a rock-physics template of organic-rich marl during maturation. The template was tested with pyrolyzed and naturally matured samples, which showed that our model can be used to characterize reservoir properties across different maturity windows.

The effect of catagenetic maturity on the formation of reservoirs with organic porosity in the Bazhenov formation and peculiarities of their extension

Results of Bazhenov formation deposits organic matter complex investigations to assess its oil generation potential and maturity are presented. Researches were performed by Rock-Eval pyrolysis, rock structure analysis using scanning electron microscopy and organic matter transformation and distribution in the bulk of rocks using luminescent microscopy. As a result of the research, the general pattern for the Bazhenov formation kerogen thermal maturity variability along Western Siberia was confirmed, and the high maturity areas delimitation around the Salym high and the Krasnoleninsky arch was significantly specified. The areas of anomalously high maturity are not related to regional patterns of sedimentation. The possible influence of thermal maturity on the unconventional reservoirs with kerogen porosity formation in the Bazhenov formation and the features of their distribution were established. High thermal maturity that refers to the end of oil window is one of the main condition for the Bazhenov formation oil capacity formation, but knowledge of maturity change through the area pattern is not a sufficient condition for unconventional reservoirs including that with kerogen porosity retrieval.

Criteria of distribution of Bazhenov’s high-carbon formation oil-productive rocks with advanced kerogen porosity

The analysis of Bazhenov high-carbon formation organic matter catagenesis zonal distribution in connection with its own reservoir’s organic matter porosity made in this work. Realized research helped to articulate regional prospecting criteria for oil deposits in Bazhenov’s formation unconventional reservoir with organic porosity.

Geochemical conditions of hydrocarbon accumulation in low-permeability shale sequences

The report is devoted to the study of conditions for the formation of organic porosity–void spaces of organic origin formed during transformation of the organic matter into hydrocarbons, and their role in the formation of hydrocarbon accumulation in low-permeability shale strata. The experience of studying and developing known shale formations of the world testifies to the fact that such strata are hybrid phenomena, that is, they are both oiland gas-bearing strata containing traditional and non-traditional accumulations of hydrocarbons. Based on the results of the programmed pyrolysis by the Rock-Eval-6 method, an estimate has been performed to quantify organic (kerogen) porosity. This estimate allows for determining the forecast retention volume of HCs generated during catagenesis.

Effect of thermal maturity on elastic properties of kerogen

We have performed spatially continuous nanodynamic mechanical analysis on four organic-rich shale samples with different thermal maturities to extract the elastic modulus of the kerogen particles. Aliquots were rigorously prepared, and three scans were acquired from each aliquot. Subcritical nitrogen adsorption pore characterization was performed to determine the abundance of kerogen-hosted porosity. To fully characterize the pore system of samples from the oil window, toluene and then chloroform extraction were performed to remove the pore-filling hydrocarbons prior to nitrogen adsorption. The statistical distribution of the measured modulus values was analyzed to extract the properties of the shale particles. In mature samples from the peak oil generation or gas window, the kerogen porosity was the dominant pore morphology. We found that significant lowering of the kerogen particle modulus resulted from intraparticle kerogen porosity. The kerogen particle modulus in mature samples was measured as being lower (7–12 GPa) than the immature sample (15–20 GPa) due to gas- or bitumen-filled pores.