Macropores generation in the domanic formation shales: Insights from pyrolysis experiments

Investigations of structural changes of the pore space induced by pyrolysis (540 °C; nitrogen flow) on the Domanic shale rocks (South-Tatarian arch of the Volga-Ural oil and gas basin, Russia). Porosity changes were studied by computer tomography measurements before and after heating. The results show that the initial rock matrix structure and organic matter content (TOC) are the main factors to control structural variations of pores, new pores formation and changes in the estimated pore connectivity. Three different pore types formed in the result of artificial thermal maturation were identified: (1) intergranular pores, (2) fractures and (3) lenticular shaped pores. Whereas intergranular pores and (micro-) fractures were dominant for samples with TOC ranging from 0.5 wt% to 20 wt%, TOC content upper than 20 wt% led to the onset of lenticular shaped pores. No correlation was found between the identified pore types and the mineral composition for the investigated samples. The study of the organic matter formation and the pore space transformation processes in the Domanic formation rocks is the key to understanding the mechanisms of oil and gas generation and determining the optimal ways of their industrial development.