47th Annual AAPG-SPE Eastern Section Joint Meeting

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Organic Matter Deformation in Overmature Mudrocks


Pores within organic matter (OM) are strongly linked to hydrocarbon generation and primary migration in fine-grained source rocks and are very important for evaluating hydrocarbon storage and flow in shale reservoirs. Under overmature stage, abundant pores are formed within the OM. The porous and ductile OM should be deformed when the original equilibrium of stress condition is altered. OM deformation at the nano- or micro-scale has rarely been discussed due to the lack of associated evidence. This research documents evidence of OM deformation observed in scanning electron microscope (SEM) images of seven overmature samples from the Longmaxi Shale, Sichuan Basin. Deformation processes of OM- hosted pores were qualitatively analyzed with assumptions. To further discuss the features of OM deformation and its effect on OM-hosted pores, the OM deformation is classified into three types (I, II and III) according to the amount of additional forces, and deformation sub-types are recognized according to the contact area of OM particles and mineral grains along which the additional force applied to the OM and overlapping of displacement fields. Two OM particles subjected to Type I deformation were analyzed quantitatively for such parameters as pore size, geometry, and orientation of long axes of elliptical pores. The reduction of OM-hosted pore volume, specific surface area and organic porosity was calculated using the two OM particles suffering from Type I deformation.