Formation mechanism and structural characteristic of pore-networks in shale kerogen during in-situ conversion process

In-situ conversion process (ICP) appears to be a promising approach to enhance hydrocarbon recovery of shale reservoirs. During the ICP, the pore-networks gradually generate underground and serve as the conduits for the storage and transport of hydrocarbon, which finally decides the recovery ability of the reservoir. Reactive molecular dynamics simulations are used to study the pyrolysis behavior of kerogen under the reservoir conditions. The pyrolysis proceeds in four stages: energy accumulation, oil window, gas window, and steady stage. And during this process, the kerogen pyrolytic pore-networks form under the combined actions of chemical bond breaking and physical deformation. Further analysis demonstrates that the structural characteristic is dependent on the maturities of kerogen and pyrolysis temperature. Low-maturity kerogen creates high-quality pore-networks (∼15% porosity), while the pores in medium- and high-maturity kerogen are scarce and isolated (∼1% porosity). In the simulation, the optimal pyrolysis temperature of pyrolysis is about 2300 K to develop high-quality pore-networks. In addition, a conversion relationship between the simulation temperatures and ICP engineering temperatures is established using Arrhenius equations, and the optimal temperature for ICP engineering is suggested to be ∼730 K.