Product migration and regional reaction characteristics in the autothermic pyrolysis in-situ conversion process of low-permeability Huadian oil shale core

Product migration and regional reaction characteristics of low-permeability oil shale cores in the autothermic pyrolysis in-situ conversion have not been investigated. In this study, an in-situ autothermic pyrolysis simulation experiment was conducted using a pressed cylindrical Huadian oil shale core, and systematic geochemical analyses were performed at different regions of the core after the experiments. The results showed that a clear thin grey-white main channel was formed inside the low-permeability core from the gas injection end to the outlet end because of the uneven advancement of the autothermic reaction after the experiment. Moreover, the free hydrocarbon products mainly transported along the main channel towards the outlet end and formed a significant accumulation at the end of the core. In addition, according to the results of pyrolysis hydrocarbon and total organic carbon determination, the core was divided into four typical reaction zones: autothermic, cracking, preheating, and virgin, which were distributed sequentially outwards along both sides of the main channel. Finally, based on the above results and analysis, two construction strategies were suggested for the autothermic pyrolysis in-situ conversion process.