Experimental study on the effects of steam temperature on the pore-fracture evolution of oil shale exposed to the convection heating

Abstract

In the convection heating technology for shale oil recovery, steam is used as a transmission medium to pyrolyze oil shale. An experiment was designed to pyrolyze oil shale via steam injection in a large reactor. The samples of oil shale and semi-coke were obtained at different pyrolysis temperatures, and the pore-fracture structure of the samples was studied. The results showed that the average pore diameter and median pore diameter increased by about 10 times when the steam temperature increased from 314 °C to 555 °C. After completion of the steam pyrolysis, we observed that the internal fractures of oil shale were mainly microfractures. At the pyrolysis temperature of 555 °C, the number of microfractures in oil shale was more than 50 times compared with those observed at normal temperature. The micro-CT results indicated that the porosity of oil shale reached 15% after pyrolysis with high-temperature steam. At this porosity, the oil content of samples after pyrolysis was 0.05–0.22%, and the internal organic matter was completely pyrolyzed. Finally, the bedding planes of rock mass exhibited significant ruptures when the oil shale was pyrolyzed with high-temperature steam, thus providing proper channels for steam injection and flows of oil and gas.