Three-dimensional numerical simulation, energy efficiency and economic benefit estimation of oil shale in situ pyrolysis process

Oil shale in situ conversion processing by the downhole burner heating technology (DBHT) has been technically proven as a field pilot project in the Songliao Basin, Northeast China. In this study, the three-dimensional numerical simulations of oil shale in situ pyrolysis with the hexagonal well pattern were conducted based on the idea of DBHT and the actual oil shale reservoir in Songliao Basin to examine the temperature field and thermal processes. The effects of different well spacings (30, 35, 40, and 45 m), gas injection rates (5, 10, 15, and 20 m s−1), and fracture spacings (2.5 and 3.5 m) on the thermal evaluation process were analyzed. The relative energy efficiency and economic viability of operating an oil shale in situ retort in various cases were evaluated. The results showed that increasing well spacing could enlarge the thermal field and improve the ultimate hydrocarbon production of oil shale, but the excessive well spacing caused the heating time to be too long. An increase in the gas injection rate can significantly boost heat transmission efficiency. The energy efficiency comparison of various cases showed that smaller well spacing was conducive to making full use of energy. The results of economic efficiency estimation indicated that a high recovery of shale oil (>80%) would be very difficult to be made with economy, but optimal conditions can be developed in some cases, determined mainly by the price of shale oil. We anticipate that this study can provide new ideas for designing the oil shale in situ conversion processing.