Analysis of Effective Pyrolysis Zone and Heat Loss in Oil Shale Reservoir with Random Fractures.

Given the unclear variation law of the effective pyrolysis zone in the process of in situ heat injection mining of oil shale, the actual pyrolysis effect cannot be accurately judged. In this paper, considering the influence of two different random fractures, the thermal-fluid-solid coupling mechanical model of oil shale in situ heat injection mining is established. The effective pyrolysis zone, steam injection pressure, and temperature-affected zone of the roof and floor rocks in the process of in situ heat injection mining of oil shale are analyzed. The results showed that interconnected and high-density fractures are important channels for superheated steam seepage, which is conducive to the efficient penetration of superheated steam in oil shale reservoirs. There are multiple pyrolysis paths in oil shale reservoirs in bedding fractures, while oil shale reservoirs in hydraulic fractures are uniformly pyrolyzed by a high-temperature network formed by superheated steam. When the bedding fracture model and the hydraulic fracture model are injected with heat for 233 and 90 days, the oil shale reservoir reaches the effective pyrolysis temperature, and the pyrolysis efficiency of the hydraulic fracture network is 2.59 times that of the bedding fracture network. The average temperature of the affected area of the overlying and overlying strata is 471.98 and 467.02 °C, respectively. When in situ heat injection mining of oil shale is carried out, it is necessary to adjust the heat injection time reasonably and keep the hydraulic fracture away from the upper and lower boundaries of the oil shale reservoir to avoid the heat dissipation of superheated steam.