Logging-Based Fracability Evaluation of Shale Oil Reservoirs in the Upper Cretaceous Qingshankou Formation, Central Daqing Placanticline, China

Fracability serves as the dominant factor governing the recoverable conditions of shale oil reservoirs. Based on logging data from the Cretaceous Qingshankou Formation in the central Daqing Placanticline, China, combined with core experimental data, correlation analysis, and the analytic hierarchy process (AHP) for weight calculation of fracability evaluation indices, this study establishes a fracability parameter interpretation model for the area. The calculation results are highly consistent with test and analytical data, featuring high accuracy and satisfying fracability evaluation demands. The results show that the Cretaceous Qingshankou Formation in the study area is characterized by a low–medium Young’s modulus, high Poisson’s ratio, high brittleness index, low stress difference, and a normal faulting stress regime. For the first member of the Qingshankou Formation, Young’s modulus ranges from 6.7 to 21.4 GPa, Poisson’s ratio from 0.26 to 0.41, brittleness index from 34.1 to 58.4%, stress difference from 1.67 to 2.41 MPa, and fracability index from 0.26 to 0.79. Class II fracability dominates the central region horizontally, with a small amount of Class I in the southeastern and western parts. Regarding the reservoirs in the second and third members of the Qingshankou Formation, Young’s modulus is 9.6–19.5 GPa, Poisson’s ratio is 0.31–0.39, the brittleness index is 39.5–50.3%, the stress difference is 1.76–2.28 MPa, and the fracability index is 0.39–0.77. Both Class I and II are well developed: Class I is mainly distributed horizontally in the western, southern and northeastern regions, while Class II shows a curvilinear zonal distribution in the central area.