INVESTIGATION ON THE GEOMECHANICAL CHARACTERISTICS AND THE HYDRAULIC FRACTURING PROCESSES OF THE LUCAOGOU SHALE OIL RESERVOIRS

The Lucaogou shale oil reservoir in the Jimusar Depression is a typical continental shale oil reservoir in China. The reservoir presents a typical thin interlayer feature with rapid changes in lithofacies and strong heterogeneities,resulting in difficult reservoir stimulations. In particular,the heterogeneities of mechanical parameters of the Lucaogou Formation reservoir and its impact on hydraulic fractures should be further studied. In this paper,high-density sampling and mechanical testing on drilling core samples of the Lucaogou Formation are conducted. The heterogeneities of mechanical parameters are revealed,and the heterogeneities of the mechanical parameters on the evolution processes of hydraulic fractures are investigated. The results show that:(1)the mechanical parameters of the Lucaogou Formation are vertically highly heterogeneous,presenting obvious thin interlayers; (2)the variation of the in-situ stress and the breakdown pressure of the Lucaogou Formation are dramatic,which may affects the cross-layer propagation of hydraulic fractures; and (3)the heterogeneities of mechanical parameters greatly influences the vertical expansion of hydraulic fractures. Increasing the injection rate and the viscosity of fracturing fluids can effectively promote the cross-layer expansion of hydraulic fractures. This study provides an important theoretical basis for the effective development of the Lucaogou shale oil reservoir,and the results can help optimize the fracturing technologies of the Lucaogou formation.