The study of the mechanical properties of formation rocks is the basis for evaluating wellbore stability and ensuring safe drilling operations. To explore the mechanical properties of rocks in the Paleogene and paleo- buried hill strata of the Huizhou Depression, the Pearl River Mouth Basin. This study conducted a comprehensive analysis of the mineral and clay content of the core rock samples taken from the formation, as well as mechanical properties experiments before and after immersion in the drilling fluid. The mechanical properties parameters and creep models of the rocks in the Paleogene and paleo- buried hill strata were obtained. By analyzing the energy evolution characteristics, the elastic—plastic characteristics of rocks were quantified, and recommendations for safe drilling operations in formations were proposed. The research results show that the quartz, potassium feldspar, and clay content of the Enping Formation each account for about 30%, while the quartz content of the Wenchang Formation accounts for about 60%. The buried hill weathering zone contains almost no clay minerals, and the content of inner buried hill is as high as 54. 69%. The uniaxial compressive strength of the Paleogene and paleo- buried hill strata is relatively low, generally ranging from 30. 20 to 48. 76 MPa. After soaking, the uniaxial compressive strength of the Enping Formation, Wenchang Formation, and inner buried hill decreased by 27. 55%, 26. 82%, and 31. 60%, respectively. The overall strength of the buried hill weathering zone is higher than that of other strata, with a larger internal friction angle and lower cohesion in the rock core. The creep curves of rock cores in various layers all exhibit attenuation creep characteristics, and the creep of the buried hill weathering zone is significantly smaller than that of other layers. The Paleogene and inner buried hill strata should ensure a safe drilling cycle and should not be operated for long periods. The drilling fluid density should be appropriately increased, and reverse sliding hole operations should be carried out on time to prevent drilling tool blockage. This study will help to solve the problem of unclear understanding of the mechanical characteristics of the lower strata in the Huizhou Depression and contribute to the safe and efficient evaluation of regional strata and drilling work.