Abstract: In view of the insufficient understanding of rock mechanical properties and energy evolution characteristics of different shale lithofacies in the marine-continental transition facies, a series of experimental studies were carried out with the downhole rock samples from the Shan₂³ sub-member of the Permian Shanxi Formation in the eastern margin of the Ordos Basin as the study object. The result shows: The mechanical properties of different shale facies are quite different. Under the uniaxial compression test, the average compressive strengths of the siliceous shale facies and clay shale facies are 58.5 and 17.9 MPa, respectively. Under the condition of uniaxial compression, different shale lithofacies have strong brittleness and split failure, with the increase of confining pressure, the plasticity increases and transforms into shear failure, and the siliceous shale facies is the most severely damaged. The energy parameters of different shale lithofacies at the peak strength point are quite different and are affected by the confining pressure to different degrees. The average total energy of siliceous shale facies, clay shale facies and mixed shale facies under uniaxial compression is 0.071, 0.016 and 0.044 J/cm³, respectively. The research results have certain reference significance for the study of wellbore stability and fracturing optimization of marine-continental transition shale reservoirs.

Key words: marine-continental transition facies, Shan₂³ sub-member of Shanxi Formation, shale, rock mechanical properties, energy evolution characteristics