川东北凉高山组砂-页互层型储层可压性测井评价方法OA

The Lianggaoshan formation sand-shale interbedded shale oil reservoirs in the Pingchang area,northeastern Sichuan basin are abundant in oil and gas resources.However,such reservoirs feature developed sand-shale interbeds,complex lithologic associations,and strong differences in interlayer rock mechanical properties and in-situ stress,making the existing fracability evaluation methods ineffective in guiding the fracturing interval selection and process design.Based on triaxial rock compression tests,Brazilian disc tests,differential strain tests and other laboratory experiments,this paper systematically analyzes the characteristics of rock mechanical properties,brittleness index,differential coefficient of two horizontal principal stresses,and equivalentizes the reservoir as a vertical transverse isotropy(VTI)medium.A fracability evaluation index tailored to the sand-shale interbedded shale oil reservoirs in the study area is established using the support vector regression algorithm,and the production performances of intervals with different fracability levels are compared.The results show that:① The elastic modulus of the Lianggaoshan formation sand-shale interbedded shale oil reservoirs in the study area ranges from 10 to 35 GPa,and the Poisson's ratio ranges from 0.14 to 0.30.Both the elastic modulus and Poisson's ratio parallel to the bedding direction are larger than those perpendicular to the bedding direction,indicating significant anisotropy.The elastic modulus and Poisson's ratio perpendicular to the bedding direction are the dominant factors affecting reservoir fracability.② Sandstone intervals with low minimum horizontal principal stress and high differential coefficient of two horizontal principal stresses,as well as sand-shale transition zones adjacent to shale intervals,exhibit superior fracability.The large differential coefficient of two horizontal principal stresses strengthens the cross-layer propagation capacity of artificial fractures,which effectively connects the sand-shale interbeds.③ High tensile strength raises the initiation pressure for reservoir stimulation,prevents fracturing fluid leakage,reduces energy loss during fracture cross-layer propagation,and keeps fractures more prone to staying open during propagation after fracturing,which is conducive to the formation of stable flow conduction channels.④ Sandstone intervals and sand-shale transition zones with high brittleness index,large differential coefficient of two horizontal principal stresses,high tensile strength and low minimum horizontal principal stress present high fracability indexes,favorable fracturing effects and high oil and gas production rates.Case verification demonstrates that the established log-based fracability evaluation method accurately characterizes the propagation potential of hydraulic fractures,and is highly consistent with the fracturing monitoring data in the post-fracturing flowback and production stage.The research results provide a basis and guidance for the design of differentiated fracturing schemes and the optimization of fracturing intervals in the development of sand-shale interbedded shale oil reservoirs.