How micromechanical stratigraphy controls vertical primary oil migration in finely laminated shale

Petrographic and geomechanical analyses were integrated to document the micrometer-scale mechanical stratigraphic controls on primary oil migration in a finely laminated lacustrine oil shale. We identified systematic vertical microfracture networks filled with oil-bearing calcite veins, strongly partitioned by alternating micritic calcite, sparry calcite, and shale laminae that exhibit pronounced elastic contrasts. These contrasts primarily determine microfracture dip, intensity, aperture, and connectivity. Our results demonstrate that micromechanical stratigraphy fundamentally controls microfracture networks and vertical primary oil migration across laminae, offering new insights for microfracture prediction and oil migration assessment in low-permeability, mechanically heterogeneous shales.