The invention discloses a method for determining a
hydrocarbon accumulation threshold of
hydrocarbon containing basin fragmentary rock. The method comprises the following steps: (1), establishing a
change model about how sandstone and mudstone change with embedded depth in a research zone; (2), establishing a relation model of sandstone and mudstone permeability and
porosity; (3), establishing a relation model of sandstone and mudstone hole radii, the
porosity and the permeability, and calculating the hole
radius values of sandstone and mudstone in different depth; (4), calculating a ratio of mudstone interface
potential energy to sandstone interface
potential energy, establishing a
change model about how the ratio changes with the embedded depth, and determining a maximum boundary and a minimum boundary when the ratio of the mudstone interface
potential energy to the sandstone interface potential energy is distributed along with the embedded depth; (5), calculating ratios of the mudstone interface potential energy to the sandstone interface potential energy about a
hydrocarbon layer and a dry layer in the research zone, and subjecting the ratios of the mudstone interface potential energy to the sandstone interface potential energy about the hydrocarbon layer and the dry layer in the research zone to the
change model established in step (4); (6), dividing a borderline about how the potential energy of the opposite interfaces of the hydrocarbon layer and the dry layer is distributed along with the embedded depth; and (7), sandstone
porosity corresponding to an intersection point between the borderline and the maximum boundary of the ratio of the mudstone interface potential energy to the sandstone interface potential energy being reservoir layer critical porosity corresponding to the hydrocarbon accumulation threshold of the research zone.