Abstract The heterogeneity of siliciclastic carrier beds is characterized by the compartmentalization of low permeability interbeds. A geologic and fluid dynamic model of siliciclastic carrier beds with architectural heterogeneity was constructed to numerically simulate and analyze the characteristics of oil and gas migration and accumulation. The formation and distribution of hydrocarbon migration pathways and eventual accumulations are strongly heterogeneous, forming a pattern that is significantly different from those in macroscopically homogeneous models. In carrier beds with architectural heterogeneity, hydrocarbons generally migrate upward and in the updip direction. However, the vertical migration pathways are commonly blocked and deviated by low-permeability barriers, so that lateral migration pathways and local accumulations can occur in any part of the carrier beds. The updip structural traps are still the favorable target of migration, but hydrocarbons can accumulate anywhere as small pools along the pathways from the source to trap. Although the volume of individual pools is small, the pools are numerous and widely distributed. Thus, the total amount of accumulation can be much greater than that in the structural trap. The simulation results of hydrocarbon migration pathways and accumulation in architecturally heterogeneous carrier beds improve our understanding of the hydrocarbon migration and accumulation processes and shed new light on the relationship between reservoir, seal, and trap. The spectrum of exploration targets should be expanded to include those along migration pathways.