The study

the clay compaction concerned

based on the data of time-depth ralationship of acoustic wave transmission from nearly 50 walls inBiying depression proves that:1)There is usually a great difference ofclay compaction in different parts

of the same depression

and the oil andgas accumulation are closely associated only with the areas where both hy-drocarbon generation and primary migration occurred;2)The anomalouscompation section of the clay after the organic matter maturation may deter-mine the possible depth of primary migration in this area;3)The rapidlycompacted zones of the anomalous compaction secion seem to be the most fa-vourable intervals for the primary migration of the hydrocarbon;4)Thedepth

favourable to primary migration

has determined the main stage of theoil and gas accumulation;5)The highly compacted clay section may forma caprock which sealed by pressure and affect the depth of longitudinal dis-tribution of oil and gas accumulation.