Keywords: 
• Laiyang Depression /
• source rock /
• petroleum inclusion /
• primary migration of petroleum

Abstract: The dark mudstone in the Shuinan Section, Laiyang Formation of the Cretaceous age from the Laiyang Depression belongs to a type of fine source rock with dominant source matter of aglinite and amorphinite. With high magnification of microscopy, a lot of petroleum inclusions were found, which occur in the fissures of sand grains and authigenic minerals in the source rock. The petroleum inclusions have a narrow range of homogenization temperature of 78～82 ℃. Combined use of the geothermal evolution history of the Shuinan Section in the borehole LK2 and the trapping temperature of the petroleum inclusions, its formation time was deduced to be 74～77 Ma. According to the PVT simulation calculation, the trapping pressure of the petroleum inclusions was in the range of 305～307 bar. The occurrence of the petroleum inclusions has shown that the source rock underwent a deep burial and petroleum generation and expulsion before the uplifting of the Laiyang Depression in Tertiary, and the Shuinan section is the important source rock in this depression. This result has provided important information for further evaluation and exploration of this depression.