Keywords: 
• Zhu Ⅲ Depression /
• diagenesis /
• hydrocarbon accumulation /
• clay mineral /
• organic inclusion

Abstract: The diagenesis and hydrocarbon accumulation w as studied by ways of petrology.mineralogy, X-ray diffraction analysis, organic inclusion and geochemistry in Zhu ⅢDepression, Pearl River Mouth Basin.It is suggested that the diagenetic stages are the early diagenesis and subphase A, B of late diagenesis.There aer different diagenetic history and genetic mechanism of secondary po re development zone in two major source sags of the depression.The hy drocarbon distribution is correlated w ith the illite/ smectite mixed layer clay min- eral conversion zone.The hydrocarbon accumulation of w enchang A Sag is in the fi rst and second clay mineral conversion zone, and over the first clay mineral conversion zone in Wenchang B Sag.The organic inclusions w ere formed in the diagenetic process.which contained rich information suchas the generation, evolution and mig ration of oil/ gas as well as reservoi r and so on.By studying the organic inclusions in Zhu Ⅲ Depression, it w as learned about the ty pe, distribution, homogenization temperature, the number of times oil/ gas mig ration and composition in the inclusions as well as the o rganic inclusion is correlated w ith the diagenesis. There are tw o migrations of oil and g as in Wenchand A Sag.The second time is the main period of oil and gas mig ration . There is only one peak of oil and gas mig ration in Wenchang B Sag.The secondary quartz in the sandstone from Zhuhai Fo rmation controls the hydrocarbon accumulatio n.