Oils produced from Wanggu-1 and Xinjiao-1 wells' Ordovician buried-hill reservoirs in the southern slope zone of Dongying depression are characterized by superhigh wax content(40%-60%)

and the wax contents of oils produced from Tertiary Kongdian Fm reservoirs in the same area are also relatively high(28.85%-31.7%).Chemical composition analysis and oil-source rock correlation of crude oils from different layers show that the origin of Ordovician high wax content oils in the study area is different from that in the overlying Tertiary Shahejie Fm.The former are derived from the deep source

as represented by the source rocks in Kongdian Fm.The latter are mianly sourced by the 4

th

member of Shahejie Fm within normal oil window.Absolute quantification of biomarkers shows that the bitumen contents of source rocks and waxy hydrocarbon contents of crude oils in this area increase with increasing maturity

indicating that thermal maturity is one of the major factors controlling the formation of highly waxy oils in this area.The Kongdian Fm source rocks of limnetic facies in Dongying depression contain relatively abundant terrigenous higher plants

which is another major factor causing the high wax content oils in this area.It is believed

based on comprehensive analysis

that the relatively high maturity and abundant parent materials capable of generating waxy hydrocarbons in the source rocks(the 2

nd

member of Kongdian Fm) are the major causes of the formation of high waxy oils in the southern slope zone of Dongying depression.Contrary to this

the influences of gas invasion and hydrocarbon migration fractionation are insignificant.