Geochemical Feature of Low-Mature Crude Oil in Sub-Sag of Guanzhen in Subei Basin

The sub-sag of Guanzhen is located in middle part of Hongze sag in Yanfu depression,Subei basin. Its low-mature crude oil is characterized by the four highs and one physical properties: the middle-higher crude density,high viscosity,high solidification point,high paraffin content and low sulfur content. The oils in wells in this sub-sag are not subjected to biodegradation,with the typical low-mature oil feature of their group compositions,which are proved by low degree of the thermal evolution data of light hydrocarbons including sterane,low m(Pr)/m(Ph) and high m(Ph)/m(nC18) ratios. The m(Pr)/m(Ph) ratio indicates the crude is product from the reducting-strong reducting environment and dominated by sapropelic kerogen. The high paraffin content of crude oils is related to those that a part of humic kerogen formed oil in low-mature stage and botryococcane in saprogelic kerogen early formed oil.