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To determine reliable molecular thermal maturity parameters for prediction of the physical properties of biodegraded oils, a suite of oils including 11 biodegraded oils from Caoqiao oilfield and 5 non-biodegraded oils from Wangjiagang oilfield in Dongying depression in Bohai-bay basin, eastern of China were analyzed. The oils were selected in a wide range of viscosity in order to investigate the relation between the parameters and oil properties. The data show the effects of biodegradation on some molecular thermal maturity parameters: C29 sterane parameters C2920S/(20S+20R) and C29ββ/(ββ+αα) increased apparently under heavy biodegradation (rank 6~7); parameters C3122S/(22S+22R), C3222S/(22S+22R), C293-methyl/C29 4-methyl, (C28+C29Tricyclics)/Ts and (C28+C29Tricyclics)/ (C28+C29Tricyclics +Ts) showed effects from heavy biodegradation (rank 6~7), and terpanes parameters Ts/(Ts+Tm), C29Ts/(C29Ts+C29Tm) and aromatic C20/(C28+C20), (C20+C21)/(C20+C21+C26+C27+C28) and D(3-6)/(D3-6+ C29 4-methylstigmastane 20R showed no effect from heavy biodegradation. Based on the comparison, the molecular maturity parameters C26 to C28 triaromatic parameters C26S/ (C26S+C28S), C27R/(C27R+C28R), C28/(C26+C27+C28) and tricyclic terpanes parameters C19/(C19+C23) were recommended to predict the physical properties of biodegraded oil for these parameters showed no effects from biodegradation(rank 6~7) and better relations with oil physical properties compared to other parameters. Some quantificational equations between these molecular thermal maturity parameters and the physical properties of biodegraded oils were inferred, which may assist in predicting the viscosity and API gravity of reservoired oils before production. |
