Geochemical Characteristics for Petroporphyrins from Liaohe Basin

In the past the studies on the "petroporphyrins" usually deal with single samples or several non-related single samples, few attention had been payed to suites of samples from the same reservoir-system or co-generic oils from the same basin, but only systematic study can reveal the true maturational progress of these biomarkers. In order to study geochemical characteristics of petroporphyrins, 19 samples of crude oils and source rocks from western Liaohe Basin have been systematically investigated (See Table). 1. Formation of rock-porphyrins in the Paleogene from western Liaohe Basin had undergone four stages.Contents of porphyrins are less than Ippm in the first stage (less than 1800m) and increased rapidly during stage two (1800-2350m), decreased quickly in the third sta (2350-2800m), and little in stage four (more than 2800m) (See Fig.2). Changes of rock-porphyrins contents with burial depth coincident with the changes of total hydrocarbons conternts in profile. The best porphyrins-generating zone occurs in 1800-2800m and as the same with of total hydrocarbons generation ( See Fig. 1).It provided that porphyrin is an effective geochemical index during low maturity of petroleum. 2.Demetallized porphyrins in the crude oil of S4 section from Gaosheng 1-6-14 well include DPEP (M-l) series (72.4%) and Rhodo-ETIO (M-l) series (27.6%) (See Fig.4).In the crude oil of S3 section from Gaosbeng 3- 7- 9 well, demetallized porphyrins are Rhodo-DPEP ( 30. 8% ), Rhodo-ETIO (20%), Rhodo-Di-DPEP (13.1%), Di-DPEP (16.3%), DPEP (12.6%) and ETIO (7.2%) (See fig.5), Correlation of oil and oil indicated that the crued oils from Gaosheng 1-6-14 and 3-7-9 wells probably come from different oil-source area, and the maturity of the former maybe higher than the latter. GC of saturated hydrocarbons of three samples in the area confirmed that the maturity of crude oil and source rock from S3 section of Gao-3 fault block was obviously lower than the crude oil from S4 section of Gao-1 fault block. (See Fig.3 and 6). 3.The case is rare at home and abrood that porphyrins are dominated by Rhodo-prphyrins as occured in crude oil of Gaosheng 3-7-9 well.This feature is similar to that of low-maturity consistent oil formd in fresh water deposit. 4.By the comparisons of metalloporphyrins in the source rock from Dujiatai oil field with the crude oils from Gaosheng oil field, it is suggested that the source rock of Du-65 well contains a little VO-ETIO series and VO-rhodo-DPEP series ( See Fig. 8) besides Ni- porphyrins. It indicated the difference of hydrocarbons source rocks between Dujiatai and Gaosheng oil field.