“…The two major types are etioporphyrin (ETIO, Figure a) and cycloalkanoporphyrins (CAPs, also referred to as deoxophylloerythroetioporphyrin (DPEP), Figure b−e), and among the CAP family, the most common one is the meso -β-cycloethanoporphyrin containing a five-membered exocyclic ring (DPEP-5, Figure b). Some other types with diverse carbon skeletons, such as tetrahydrobenzo-DPEP (Figure f), benzo (Figure g), and benzo-DPEP (Figure h), have also been identified in petroleum. − The ∑DPEP/∑ETIO porphyrin ratio is an important geochemical parameter, and many studies have indicated a close correlation between this ratio and the geochemical state of petroleum: with increasing maturity of petroleum, this ratio tends to decrease. − 1 Different types of petroporphyrins (M = VO 2+ or Ni 2+ ): (a) ETIO, (b−e) DPEP, (f) tetrahydrobenzo-DPEP, (g) benzo, and (h) benzo-DPEP.…”
Petroporphyrins were extracted from two typical Chinese heavy crude oils, Tahe and Du84, and then purified by silica gel chromatography, followed by demetallization by methyl sulfonic acid. The extraction and purification were monitored using ultraviolet-visible spectroscopy, and the final petroporphyrins were analyzed using laser desorption ionization time-of-flight mass spectrometry. The soft ionization mass spectrometric technique proved to be effective for the characterization of petroporphyrins. The results show that, in Tahe crude oil, vanadium is more abundant than nickel and 75% of the vanadyl porphyrins are of the etioporphyrin (ETIO) type, with remaining fractions attributed to deoxophylloerythroetioporphyrin (DPEP) and benzo types. The ∑DPEP/∑ETIO ratio was found to be 0.18. In contrast, the Du84 heavy crude oil contains more abundant nickel than vanadium, with its nickel porphyrins comprising mainly DPEP and ETIO types, with each occupying 45%, and the tetrahydrobenzo-DPEP and benzo types attributed to the remaining 10%. The ∑DPEP/∑ETIO ratio is ∼1.1. These results suggest that the Tahe crude oil has higher thermal maturity than the Du84 crude oil, and the former is in its mature stage, whereas the latter is in its evolution stage.
“…The two major types are etioporphyrin (ETIO, Figure a) and cycloalkanoporphyrins (CAPs, also referred to as deoxophylloerythroetioporphyrin (DPEP), Figure b−e), and among the CAP family, the most common one is the meso -β-cycloethanoporphyrin containing a five-membered exocyclic ring (DPEP-5, Figure b). Some other types with diverse carbon skeletons, such as tetrahydrobenzo-DPEP (Figure f), benzo (Figure g), and benzo-DPEP (Figure h), have also been identified in petroleum. − The ∑DPEP/∑ETIO porphyrin ratio is an important geochemical parameter, and many studies have indicated a close correlation between this ratio and the geochemical state of petroleum: with increasing maturity of petroleum, this ratio tends to decrease. − 1 Different types of petroporphyrins (M = VO 2+ or Ni 2+ ): (a) ETIO, (b−e) DPEP, (f) tetrahydrobenzo-DPEP, (g) benzo, and (h) benzo-DPEP.…”
Petroporphyrins were extracted from two typical Chinese heavy crude oils, Tahe and Du84, and then purified by silica gel chromatography, followed by demetallization by methyl sulfonic acid. The extraction and purification were monitored using ultraviolet-visible spectroscopy, and the final petroporphyrins were analyzed using laser desorption ionization time-of-flight mass spectrometry. The soft ionization mass spectrometric technique proved to be effective for the characterization of petroporphyrins. The results show that, in Tahe crude oil, vanadium is more abundant than nickel and 75% of the vanadyl porphyrins are of the etioporphyrin (ETIO) type, with remaining fractions attributed to deoxophylloerythroetioporphyrin (DPEP) and benzo types. The ∑DPEP/∑ETIO ratio was found to be 0.18. In contrast, the Du84 heavy crude oil contains more abundant nickel than vanadium, with its nickel porphyrins comprising mainly DPEP and ETIO types, with each occupying 45%, and the tetrahydrobenzo-DPEP and benzo types attributed to the remaining 10%. The ∑DPEP/∑ETIO ratio is ∼1.1. These results suggest that the Tahe crude oil has higher thermal maturity than the Du84 crude oil, and the former is in its mature stage, whereas the latter is in its evolution stage.
“…Oil exploration studies conducted in the Maracaibo Basin, northwest of Venezuela, have determined that La Luna Formation (Cenomanian-Coniacian) is the main source rock for most of the oil accumulated in reservoirs (1)(2)(3)(4). However, towards the southwest of the Maracaibo Basin, there are several oil fields with different geochemical characteristics as compared with those reported for La Luna Formation and which origin is not entirely defined, e.g., Los Manueles field.…”
Section: Introductionmentioning
confidence: 99%
“…Previous studies of these oils suggest their terrigenous origin (2,4,5), and might be considered a product of generation from single source rocks containing both marine and terrigenous organic matter or by the mixture of oils from two source rocks with different organic matter. Considering that La Luna Formation, the main source rock of the Maracaibo basin, is characterized by marine organic matter (1,2,3,6), the terrigenous components found in crude oils from Los Manueles suggest that a secondary source rock, associated with the Maracaibo basin, has also contributed to the generation of these oils (7). Located in the southwestern of the Maracaibo Basin is the hypothetical Orocué petroleum system, represented by a coaly source rock containing type III kerogen.…”
Seven crude oil samples from Los Manueles field, Maracaibo Basin, Venezuela, were analyzed to evaluate oil mixtures associated with different oil charges into the reservoirs. Analyses of the bulk physicochemical parameters suggest variations in the API gravity, the concentration of saturated and aromatic hydrocarbons, NSO compounds + asphaltenes, sulfur, vanadium, nickel, and the biomarkers distribution. The oils were divided in two groups: G-I with high saturated hydrocarbons and low NSO compounds + asphaltenes, sulfur, vanadium and nickel, a bimodal distribution of n-alkanes, high Pr/Ph and oleanane index, low steranes index, low abundance of tricyclic terpanes and C35S/C34S < 0.54 and G-II with low saturated hydrocarbons and high NSO compounds+ asphaltenes, sulfur, vanadium and nickel, an unimodal distribution of n-alkanes with low Pr/Ph and oleanane index, high steranes index, abundance of tricyclic terpanes and C35S/C34S > 0.70. G-I has a higher contribution of terrigenous organic matter compared to G-II, characterized by a higher contribution of marine organic matter. Source rock lithology biomarker indicators suggest marine shale as the source rock for oils of terrigenous origin. The results indicate that oils were generated by two independent source rocks, La Luna Formation and a secondary source rock with terrigenous organic matter, probably represented by the Capacho Formation.
“…Samples of La Luna from the vicinity of the ALP-6 core are thermally mature with regard to petroleum formation but generally do not exceed the oil window (Bockmulen et al, 1983;Talukdar et al, 1986;Gallango and Cassani, 1992).…”
Concentrations of organic carbon and selected major and trace elements are presented stratigraphically for a 100-m cored section of Cenomanian through Santonian calcareous black shales from the Maracaibo Basin, western Venezuela. Significant geochemical variation within these laminated, organic-rich marls suggests a five-part stratigraphic subdivision for the La Luna Formation in the Alpuf-6 (ALP-6) core recovered by Maraven, South America. Geochemical variation is interpreted to reflect the combined influences of relative sea level change, episodic volcanism, variations in the intensity of upwelling, and subtle geochemical alteration. High concentrations of organic carbon and trace metals in La Luna strata are inferred to result from (1) moderately high accumulation rates of organic matter resulting from pulsed high primary productivity, (2) recurrent episodes of widespread oxygen depletion that enhanced accumulation of both organic carbon and trace metals in localized areas, and (3) reduced terrigenous dilution of marine organic carbon and trace metals caused by high sea level and low rates of bulk sedimentation in pelagic settings.A refined biostratigraphic framework for the ALP-6 core allows calculation of accumulation rates for early-middle Turonian, late Turonian, Coniacian, and Santonian time intervals. Calculated accumulation rates of organic carbon and trace metals are highest during the late Turonian, when bulk sedimentation is highest. Concentrations of organic carbon are highest during the Coniacian, when bulk sedimentation rates are lowest. Calculated organic carbon accumulation rates for the La Luna in ALP-6 range from approximately 100 to 400 mg/cm 3 /k.y., similar to rates estimated for mid-Cretaceous strata from a number of other sites but approximately an order of magnitude lower than rates measured beneath modern upwelling zones. Relative to organic carbon and bulk sediment accumulation rates, the calculated accumulation rates of selected metals in La Luna strata are unusually high when compared with rates of metal accumulation in many modern Davis, C., Pratt, L.
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