Study of Pyrolysis Kinetics of Asphaltenes in Silurian Oilsands in the Tarim Basin

It is a special petroleum geological phenomenon that Silurian oilsands are extensively distributed in the central and northeast Tarim basin. Some geochemical studies of the oilsands have been carried out, but there is still great controversy over the hydrocarbon-regenerating potential of oilsands and the possibility of Silurian oilsands as hydrocarbon source rocks. In this study, the kinetics of asphaltenes pyrolysis was directly used to simulate the potential of Silurian oilsands for regenerating hydrocarbons. According to the experimental results, combined with other related organic geochemical analysis, it is considered that Silurian oilsands in the Tarim basin have a high hydrocarbon-regenerating potential and are latent hydrocarbon source rocks.

Origin of natural sulphur-bearing immiscible inclusions and H_(2)S in oolite gas reservoir, Eastern Sichuan

Based on results of microscopic observation and laser Raman analysis about fluid in-clusions,multiple special forms of immiscible inclusions that contain sulphur,liquid hydrocarbon,bi-tumen,etc.were discovered in samples collected from the H_(2)S gas reservoir-containing carbonates in the Lower Triassic Feixianguan Formation in the Jinzhu-Luojia area,Kai County,Sichuan Province.Based on the lithology and burial history of the strata involved as well as measurement results of homogenization temperature of fluid inclusions,bitumen reflectivity,etc.,it is concluded that the H_(2)S in the gas reservoir resulted from the thermal reaction between hydrocarbons in reservoir and CaSO_(4)in the gypsum-bearing dolostone section at the high temperature(140℃―170℃)oil-cracked gas for-mation stage in Late Cretaceous.Thereafter,research on a great number of immiscible inclusions in the reservoir reveals that elemental sulphur resulted from oxidation of part of the earlier-formed H_(2)S and further reaction between sulphates,hydrocarbons and H_(2)S in geological fluids in H_(2)S-bearing gas reservoir at a temperature of 86℃―89℃and a pressure of 340×10^(5)Pa and during the regional uplift stage as characterized by temperature decrease and pressure decrease in Tertiary.Meanwhile,gyp-sum,anhydrite and calcite formed at this stage would trap particles like elemental sulphur and result in a variety of special forms of immiscible inclusions,and these inclusions would contain information concerning the complexity of the fluids in the reservoir and the origin of H_(2)S and natural sulphur in the gas reservoir.

Quantitative assessment of gas washing of oils in the Tazhong area of the Tarim Basin,Northwest China

Gas washing has been known in the Tazhong area of the Tarim Basin,but its quantitative assessment has not yet been reported.Here the influence of gas washing fractionation in the area was discussed based on the gas chromatogram data of 68 oils and the results of the mixing experiments of a black oil and a condensate.The results show that the intensity of gas washing fractionation decreased generally from northern to southern part and vertically from deep reservoirs to shallow reservoirs.The gas washing fractionation was mainly controlled by fault systems in this area,with the increase of n-alkane mass depletion positively correlated to the number and scale of faults.Gas washing fractionation appears to have affected the hydrocarbon property,and as a result the diversity of the crude oils is markedly controlled by gas washing.In addition,the occurrence of waxy oil in this area may be resulted from multiple factors including gas washing,mixed filling and migration fractionation.

The comparison of biomarkers released by hydropyrolysis and Soxhlet extraction from source rocks of different maturities

The Permian Dalong Formation(P2d) source rocks from the mature Guangyuan outcrop section and the overmature Wangcang outcrop section in Sichuan Basin were selected.The Soxhlet extraction and kerogen catalytic HyPy were conducted on the P2d source rocks.The biomarkers obtained by both methods were compared to discuss their difference and the influence extent of thermal maturation on covalently bound biomarkers.The results show that covalently bound biomarkers can hardly be correlated to the corresponding free biomarkers due to severe thermal alterations and/or interference of migrated hydrocarbons in both outcrop sections and thermal maturation have much lower influence on covalently bound biomarkers in kerogens than on free biomarkers in Soxhlet extracts.The application of HyPy in study of biomarker geochemistry can reduce the thermal maturation effect on biomarkers(Ro≤2.4%) to a greater extent and the interference of migrated hydrocarbons between interbedded layers.The covalently bound biomarkers released by HyPy are useful in the study of biomarker geochemistry and oil-source correlation on high-overmature source rocks.

Mass balance calculation of the pyrolysates generated from marine crude oil:A prediction model of oil cracking gas resources based on solid bitumen in reservoir

Oil cracking gas plays an important role in the resources of natural gas in the basins with high and over mature marine source rocks in China. The prediction of the oil cracking gas resources becomes nec-essary and urgent in the gas exploration in these basins. A marine crude oil sample was pyrolyzed using sealed gold tubes system. The pyrolysates including gas,liquid and solid were quantitatively analyzed. Based on the pyrolysis data and kinetic calculation,the yield correlativity among gas,liquid and solid products was regressed with high correlative coefficients to establish a prediction model suitable for the resource estimation of oil cracking gas. The verification formula for this model was also established on the principle of mass conservation. The affecting factors and the application precondi-tions of this prediction model were discussed. This model would enlighten and provide some new ideas for the resource assessment of natural gas in the high and over mature marine carbonate source rock areas in China. It is expected to be valuable in gas exploration.

Kinetic studies on the pyrolysis of asphaltenes from different types of kerogens

The pyrolysis kinetics of a series of asphaltenes, from different types of kerogens, are studied in this work. The results indicate that the distributions of activation energy are over a wide range for the asphaltenes from type I kerogens. There is still a large potential of hydrocarbon generation in case the activation energy is above 350 kJ·mol-1. While the distributions of activation energy are comparatively over a narrow range for the asphaltenes from type Ⅱ and Ⅲ kerogens, there is a little or almost no potential of hydrocarbon generation with the activation energy above 350 kJ· mol-1 respectively. For the asphaltenes from some specific type of kerogens, the pyrolysis kinetics can be applied to marking their maturity. Furthermore, based on detailed discussions of the kinetics parameter frequency factor, the asphaltenes from type I kerogens are considered to be of great potential to regenerate oils, while the asphaltenes’ potential for oil-to-gas conversion tends to go down in order of

Determination of carbon isotopic composition of individual light hydrocarbons evolved from pyrolysis of source rocks by using GC-IRMS

The carbon isotopic composition of individual light hydrocarbons generated from source rocks that had been pyrolysed in vacuum glass tube were determined by using the GC-IRMS techniques. The results indicate that abundant CO2 in the pyrolysates has a remarkable effect on the determination of CH4δ13C. Running cryogenically with an initial temperature of -40℃ can effectively eliminate the effect. In addition, it conduces to measuring the δ13C of C2+ hydrocarbons by increasing the injection volume and/or absorbing CO2 with the solution of sodium hydroxide. The above measures will help to get the carbon isotopic composition of C1-C7 components, which is of great significance for gas/source rock correlation and for study on the genesis of natural gas.