The Xushen gas field,located in the north of Songliao Basin,is a potential giant gas area for China in the future.Its proved reserves have exceeded 1000×10 8 m 3 by the end of 2005.But,the origin of natural gases...The Xushen gas field,located in the north of Songliao Basin,is a potential giant gas area for China in the future.Its proved reserves have exceeded 1000×10 8 m 3 by the end of 2005.But,the origin of natural gases from the deep strata is still in debating.Epimetamorphic rocks as a potential gas source are widely spreading in the northern basement of Songliao Basin.According to pyrolysis experiments for these rocks in the semi-confined system,gas production and geochemistry of alkane gases are discussed in this paper.The Carboniferous-Permian epimetamorphic rocks were heated from 300℃to 550℃,with temperature interval of 50℃.The gas production was quantified and measured for chemical and carbon isotopic compositions.Results show thatδ13C 1 is less than?20‰,carbon isotope trend of alkane gas isδ13C 1 <δ13C 2 <δ13C 3 orδ13C 1 <δ13C 2 >δ13C 3 ,these features suggest that the gas would be coal-type gas at high-over maturity,not be inorganic gas with reversal trend of gaseous alkanes (δ13C 1 >δ13C 2 >δ13C 3 ).These characteristics of carbon isotopes are similar with the natural gas from the basin basement,but disagree with gas from the Xingcheng reservoir.Thus,the mixing gases from the pyrolysis gas with coal-typed gases at high-over maturity or oil-typed gases do not cause the reversal trend of carbon isotopes.The gas generation intensity for epimetamorphic rocks is 3.0×10 8 ―23.8×10 8 m 3 /km 2 ,corresponding to Ro from 2.0%to 3.5%for organic matter.展开更多
Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid incl...Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid inclusions, and formation water, the fluid interaction mechanism and diagenetic reformation of fracture-pore basement reservoirs of epimetamorphic pyroclastic rock in the Beier Sag, Hailar Basin were studied. The results show that:(1) Two suites of reservoirs were developed in the basement, the weathering section and interior section, the interior section has a good reservoir zone reaching the standard of type I reservoir.(2) The secondary pores are formed by dissolution of carbonate minerals, feldspar, and tuff etc.(3) The diagenetic fluids include atmospheric freshwater, deep magmatic hydrothermal fluid, organic acids and hydrocarbon-bearing fluids.(4) The reservoir diagenetic reformation can be divided into four stages: initial consolidation, early supergene weathering-leaching, middle structural fracture-cementation-dissolution, and late organic acid-magmatic hydrothermal superimposed dissolution. Among them, the second and fourth stages are the stages for the formation of weathering crust and interior dissolution pore-cave reservoirs, respectively.展开更多
Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming ...Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming processes of Yinshan deposit. It is not sufficient to show the mobility only by the absolute abundance of trace elements changes before and after alteration. This can simply result from dilution or concentration if other elements are added to or removed from the rock. As shown by that in Yinshan deposit, less than 20% of the increment of RE was caused by the 'condensed' of leaching some of major elements (e.g. Si, Na) from the rock. The principal factor which should be responsible for the higher contents of RE in altered rock is the addition of RE into the rock by hydrothermal fluids. Eu is selectively leached from the altered sericite phyllite by a mild acidity and reducing fluid which is characterized by much lower LRE/HRE ratio and a large positive Eu anomaly. A major effect on the RE patterns is the tendency to develop relatively flatter chondrite-normalized patterns. The RE characteristics may be used to distinguish between small and large ore bodies at a later stage of exploration.展开更多
The Lengjiaxi and Banxi groups of the Meso-Neoproterozoic and the Lower Paleozoic along the profile at Huangtudian-Xianxi of the central-northern Hunan Province, China underwent very low-grade metamorphism. Illite cry...The Lengjiaxi and Banxi groups of the Meso-Neoproterozoic and the Lower Paleozoic along the profile at Huangtudian-Xianxi of the central-northern Hunan Province, China underwent very low-grade metamorphism. Illite crystallinity (IC) data of the <2 μm fractions range from 0.18-0.21°Δ2θ for the Lengjiaxi Group to 0.19–0.23°Δ2θ for the Banxi Group to 0.20–0.29°Δ2θ for the Sinian to the Lower Paleozoic (Kübler index, corrected with Kisch IC set, 1991). This indicates that the metamorphic grade of the Lengjiaxi Group is in the epizone, the Banxi Group in the epizone-high anchizone, and the Sinian to the Lower Paleozoic mostly in the high anchizone along the profile investigated. The peak metamorphic temperature evaluated is roughly 340–240°C. This result does not agree with the greenschist or subgreenschist facies of the Lengjiaxi and Banxi groups and neither with the lower-greenschist facies or diagenitic zone of the Sinian to the Lower Paleozoic, of which most previous researchers thought. The illites (K-mica) b 0 values range from 0.8989–0.9050 nm for the Lengjiaxi Group to 0.8984–0.9037 nm for the Banxi Group to the Lower Paleozoic. Based on the cumulative frequency curves of illite (K-mica) b 0, the peak metamorphic pressure of the Banxi Group to the Lower Paleozoic along the profile was derived in a low-intermediate pressure type. Illites occur as 2M1 polytype in the Lengjiaxi and Banxi groups and as 2M1+1 M types in some samples of the Lower Paleozoic. This indicates that the transformation of illite polytype from 1M to 2M1 was fulfilled within the high anchizone.展开更多
文摘The Xushen gas field,located in the north of Songliao Basin,is a potential giant gas area for China in the future.Its proved reserves have exceeded 1000×10 8 m 3 by the end of 2005.But,the origin of natural gases from the deep strata is still in debating.Epimetamorphic rocks as a potential gas source are widely spreading in the northern basement of Songliao Basin.According to pyrolysis experiments for these rocks in the semi-confined system,gas production and geochemistry of alkane gases are discussed in this paper.The Carboniferous-Permian epimetamorphic rocks were heated from 300℃to 550℃,with temperature interval of 50℃.The gas production was quantified and measured for chemical and carbon isotopic compositions.Results show thatδ13C 1 is less than?20‰,carbon isotope trend of alkane gas isδ13C 1 <δ13C 2 <δ13C 3 orδ13C 1 <δ13C 2 >δ13C 3 ,these features suggest that the gas would be coal-type gas at high-over maturity,not be inorganic gas with reversal trend of gaseous alkanes (δ13C 1 >δ13C 2 >δ13C 3 ).These characteristics of carbon isotopes are similar with the natural gas from the basin basement,but disagree with gas from the Xingcheng reservoir.Thus,the mixing gases from the pyrolysis gas with coal-typed gases at high-over maturity or oil-typed gases do not cause the reversal trend of carbon isotopes.The gas generation intensity for epimetamorphic rocks is 3.0×10 8 ―23.8×10 8 m 3 /km 2 ,corresponding to Ro from 2.0%to 3.5%for organic matter.
基金Supported by the PetroChina Science and Technology Project(2017-5307034-000002).
文摘Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid inclusions, and formation water, the fluid interaction mechanism and diagenetic reformation of fracture-pore basement reservoirs of epimetamorphic pyroclastic rock in the Beier Sag, Hailar Basin were studied. The results show that:(1) Two suites of reservoirs were developed in the basement, the weathering section and interior section, the interior section has a good reservoir zone reaching the standard of type I reservoir.(2) The secondary pores are formed by dissolution of carbonate minerals, feldspar, and tuff etc.(3) The diagenetic fluids include atmospheric freshwater, deep magmatic hydrothermal fluid, organic acids and hydrocarbon-bearing fluids.(4) The reservoir diagenetic reformation can be divided into four stages: initial consolidation, early supergene weathering-leaching, middle structural fracture-cementation-dissolution, and late organic acid-magmatic hydrothermal superimposed dissolution. Among them, the second and fourth stages are the stages for the formation of weathering crust and interior dissolution pore-cave reservoirs, respectively.
文摘Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming processes of Yinshan deposit. It is not sufficient to show the mobility only by the absolute abundance of trace elements changes before and after alteration. This can simply result from dilution or concentration if other elements are added to or removed from the rock. As shown by that in Yinshan deposit, less than 20% of the increment of RE was caused by the 'condensed' of leaching some of major elements (e.g. Si, Na) from the rock. The principal factor which should be responsible for the higher contents of RE in altered rock is the addition of RE into the rock by hydrothermal fluids. Eu is selectively leached from the altered sericite phyllite by a mild acidity and reducing fluid which is characterized by much lower LRE/HRE ratio and a large positive Eu anomaly. A major effect on the RE patterns is the tendency to develop relatively flatter chondrite-normalized patterns. The RE characteristics may be used to distinguish between small and large ore bodies at a later stage of exploration.
基金This work was suppored by the National Natural Science Foundaition of China(Grant No.49872033).
文摘The Lengjiaxi and Banxi groups of the Meso-Neoproterozoic and the Lower Paleozoic along the profile at Huangtudian-Xianxi of the central-northern Hunan Province, China underwent very low-grade metamorphism. Illite crystallinity (IC) data of the <2 μm fractions range from 0.18-0.21°Δ2θ for the Lengjiaxi Group to 0.19–0.23°Δ2θ for the Banxi Group to 0.20–0.29°Δ2θ for the Sinian to the Lower Paleozoic (Kübler index, corrected with Kisch IC set, 1991). This indicates that the metamorphic grade of the Lengjiaxi Group is in the epizone, the Banxi Group in the epizone-high anchizone, and the Sinian to the Lower Paleozoic mostly in the high anchizone along the profile investigated. The peak metamorphic temperature evaluated is roughly 340–240°C. This result does not agree with the greenschist or subgreenschist facies of the Lengjiaxi and Banxi groups and neither with the lower-greenschist facies or diagenitic zone of the Sinian to the Lower Paleozoic, of which most previous researchers thought. The illites (K-mica) b 0 values range from 0.8989–0.9050 nm for the Lengjiaxi Group to 0.8984–0.9037 nm for the Banxi Group to the Lower Paleozoic. Based on the cumulative frequency curves of illite (K-mica) b 0, the peak metamorphic pressure of the Banxi Group to the Lower Paleozoic along the profile was derived in a low-intermediate pressure type. Illites occur as 2M1 polytype in the Lengjiaxi and Banxi groups and as 2M1+1 M types in some samples of the Lower Paleozoic. This indicates that the transformation of illite polytype from 1M to 2M1 was fulfilled within the high anchizone.
