Differences between Kerogen-and Oil-cracked Gases in Sinian Reservoirs of Weiyuan and Ziyang Area
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摘要: 根据威远、资阳震旦系气藏天然气组成、天然气碳同位素特征、储层包裹体的对比研究认为威远气田震旦系气藏的天然气主要来源于下寒武统泥岩。由于威远、资阳构造形成时间差异,威远为燕山期形成的构造,资阳为印支期形成,燕山消失,因此天然气的捕获时期不同,导致威远天然气主要是干酪根裂解气,次为油裂解气;而资阳主要是油裂解气Abstract: Bv comparing nonhvdrocarhon compositions carbon isotope ratios of natural gases and reservoir inclusions in Wcivuan Areas( W ) and Zivang Areas( Z ) and lower Cambrian black shale is the main sources of natural gas.Time of structure formation is different between W and Z.The former is during Yanshanian orogcny and the latter Indosinian Orogcny, but Z structurc disappeared in Yanshanian Orogcny.So, natural gases for W arc made up of oil and kcrogcn-cracked gases, but the latto is important.However natural gases in Z are mainly made from oil-cracked gases. C1 / C1+ ratios of natural gases in W and Z are more than 99.62 %,therefore natural gases arc high and over-matured gases, and hydrocarbon gases of natural gases in Z are more abundant in high-yield wells than in low-yield ones.Contents of nitrogen gas in W Arca is higher than 6%,and less than 1.22% in high-yield wells and higher than 4.17 % in low-yield well in Z Arca. C1/C1+,contents of hydrocarbon gases and nitrogen hold out that natural gases in W are high and over-ma- turgid, and nitrogen gas originate from high and over-matured lower Cambrian black shale.Natural gases with high content of nitrogen and helium gases in W are mainly kcrogcn-cracked.Natural gases in high-yield wells in Z are oil-cracked.Because content of radioactive element and nitrogen in oil are much lower than in source rock oil-cracked gases must contain low content of helium and nitrogen gases.Natural gases in low-yield wells intcrfuscd by kcrogcn-cracked gases contain high con- tent of helium and nitrogen gases.Methane carbon isotope ratios are nearly 5‰ higher in W than in Z.Ra(%),based on δ13C1(‰)-Ra(%) formula, is 1% higher in W than in Z.Furthermore natural gases in W arc kcrogcn-cracked and those in Z are oil-cracked. Homogeneous temperatures( HT) of liquid hydrocarbon inclusions in W is in the range of 80℃ and 160℃,and amount of liquid hydrocarbon inclusions is small.Homogeneous temperature of abundant gaseous hydrocarbon inclusions in Wis in the range of 200℃ and 240℃.Homogeneous temperature of hydrocarbon inclusions in Z is in the range of 80℃ and 248℃,and having licquid, gaseous gaseous- liquid liquid-gaseous mainly liquid hydrocarbon inclusions.HT of liquid hvdrocarbon inclusions is in the range of 80℃ and 160℃,and the rest are in the range of 1500C and 2480C.Accumulated oil is small and hiodegraded, and oil-cracked gases in W are lack.Accumulated oil is large and oil-cracked gases in Z are ahundant. Differences of nitrogen and helium gas, methane carbon isotope ratios, HT and phase of hvdrocarhon inclusions prove that natural gases originating from lower Cambrian black shale in W are kerogen-cracked and those in Z are oil-cracked.
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