威远、资阳震旦系干酪根与油裂解气的鉴别

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

Differences between Kerogen-and Oil-cracked Gases in Sinian Re servoirs of Weiyuan and Ziyang Area

By comparing nonhydrocarbon compositions，carbon isotope ratios of natural gases and reservoir inclusions in Weiyuan Area(W) and Ziyang Area(Z) and lower C ambrian black shale is the main sources of natural gas.Time of structure formati on is different between W and Z. The former is during Yanshanian orogeny and th e latter Indosinian Orogeny，but Z structure disappeared in Yanshanian Orogen y. So，natural gases for W are made up of oil and kerogen-cracked gases，but the latter is important. However，natural gases in Z are mainly made from oil- cracked gases. 　　C1/C+1 ratios of natural gases in W and Z are more than 99.62%，therefore ，natural gases are high and over-matured gases，and hydrocarbon gases of natu ral gases in Z are more abundant in high-yield wells than in low-yield ones．Contents of nitrogen gas in W Area is higher than 6% ，and less than 1.22% in hi gh-yield wells and higher than 4.17% in low-yield well in Z Area. C1/C1+ ，contents of hydrocarbon gases and nitrogen hold out that natural gases in W are high and over-matured，and nitrogen gas originate from high and over-m atured lower Cambrian black shale. Natural gases with high content of nitrogen a nd helium gases in W are mainly kerogen-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 con tent of helium and nitrogen gases. Natural gases in low-yield wells interfused by kerogen-cracked gases contain high content of helium and nitrogen gases. Me thane carbon isotope ratios are nearly 5‰ higher in W than in Z . Ro(%) ，based on δ13C1(‰)—Ro(%) formula， is 1% higher in W than in Z . Furthermore，natural gases in W are kerogen-cracked and those in Z are oil- cracked. 　　Homogeneous temperature(HT) of liquid hydrocarbon inclusions in W is in the ran ge of 80℃ and 160℃，and amount of liquid hydrocarbon inclusions is small. Homo geneous temperature of abundant gaseous hydrocarbon inclusions in W is in the ra nge of 200℃ and 240℃. Homogeneous temperature of hydrocarbon inclusions in Z is in the range of 80℃ and 248℃，and having liquid，gaseous，gaseous-liquid， liquid-gaseous，mainly liquid hydrocarbon inclusions. HT of liquid hydrocarbon inclusions is in the range of 80℃ and 160℃，and the rest are in the range of 150℃ and 248℃. Accumulated oil is small and biodegraded，and oil-cracked gase s in W are lack．Accumulated oil is large and oil-cracked gases in Z are abundant. 　　Differences of nitrogen and helium gas，methane carbon isotope ratios，HT and ph ase of hydrocarbon inclusions prove that natural gases originating from lower C ambrian black shale in W are kerogen-cracked，and those in Z are oil-cracked.