深层多途径复合生气模式及潜在成藏贡献

深层—超深层是当前和未来油气勘探的重要方向，明确高演化阶段天然气的生气途径、机制和潜力，将有助于发展天然气成因理论和指导深层油气勘探。结合大量模拟实验和动力学计算，探讨了不同母质和途径生气的成熟度和温度界限（生气时限）及贡献，建立了深层多途径复合生气模式。提出I/II型有机质或干酪根直接热降解（初次裂解）生气下限可延至R_O=3.5%，最大生气量可达120~140 m³/t_TOC，R_O>2.0%阶段的生气量可达20~40 m³/t_TOC。系统认识了原油全组分裂解动力学过程，提出在2 ℃/Ma地质升温速率条件下，液态烃大规模裂解的地质温度为190~220 ℃，对应的成熟度为R_O=2.0%~2.3%；源内残留烃和源外液态烃裂解生气贡献分别为约80 m³/t_TOC和200 m³/t_TOC，乙烷裂解温度要高于230 ℃。硫酸盐热化学还原作用（TSR）导致液态烃裂解温度降低20~40 ℃，加速高含硫化氢（H₂S）天然气藏的高效聚集；无机流体和矿物参与的加氢生气作用可提高天然气生成潜力20%~30%，是深层高—过成熟天然气生成的途径之一。多途径生气过程构成了天然气形成的完整演化序列，揭示在传统油气“死亡线”之下，深层—超深层仍具有天然气勘探潜力。

The multi-path gas generation model and its potential contribution to petroleum accumulation in deep formations

Deep to ultra-deep formations are important breakthroughs in oil and gas exploration at present and in the future. Understanding of the generation pathway， mechanism and potential of natural gas at high thermal maturation stages is beneficial to develop natural gas generation theory and to guide petroleum exploration in deep formations. Combined with extensive pyrolysis experiments and kinetic calculations， the maturity and temperature stages （gas generation time-limit） as well as potential of gas generation from various sources and pathways were discussed， and a multi-path gas generation model was established. The gas generation from thermal degradation of type I/II kerogens （kerogen primary cracking） can extend to R_O of 3.5% with the maximum yield of 120-140 m³/t_TOC， the potential of kerogen cracking gas at R_O>2.0% can reach 20-40 m³/t_TOC. The kinetics for the cracking of whole oil components were also addressed. It is proposed that intensive cracking of liquid hydrocarbons at a heating rate of 2 ℃/Ma mainly occurs at 190-220 ℃ with the corresponding maturity of R_O=2.0%-2.3%. The contributions of gas derived from thermal cracking of residual hydrocarbons in source rocks and hydrocarbons outside the source are ~80 m³/t_TOC and 200 m³/t_TOC， respectively. The onset temperature for ethane cracking is higher than 230 ℃. Thermochemical sulfate reduction （TSR） leads to a decrease of 20–40 ℃ in temperature for the occurrence of oil cracking， accelerating the efficient accumulation of natural gas with high content of hydrogen sulfide （H₂S）. Besides， gas generation via hydrogenation involving inorganic fluids and minerals promotes gas potential for about 20%-30%， and is one of the pathways for the generation of high-over mature gas in deep formations. The multi-path gas generation process constitutes an integrated evolution sequence of natural gas formation， revealing that there is large-scale gas exploration potential under the traditional “deadline” of oil and gas in deep to ultra-deep formations.