含膏层系低丰度烃源岩生烃潜力与气源对比：以川西坳陷雷口坡组为例

Natural gas exploration in the gypsum-bearing strata in China has achieved a continuous significant breakthrough in recent years, and the hydrocarbon potential of source rocks with low organic abundance and the source of H2S-bearing natural gas have caused wide concern. The applicants intend to conduct a case study of the Middle Triassic Leikoupo Formation in the Western Sichuan Depression. Both organic and inorganic geochemical methods will be taken to clarify the sedimentary environment of the gypsum-bearing source rocks with low organic abundance, and the reason of low TOC (total organic carbon) content will be revealed by the study on the original organic abundance. The applicants intend to conduct thermal simulation experiments on the hydrocarbon generation and expulsion of the kerogen with and without the gypsum, in order to clarify the hydrocarbon generation mechanism of gypsum-bearing source rocks with low organic abundance and the controlling of the gypsum, and further to comprehensively evaluate the original hydrocarbon potential of the gypsum-bearing source rocks in the Leikoupo Formation. Based on the synthetic analysis of the geochemical characteristics of natural gas, formation water, oil seepage and source rocks, the generation mechanism of H2S-bearing natural gas will be identified and the gas-source correlation will be carried out. In combination with mixed-source simulation calculation, the applicants further intend to determine the main source of H2S-bearing natural gas and the relative contribution of different sets of source rocks especially the gypsum-bearing source rocks in the Leikoupo Formation. This study will not only strengthen and enrich the understanding of the hydrocarbon generation mechanism of marine source rocks in gypsum-bearing strata, but also provide scientific proofs for revealing the generation mechanism, the accumulation process and enrichment regulation of natural gas in marine gypsum-bearing strata. It also has positive significance on the expansion of deep oil and gas exploration.

近年来含膏层系天然气勘探不断取得重要突破，其低丰度烃源岩的生烃潜力和含H2S天然气的来源引起了广泛关注。本项目拟以川西坳陷中三叠统雷口坡组为例，通过有机和无机地球化学手段，阐述含膏盐岩低丰度烃源岩沉积环境，并通过原始有机质丰度的研究，分析有机碳含量普遍较低的原因；通过对加膏盐和不加膏盐条件下干酪根生排烃热模拟实验，揭示含膏低丰度烃源岩的生烃机制和膏盐岩对其控制作用，进而对雷口坡组含膏烃源岩的原始生烃潜力进行综合评价；通过对天然气、地层水、油苗及烃源岩地化特征的综合分析，揭示含H2S天然气形成机理，开展气源对比，并通过混源模拟计算，确定雷口坡组含H2S天然气的主力气源和不同烃源岩特别是雷口坡组烃源岩的相对贡献。本次研究不仅可以加强和丰富对海相含膏盐岩层系烃源岩生烃机理的认识，而且可以为揭示海相含膏盐岩层系天然气形成机制、成藏过程和富集规律提供科学依据，对拓展深层油气勘探领域也有积极的意义。

四川盆地川西坳陷中三叠统雷口坡组发育含膏碳酸盐岩，近年来该层系的天然气勘探不断取得重要突破，但在该层系碳酸盐岩烃源岩的生烃潜力和含硫化氢天然气的来源方面认识存在分歧。本项目主要研究内容包括：（1）雷口坡组含膏层系烃源岩生烃潜力及烃源岩有效性；（2）川西坳陷雷口坡组天然气成因鉴别和气源对比；（3）雷口坡组储层沥青特征对天然气来源的指示及与阆中灯影组沥青对比；（4）川西须家河组与雷口坡组天然气对比；（5）川西雷口坡组气藏动态成藏过程；（6）四川盆地雷口坡组天然气来源及勘探方向。通过本项目研究取得的重要结果包括：（1）川西坳陷雷口坡组碳酸盐岩整体上有机质丰度偏低，其中含膏碳酸盐岩相对较为有利，具有一定生烃能力，但整体生烃潜力较为有限。（2）川西雷口坡组天然气为原油二次裂解气，主要为龙潭组生成的原油后期发生裂解并直接充注形成，雷口坡组烃源岩也有少量贡献。（3）雷口坡组中少量的储层沥青为雷口坡组自身碳酸盐岩烃源岩生成的原油后期发生裂解所形成，气藏主体并非由雷口坡组古油藏原位裂解而来。（4）川西坳陷成都气田侏罗系天然气为典型煤成气，而川西须二段天然气主体为混合成因，与雷口坡组天然气有明显差异。（5）雷口坡组经历了三叠纪末—侏罗纪古油藏形成和原油裂解、侏罗纪油气共存期、白垩纪以来的气藏调整定型期这三个演化阶段。（6）四川盆地不同地区雷口坡组天然气在成因和来源及源储组合方面具有差异。关键数据主要是川西坳陷雷口坡组天然气的组分和碳氢同位素等数据。所开展相关研究的科学意义主要是明确了川西坳陷雷口坡组含膏碳酸盐岩的生烃潜力，揭示了雷口坡组含硫化氢天然气的成因和来源及聚集成藏过程。相关认识可以为四川盆地雷口坡组含膏层系天然气勘探提供较为可靠的气源认识，为勘探领域的拓展提供科学依据，同时也丰富了海相烃源岩评价和天然气成因鉴别与气源对比的研究内涵，为相关手段的拓展应用和推广提供了较好的借鉴。