石油学报 ›› 2020, Vol. 41 ›› Issue (4): 433-445.DOI: 10.7623/syxb202004006

• 地质勘探 • 上一篇    下一篇

四川盆地西北部中二叠统海相混合型烃源岩的证据及对双鱼石大气藏的成藏贡献

高国辉1, 曹剑1, 罗冰2, 肖笛1, 张亚2, 陈聪2   

  1. 1. 南京大学地球科学与工程学院 江苏南京 210023;
    2. 中国石油西南油气田公司勘探开发研究院 四川成都 610000
  • 收稿日期:2019-11-09 修回日期:2020-02-20 出版日期:2020-04-25 发布日期:2020-05-09
  • 通讯作者: 曹剑,男,1978年10月生,1999年获西南石油学院学士学位,2005年获南京大学博士学位,现为南京大学地球科学与工程学院教授、博士生导师,主要从事石油地质学及有机地球化学的研究和教学工作。Email:jcao@nju.edu.cn
  • 作者简介:高国辉,男,1995年9月生,2017年获长江大学学士学位,现为南京大学地球科学与工程学院硕士研究生,主要从事有机地球化学研究。Email:mg1729048@smail.nju.edu.cn
  • 基金资助:

    国家自然科学基金面上项目(No.41802147)和国家自然科学基金重点项目(No.41830425)资助。

Evidence of the Middle Permian marine mixed type source rocks in the northwestern Sichuan Basin and its contribution to large gas reservoirs in Shuangyushi area

Gao Guohui1, Cao Jian1, Luo Bing2, Xiao Di1, Zhang Ya2, Chen Cong2   

  1. 1. School of Earth Sciences and Engineering, Nanjing University, Jiangsu Nanjing 210023, China;
    2. Research Institute of Exploration and Development, PetroChina Southwest Oil and Gas Field Company, Sichuan Chengdu 610000, China
  • Received:2019-11-09 Revised:2020-02-20 Online:2020-04-25 Published:2020-05-09

摘要:

四川盆地天然气勘探最近在西北部双鱼石构造带中二叠统栖霞组取得重大突破,揭示了新的勘探领域,但其天然气地球化学特征却与预期认识不符,没有表现出典型下寒武统筇竹寺组来源油裂解气特征。为解释这一矛盾,通过野外剖面地质调查和井下岩心样品分析,结合地质背景进行了研究。研究结果发现,中二叠统栖霞组和茅口组海相混合型泥灰岩可能是区域有效烃源岩,这2套烃源岩在四川盆地西北部广泛分布,厚度分别为0~30 m和30~150 m;烃源岩形成于海相、盐度较低的还原环境,有机碳含量为0.86%~7.15%,有机质类型主体为Ⅱ型,现今热演化程度主体处于过成熟阶段,激光拉曼光谱等效镜质体反射率为1.94%~3.39%,总体属于中等-优质烃源岩,具有良好的生烃潜力,并对双鱼石构造带栖霞组大型天然气藏产生了实质贡献,是主力烃源;断裂与下伏烃源的导通程度是决定寒武系和二叠系烃源差异的关键因素,圈闭的稳定保持和良好的油气保存条件是天然气规模成藏的关键。

关键词: 海相混合型烃源岩, 混合气, 冲断带, 栖霞组, 茅口组, 四川盆地

Abstract:

Gas exploration has made a major breakthrough in Permian Qixia Formation of the Shuangyushi structural belt in the northwest of Sichuan basin, revealing a new exploration field. However, the geochemical characteristics of gas are not in line with the typical characteristics of oil cracking gas from the Cambrian Qiongzhusi Formation as expected. To explain this contradiction, the paper conducts a study through the geological survey of field sections and analysis of downhole core samples in combination with the geological background. The research results show that the marine mixed marls in Middle Permian Qixia Formation and Maokou Formation may be regional effective source rocks. These two sets of source rocks are widely distributed in the northwestern Sichuan Basin, with thicknesses of 0-30 m and 30-150 m, respectively. The source rocks were formed in a marine reducing environment with low salinity. The organic carbon content is 0.86%-7.15%, and the type II organic matter type is dominant. At present, the thermal evolution is mainly in the over mature stage. The equivalent vitrinite reflectance of laser Raman spectroscopy is 1.94%-3.39%. Generally, they are medium-high quality source rocks with good hydrocarbon generation potential, and as the major source rocks, have made substantial contributions to the development of large gas reservoirs in Qixia Formation of the Shuangyushi structural belt. The connectivity between faults and underlying hydrocarbon sources is the key factor determining the differences between Cambrian and Permian hydrocarbon sources. The stable maintenance of traps and good preservation conditions of oil and gas are the key to natural gas accumulation on a large scale.

Key words: marine mixed type source rocks, mixed-type gas, thrust belt, Qiaxia Formation, Maokou Formation, Sichuan Basin

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