渤海湾盆地临清坳陷西部山西组—太原组海陆过渡相泥页岩沉积环境及有机质富集^*

Sedimentary environment and organic matter enrichment of marine-continental transitional shale in the Shanxi-Taiyuan Formations in western Linqing Depression, Bohai Bay Basin, China

摘要

海陆过渡相页岩气勘探开发处于初级阶段,而渤海湾盆地临清坳陷西部石炭—二叠系山西组—太原组泥页岩具有良好的生烃潜力,也是中国海陆过渡相页岩气开发的重要层位。为研究山西组—太原组泥页岩沉积环境与有机质富集关系,以XJ1井为研究对象,系统开展了岩石矿物、有机地球化学、元素地球化学以及数值分析等工作。研究表明: 研究区山西组—太原组泥页岩脆性矿物含量低、黏土矿物含量高,压裂难度大,TOC含量平均值为4.03%,属于优质烃源岩,具备页岩气勘探开发潜力; 太原组泥页岩沉积时期处于温暖湿润的气候条件,具有频繁变化的陆源碎屑输入、较低的沉积速率以及低—中等古生产力水平,沉积水体为海水沉积,处于缺氧还原和中等滞留环境; 山西组泥页岩沉积时期,古气候条件复杂多变,具有稳定且较高的陆源碎屑输入、中等的沉积速率以及中—高等古生产力水平,沉积水体为微咸水—海水沉积,处于缺氧还原和中等—强滞留环境。根据古环境条件与TOC含量的线性相关性、灰色关联度以及稳健回归分析,认为太原组泥页岩有机质富集主要受控于古气候、古氧化还原以及古水体盐度条件,而山西组泥页岩有机质富集主要受控于古气候以及陆源碎屑输入条件。

Abstract

The exploration and development of marine-continental transitional shale gas is in the primary stage. The Shanxi-Taiyuan Formations shale has good hydrocarbon generation potential and is also an important horizon for the development of marine-continental transitional shale gas in China. In order to explore the relationship between sedimentary environment and organic matter enrichment of the Shanxi-Taiyuan Formations shale in the western Linqing Depression,Bohai Bay Basin,Well XJ1 was investigated in detail by means of petrology,organic geochemistry,element geochemistry and numerical analysis. The results show that the Shanxi-Taiyuan Formations shale is characterized by a low content of brittle minerals,a high content of clay minerals and a high resistance to hydraulic fracturing. It is also found that the Shanxi-Taiyuan Formations shale comprises a high-quality source rock with an average TOC content of 4.03%,which has the potential for shale gas exploration and development. During the deposition of the Taiyuan Formation mudstone/shale,the study area featured an anoxic,moderately stagnant oceanic environment under a warm and humid climate,with frequent variaions in terrigenous debris influx,low deposition rate and low to medium paleoproductivity level. During the deposition of the Shanxi Formation mudstone/shale,the study area featured anoxic,moderately to strongly stagnant and brackish to brine seawater under complex and ever-changing paleoclimatic conditions,with a stable and high terrigenous debris influx,medium deposition rate and medium to high paleoproductivity level. Given the linear correlation,grey correlation and robust regression analysis between paleoenvironmental conditions and TOC content,it is concluded that the enrichment of organic matter in the Taiyuan shale is mainly controlled by paleoclimate,paleoredox and ancient water salinity conditions,while the enrichment of organic matter in the Shanxi shale is mainly controlled by paleoclimate and terrigenous debris input conditions.

关键词

渤海湾盆地 / 临清坳陷西部 / 山西组—太原组 / 海陆过渡相泥页岩 / 沉积环境 / 有机质富集

Key words

Bohai Bay Basin / western Linqing Depression / Shanxi-Taiyuan Formations / marine-continental transitional shale / sedimentary environment / organic matter enrichment

基金资助

*国家自然科学基金项目(编号: 42172156,41802183,42030810)和中国矿业大学英才培育工程专项(编号: 2022YCPY0201)联合资助