沉积环境对煤层含气量的控制: 以沁水盆地寿阳地区太原组15^#煤为例^*

Control of sedimentary environments on gas contents of coal seams: a case study of No.15 coals bed of the Taiyuan Formation in Shouyang area,Qinshui Basin

摘要

煤层性质的差异是影响煤层气富集及高产的重要因素。沉积环境控制了煤层厚度及展布、煤岩煤质特征、有效盖层厚度和岩性组合等,对煤层气富集具有重要控制作用。本研究根据钻井岩心、录井、测井及前人研究成果,对沁水盆地北部寿阳地区太原组进行了沉积环境及层序地层综合分析,并对15^#煤顶、底板系统的沉积环境及岩相古地理进行精细刻画,总结沉积环境对煤层含气量的控制作用,并进一步划分有利煤储集层沉积相带。寿阳地区太原组下部主要发育浅海陆棚—障壁岛—潟湖沉积体系,上部主要发育三角洲平原沉积体系。太原组沉积时期为1个三级层序尺度的海侵—海退过程,并进一步可划分为6个四级层序(S₁—S₆)。四级层序S₁发育潮坪—潟湖—障壁岛沉积体系,各沉积相与15^#煤含气量关系由好到差依次为潟湖、潮坪、障壁岛; S₂发育障壁岛—潟湖—潮坪—浅海陆棚沉积体系,各沉积相与15^#煤含气量关系由好到差依次为潟湖(灰岩厚)、泥质陆棚、碳酸盐岩陆棚、潟湖、潮坪、障壁岛。根据S₁、S₂沉积相与15^#煤含气量关系,将15^#煤划分为Ⅰ、Ⅱ、Ⅲ类煤储集层沉积相带,Ⅰ类煤储集层沉积相带分布区是煤层气勘探有利区,主要分布于研究区东部; Ⅱ类煤储集层沉积相带分布区是煤层气勘探较有利区,主要分布于东部及西部; Ⅲ类煤储集层沉积相带分布区煤层气勘探前景较差,主要分布于研究区的西北部及中部。

Abstract

The property of coal seams is a dominant factor for the enrichment and high-yield of coal-bed methane(CBM). Sedimentary environments control the distribution and thickness of coal seams,the maceral composition and properties of coal,and the superimposed model of surrounding rocks as well as their thickness,and thus controlling the enrichment of CBM. In this study,sedimentary environments and sequence stratigraphy of the Taiyuan Formation in Shouyang area,northern Qinshui Basin were analyzed based on drilling cores,loggings and previous studies. Lithofacies and palaeogeography of the roof and floor systems of the No.15 coal bed were described in detail. The relationship between sedimentary environments and gas contents of the CBM was finally summarized,and the favorable zone for CBM exploration was delineated. The lower part of the Taiyuan Formation in Shouyang area mainly developed in shallow marine shelf,barrier island,and lagoon depositional system,whereas the upper part formed in the delta plain. The Taiyuan Formation records a 3^rd-order transgressive-regressive sequence,which can be further divided into six 4th-order sequences(S₁-S₆). The S₁ mainly developed on tidal flat,lagoon and barrier island. The gas content of different sedimentary facies declines is an order from lagoon,tidal flat to barrier island. The S₂ mainly formed in barrier island,lagoon,tidal flat,shallow marine shelf depositional system. The gas content declines in an order of lagoon(with thick limestone),muddy shelf,carbonate shelf,lagoon,tidal flat,and barrier island. According to the relationship between sedimentary facies of the S₁ and S₂ and gas content of No.15 coal bed,the CBM reservoir of No.15 coal bed was subdivided into three types. Type Ⅰ reservoir is favorable for CBM exploration,which is mainly distributed in the east of the research area. Type Ⅱ reservoir is relatively favorable for CBM exploration,which is distributed in the east and west of the research area. Type Ⅲ is of poor CBM exploration prospect,which is mainly distributed in the northwest and the middle area the research area.

关键词

沁水盆地 / 寿阳地区 / 太原组 / 沉积环境 / 煤层甲烷 / 层序古地理

Key words

Qinshui Basin / Shouyang area / Taiyuan Formation / sedimentary environment / coalbed methane / sequence palaeogeography

基金资助

*中海油有限公司项目“煤层气地质工程关键参数表征及甜点区评价技术”(编号: KJGG2022-1001)、“煤储层精细描述与产能主控因素研究”(编号: 20210T-XNY09)及“寿阳区块南燕竹产水规律及开发技术研究”(编号: 2022-YXKJ-013)联合资助