煤田地质与勘探2025，Vol.53Issue(2)：1-12,12.DOI:10.12363/issn.1001-1986.24.07.0465
辫状河-曲流河及转换中煤沉积特征
Sedimentary characteristics of coals in meandering river and braided river facies and during their transitions:A case study the Walloon Subgroup in the F8 block in the Surat Basin,Australia
摘要
Abstract
[Objective]Australia is recognized as the fourth largest producer and the second largest exporter of coals in the world.The Bowen-Surat Basin is the largest coal producing basin in this country.The Surat Basin exhibits coal-bear-ing layers of the Middle Jurassic Walloon Subgroup.This subgroup features a sedimentary environment of fluvial facies,necessitating clarifying the differential sedimentary characteristics and patterns of coal seams in braided river and mean-dering river facies and during their transitions.[Methods]Using comprehensive geological analysis methods,as well as seismic data,logs,and core data,this study established the sedimentary pattern of the study area.Using seismic horizon tracking and base-level cycles,this study divided the study area into six fourth-order stratigraphic cycles and categorized the log curves of 37 wells into five combinations based on the morphological characteristics of the curves and contact re-lationships.The observations of cores from 14 wells revealed six typical lithofacies in the Walloon Subgroup.In com-bination with the characteristics of log curves and lithofacies,this study determined two sedimentary facies:braided river to meandering river facies.The sedimentary facies can be further divided into eight microfacies.Using two horizontal and vertical cross-well sections,this study characterized coal distribution and analyzed the differential sedimentary char-acteristics of coal seams in the braided river and meandering river facies and during their transitions.[Results and Con-clusions]In the case of a high base level,the study area was in a sedimentary environment of the meandering river fa-cies.In this case,coals were well-developed,exhibiting the superimposition of multiple coal seams.As the base level dropped,the meandering river facies gradually transitioned to the braided river facies,with the lithofacies changing from fine-to coarse-grained rocks and the amplitude of bedding structures increasing.During this period,high-energy water flow washed away coal seams formed previously,leaving scattered coal deposits in braided river channels.When the base level approached its minimum,the study area exhibited a sedimentary environment of the braided river facies.This period witnessed the lowest level of coal development,with a minor presence of coals in overflow sands.As the base level rose,the braided river facies transitioned to the meandering river facies.During this period,the water body energy decreased,and the lithofacies varied,exhibiting Gm-St-Sp-SH-Fr/C sequentially.Meanwhile,an increasing number of coal seams were deposited.In the transition from the meandering river facies to the transition zone and then to the braided river facies,the three-dimensional coal distribution was characterized by increasingly reduced planar continuity and range,lateral continuity in sections,vertical stacking and thickness.As the base level changed,the sedimentary mi-crofacies that was the most favorable for coal accumulation was coal swamps,followed by floodplains and overflow sands.The achievements of this study can serve as a guide for the analysis of the distribution range of coal seams.Dur-ing well emplacement in the Surat block,the results of this study can help confirm the"sweet spots"of the targets for coal coalbed methane(CBM)production.关键词
煤层/辫状河-曲流河转换/沉积特征/Surat盆地/Walloon组Key words
coal seam/transition from braided river facies to meandering river facies/sedimentary characteristic/Surat Basin/Walloon Subgroup分类
地质学引用本文复制引用
崔泽宏,赵一波,李志华,李胜利,李伟茹..辫状河-曲流河及转换中煤沉积特征[J].煤田地质与勘探,2025,53(2):1-12,12.基金项目
国家科技重大专项课题(2016ZX05029-005) （2016ZX05029-005）
国家自然科学基金项目(42172112) （42172112）
中国石油天然气股份有限公司"十四五"前瞻性基础性科技项目(2021DJ3304) （2021DJ3304）
