杭锦旗地区山西组辫状河三角洲的判定及其沉积演化

Judgment and sedimentary evolution of braided river delta of Shanxi formation in Hangjinqi area

针对杭锦旗地区山西组勘探中对于沉积相研究方面存在的问题,以岩芯资料的精细分析为基础,结合杭锦旗地区山西组区域地质特征及测井、录井、粒度等资料进行了综合研究。研究表明,其沉积物组分由北向南稳定组分含量及成熟度有逐渐增加的趋势,粒度累计概率曲线表现为双向水流的特点;楔状交错层理、波状层理、砂纹交错层理及泥岩撕裂屑等反映了稳定-动荡的水体环境的沉积构造均较发育,泥岩颜色变化呈现出水下沉积到陆上沉积过渡带。综合研究认为:研究区山西组沉积相类型为辫状河三角洲,研究区从山1段到山2段经历了湖岸线南移、辫状河三角洲前缘亚相到平原亚相的沉积演化,使得山西组沉积形成以"陆进水退"为特征的辫状河三角洲沉积体系,辫状河三角洲前缘分流河口砂坝发育较差,水下分流河道在沉积砂体中占主导性地位。超补偿型辫状河三角洲的厚层砂体作为优质储层在研究区广泛发育,可以成为油气储层及运移通道。支流间湾沉积的碳质泥岩为煤层及煤成气的形成创造了有利条件。

Aiming at making clear the issues that existed in the exploration about the types of sedimentary facies,a series of study was carried out. Based on the detailed core observation,a series of phenomenon can be seen in Shanxi formation of Hangjinqi area,in combination with regional geological data,logging,well log and particle size data. The content and maturity of stable minerals tend to be increased gradually from the north to south. The grain-size accumulative probability curve is characterized by bidirectional current. The sedimentary structures such as wedge-shaped cross-bedding,wave bedding,sand grain cross-bedding and mudstone ripup,reflect the stable-agitated high-energy water environment. The change of mud color draws the sedimentary outline of a transitional zone from subaqueous to subaerial deposit. In consideration of a series of evidences concerned above,it draws an conclusion that the braided river delta is developed in the Shanxi formation and the study area has experienced the evolution from braided river delta front to braid-river delta plain,and the lake range has moved the south from Shan-1 formation to Shan-2 formation,which shows that the Shanxi formation developed the sedimentary system of braided river delta characterized by ＂deposits progradation and lacustrine regression ＂. The microfacies of a distributary mouth bar develop little and underwater distributary channel dominates the distribution of depositions. The thick sand bodies of the super-compensation braided river delta,which can be acted as reservoir and hydrocarbon migration channel,have developed much in the study area. The carbonaceous mudstone in the tributary bay provides favorable conditions for the formation of coalformed gas and coal.