三塘湖盆地石炭系哈尔加乌组上、下段烃源岩特征及差异

Characteristics and differences of source rocks in the lower and upper members of Carboniferous Ha'erjiawu Formation in the Malang Sag of the Santanghu Basin,NW China

三塘湖盆地石炭系碎屑岩与火山岩交互分布,烃源岩分布具有强烈的非均质性。石炭系哈尔加乌组可分为上段和下段,2段的烃源岩岩性和形成环境都存在一定差异,其地球化学特征也存在较大差异。通过岩心、薄片观察、测井岩性识别、TOC预测和有机地球化学实验等方法分析了三塘湖盆地马朗凹陷哈尔加乌组烃源岩的岩性特征、纵向分布特征和地球化学特征,并对上、下段烃源岩特征进行了精细对比,结合沉积环境分析了TOC平面分布的差异性。研究表明,哈尔加乌组烃源岩岩性为炭质泥岩和凝灰质泥岩,前者主要发育于下段,后者主要发育于上段;炭质泥岩的有机质丰度高于凝灰质泥岩,下段烃源岩有机质丰度高于上段;烃源岩下段的中上部TOC高于底部,上、下段烃源岩TOC在平面发育多个高值中心,高值区与沉积中心分布具有较好的一致性,由于上、下段的沉积中心的迁移,导致哈尔加乌组上、下段烃源岩TOC平面分布具有较大差异;烃源岩有机质类型以Ⅰ型和Ⅱ型为主,有机质类型上段稍好于下段。

The Ha＇erjiawu Formation in the Santanghu Basin can be divided into the lower and upper members which differ in the lithologies and forming environments of their source rocks,resulting in the greater differences in their geochemical characteristics of source rocks as well.In this paper,the Carboniferous Ha＇erjiawu Formation source rock in the Malang Sag of the Santanghu Basin has been analyzed based on core and thin section observations.By single-well lithology identification,the longitudinal developmental features of source rocks have been clarified;geochemical characteristics of source rocks have been studied through TOC measurements,Rock-Eval analysis,carbon isotope of kerogen,ROmeasurements,and maturity parameters from biomarkers.Single-well TOC value was predicted by using theΔLogR method and the differences in plane distribution were analyzed.It is indicated in the results that the Ha＇erjiawu Formation source rocks mainly contain carbonaceous mudstone and tuffaceous mudstone,with the former mainly in the lower member and the latter in the upper member;the organic matter abundance of carbonaceous mudstone is higher than that of tuffaceous mudstone;for the Ha＇erjiawu Formation source rocks,the middleupper part contains higher TOCvalues than that in the bottom.For the plane distribution of TOCvalues in the upper and lower members of the Ha＇erjiawu Formation,it developed several high value centers which are in agreement with depositional centers.Due to the migration of depositional centers in the upper and lower members,plane distribution of TOCvalues in the lower and upper members of the Ha＇erjiawu Formation is quite different;the source rock mainly contains TypeⅠand TypeⅡ organic matter,and the upper member is slightly better than the latter for organic matter type.