敦煌盆地有效烃源岩的发现及地质意义

IDENTIFICATION AND GEOLOGIC SIGNIFICANCE OF EFFECTIVE SOURCE ROCKS IN DUNHUANG BASIN

敦煌盆地的近期油气勘探工作中,XC1井揭示较好的湖相烃源岩,录井见油斑、油迹6 m/8层,荧光16.5m/7层;压裂后试油,日液0.16～10.7 m3,日油0.02～1.53 m3,累产油12.1 m3。基于中石化近几年投入的实物工作量和XC1井钻探成果,笔者通过对样品的地化分析数据和油源对比结果,认为中下侏罗统是潜在烃源岩的主要发育层段,中间沟组1段的湖相泥岩集中段为有效烃源岩,藻类体和角质体是这套源岩的主要生烃显微组分,有机质类型最好可达Ⅰ—Ⅱ1型,现有资料显示在五墩凹陷保存较完整;XC1井所发现的油藏为一次生烃的原生油藏,具有＂早期生烃、早期聚集、晚期定型＂的＂两早一晚＂的成藏特点,今后勘探关键是研究其成烃过程与圈闭配套史的关系,近源保存条件较好的岩性或构造—岩性油气藏是首选的目标。

In the recent oil and gas exploration of Dunhuang Basin, XC1 Well reveals a set of good lacustrine mudstone source rock. The mud logging shows the well has 8 oil patch and oil trace layers（6m）, 7 fluorescence layers（16.5m）. The well logging interpretation indicates that there are 8 oil layers（17.3m）. After being fractured,the well oil production is 0.16~10.07m3/ d, water production is 0.02 ~1.53 m3/ d and total oil production is 12.1m3. In this paper, we conduct geochemical analysis of samples and oil-source correlation based on the work of SINOPEC in recent years and drilling results of XC1 Well. In our view, the middle and lower Jurassic is the main section of potential source rocks, and the lake facies mudstone sections in member one of Zhongjiangou Formation are effective source rocks. Alginate and cutinite are the main hydrocarbon generation maceral of the source rocks,and organic matter could reach type I-II1, which is preserved well in Wudun depression as shown in existing data. Reservoir found by XC1 Well is primary oil reservoir of primal hydrocarbon generation. It has the characteristics called ＂two early and one later＂, which means hydrocarbon generation and gathering occur at the early stage and forming completes at the later stage. The key issue of exploration in the next step is to study the relationship between its hydrocarbon generation process and trap match history, and source-proximal oil and gas reservoirs of lithology or structure-lithology with good preservation conditions are the primary targets.