准噶尔盆地上三叠统烃源岩评价与有效烃源灶分布预测

Source rock evaluation and prediction of effective hydrocarbon kitchen distribution of Upper Triassic in Junggar Basin

准噶尔盆地蕴含丰富的油气资源,已于多个层位取得油气勘探发现。然而,上三叠统厚层泥岩能否作为盆地有效烃源岩一直没有明确的定论,亟需开展全盆范围内上三叠统烃源岩评价工作并进行有效源灶分布预测,为该层系下一步勘探部署提供依据。为进一步明确准噶尔盆地上三叠统烃源岩时空分布特征及其生烃潜力,落实有效烃源灶分布范围内生烃强度,基于资料收集、剖面实测、钻孔岩屑观察采样和有机地球化学测试,利用多个地化参数开展了全盆范围上三叠统烃源岩有机质丰度、类型、成熟度评价,优选关键参数利用多层次模糊数学评价方法,圈定有效源灶范围。结果表明,上三叠统烃源岩分布范围广(基本全盆分布)、厚度大(可达350 m)、腹部埋深大(最大埋深11 km);烃源岩TOC含量为0.75%~8.3%,平均值为1.74%;S_(1)+S_(2)平均为2.78 mg/g,氯仿沥青“A”平均为0.354%;有机质类型以Ⅲ型和Ⅱ2型为主,陆源高等植物输入占优,相对较好的母质类型主要沿盆1井西凹陷—阜康凹陷方向分布,有机质成熟度处于低成熟—成熟热演化阶段,局部达高—过成熟阶段。按照中国煤系泥岩生烃潜力评价标准,上三叠统泥岩整体为一套差—中等质量烃源岩,烃源岩总体上具有一定的生烃潜力,特别是生气潜力。有效烃源灶分布于中央坳陷腹部的阜康凹陷西部—沙湾凹陷东部一带以及南缘冲断带的霍玛吐背斜带,有效烃源灶范围内烃源岩Ro大于1.3%,生油强度在50×10^(4)t/km^(2)以上,生气强度在3×10^(8)m^(3)/km^(2)以上。

The Junggar Basin is known for its high potential of petroleum resources,showcasing significant oil and gas discoveries across various layers.However,the potential of utilizing the thick mudstone of the Upper Triassic as a viable source rock in the basin remains uncertain.Therefore,an urgent need exists to assess the Upper Triassic source rock across the basin and predict the distribution of effective source rocks.This evaluation is crucial for informing future exploration strategies in this layer.To shed light on the spatiotemporal distribution characteristics and hydrocarbon generation potential of the Upper Triassic source rocks in the Junggar Basin,as well as to determine the hydrocarbon generation intensity within the effective hydrocarbon kitchen’s distribution range,a comprehensive evaluation was conducted.This evaluation involved assessing organic matter abundance,type,and maturity of the Upper Triassic source rock across the basin using various geochemical parameters derived from data collection,profile measurement,drill cuttings observation and sampling,and organic geochemistry testing.Key parameters were then selected,and a multi-level fuzzy mathematical evaluation method was employed to map out the development range of the effective hydrocarbon kitchen.The findings indicate that the Upper Triassic source rock exhibits a broad distribution range spanning the entire basin,with considerable thickness(reaching up to 350 m)and significant burial depth in the central region(up to 11000 m).The total organic carbon(TOC)content of source rocks varies from 0.75%to 8.30%,with an average value of 1.74%.Additionally,the average values of S1+S2 and chloroform asphalt“A”are 2.78 mg/g and 0.354%,respectively.The predominant organic matter types in the area are typeⅢand typeⅡ2,indicating a dominance of terrestrial higher plant inputs.The favorable kerogen types are primarily located from the western sag to the Fukang Sag.The thermal evolution of the organic matter ranges from low-maturity to mature stages,with some areas reaching high to over-maturity levels.As per the evaluation criteria for hydrocarbon generation potential of coal-bearing mudstone in China,the Upper Triassic mudstone generally represents poor to medium-quality source rocks with significant hydrocarbon generation potential,particularly for gas.The key hydrocarbon source kitchens are situated from the western part of the Fukang Sag to the eastern part of the Shawan Sag in the central depression,and in the Huomatu Anticline of the southern margin thrust belt.Within these areas,the Ro value of the source rock exceeds 1.3%,with oil and gas generation intensities reaching 50×10^(4) t/km^(2) and 3×10^(8) m^(3)/km^(2),respectively.