塔里木盆地阿瓦提断陷中-上奥陶统萨尔干组沉积地质模型与烃源岩分布预测

中-上奥陶统萨尔干组烃源岩是塔里木盆地重要的海相烃源岩。针对阿瓦提断陷中-上奥陶统埋深大、缺乏钻井进行层位标定,以及萨尔干组烃源岩发育层段的地震响应特征不明的问题,用传统的技术手段识别该套烃源岩的分布范围可能难以取得好的效果。通过对柯坪地区露头剖面中-上奥陶统萨尔干组及其上下地层不同岩性及地层结构的认识,建立沉积地质模型,进行地震正演模拟,将地质模型和地震模型有机地结合起来,为烃源岩地震相识别追踪提供依据;在对研究区内二维地震测线逐条解释的基础上,依据地震反射波组的反射特征,进行地震相-沉积相分析;针对露头发育烃源岩而断陷内未有钻井揭示的地区,建立了海相烃源岩识别方法和流程,对研究区中-上奥陶统萨尔干组烃源岩进行了重新识别和空间展布预测。研究表明,萨尔干组烃源岩的发育受海平面上升控制作用明显,属于深水陆棚相沉积;萨尔干组烃源岩在区内广泛分布,厚度范围约为0～120 m,在西南部最厚,受控于阿恰断裂和吐木休克断裂,向东北部减薄,向北超覆尖灭于英买3井以南,向东至阿-满过渡带西缘仍有少量分布。

Sedimentary geological model and distribution prediction of source rocks in the Saergan Formation(Middle-Upper Ordovician) in Awati fault depression,Tarim Basin

Saergan Formation hydrocarbon source rocks of the Middle-Upper Ordovician are important marine source rocks in the Tarim Basin.Due to the large burial depth of the Middle-Upper Ordovician, a lack of drilling data for horizon calibration in Awati fault depression, and the insignificant seismic response characteristics of hydrocarbon source rocks in the Saergan Formation, it is difficult to accurately predict the distribution of the source rocks with traditional techniques.Based on the analysis of lithology types and stratigraphic configuration in the Saergan Formation together with its overlying and underlying strata on the outcrops in Kalpin area, we established a geologic model for seismic forward modeling.The combination of geological model and seismic model provides a basis for identifying and tracing seismic facies of the source rocks.Following the interpretation of 2D seismic lines one by one in the study area, we analyzed both the seismic and sedimentary facies according to the features of reflection wave groups.As to areas where source rocks occur on the outcrops but are not penetrated by wells emplaced in fault depression, we worked out methods and established the workflow for marine source rock identification, and re-recognized and predicted the spatial distribution of marine source rocks in the Middle-Upper Ordovician Saergan Formation.The results show that the Saergan Formation source rocks, developed under the control of sea level rising, belong to deposits of the deep shelf facies.The Saergan Formation source rocks are widely distributed in the study area with a predicted thickness range of about 0-120 m.It is the thickest in the southwest, thins progressively toward the northeast under the control of the Aqia and Tumuxiuke fault belts, and overlaps to the north till pinches out to the south of Well Yingmai 3;moreover, it still occurs sporadically at the western margin of Aman transitional belt to the east.