玛湖凹陷二叠系上乌尔禾组扇三角洲沉积特征及控制因素

近年来,准噶尔盆地玛湖凹陷上二叠统砂砾岩储集体中获得重大油气勘探突破。为研究玛湖凹陷上乌尔禾组扇三角洲沉积特征及控制因素,开展了岩相分析、偏光显微镜鉴定、物性分析及成岩作用研究。结果表明:①上乌尔禾组砂砾岩储层自下而上粒度逐渐变细,砾石含量逐渐减少,为典型湖侵退覆式沉积。②上乌尔禾组发育3类11种岩相类型,不同岩相在成岩作用改造下,岩石结构和储层性质差异明显,以牵引流及密度流形成的岩相具有较高的储层质量。③上乌尔禾组储层质量自下而上依次变好,沉积环境控制储层质量的宏观变化,泥杂基破坏孔隙的连通性,粒度的集中程度及发育范围控制优质储层的规模。溶蚀作用有效改善储层储集能力,平均孔隙度增量为3.2%。该研究成果对玛湖凹陷上乌尔禾组砂砾岩勘探具有借鉴意义。

Sedimentary characteristics and controlling factors of fan-delta of the Upper Urho Formation of Permian in Mahu Sag

In recent years,a great breakthrough has been made in oil and gas exploration of glutenite reservoirs of the Upper Permian in Mahu Sag,Junggar Basin.In order to study the sedimentary characteristics and controlling factors of the fan-delta of the Upper Urho Formation,the analyses of lithofacies,polarizing microscope identification,physical property and diagenesis were carried out.The results show that:(1)The reservoir studied developed in a retrogradation fan-delta complex that is the grain size of glutenite reservoirs of the upper Urho Formation gradually became finer and the gravel content gradually decreased from bottom to top,which is a typical lake transgressive and retrogressive deposit.(2)There are three categories and 11 kinds of lithofacies developed in the Upper Urho Formation.The rock structure and reservoir properties of different lithofacies are obviously different under the transformation of sedimentary and diagenetic processes.The lithofacies formed by traction flow and density flow has higher reservoir quality.(3)The reservoir quality of the Upper Urho Formation gets better from bottom to top.The sedimentary environment controls the macroscopic changes of the reservoir quality,the mud matrix destroys the pore connectivity,and the concentration degree and development range of grain size control the scale of the high-quality reservoir.Dissolution effectively improved the reservoir capacity,with an average porosity increment of 3.2%.The research results are of reference significance for glutenite exploration of Upper Urho formation in Mahu Sag.