玛湖凹陷玛 2 井区下乌尔禾组扇三角洲沉积及有利储层分布

通过岩心和薄片观察及样品物性分析，对玛湖凹陷玛 2 井区下乌尔禾组的沉积相进行了再认识，并对其有利储层的发育规律及分布特征进行了研究。结果表明：研究区下乌尔禾组为一套冲积扇入湖形成的扇三角洲沉积，并非之前所认为的水下扇沉积；其沉积物总体显示牵引流和重力流交替沉积作用过程；可进一步识别出扇三角洲平原、扇三角洲前缘及前三角洲 3 个亚相，以及泥石流、漫流、扇面河道、水下分流河道、碎屑流、支流间湾、河口坝、远砂坝、前三角洲泥及滑塌等 10 个微相，其中水下分流河道及碎屑流沉积非常发育；沉积微相类型对储层的储集物性和含油性等具有明显的控制作用，其中水下分流河道、扇面河道微相内发育的牵引流砂砾岩储层泥质杂基含量低，储集性能好，为研究区的有利储层。各沉积时期内发育的水下分流河道、扇面河道砂砾岩体是研究区开展后续油气评价及开发的首选目标。

Fan delta sedimentation and favorable reservoir distribution of the lower Urho Formation in Ma 2 well block of Mahu Depression

Based on observation of cores and thin section and property analysis of typical samples, the sedimentary facies of the lower Urho Formation in Ma 2 well block was recognized again, and the development rule and distribution characteristics of favorable reservoirs were studied. Theresults show that the sedimentary facies of the lower Urho Formation is fan delta which formed as a set of alluvial fan prograded into a lake, not underwater fan deposition, and the sediments generally show an alternate deposition process of tractive current and gravity flow. The sedimentary facies can be divided into 3 subfacies of fan delta plain, fan delta front and predelta, and 10 microfacies of debris flow, sheetflood, stream channel, underwater distributary channel, clastic flow, interdistributay bay, mouth bar, distal bar, prodelta mud and slump, among which debris flow and underwater distributary channel deposition developed very well. The sedimentary microfacies have obvious controlling effect on the reservoir properties and oiliness. The glutenite reservoir developed in the stream channel and underwater distributary channel microfacies is favorable reservoir because of the low content of argillaceous matrix and good reservoir properties. So the glutenite of distributary channel and underwater distributary channel microfacies in each sedimentary period are the first target of oil and gasevaluation and development in the study area in the future.