北部湾盆地涠洲11A油田流一中亚段沉积储层研究

A study of the sedimentary reservoir in the middle sub-member of the first member of the Liushagang Formation in the Weizhou-11A Oilfield,Beibu Gulf Basin

北部湾盆地涠西南凹陷涠洲11A油田流沙港组一段中亚段沉积岩性复杂,储层纵横向变化快,分布规模和连通性难以预测,严重影响油田开采效果。通过岩心观察描述、三维地震解析、岩石粒度、岩相、测井相、现代沉积类比分析研究认为,流一中亚段沉积流体作用控制着砂体及储层类型,其中辫状溪流底负载沉积(槽状交错层理砂岩相St、板状交错层理砂岩相Sp、沙纹层理砂岩相Sr)、砂质碎屑流沉积(块状层理颗粒支撑砾岩相Gmg、正粒序砂砾岩相Gn)与浊流沉积(正粒序水平层理粉砂岩相Fhn)可形成有利储层,主要分布于扇三角洲前缘辫状水道、辫流坝、河口坝和席状砂微相中;探讨了油田流一中亚段4个中期旋回沉积微相空间展布规律和几何形态;提出扇三角洲前缘5类8种砂体叠置模式、连通特征和成因机制,建立了储层概念模型和主力沉积微相宽度、厚度和宽厚比经验值,为油田后续开发井网部署提供科学依据。

The sedimentary lithology is complex in the middle sub-member of the first member of the Liushagang Formation(L1-M)of the Weizhou-11A oilfield in the southwest Weizhou depression of the Beibu Gulf Basin.The reservoir changes rapidly in both vertical and horizontal directions,and the distribution scale and connectivity are challenging to predict,which seriously affects the oilfield development effect.Through core observation and description,3D-seismic analysis,rock grain size,lithofacies,logging facies,and modern deposit analogy analysis,it is believed that the depositional fluids control the sand bodies and reservoir types.Braided stream bottom-load deposits(St,Sp,Sr),sandy debris flow deposits(Gmg,Gn),and turbidity deposits(Fhn)can form favorable reservoirs,which are mainly distributed in the braided channel,braided flow bar,mouth bar and sheet sand microfacies of fan delta front.We discussed the spatial distribution law and geometric shape of sedimentary microfacies in four middle-term cycles and proposed five types and eight kinds of sand-body stack types and connectivity characteristics of the fan delta front.The reservoir model and the empirical values of width,thickness,and the width-to-thickness ratio of main sedimentary microfacies are established,which provide a scientific basis for the oilfield development.