碎屑-牵引流控冲积扇储层构型特征及模式——以沧东凹陷小集油田为例

Reservoir architecture characteristics and mode of middle and edge alluvial fan controlled by debris flow and traction flow: A case study of Xiaoji oilfield, Cangdong sag

为了更好的探讨碎屑流和牵引流共同控制的冲积扇储层在顺物源方向上的强非均质性特征,以沧东凹陷内小集油田枣Ⅲ—枣Ⅱ油组为研究对象,通过单井岩心精细描述及各级次构型单元的精确表征与定量统计,明确了冲积扇单一成因砂体及各类隔夹层特征,提出了冲积扇区带划分方案,建立了碎屑流和牵引流共同控制的冲积扇储层构型模式.研究结果表明:碎屑流和牵引流共同控制的冲积扇扇中-扇缘按顺物源方向可进一步划分为扇中内带、扇中中带以及扇中外带—扇缘带.扇中内带水动力条件以牵引流和碎屑流为主,辫流带砂体呈连片状,辫流砂岛单砂体规模最大,平均长300～800 m,宽150～450 m,厚5～12 m,夹层最为发育,发育中孔中渗储层,非均质性较强,开发潜力大;扇中中带发育牵引流沉积,碎屑流沉积少见,辫流带砂体呈连片状向条带状过渡的形态,辫流砂岛单砂体平均长250～65 0 m,宽150～300 m,厚3～9 m,夹层数量减少、规模减小,发育中孔低渗储层,非均质性最强,是油气开发的备选区带;扇中外带-扇缘带仅发育牵引流沉积,辫流带(径流带)砂体呈条带状,辫流砂岛单砂体规模最小,平均长200～500 m,宽100～250 m,厚2～6 m,夹层仅可见少量辫流砂岛内落淤层,发育低孔低渗储层,非均质性中等,不建议作为常规油气开发区带.

To discuss the reservoir architecture heterogeneity along the source direction of the alluvial fan controlled by debris flow and traction flow, the third and the second Zaoyuan formation of Xiaoji oilfield in Cangdong sag was taken as the study object. Based on the description of single well cores and the accurate representation and quantitative statistics of each order architecture elements, the characteristics of single sand body and each type of interlayers were described. A zoning plan of alluvial fan was proposed, and the reservoir architecture mode of alluvial fan controlled by debris flow and traction flow was established. The research results show that the alluvial fan controlled by debris flow and traction flow can be divided into inner belt of middle alluvial fan, middle belt of middle alluvial fan and outer belt of middle alluvial fan and edge alluvial fan belt. The inner belt, which has the greatest potential for development, is dominated by traction flow and debris flow in terms of hydrodynamic conditions, with flake-like braided-flow sand body. The single braided sand island has the largest scale with the average length of 300-800 m, width of 150-450 m and thickness of 5-12 m. The reservoir is characterized by middle porosity and middle permeability with strong heterogeneity. The middle belt, which is prepared for oil and gas development, is dominated by traction flow with little debris flow sediments. The architecture of braided-flow sand body transforms from sheet to belt. The single braided sand island has the second large scale with the average length of 250-650 m, width of 150-300 m and thickness of 3-9 m. The reservoir is characterized by middle porosity and low permeability with the strongest heterogeneity. The outer middle alluvial fan and edge alluvial fan belt, which is not recommended as conventional oil and gas development belt, develops traction flow only. The architecture of braided-flow(runoff-flow) sand body is belt. The single sand body is the smallest with the average length of 200-500 m, width of 100-250 m and thickness of 2-6 m. Only a small amount of falling silt layer can be seen in the interlayer. The reservoir is characterized by low porosity and low permeability with middle heterogeneity.