水下分流河道储层内部结构表征——以胜坨油田沙二段8~1层为例

Inner architecture characterization of underwater distributary channel-case of Es_28~1 sand unit of Shengtuo oilfield

储层内部结构表征是特高含水期老油田改善水驱开发效果、提高采收率的基础和关键。以胜坨油田沙二段81层三角洲前缘水下分流河道为例,利用密井网条件下的储层构型分析方法,系统揭示了水下分流河道储层内部结构。研究结果表明,研究区水下分流河道储层中的沉积界面可分为5个等级:五级界面是限定水下分流河道复合砂体的界面,为分布稳定的泥岩,呈近水平产状;四级界面是复合砂体内部单一河道间的沉积界面,为泥质薄夹层或岩性突变面,在相同单一河道中以近水平产状连续分布,在不同单一河道间分布不连续;三级界面是单一河道内部增生体的界面,界面上下岩相一致,分布范围局限在单一河道砂体内部,也为近水平产状;二级和一级界面分别为岩心规模的层系组或交错层系界面。水下分流河道复合砂体由单一河道垂向叠置和侧向拼合而成,综合利用分流间湾、河道边缘、砂体顶面高程差异、砂体规模差异等特征可识别出单一河道的侧向边界,单一河道的同期不同体现象是水下分流河道最重要的储层内部结构。

The inner architecture characterization of reservoir is the base and key factor to improve the waterflooding effectiveness and enhance the oil recovery. Taking the Es281 sand unit of Shengtuo oilfield in Dongying depression as an example, which is a typical underwater distributary channel of delta front reservoir, the inner architecture of the composite sand body was characterized by close spacing architectural analysis. The study shows that the depositional interfaces in the underwater distributary channel can be classified into 5 levels. The fifth level interface restricts the composite underwater distributary channel, which is the stable mudstone with major thickness and near horizontal attitude. The fourth level interface restricts the single channel, which is mainly the muddy intercalation or lithological discontinuity surface with near horizontal attitude and continuous distribution in same single channel, but with discontinuous distribution among the different single channels. The third level interface restricts the accretion sand body in the single channel, and the upper and lower lithofacies of the third level interface is accordant. The distribution range of the third level is confined by single channel and the attitude is also near horizontal. The second and first level interfaces restrict the bedding system and cross bedding with core scale. The composite underwater distributary channel sand body is overrode vertically and built up laterally by single channel. The lateral border of the single channel can be identified by inter-distributary bay, channel marginal deposit, top surface altitude difference of sandbody and scale difference of sand body. The most important inner architecture characteristic of the underwater distributary channel is the contemporaneous deposit of single channel but independent sand body.