三角洲前缘储层中钙质夹层分布及成因探讨

A Discussion on Distribution Pattern and Genesis of the Calcareous Intercalation in Delta Front Reservoir

综合利用岩芯、密井网测井资料,系统总结了胜坨油田三角洲前缘储层中钙质夹层的岩电特征和识别方法,在精细地层对比的基础上,揭示了钙质夹层在高分辨率层序地层格架中的分布特征,提出了钙质夹层的生物成因机制。研究表明:在三角洲前缘复合砂体中,钙质夹层的分布具有选择性,纵向上主要分布在短期基准面下降半旋回所形成的砂体顶部,横向延伸规模小,常过渡为泥质、粉砂质的沉积界面,是良好的层序界面和复合砂体分期界面;平面上主要分布在与水下分流河道相对应的河口坝局部区域,呈相互独立的团块状;钙质夹层中发现密集的阶状似瘤田螺化石,其生存、聚集规律与钙质夹层的选择性空间分布特征高度吻合,指示了钙质夹层的生物成因机制。

By using of core and close spacing log information, the lithologic features and log response features of the cal- careous intercalation in delta front reservoir of Shengtuo Oilfield were proposed systematically, on that basis, we recognize the distribution pattern of calcareous intercalation in high-resolution sequence stratigraphic framework based on the accurate strata correlation. The biogenesis mechanism was presented to improve the genetic model of calcareous intercalation. The study shows that the distribution of calcareous intercalations has selectivity, which is always in the top of sandbody formed in short-term downward base level cycle. The extension scale of calcareous intercalation in strata profile is not big, and always transits to be muddy or silty depositional interface, which shows the calcareous intercalation as an approved sequence interface or subdivision interface of composite sandbody in the delta front reservoir. The areal distribution of the calcareous intercalation is correlated with the depositional microfacies, which is selectively located in the regional debouch bar near the subaqueous distributary channel in a single depositional unit, and presented as separate lump shape. The intensive tulotomoides terrassa are found in the calcareous intercalation, and the subsistence and aggregation patterns of tulotomoides terrassa coincided with the selective distribution pattern of calcareous intercalation, which indicates the biogenesis mechanism.