东营凹陷古近系沙四上亚段近岸水下扇砂体碳酸盐胶结物的分布特征

依据岩心、薄片、测井等资料对东营凹陷北部陡坡带永安地区古近系沙河街组沙四上亚段近岸水下扇砂体中碳酸盐胶结物的分布特征进行研究。结果表明:碳酸盐胶结物(体积分数)含量高(>15%)的砂岩在近岸水下扇外扇及滑塌浊积扇等薄层粉细砂岩中分布普遍,碳酸盐胶结物含量低(<10%)的砂岩往往出现在近岸水下扇中扇沟道微相的厚层砂岩中;外扇胶结层的横向连续性好,中扇的碳酸盐胶结带仅位于沟道砂岩的顶底部、横向延伸小、铁白云石普遍;中扇、外扇的胶结层单层厚度通常小,内扇的胶结层单层厚度较大,砾岩中灰岩砾石及钙质杂基含量较高、压实强;砂体中的长石能缓冲酸性地层水,方解石在砂体边缘附近区域富集形成胶结层,胶结层往往对应于斜长石溶蚀而现今斜长石含量较低的层段;碳酸盐胶结层造成近岸水下扇储层非均质性强,发育内扇物性遮挡的岩性油气藏。

Distribution characteristics of carbonate cement of nearshore subaqueous fans in Upper Es4 of paleogene of Dongying depression

Distribution characteristics of carbonate cement were studied by the analysis of cores, thin-section,well logging et al in sand bodies of nearshore subaqueous fan of Upper Es₄ of Paleogene Shahejie formation in Yongan area of the northern steep slope belt in Dongying depression. The results show that high carbonate cement sandstones (>15%) are common in the thin fine sandstones of the outer fan of nearshore subaqueous fan and the slump turbidite fan. The low carbonate cement sandstones (<10%)are common in the thick sandstones of the mid-fan channel of nearshore subaqueous fan. Cement layers of the outer fan are of well continuity, while those of middle fan only distribute on the top and bottom of the channel sandstones with weak continuity and rich ankerite. The cement layers in middle fan and outer fan are generally thin, but those in inner fan are thick. The content of the limestone gravel and calcareous heterobase in conglomerate is high, and the compaction is strong. Feldspar in sand-bodies can buffer the acid formation water, while calcite cement layers are formed in the edge of the sand body and nearby regions. Cement layers usually correspond with the layer sections where plagioclase is dissolved and the current content of plagioclase is low. The strong heterogeneity of reservoirs of nearshore subaqueous fan is caused by calcite cementation layers and physically blocked lithologic reservoirs are formed.