Characteristics of Carbonate Cements and Reservoir Quality of the Lower Cretaceous Sandstone in Jiudong Sag
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摘要: 碳酸盐胶结物是酒东坳陷下白垩统砂岩内一种重要的自生矿物，其对深部储层储层质量有着重要影响。本文通过薄片观察、扫描电镜、能谱分析及碳氧同位素分析，认为碳酸盐胶结物主要为铁方解石、白云石和铁白云石，并且以后者为主，其分布具有不均一性且分带性明显。碳酸盐胶结物均为成岩作用后期产生，形成该矿物所需的物质主要来源于泥岩的黏土矿物转化和有机质热演化，还有一部分钙来源于斜长石的蚀变。碳酸盐胶结物的溶蚀溶解是深部低渗透储层中发育较为优质储层的重要原因，该溶蚀溶解必须存在流体运移的通道，另外，碳酸胶结物含量也对储层质量有所影响，当碳酸盐含量大于5%时，储层孔隙度随碳酸盐胶结物含量增加而降低，而当其含量小于5%时，储层孔隙度与碳酸盐胶结物含量之间没有明显对应关系。Abstract: The deep burial sandstone reservoir quality is seriously affected by the carbonate cements which is an essential autogenic mineral in the Lower Crataceous formation in Jiudong sag. The thin sections and scanning electron microscope are analyzed, the energy spectroscopy ,carbon and oxygen isotopes of carbonate cements are tested. The study results indicate that the carbonate cements of Lower Crataceous sandstone from the Jiudong sag are mainly ferrous dolomite, ferrous calcite and dolomite with heterogeneous distribution and apparent zonation. They were formed in the late stage of diagenesis and the source are mainly derived from clay minerals transformation, thermal evolution of organic matter in the mudstone and the part of the calcium from the alteration of plagioclase. The key reason for development of the highquality reservoir in the deep burial lowpermeability reservoirs is the dissolution of carbonate cements. In addition, the content of carbonate cement also have an impact on reservoir quality, if the content is greater than 5%, with the increase of the content of carbonate cements the porosity decreases, while it's less than 5%, there is no obvious correlation between porosity and carbonate cement content.
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Key words:
- Jiuquan Basin /
- Ying'er Depression /
- carbonate cements /
- carbon and oxygen isotopes /
- material source
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