摘要:
川西坳陷中部新场构造带须家河组砂岩主要分布在须二段和须四段,由于埋藏深,普遍经历了复杂的成岩作用,普遍为特低孔隙、低渗透超致密砂岩,但仍较发育有一定数量的相对优质储层并形成致密砂岩气藏.为了更有效地预测和扩展须家河组致密砂岩的相对有利优质储层,则需理清相对优质储层的形成机理.本文通过薄片鉴定、扫描电镜、物性测试、阴极发光及电子探针等测试分析手段,以岩石与矿物学特征、储层特征、成岩作用研究为基础,重点分析物质组成、结构特征、早期胶结作用、流体-岩石相互作用、构造活动、生排烃期次等对于原生孔隙保存及次生孔隙的形成、保存两大方面的影响,最终达到对研究区须家河组致密砂岩中相对优质储层形成机理的系统性研究和认识.结果表明,主要形成机理包括残余原生孔隙的保存和次生孔隙的形成两个方面,其中残余原生孔隙的保存机制主要为早期绿泥石环边、早期适度碳酸盐胶结、部分裂缝导致的油气充注,而次生孔隙则主要来自于长石和少量不稳定岩屑的溶蚀作用,以及破裂作用形成裂缝及其引起的溶蚀作用.
Abstract:
In the Xinchang structural belt of the middle part of the western Sichuan depression, the sandstones of the Xujiahe Formation which belong to the ultra-tight sandstones with the deep burial and complicated diagenesis are mainly distributed in the second and fourth member of Xujiahe Formation. However, the tight sandstone gas reservoirs of the Xujiahe Formation were formed in the relatively high-quality reservoirs and proved to be the important gas exploration targets in the western Sichuan depression. For efficient predicting and extrapolating the tight sandstone gas reservoirs, the formation mechanism of relatively high-quality reservoirs need to be better understood. Based on the research on petrology, reservoir characteristics and diagenesis, the authors used thin-section analysis, physical property measurement, scanning electron microscope analysis, cathodoluminescence, X-ray diffraction analysis, homogenization temperatures of fluid inclusions and electron microprobe analysis to investigate material composition, texture feature, early cementation, interaction of fluid and rock, tectonic activity, hydrocarbon generation-expulsion history and their impact on the preservation of the remains of primary pores and the formation of secondary pores, so as to systematically study and understand the formation mechanism of the relatively high-quality reservoirs in the tight sandstones of the Xujiahe Formation and provide the important basis for the prediction of favorable reservoirs. The research results show that the formation mechanism of relatively high-quality reservoirs mainly consisted of the preservation of the residual primary pores and the formation of the secondary pores. The former included the protection of the early chlorite rim and calcite cement, and the early injection of hydrocarbon created by some fractures, whereas the formation of the secondary pores was generated by the interaction of fluid and rock dominated by the dissolution of feldspar and a little unstable rock debris, and was produced or enlarged by the fractures.
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