环开江-梁平海槽长兴组台缘礁滩相储层特征及成岩作用
Characteristics and diagenesis of platform margin reef-shoal reservoirs of Upper Permian Changxing Formation around Kaijiang-Liangping Trough, eastern Sichuan Basin
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摘要: 通过岩心观察、薄片鉴定、电镜扫描、阴极发光、物性分析，对四川盆地东部环开江-梁平海槽上二叠统长兴组礁滩相储层特征、储层成岩作用进行研究，并初步建立成岩演化序列。储层特征研究发现，长兴组储层发育良好，储集岩以“花斑状”生屑云岩和生物礁云岩为主，粒间孔、粒间溶孔和粒内溶孔较为发育，孔隙度总体介于2%~6%，渗透率集中在0.1~1 mD，结合孔渗相关关系将其划分为4种储层类型：“低孔高渗”型、“中孔中渗”型、过渡型、“高孔低渗”型。储层成岩作用研究发现，储层在成岩阶段经历了多期胶结、压实、白云岩化、溶蚀、构造破裂等成岩作用。由于成岩作用对孔隙结构的改造，孔隙演化整体上呈减小趋势。胶结作用及压实作用使得原生孔隙大幅度减少，对储层的形成具有破坏性作用，溶蚀及白云岩化作用对储层的形成具有建设性作用，构造破裂对储层进一步优化改造。研究表明原生粒间孔和早成岩期岩溶及热液白云岩化作用形成的早期次生孔隙不仅是现今储层储集空间的雏形，也基本决定了储层的最终面貌。Abstract: In this paper, the authors utilized cores and thin sections observations, SEM, cathodoluminescence and physical property analysis to study characteristics and diagenesis of the reservoir within Upper Permian Changxing Formation, and preliminarily established diagenetic evolution sequence. The interval is mainly featured by platform margin reef-shoal around KaijiangLiangping trough in eastern Sichuan Basin. Reservoir characteristics reveal that the Changxing reservoirs are developed well. Reservoir rocks are composed of"piebald"bioclastic dolomite and reef dolomite dominate, whereas reservoir spaces mainly comprise intergranular pores, dissolved intergranular pores and dissolved intragranular pores. The reservoir porosity is mainly between 2% and 6%, and the permeability is between 0.1 mD and 1 mD. Four types of reservoirs were found, i.e., "low-porosity and high-permeability" type, "medium-porosity and medium-permeability" type, transitional type and "high-porosity and lowpermeability" type. The diagenetic evolution indicates that Changxing Formation experienced cementation, compaction, dolomitization, dissolution and tectonic fracturing. A decreasing trend in porosity due to the superimposed modification by multiplephase diagenesis was observed. Cementation and compaction occupied most of primary pores and reduced the porosity after the deposition. Karstification and dolomitization improved the porosity by transforming the textures of pores. Tectonic fractures further optimized the reservoir. Research shows that primary intergranular pores and eogenetic secondary pores formed by eogenetic karstification and hydrothermal dolomitization not only serve as the prototype of reservoir space but also generally determine the final appearance of the reservoir.
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