深层白云岩储层溶蚀作用成因及其对储层的影响

Genesis and impact of dissolution in deep dolomite reservoirs： A case of the 2nd member of the Sinian Dengying Formation， Penglai area， central Sichuan Basin

谭谦 袁海锋 王涛 马自立 唐渤钧 彭秋 李文杰

Qian TAN Haifeng YUAN Tao WANG Zili MA Bojun TANG Qiu PENG Wenjie LI

为进一步明确四川盆地震旦系灯影组深层白云岩储层成因， 通过岩心观察、薄片鉴定和阴极发光实验，分析了川中蓬莱地区灯影组二段（灯二段）白云岩储层不同类型溶蚀孔洞的发育和充填特征，结合包裹体、碳-氧-锶同位素、U-Pb同位素定年以及主-微量元素和稀土元素等分析测试，研究了溶蚀作用期次和成因机理。研究结果表明：① 川中蓬莱地区灯二段白云岩储层主要经历了同生期—准同生期溶蚀、风化壳岩溶和热液溶蚀3期溶蚀作用的叠加改造，储集空间类型多样，储层非均质性强。② 组构选择性溶蚀孔和网格状溶蚀孔洞发育在沉积旋回的中-上部，纵向上多套叠置具韵律性分布特征，以纤维状和放射状负延性白云石胶结物充填为主，具有独特的葡萄花边和葡萄石结构，是海平面频繁变化驱动下同生期—准同生期溶蚀的产物。③ 角砾化溶洞和蜂窝状溶蚀孔洞主要发育在灯二段不整合面之下，角砾化溶洞为岩溶垮塌角砾和泥质充填，蜂窝状溶蚀孔洞则以放射状正延性白云石胶结物半充填为特征，是桐湾运动期风化壳岩溶叠加改造的产物。④ 高角度缝洞发育在东西向走滑断裂附近，与海西晚期峨眉山火山活动引起的富CO热液溶蚀有关，多被热液矿物组合半充填。综合研究认为，同生期—准同生期溶蚀改造的丘滩沉积是优质储层形成的基础，风化壳岩溶的叠加改造是优质储层形成的关键，热液溶蚀重新分配储集空间进而控制优质储层的分布。

To further determine the genesis of deep dolomite reservoirs in the Sinian Dengying Formation within the Sichuan Basin， we analyze the developmental and filling characteristics of various dissolution pores and vugs in dolomite reservoirs in the 2nd member of the Dengying Formation （also referred to as the Deng 2 Member） in the Penglai area， central Sichuan Basin， through core observation， thin section identification and cathodoluminescence （CL） imaging. In addition， by integrating the analyses and tests of inclusions， carbon-oxygen-strontium isotopes， major and trace elements， and rare earth elements （REEs）， as well as U-Pb isotopic dating， we investigate the stages and genetic mechanisms of dissolution in the dolomite reservoirs. The results indicate that the dolomite reservoirs in the Deng 2 Member primarily underwent the superimposed modification of three stages of dissolution， namely the syngenetic to penecontemporaneous dissolution， weathered-crust karstification， and hydrothermal dissolution. Such superimposed modification produced a spectrum of storage spaces and strong reservoir heterogeneity. The fabric-selective dissolution pores and reticulate dissolution vugs in the reservoirs occur in the middle to upper part of sedimentary cycles， exhibiting multi-set superimposition and vertical rhythmicity. These pores and vugs are predominately filled by fascicular fast dolomite （FFD） cements， exhibiting unique botryoidal-lace and prehnite textures. They are the product of syngenetic to penecontemporaneous dissolution driven by frequent sea-level fluctuations. Brecciated karst caves and dissolution vugs in honeycomb pattern are principally found beneath the unconformities of the Deng 2 Member. The former is filled with collapsed karst- breccia and argillaceous materials， while the latter is half filled with radial slow dolomite （RSD） cements， both resulting from the superimposed modification of weathered-crust karstification during the Tongwan Movement. High-angle fractures and vugs in the reservoirs are distributed near E-W-trending strike-slip faults. They are associated with CO-rich hydrothermal dissolution caused by the Emeishan volcanism during the Late Hercynian and are largely half filled with hydrothermal mineral assemblages. The comprehensive analysis reveals that the mound-shoal deposits modified by syngenetic to penecontemporaneous dissolution provide a basis for the formation of high-quality reservoirs， while the superimposed modification of weathered-crust karstification is critical to their formation. Additionally， hydrothermal dissolution leads to the redistribution of reservoir spaces， thus governing the distribution of high-quality reservoirs.

10.11743/ogg20250308