川南云锦地区茅口组储集层溶蚀期次及模式

为确定川南云锦地区中二叠统茅口组碳酸盐岩储集层成因,通过岩心及薄片观察、岩石学特征分析和同位素地球化学特征分析,对溶蚀作用期次与机制开展研究。云锦地区茅口组储集层存在3期溶蚀作用,表生期大气淡水岩溶作用的流体为大气降水,东吴运动期裂缝为渗流通道,表现为由裂缝向溶蚀缝洞和岩溶洞穴转化,不整合面和古地貌为主要控制因素;早成岩期热液溶蚀作用,与峨眉山玄武岩喷发相关的岩浆期后幔源深部热液,沿断裂上移到茅口组内部并进行改造,鞍形白云石发育;晚成岩期埋藏溶蚀作用流体为二叠系碳酸盐岩内部流体与泥岩成岩转变流体的混合酸性流体,在上覆地层压力下,燕山运动期裂缝和缝合线为流体渗流通道,沿裂缝和缝合线溶蚀缝洞发育。整体而言,表生期大气淡水岩溶作用是研究区储集层形成的决定性成岩作用,早成岩期热液溶蚀作用和晚成岩期埋藏溶蚀作用可以形成少量溶蚀孔洞和溶蚀缝,提高储集层的储集性能。

Dissolution Stage and Pattern of Reservoirs in Maokou Formation in Yunjin Area,Southern Sichuan Basin

In order to determine the genesis of the carbonate reservoirs in the Middle Permian Maokou formation in Yunjin area, southern Sichuan basin, the dissolution stage and mechanism were investigated through core and thin section observations, petrological analysis and isotopic geochemical analysis. There are three stages of dissolution in the reservoirs of the Maokou formation in the study area: (1) atmospheric water karstification in the supergene stage, with atmospheric precipitation as the karstification fluid and the fractures formed in the Dongwu movement period as the flow channels, which showed the transformation from fractures to dissolution fractures/vugs and karst cavities, mainly under the control of unconformity surface and paleomorphology; (2) hydrothermal dissolution in the early diagenetic stage, when the deep mantle-derived hydrothermal fluid in the post-magmatic stage related to the eruption of the Emeishan basalt moved up along the fault to the interior of the Maokou formation and reformed the formation, and saddle-shaped dolomite was developed; and (3) burial dissolution in the late diagenetic stage, when the dissolution fluid was mainly the mixed acid fluid composed of the fluid in Permian carbonate rock and the fluid in mudstone diagenetic transition, and the flow channels were mainly the fractures and stylolite formed in the Yanshan movement period, with dissolution fractures/vugs developed along fractures and stylolite. On the whole, the atmospheric water karstification in the supergene stage is the decisive diagenesis for the formation of the reservoirs in the study area, and the hydrothermal dissolution in the early diagenetic stage and the burial dissolution in the late diagenetic stage allowed the formation of a small amount of dissolution pores/vugs and dissolution fractures, which could improve the storage performance of the reservoirs.