四川盆地北部中二叠统茅口组碳酸盐岩溶蚀模拟实验与岩溶层组特征

Experimental dissolution and karst strata association of Middle Permian Maokou carbonate rocks in the northern part of Sichuan Basin

四川盆地北部中二叠统茅口组岩溶储层发育,是该区重要储层类型之一。基于野外露头、钻井岩心资料,采用宏观与微观结合的方法,根据薄片鉴定、扫描电镜、主微量元素等资料、辅于溶蚀模拟实验等技术方法,对四川盆地北部茅口组岩溶层组特征进行了研究。该区茅口组一段以泥质灰岩、生屑泥晶灰岩为主,酸不溶物含量较高;茅二段、茅三段以泥晶生屑灰岩、亮晶生屑灰岩为主,酸不溶物含量较低。溶蚀模拟实验结果表明,碳酸盐矿物类型、化学成分等是影响茅口组岩石可溶性的主要因素,样品溶蚀速率、溶液离子浓度及微观溶蚀变化特征均表现为生屑灰岩>泥晶灰岩>白云岩>泥质灰岩。茅口组岩溶层组类型可划分为2类3型9亚型,不同岩溶层组类型岩溶作用条件、岩溶化程度不同,缝洞型岩溶储层发育规模也存在差异。

Kart reservoir is important for the Middle Permian Maokou Formation in the northern part of Sichuan Basin. Based on field outcrops and drilling core data, combining both macro and micro methods, the characteristics of karst strata association of the Maokou Formation in this area was studied by the means of thin section observation, scanning electron microscope, major and trace elements and experimental dissolution. The first member of the Maokou Formation is dominated by marl and bioclastic micritic limestone, and the content of acid insoluble matter is high. The second and third members of the Maokou Formation are dominated by micritic bioclastic limestone and bright crystal bioclastic limestone, and the content of acid insoluble matter is low. The results of dissolution experiments show that the mineral type and chemical composition of carbonate rock are the main factors affecting the solubility of rock. The change characteristics of the dissolution rate of samples, solution ion concentration and micro dissolution are as follows: bioclastic limestone>micrite limestone>dolomite>argillaceous limestone. The karst strata association types of the Maokou Formation can be divided into 2 groups, 3 types and 9 subtypes. The karstification conditions and rock dissolution degree of different karst formation types are different, and the development scale of fracture cave karst reservoir is also different.