In gypsum–carbonate rock assemblages, multistage and complex fluids control the formation of dolomite reservoirs that are a focus of hydrocarbon exploration. It is difficult to determine the types of dolomite reservoirs and their formation mechanisms due to the diverse rock assemblages and multiple stages of diagenesis. In this study, we investigated the petrology, reservoir physical properties, and geochemistry of the 6th sub-member of member five of the Majiagou Formation (i.e. Ma₅⁶) in the Ordos Basin, China. These data were used to determine the nature and types of gypsum–carbonate rocks, and constrain their reservoir characteristics and diagenetic history, and fluid-related mechanisms that led to dolomite reservoir development and preservation. The Ma₅⁶ was deposited on a restricted evaporatic platform in the North China Craton, and contains three main types of dolomite reservoirs with variable types of reservoir space. Dolomite reservoir formation was closely related to penecontemporaneous dolomitization, karstification, and differential cementation. Early large-scale dolomitization produced dolomitized carbonate sediments that were resistant to compaction and dissolution, which was conducive to the preservation of primary and secondary pores. The intermittent exposure and dissolution of mound–shoal facies sediments, due to high-frequency sea-level fluctuations, was the dominant mechanism for formation of secondary dissolved pores and high-quality reservoirs. During burial, differential cementation occurred due to interaction between fluids and pore size, which determined the extent of reservoir preservation. In general, the studied dolomite reservoirs have undergone multistage diagenesis and alteration, which led to complex and multistage development of the reservoir porosity. However, the reservoir lithology and pore space developed mostly in the depositional to penecontemporaneous stages. Our results provide new insights into the origins of deeply buried dolomite reservoirs in carbonate–evaporite successions.

在石膏-碳酸盐岩组合中，多级复杂流体控制着白云岩储层的形成，这是油气勘探的重点。由于岩石组合多样、成岩作用多阶段，难以确定白云岩储层的类型及其形成机制。本研究对鄂尔多斯盆地马家沟组五段六亚段（即马₅ ⁶）的岩石学、储层物性和地球化学进行了研究。这些数据用于确定石膏-碳酸盐岩的性质和类型，并限制其储层特征和成岩历史，以及导致白云岩储层开发和保存的流体相关机制。马₅ ⁶沉积在华北克拉通的一个受限蒸发平台上，包含三种主要类型的白云岩储层，储层空间类型不同。白云岩储层的形成与准同生白云岩化、岩溶作用和差异胶结作用密切相关。早期大规模白云石化作用产生的白云石化碳酸盐岩沉积物具有抗压实和溶解能力，有利于原生、次生孔隙的保存。由于海平面的高频波动，丘滩相沉积物的间歇性暴露和溶解是次生溶孔和优质储层形成的主要机制。在埋藏过程中，由于流体和孔隙尺寸之间的相互作用，发生了差异胶结作用，这决定了水库保存的程度。总体而言，所研究的白云岩储层经历了多期成岩和蚀变，导致储层孔隙度复杂、多期发育。但储集层岩性和孔隙空间主要发育于沉积至准同生期。我们的研究结果为碳酸盐岩-蒸发岩层序中深埋白云岩储层的起源提供了新的见解。