DIAGENESIS OF THE CARBONATE ROCKS OF THE MAJIAGOU FORMATION IN THE ORDOS BASIN:FRACTURES AND THEIR IMPLICATIONS FOR OIL AND GAS STORAGE

Fractures are well developed in the carbonate rocks of the Ordovician Majiagou For-mation in the Ordos Basin.In this paper,the fractures investigated are interpreted as the products of diagenesis,and underwent seven stages of evolution,which have been distin-guished in terms of the crosscutting relationships between the fractures,relationships be-tween fractures and diagenetic fabrics,types and geochemical characteristics of the fillings within the fractures.Viewed from the history of the fracture formation,matching with that of organic matter maturation,the Ⅵ and Ⅶ stages of fractures created by Yanshanian and Himalayan Movements,respectively may become valid fractures for oil and gas storage,and play an important part in the migration and accumulation of oil and gas in the central part of the basin and the Tertiary faulted trough areas.