Reservoir Capacity of Cambrian Carbonate of Foreslope Facies in Danzhai and Sandu, Eastern Guizhou
ZHANG Xiulian (School of Earth and Space Sciences, Peking University, Beijing, 100871)
Algae-rich carbonate of Cambrian is typical sediment of foreslope facies in Sandu and Danzhai, eastern Guizhou province. After sediment, it experiences many changes of diagenetic environment, and takes place much diagenetic altercation, among which the biggest is salt water dolomilization, and then is compaction, recrystallization, pressure solution, organic dissolution, burial dolomilization, cementation and silicification. Diagenesis not only can change mineral composition, fabric component, and texture, etc., but more important it can change the reservoir capability greatly, that is, it can build up, or reduce, or enlarge original pores, and even form a series of diagenetic crack. Those secondary pores and cracks are important to improve reservoir capability, especially for carbonate.Deep dissolution is the important diagenesis for forming pores because of its fast buried rate and good preservation of organic matter. The difference is that deep dissolution is strong and fills large amount of bitumen in the section of Danzhai, which shows they are pores when the oil and gas assembled; but pores are comparatively less in the section of Sandu.To sum up, the algae-rich carbonate of foreslope facies can form all kinds of bitumen -associated dissolved pores after experiencing burial dissolution, so it can have good capability of bearing oil and gas.