Abstract:

The coarse-grained and low permeability sandstone reservoirs in Jurassic coal measures in west-central China is characterized by high content of authigenic clay minerals. Especially, the content of kaolinite is very high relative to other clay minerals. The study made in Yanqi basin shows that the total content of clay minerals and kaolinite content decreases with depth below the unconformity, but the content of illite and chlorite increases with depth. At same burial depth, the sandbodies with higher feldspar content and larger thickness in the main channel have more abundant kaolinite. The acidic fluid medium environment was the key factor controlling the formation of clay minerals in coal measure strata. The existence of abundant clay minerals has reduced the permeability and enhanced the sensibility of reservoir, and strongly affected the EOR efficiency in the oilfield.

Key words: coal measure strata, low permeability reservoir, clay minerals, reservoir properties