Abstract: Detailed investigation of the grain size analysis data in tertiary pilot area, middle District No. 2, Karamay oilfield got the idea that the result from flushing precipita-tion became apparently distorted. especially the shaly content, while the data from sieve .analysis accord well with the actual conditions of the reservoir. Because of low shaly con-tent in conglomerate reservoir, it doesn't obviously affect the reservoir permeability.

Key words: Karamay oilfield, Conglomerate, reservoir, Grain, size analysis, Shaly content, Permeability