| The proven ashore un-producing reserves in China is 34. 9384 hundred. million ton by the end of the year 2003, 56 percent of which lies in low or ultra-low permeability reservoirs. Now it is difficult for low permeability reservoirs to have an economic production effect, the producing degree is much different for reservoirs which have close permeability but lying in different regions. The main difference between low permeability reservoir and middle, high permeability reservoir is pore structure. Pore structure is the fundamental factor affect flowing ability and oil displacement efficiency. Pore structure and its effects on flowing ability, production effect and reservoir evaluation are investigated with constant rate mercury injection apparatus and maximum bubble method. Comparative study for Daqing and Changqing oil fields is carried out. Laboratory tests shows that: throat size and distribution law of cores with close permeability in different regions is different, permeability measured with water is different too, which indicates that pore structure is the intrinsic dominating element; Permeability measured with water under reservoir condition is not a constant, but a . variable of pressure gradient. The inflexion value of permeability curve. measured with water in Daqing oil field is 10 times of that in Changqing oil field. Permeability measured with gas has its limitation for low permeability reservoir, average throat radius is more suitable. Low permeability reservoir can be evaluated based on result measured with constant rate mercury injection apparatus. Average throat radius is sufficient and necessary in evaluating reservoir; production effect of low permeability reservoir in Changqing oil field is better than that with close permeability in Daqing oil field, because permeability measured with gas can not reflect reservoir flowing ability and production effect, microcosmic pore structure character is the intrinsic... |
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