Pore structure of reservoir rock is one of the most important factors to affect microscopic oil and water flowing in porous media and the development efficiency of an oil field developed by water injection. There are now many methods for describing pore structure. However, much attention is being paid to develop better and more efficient methods. Fractal dimension has been used to quantitatively describe the heterogeneity of pore structure in this paper. It has been showed that the larger the fractal dimension of pore structure, the more heterogeneous the pore structure for sandstones, sandstones with gravel and pinhole dolomite rocks. The fractal dimension of pore structure is calculated from the mercury-injection capillary pressure curve of the rock.

The typical two-section fractal behaviour of sandstone pore structure in Lamadian Oilfield, Daqing has been studied in this paper. It has been found that there is a good correlation between the fractal dimension of large pores with fractal behaviour and the oil recovery at water breakthrough while there is also a good relationship between the fractal dimension of the small pores with fractal behaviour and irreducible water saturation. This shows that the large fractal pores affect the amount of oil recovery at water breakthrough and the small fractal pores affect the amount of irreducible water saturation for this type of sandstones from Lamadian Oilfield. It has also been found that there is no relationship between the fractal dimension of pore structure and the oil recovery at water breakthrough if the pore structure of sandstone from Lamadian Oilfield was treated as one-section fractal structure.

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