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Figures are missing from the paper. Abstract Much attention is now paid to the development of low permeable reservoirs. However, there is almost a dearth of literature on the study of relative permeabilities in rock samples with low permeability. Group J2S of QL Reservoir is characteristics of low porosity, low permeability and low crude oil viscosity. Oil-water relative permeabilities of QL Reservoir have been measured at two different oil/water viscosity ratios by using unsteady-state method. The experimental results showed that the oil-water relative permeabilities change with the changing of oil/water viscosity' ratio. It is explained that the oil-water relative permeabilities measured at oil/water viscosity ratio close to the oil/water viscosity ratio under reservoir condition coincide with the practical situation of QL Reservoir by comparing the injection-production ratio calculated from laboratory water flooding data with the practical one. The irreducible water saturations in QL Reservoir rocks range from 27.7% to 35.8% and its average value is 31.5%. The water flooding residual oil saturations range from 11.6% to 21.7% and its average value is 14.8%. Most of the water relative permeabilities at residual oil saturations range from 0.23to 0.50 and its average value is about 0.388. Oil-water 2-phase flowing limit ranges from 47.8% to 59.0% and its average value is about 53.7%. Moreover, the end water relative permeabilities are correlated with the air permeabilities of rock samples. That is, the bigger the air permeabilities of the rock samples, the higher the end water relative permeabilities. Introduction The development of a reservoir by water injection usually includes an oil-water 2-phase or an oil-gas-water 3-phase flowing in porous media(reservoir rock). The efficiency of development by water injection is closely related to the multi-phase flow in porous media which is dependent on rock permeability, pore structure, wettability, capillary pressure, interfacial tension, viscosity of fluid and relative permeability of each phase. The basic idea of relative permeability is simple. However, the factors to affect relative permeability are very complex. Many literatures about relative permeability published now explain that it is very difficult to obtain really representative and true relative permeability data. P. 497
Quantitative Description for the Heterogeneity of Pore Structure by Using Mercury Capillary Pressure Curves
Shen, Pingping (Research Institute of Petroleum Exploration and Development, P.R. China) | Li, Kevin (Research Institute of Petroleum Exploration and Development, P.R. China) | Jia, Fenshu (Research Institute of Petroleum Exploration and Development, P.R. China)
Abstract 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. Introduction There are now two basic methods to study pore structure. One of them is to use mercury-injection capillary pressure curve(mercury-injection method). Another is image analysis method. Relatively, mercury-injection method is used more frequently. Some characteristic and statistical factors of a capillary pressure curve such as pore geometry factor G, threshold pressure Pd proposed by Thomeer, puzzler coefficient proposed by Dullien and microscopic homogeneous coefficient a proposed by Shen Pingping et al are usually used to describe pore structure when mercury-injection method is applied. In recent years, it was found that pore structures of sandstones or other porous media are fractals. P. 447