MICROSCOPIC PORE-THROAT DISTRIBUTIONS AND CORRESPONDING DIFFERENCE ANALYSES OF TIGHT SANDSTONE RESERVOIRS -A CASE STUDY IN CHANG 6 RESERVOIRS OF HUAQING AREA AND GANGUYI AREA IN ORDOS BASIN-

The microscopic characteristics of pore-throat distribution and corresponding differentiation of the Chang 6 reservoir in Huaqing area and Ganguyi area of Ordos basin are studied by means of thin section, scanning electron microscope, X-ray diffraction, image analysis of porosity, rate-controlled mercury injection, and nuclear magnetic resonance. The results approve that the pore types in these two areas both are dominated by residual intergranular pores and dissolved pores whereas there exist differences for the development of throats. The throats distribution of Chang 6 reservoir in Ganguyi area is more concentrated than that in Huaqing area. In Huaqing area, the radius of most throats (micro-thin throats) are less than 0.5 mu m and little large throat is developed. On the other hand, the medium-thin throats can be observed in Ganguyi area with radius larger than 0.5 mu m. Generally, the development of the number of effective pores and throats in Ganguyi area is more desirable compared with Huaqing area. Throat radius and pore-throat ratio have important effects on reservoir seepage capacity in both areas. However, the radius of throats has a greater impact on energy storage and seepage capacity in Ganguyi area than that in Huaqing area. Furthermore, the movable fluid saturation and the movable fluid porosity of the reservoirs in two areas can be obviously influenced by the change of pore-throat ratio. The change of pore throat ratio is able to preferably characterize the seepage capacities of tight sandstone reservoirs in the areas.