Micropore structure and water driving characteristics of tight sandstone reservoirs in Ordos Basin

In order to explore the influence of the micropore structure of the tight sandstone reservoir in the water driving characteristics, the studies on the Chang 6 tight sandstone reservoir of the middle-western part of Ordos Basin are carried out by various experiments such as cast-thin section analysis, scanning electron microscopy, high-pressure mercury injection and micro-water driving. The result shows that the permeability contribution curves of samples shift to the left as the sample permeability decreases, indicating that the greater the permeability, the greater the proportion of large pores. The permeability is mostly dominated by pores with the radius larger than R50–R60. There are big differences in the water driving type, oil-driven efficiency and residual oil distribution characteristics between reservoirs of different types. The type II reservoir is the major target of subsequent exploration and development, where water driving types consist of mesh and finger, leaving the residual oil mainly locked by water or isolated as oil drops. The size and distribution feature of pores are the key factors dominating the oil-driven efficiency.