Abstract:

Physical properties, petrological properties, and microscopic pore structure are key factors controlling movable fluids in tight sandstone reservoirs. To reveal the differences of the movable fluids in the reservoirs of the Shan-1 member in the Sulige gas field, northern Ordos Basin and in the Qingyang gas field, southwestern Ordos Basin, by employing multiple techniques such as X-ray diffraction, scanning electron microscopy, cast thin section analysis, high-pressure mercury intrusion, and nuclear magnetic resonance (NMR), the differences in microscopic pore structure of reservoirs were clarified, and then the differences of movable fluids from the Shan-1 member reservoirs in the two areas were identified. The results show that the pore structures in the two parts can be classified into three types based on pore-throat radius distribution and reservoir physical properties. Type I pore structures are relatively well-developed, with movable fluids present across a wide range of pore radii, and the movable fluid content significantly sensitive to the sorting coefficient. Type II pore structures exhibit uneven pore-throat distribution, with the movable fluid content notably affected by the median pore-throat radius. Type III pore structures have a smaller range of pore radius distribution, with movable fluids mainly concentrated in small pores, and the movable fluid content primarily influenced by clay mineral content. In the Sulige gas field, the Shan-1 member is dominated by Type II pore structures, with a movable fluid content of 24.11%, which is influenced by permeability, median pore-throat radius, and illite content. In the Qingyang gas field, the Shan-1 member is dominated by Type III pore structures, with the movable fluid content mainly influenced by porosity, permeabilty, and clay mineral content.

Key words: Ordos Basin, Sulige gas field, Qingyang gas field, Shan-1 member, tight sandstone reservoir, movable fluid, pore structure, NMR