PORE STRUCTURES CHARACTERISTICS AND POROSITY EVOLUTION OF TIGHT SANDSTONE RESERVOIR: TAKING THE CHANG 63 TIGHT SANDSTONES RESERVOIR OF HUAQING AREA IN ORDOS BASIN AS AN INSTANCE

The tight sandstone reservoir of Chang 6(3) Formation of Huaqing Area in Ordos Basin were divided into three types based on its different pore types: formation with intergranular pore type, dissolved-intercrystalline pore type and pore plus fracture type reservoirs, which were dominated by casting thin sections, scanning electron microscope(SEM), granularity image, high-pressure mercury injection, constant-rate mercury injection, nuclear magnetic resonance and real sandstone micro model experiment, and the porosity evolution path in each type were studied. The study shows that: The physical property, pore structure, and type of displacement in each reservoir type have obvious differences, which indicate that the reservoir classification evaluation which is based on pore assembly type has its own applicability in research region. Combined with parameters such as buried depth and temperature, the porosity evolution path has apparent control on pore structure. The porosity evolution of reservoirs with different pore types reveals the effect of increased and decreased porosity on the reservoir's quality. Pore structures have close relationship with productivity law.