Pore throat structure characteristics of tight sandstone reservoirs and their influence on movable fluid occurrence: Taking the Chang-7 Member of Qingcheng area of Ordos Basin as an example

Abstract

Objective The analysis of pore structure and movable fluid distribution characteristics is the key element of reservoir research and is also the focus and hotspot of current research. It is of great significance for exploring tight sandstone oil and gas and improving oil and gas recovery. Methods The Chang-7 Member tight sandstone reservoir in the Qingcheng area of Ordos Basin was selected as the research object in this paper. Combined with fractal theory, through physical property tests, casting thin section, scanning electron microscopy (SEM), high-pressure mercury injection, and nuclear magnetic resonance (NMR) experiments, the pore throat structure, heterogeneity, and movable fluid distribution characteristics of tight sandstone reservoirs were analysed, and the influence of the pore throat structure and heterogeneity on movable fluid occurrence was discussed. Results The results show that the reservoir space of the Chang-7 Member reservoir in the study area is mainly contributed by micro-nanopores, which have poor pore connectivity. The pore throat radius is mainly 0.050-0.500 μm. The heterogeneity of the pore throat structure is strong, and the fractal dimension distribution is between 2.65 and 2.90. The fluid mobility is poor, and the movable fluid saturation is distributed between 16.68 % and 51.74 %, the movable fluid is mostly distributed in medium and small pores. The Chang-7 Member reservoirs in the study area can be divided into three types. From the type Ⅰ reservoir to the type Ⅲ reservoir, the development of residual intergranular pores and intergranular dissolution pores decreases, and the pore connectivity becomes poorer, and the pore throat size decreases, and the content of larger pore throats decreases, and the heterogeneity becomes stronger, and the fluid mobility is worse, and the movable fluid content in the medium and large pores tends to decrease, and movable fluid tends to occur in the small pores. Conclusion This study provides a theoretical basis for tight sandstone oil and gas exploration and improving oil and gas recovery.

Keywords

• chang-7 member
• tight sandstone reservoir
• pore throat structure
• heterogeneity
• movable fluid saturation
• ordos basin