Studying the Accumulation Characteristics of Crude Oil in an Oil Formation in the Aspect of Predicting the Effectiveness of Crude Oil Exploration

The development of tight oil sandstones in the Extension Formation in the southwestern Ordos Basin and the mode of crude oil migration is a hotspot. A large number of geochemical experiments and computational methods were used to systematically study the crude oil transport characteristics of the Yanchang Formation in the Huaqing area. The results show that four typical types of inclusions are developed in the Yanchang Formation: inclusions in quartz fissures, inclusions in quartz colluvium and large rims, inclusions in calcareous colluvium, and inclusions in sodium feldspar. There are two peaks in the homogenization temperature of the inclusions: 80-100°C and 120-130°C. The Chang 6 and Chang 8 reservoirs in the Huaqing area have experienced the process of densification while forming reservoirs, and the physical properties of the sand body reservoirs during the maximum hydrocarbon discharge period are good, which is an effective channel for oil and gas transportation. The minimum oil column heights for oil and gas transportation in Chang 6 and Chang 8 Members are 7.48m and 15.68m, respectively. Proximity vertical transportation is an important mode of crude oil transportation and aggregation in the Yanchang oil group in the Huaqing area. The physical properties of crude oil in Huaqing area are good, showing low density, low viscosity, low freezing point and good fluidity. The hydrocarbon source rocks of the Chang 7 Member were transported under excess pressure and buoyancy along channels such as cheese root networks, connected sands and microfractures, and thus large composite lithologic reservoirs were formed in the Chang 6 and Chang 8 Members.