Characteristics of fluid inclusions in quartz fractures in Ledong area of Yinggehai Basin and its constraints on gas accumulation

Ledong area in Yinggehai basin is a typical field of high temperature and overpressure gas exploration in China. A large number of fluid inclusions are trapped in the quartz grains of sandstones in Huangliu Formation. Studying its characteristics and composition can analyze the information of gas accumulation in this area. According to the petrography, micro temperature measurement and laser Raman analysis of fluid inclusions, there are two types of fluid inclusions in the Huangliu formation quartz grain fracture: homogeneous and heterogeneous capture. The normally trapped fluid inclusions are mainly distributed between 155-165℃ and 170-180℃, and the compositions of fluid inclusions are CO₂ (gas) and H₂O (liquid) or CO₂ (gas) and CO₂ (liquid) and H₂O (liquid). The characteristics of fluid inclusions indicate that the Huangliu formation in Ledong area experienced at least two periods of CO₂ rich hydrothermal activity, recording the information of inorganic CO₂ filling and reservoir formation in the late burial stage during volcanic activity or deep fault development.