Abstract:

The characteristic that the methane gas solubility changes with temperature, pressure and salinity is illustrated based on determining the solubility of the methane-rich gas in sodium bicarbonate solution at various temperatures（90-200 ℃）and pressures（20-120 MPa）. On the basis of previous studies, the relationships between the solubility of natural gas and temperature are divided into three stages: ①Slowly descending phase(0-80 ℃)；②Rapidly increasing phase (>80-150 ℃); ③Slowly increasing phase (>150 ℃). With the buried depth increasing, the solubility of natural gas changes in different phases under the synergetic effects of temperature and pressure. When temperature and pressure of formation water are high enough, the dissolving capacity of methane may be closer to a particular limit. Applying solubility regression equation is favor to estimate the boundary of natural gas segregation. There are four accumulation models in China that water-soluble gas is segregated formation water associated with the structure and percolation-related，including lateral phase degassing, fault-diapiric degassing, caprock percolation degassing, structures uplift degassing.

Key words: temperature, pressure, methane, solubility, water-soluble gas, gas accumulation models