富甲烷天然气溶解实验及水溶气析离成藏特征

Solubility Experiment of Methane-Rich Gas and Features of Segregation and Accumulation

对不同温度（90~200℃）和压力（20~120 MPa）条件下的富甲烷天然气在碳酸氢钠溶液中的溶解度值进行了实验测定,阐述了甲烷溶解度随温度、压力及矿化度的变化特征。综合前人的实验结果,将天然气的溶解度与温度的关系划分为3个阶段：①缓慢递减阶段（0~80℃）;②快速递增阶段（〉80~150℃）;③缓慢递增阶段（〉150℃）。在温压的共同作用下,溶解度随埋藏深度的增加,也具有不同的阶段变化特征;且当地层水温度、压力足够高时,甲烷的溶解能力趋近于某一极限值。利用甲烷溶解度回归方程有助于对不同地区水溶气析离脱气界限的估算。我国主要存在包括侧向阶段脱气、断裂-底辟脱气、盖层渗滤脱气和构造抬升脱气4种与构造和渗滤作用有关的水溶气析离成藏模式。

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.