川西坳陷新场气田须家河组五段流体赋存状态

川西坳陷新场气田上三叠统须家河组五段气藏试采均表现出气水同产，天然气究竟是以水溶气还是游离气为主尚无定论。为此，对该区须五段地层水开展了不同温压条件下的甲烷溶解度实验，并与1 mol/kg NaCl溶液中甲烷的溶解度进行对比，并结合现今产出流体气水比和理想气体状态方程，明确了须五段中流体的赋存状态。研究结果表明，在现今平均埋深和历史最大埋深状态下，新场须五段地层水中甲烷的溶解度分别为2.260 m³/m³和3.194 m³/m³。受白垩纪末以来地层抬升影响，新场须五段水溶气脱溶主要是地层抬升减压降温脱溶。在不同埋深状态下，游离气和地层水在孔隙中所占体积比例分别普遍低于和高于50%，白垩纪末以来地层温压降低使得须五段中游离气体积发生膨胀，所占体积比例略有增大，而地层水被驱替排出，所占体积比例有所降低。地层温压降低导致部分水溶气脱溶出来，在总的天然气中游离气所占比例增大而水溶气所占比例降低，须五段天然气以游离气为主，水溶气所占比例不足5%。在地层抬升过程中，新场须五段有约29.3%的水溶气脱溶成为游离气，地层水共脱溶出了约1.8×10⁹ m³的天然气。

Fluid state in the 5th Member of the Upper Triassic Xujiahe Formation in the Xinchang gas field,Western Sichuan Depression in Sichuan Basin

Gas and water are simultaneously produced from the reservoirs in the 5^th Member of the Upper Triassic Xujiahe Formation (T₃x⁵) in the Xinchang gas field in the Western Sichuan Depression,and there is no consensus on whether the gas is free or dissolved.For this purpose, methane solubility experiments were conducted under different temperatures and pressures on the T₃x⁵ formation water,and the results were compared with the methane solubilities in 1 mol/kg NaCl solution.The fluid state in T₃x⁵ was demonstrated in combination with the gas/water ratio of the produced fluid and ideal gas state equation.The results indicate that methane solubilities in T₃x⁵ formation water under present average depth and historical largest depth are 2.260 m³/m³ and 3.194 m³/m³,respectively.The water-soluble gas in T₃x⁵ formation water was mainly released by reduction of pressure and temperature during uplifting since the end of Late Cretaceous.The volumetric proportions of free gas and formation water in the T₃x⁵ pores were generally lower and higher than 50%,respectively.The volumetric proportion of free gas increased slightly due to the volumetric expansion caused by reduction of pressure and temperature since the end of Late Cretaceous,whereas that of formation water decreased as the water was displaced.Due to the partial degasification of water-soluble gas by reduction of pressure and temperature,the proportions of free gas in the total natural gas increased while that of water-soluble gas decreased.The T₃x⁵ natural gas was dominated by free gas,with water-soluble gas accounting for less than 5%.Moreover,about 29.3% of the T₃x⁵ water-soluble gas was released and turned into free gas by reduction of pressure and temperature during uplifting,and the total amount of gas released from the T₃x⁵ formation water reached 1.8×10⁹ m³.