渤海湾盆地廊固凹陷杨税务潜山油气成藏的流体包裹体证据

Evidence from fluid inclusions for hydrocarbon accumulation of Yangshuiwu buried hill in Langgu sag,Bohai Bay Basin

廊固凹陷杨税务潜山凝析油天然气藏是近年来渤海湾盆地的重要勘探发现,但对其油气成藏过程的认识还不够深入。通过对潜山储层中的流体包裹体进行岩相学、显微测温、拉曼光谱和PVT模拟等分析表明,储层中主要发育5类流体包裹体,即气液两相盐水包裹体、气体包裹体、气液两相烃类包裹体、气液两相富气包裹体和单液相烃类包裹体。杨税务潜山主要发育2期油气成藏过程,以晚期天然气充注为主。第1期烃类包裹体主要发蓝绿色荧光,单相烃类包裹体较多,气液两相烃类包裹体较少,共生盐水包裹体较少,未见含甲烷的富气包裹体,以原油充注为主,形成于东营组沉积期成藏阶段。第2期烃类包裹体以气液两相富气包裹体为主,其气液比相对较大,液相发蓝色荧光,为高成熟度凝析油,富气包裹体中含甲烷等气体,说明成藏的天然气为湿气,成藏期为明化镇组沉积期至今。成藏期的古压力计算表明,第1期成藏的压力系数在1.00~1.17,属于正常压力油气藏;第2期成藏的压力系数相对较高,在0.95~1.33,总体属于正常压力范围,个别井区达到异常高压范围(压力系数大于1.20)。杨税务潜山油气藏的古今压力系数变化不大,表明其封闭性较好,有利于油气保存。

Condensate gas reservoir in Yangshuiwu buried-hill of Langgu sag is an important exploration discovery in Bohai Bay Basin in recent years,but there is still no deep understanding of its hydrocarbon accumulation process.Through the analyses of petrography,microthermometry,Raman spectroscopy and PVT simulation of the fluid inclusions in buried-hill reservoirs,it is shown that five types of fluid inclusions are mainly developed in the reservoirs,including two-phase(vapor-liquid)aqueous inclusions,monophase all-vapor inclusions,two-phase(vapor-liquid)hydrocarbon inclusions,two-phase vapor-rich inclusions and monophase all-liquid hydrocarbon inclusions.There are two periods of oil and gas accumulation developed in Yangshuiwu buried hill area,dominated by late natural gas charging.The hydrocarbon inclusions in the first period mainly show blue-green fluorescence.Among them,there are more monophase hydrocarbon inclusions,less two-phase(vapor-liquid)hydrocarbon inclusions,less coeval aqueous inclusions,and no vapor-rich methane-bearing inclusions,indicating oil charging and accumulation in the sedimentary period of Dongying Formation.In the second period,hydrocarbon inclusions are dominated by two-phase vapor-rich inclusions.The vapor-liquid ratio is relatively large,and the liquid phase shows blue fluorescence,indicating high maturity condensate.The vapor-rich inclusions contain methane and other gases,indicating that the wet natural gas accumulated in the reservoir,and the accumulation period is from the sedimentary period of Minghuazhen Formation to the present.The calculation of paleo-fluid pressure in the accumulation period shows that the pressure coefficient in the first accumulation period is in the range of 1.00 to 1.17,indicating a normal pressure reservoir.The pressure coefficient in the second accumulation period is relatively high,ranging from 0.95 to 1.33.It is generally within the normal pressure range,but reaches to the abnormal high pressure range in several well areas(the pressure coefficient is greater than 1.20).The pressure coefficient of Yangshuiwu buried-hill oil and gas reservoir has little difference between the past and present,indicating that the reservoir has good sealing properties,which is conducive to oil and gas preservation.