Determination of paleo-pressure for a natural gas pool formation based on PVT characteristics of fluid inclusions in reservoir rocks——A case study of Upper-Paleozoic deep basin gas trap of the Ordos Basin

~~Determination of paleo-pressure for a natural gas pool formation based on PVT characteristics of fluid inclusions in reservoir rocks——A case study of Upper-Paleozoic deep basin gas trap of the Ordos Basin~~     

利用储层流体包裹体的PVT特征模拟计算天然气藏形成古压力——以鄂尔多斯盆地上古生界深盆气藏为例

利用PVTsim软件, 通过对鄂尔多斯盆地上古生界山西组砂岩储层中的次生液态烃包裹体和同期含气态烃包裹体的研究, 建立起利用它们的二元一次等容线方程二者联立求得该期包裹体的捕获温度和压力的方法. 研究结果表明, 鄂尔多斯盆地上古生界石炭-二叠系储层砂岩次生包裹体的捕获压力为21~32 MPa, 均一温度在100~110℃范围的含气态烃包裹体, 其最小捕获压力比真正捕获压力低6~7 MPa, 其均一温度比捕获温度低2~3℃; 包裹体的捕获温度和压力从南向北有逐渐减小的趋势; 包裹体的捕获压力远小于当时的静水压力. 这些特征与该深盆气藏形成的地质地球化学条件相一致.     

鄂尔多斯盆地上古生界储层中包裹体最小捕获压力的PVTsim模拟

应用传统的方法求取包裹体的捕获压力存在许多问题。近几个发展起来的PVTsim软件已广泛应用于计算机含油气盆地中液态烃包裹体的捕获压力，然而利用该软件缺乏液态烃包裹体的天然气藏储层中包裹体的捕获压力的文章尚未见报道。在对鄂尔多斯盆地上古生界储层砂岩中次生盐水包裹体进行有关测定和分析的基础上，利用PVTsim软件对该类包裹体捕获压力进行了模拟计算。结果表明，包裹体的最小捕获压力为16－21MPa，并有从南向北逐渐减小的趋势，而且包裹体的捕获压力远小于深盆气藏形成时的静水压力，这一特征与深盆气藏形成的地质地球化学条件相一致。     

Determination of paleo-pressure for a natural gas pool formation based on PVT characteristics of fluid inclusions in reservoir rocks--A case study of Upper-Paleozoic deep basin gas trap of the Ordos Basin

It has been proved to be a difficult problem to determine directly trapping pressure of fluid inclusions. Recently, PVT simulation softwares have been applied to simulating the trapping pressure of petroleum inclusions in reservoir rocks, but the reported methods have many limitations in practice. In this paper, a method is suggested to calculating the trapping pressure and temperature of fluid inclusions by combining the isochore equations of a gas-bearing aqueous inclusion with its coeval petroleum inclusions. A case study was conducted by this method for fluid inclusions occurring in the Upper-Paleozoic Shanxi Formation reservoir sandstones from the Ordos Basin. The results show that the trapping pressure of these inclusions ranges from 21 to 32 MPa, which is 6-7 MPa higher than their minimum trapping pressure although the trapping temperature is only 2-3℃ higher than the homogenization temperature. The trapping pressure and temperature of the fluid inclusions decrease from southern area to northern area of the basin.The trapping pressure is obviously lower than the state water pressures when the inclusions formed. These data are consistent with the regional geological and geochemical conditions of the basin when the deep basin gas trap formed.     

江苏句容-黄桥地区有机包裹体形成期次和捕获温度、压力的PVTsim模拟计算

据流体包裹体显微镜观测和石油包裹体群的气体色谱和全烃色谱、色谱-质谱分析结果，句容和黄桥地区三叠系和下二叠系地层中的石油包裹体明显不同，句容地区三叠系灰岩储层中的石油包裹体的个体较大，在透光下为黄色一棕黄色，荧光显微镜下发亮黄色荧光，包裹体中气态烃的C1／C2-5，比值较低，液态烃中三环萜炕、五环三萜烷和规则甾烷系列的生物标志物化合物含量比较丰富，而句容和黄桥地区下二叠系石油包裹体比较细小，发黄色-黄绿色荧光，包裹体中气态烃的C1／C2-5。比值较高，液态烃中均难检测到甾萜烷系列的生物标志物。由流体包裹体均一温度等观测资料与捕获温度、捕获压力的PVTsim的模拟计算结果：句容地区三叠系储层的石油包裹体捕获温度Tr=107．9℃，捕获压力Pr=289bar，约相当于白垩纪晚期（90～83Ma）充注成藏。句容地区下二叠深灰色灰岩中分布的油包裹体的捕获温度Tr=123℃，捕获压力Pr=305．95bar，反映白垩系晚期还有一期温度比较高的含烃流体充注的现象。黄桥地区在含CO2气藏的下二叠系存在有交切关系的，黄色和黄绿色两种荧光性质不同的石油包裹体，前者模拟计算的捕获温度Tr=97．3℃，捕获压力Pr=184．75bar，后者模拟计算的捕获温度Tr=145．5℃，捕获压力Pr=220．05bar，分别相当于白垩纪晚期（95～90Ma）和白垩纪末期（65～60Ma）有合烃流体运聚现象。但是，由于在白垩纪末-第三纪的抬升作用阶段，油气大量散失，因此在喜山期大量无机CO2充注成藏时期，储层中已不合烃类流体。