柴达木盆地东部第四系气藏盖层疏松未成岩，具有高孔、高渗的特征，但盖层具独特的封闭机理及模式，封盖了大规模的天然气。通过计算盖层与储集层的排替压力差和理论封盖气柱高度，评价了盖层的有效性，同时计算了生物气藏中气体突破盖层时间和气体渗流速率，揭示气藏的封盖过程。结果表明，未成岩盖层有效性随埋藏深度的增加变好，而且当气藏储集层中气柱高度大于盖层理论封盖气柱高度时，下部气体可以通过盖层渗流散失，但渗流过程是短暂的，之后气藏又处于封盖状态。总之气藏的封盖-渗流是动态平衡过程，因此叠置的储集层与盖层依靠排替压力差仍可封盖一定量的气体，这就是未成岩气藏盖层的叠加式封盖模式。%The gas reservoir of the Quaternary in eastern Qaidam basin is characterized by unconsolidated and un-diagenetic cap rocks with high porosity and permeability. It has unique sealing mechanism and model for formation of large-scale gas reservoir. This paper calcu- lates the displacement pressure difference between cap rock and reservoir, the theoretical sealed gas-column height, and then evaluates the sealing efficiency, obtains the time that biogas broke through the cap rock and the gas seepage flow rate, and reveals the sealing process of the gas reservoir. The results show that the effectiveness of the un-diagenetic cap rock is becoming better with increase of buried depth, and when real gas reservoir's gas-column height is bigger than the theoretical sealing gas-column height, the gas below it can percolate and he lost through the cap rock. However, the flow process is short, and then the gas reservoir is also in sealing condition. It is concluded that it is dynamic balancing process for the sealing and seepage of gas reservoir, so the stacked reservoir and cap rock can still seal a certain amount of gas by displacement pressure difference. This could be the stacked sealing model for un-diagenetic gas cap rocks.
展开▼
