济阳坳陷中浅层气溶脱机制及成藏规律

Exsolution Mechanism and Gas-Accumulation Feature in Shallow-Middle Depths in Jiyang Depression

济阳坳陷中的石油伴生气是中浅层气藏的主要来源，生物气和油藏中原油降解形成的甲烷气也可以提供部分气源。中浅层气藏形成的关键在于溶解气的脱气及其进一步封存，影响脱气的主要因素是压力、温度和油气性质，其中压力是主导因素。在济阳坳陷，中浅层气藏分布在500～2000m间。地下温压场对该区中浅层天然气藏的形成和分布起控制作用，只有当地层饱和压力差低于3MPa时，才会形成气顶或气层，济阳坳陷脱气点的对应深度是1500～2000m。中浅层气藏在济阳坳陷中的分布主要与断层有关，断层是天然气垂向运移的主要通道，运移过程中的分异是中浅层气藏形成的重要机制。

The gas pools existing in shallow-middle depths are important gas exploration targets in the oilproducing basins in East China. This kind of gas pool has secondary genesis and associate gas is dominant source. Moreover,the biogas and methane derived from degradation of oil provide part of sources in Jiyang basin. The main gas-reservoir dynamics is the exsolution of dissolved gas and trapping. The factors controlling the exsolution are pressure, temperature and physical-chemical property of the crude oil,in which pressure is the most important. This kind of gas pool occurs at 500-2 000 m in the Jiyang basin. The subsurface temperature-pressure field is responsible to the gas accumulation and distribution. In case of difference between formation pressure and saturation pressure of oil reservoir below 3 MPa, natural gases are isolated from crude oil and water, thus forming gas cap and gas bed. The exsolution point is responds to 1 500- 2 000 m. The faults are important pathway of gas migration vertically. The differentiation of oil and gas along the fault is important accumulating mechanism. The distribution of the gas pools in shallow-middle depths in the basin are related with the faulting zone.