成藏期间的流体势是控制油气分布的主要因素，其中古埋深及古压力2个因素直接决定了油气运移方向和聚集部位。利用数值模拟技术恢复了榆林气田上古生界地层压力的发展过程。模拟结果显示，中二叠世~早侏罗世和中侏罗世~晚白垩世山西组内曾发生2次压力积累消散的旋回，晚三叠世和早白垩世为2次超压高峰时期，超压幅度可达10MPa以上，第二次超压高峰与主成藏期同期，扩散作用导致古近纪之后的低压状态。结合古埋深结果分析表明，现今气田主要分布于成藏期的低势区内，空间上受流体势控制明显。

Fluid potential is the key factor of distribution of hydrocarbon. The development of pressure in Upper Palaeizoic group in Yulin region was simulated by basin modeling technique. There are two recurrent processes of pressure development in Shanxi formation. The first occurred from middle Permian to early Jurassic, and the other took place from middle Jurassic to later Cretaceous. In later Triassic and early Cretaceous, there were two peaks of overpressure. The maximum value of overpressure surpassed 10 MPa. It took the same time as that of the hydrocarbon generation and the second peak of overpressure. From Paleogene to nowadays, gas diffusion decreased the coefficient of pressure from 1.4 to 0.8. Nowadays, the gas pool is located in the region of lower fluid potential in the period of hydrocarbon generation. It is suggested that paleo-fluid-potential controlled the distribution of hydrocarbon migration and accumulation in Yulin region.