莺—琼盆地温压场与天然气运聚关系

INFLUENCE OF GEOTHERM GEOPRESSURE FIELD ON THE MIGRATION AND ACCUMULATION OF NATURAL GAS IN YING QIONG BASIN

莺—琼盆地位于海南岛以南，是一个年轻的高温超压新生代沉积盆地，它由彼此相邻的莺歌海、琼东南盆地组成。存在异常高温有水层、气层、泥拱带及一号断裂带东南部，地温梯度多数大于４．０℃／１００ｍ。该盆地异常高压的产生主要是由于晚期快速沉降、压实与排液不均衡、新生流体作用、水热增压作用、压力沿破裂带或渗透性地层传递等因素所造成。通过分析盆地温压场特征，认为异常温压对生储盖层和天然气运聚有明显的影响：高地温梯度使烃源岩成熟门限深度变浅，超压抑制烃源岩的演化速度、延长有效生烃期；异常温压增强了天然气水相运移，水势差是天然气运移的主要动力，低势区和超压带的上下是天然气成藏的有利区带。莺歌海和琼东南盆地各自存在３个水动力系统，用地震速度预测出每个系统的流体势分布，进而分析得出琼东南ＹＣ１３—１、莺歌海等一批构造是天然气运聚的有利区带。

Ying Qiong Basin is located in the south of Hainan Island,being a youthful Cenozoic sedimentary basin with high geotherm and overpressure.It is composed of the Yinggehai and Qiongdongnan Basins which are adjacent to each other.In these basins there are abnormal high geothermal water bearing formation,gas bearing formation and mud diapir belt,etc.,most of the geothermal gradients in the southeast of Fault,No.1 being more than 4℃/100 m.The formation of abnormal high geopressure in the basin is mainly attributed to the factors as the late period fast subsidence,unbalanced compaction and impeded liquid expelling,the effect of neogenic fluid,the effect of hydrothermal pressure increase and the pressurization along fractured zone or permeable formation,etc.Through analyzing the characteristics of the geotherm geopressure field in the basin,it is thought the abnormal geotherm geopressure has an obvious effect on the source bed,reservoir and caprock and on the migration and accumulation of natural gas.The high geotherm gradient can cause the source rock's mature threshold depth to be shallowed and the overpressure may restrain the maturation of source rock,extending its hydrocarbon generation period,as well as the abnormal geotherm and geopressure can strengthen the gas migration in water dissolved state.The potential difference is the main dynamic force of gas migration,therefore the lower potential areas and the intervals up and/or below the overpressure zones are the regions favourable for forming gas reservoirs.There are three hydrodynamic systems in the Yinggehai and Qiongdongnan Basin respectively and the potential distribution in each system is forecasted by use of the seismic velocity data.Through analyzing,it is concluded that a lot of structures including the YC13—1 structure belt in Qiongdongnan Basin and the DF1—1 structure belt in Yinggehai Basin are the areas favourable for the migration and accumulation of natural gas.