渤南洼陷流体包裹体特征与成藏期流体压力恢复

Restoration of Fluid Pressure during Hydrocarbon Accumulation Period and Fluid Inclusion Feature in the Bonan Sag

渤南洼陷油气资源丰富,成藏过程复杂,但其油气成藏时期的动力条件尚不明确.利用流体包裹体显微荧光、均一温度和冰点测试技术,恢复了渤南洼陷主力储层油气成藏期次及其对应的地层压力.研究区沙三段烃类包裹体发黄白色和黄绿色荧光,均一温度为80~130℃,为明化镇中后期至今一期成藏;沙四段烃类包裹体灰黄色、黄绿、蓝绿色3种荧光,存在70~80℃和90~130℃两个温度区间,对应着东营期、明化镇初期至今两期油气充注,且以晚期充注为主.油气运聚时期普遍发育异常高压,第一期成藏时压力系数相对较低;第二期随着烃源岩生烃量的增加,异常压力持续增大、超压范围不断扩展,压力系数高达1.80,为大规模的油气运移提供了充足的动力条件,并控制了洼陷区油气的聚集与宏观分布.

Bonan sag is rich in oil and gas resources,yet its complicated accumulation process results in a poor understanding of its dynamic conditions during hydrocarbon accumulation.In this study,the fluid pressure in the hydrocarbon accumulation period was recovered in the Bonan sag using such fluid inclusion analysis techniques as microscopic fluorescence,homogenization temperature and freezing point.The results show that the fluorescence of hydrocarbon inclusions in Es3 Member reservoir is yellow-white,and yellow-green,and the homogenization temperatures of fluid inclusions are 80-130℃,indicating that hydrocarbons were accumulated during the period from the middle and late stage of Minghuazhen Formation deposition to present.Whereas the fluorescence of hydrocarbon inclusions in the Es4 Member reservoirs is yellow,yellow-green and blue-green,and the homogenization temperatures of fluid inclusions are 70-80℃and 90-130℃,corresponding to the two stages of hydrocarbon accumulation,namely the Dongying stage and the early stage of Minghuazhen to present,of which the latter is dominant.Meanwhile,reservoirs were generally with abnormal pressure in the period of hydrocarbon accumulation on a large scale.In the first period of hydrocarbon charging,the hydrocarbon generation was limited with the weak pressure coefficient,but in the second period of hydrocarbon charging,due to a large amount of hydrocarbons generated by the matured source rocks,the abnormal pressure gradually increased,the overpressure area enlarged,and the formation pressure coefficient reached 1.80.The overpressure could have provided sufficient driving force,and affected the directions of hydrocarbon migration and accumulation.