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

Liu Hua; Jiang Youlu; Lu Hao; Liu Yali; Jing Chen

doi:10.3799/dqkx.2016.109

Abstract：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 peri-od 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 Es 3 Member reservoir is yellow-white,and yellow-green,and the homogenization temperatures of fluid inclusions are 80-130 ℃,indicating that hydro-carbons 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 hydrocar-bon 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 sec-ond period of hydrocarbon charging,due to a large amount of hydrocarbons generated by the matured source rocks,the abnor-mal pressure gradually increased,the overpressure area enlarged,and the formation pressure coefficient reached 1.80.The over-pressure could have provided sufficient driving force,and affected the directions of hydrocarbon migration and accumulation.