东营凹陷北带民丰洼陷深层凝析油藏成藏史及其勘探意义

Accumulation history of the deeply buried condensate reservoir in Minfeng sag of the northern Dongying depression and its exploration significance

盆地深层高温、高压特点决定其油气成藏的复杂性。在东营凹陷北带民丰洼陷丰深1井深层流体包裹体宿主矿物成岩序次、烃类包裹体荧光光谱分析、显微测温以及石油包裹体热动力模拟研究的基础上,结合盆模技术、天然气碳同位素地球化学和原油裂解动力学,探讨了东营凹陷北带深层丰深1井凝析油气成藏过程中的PVTx-t(压力-体积-温度-组分-时间)演化史。结果表明,丰深1井沙河街组四段下亚段(简称沙四下亚段)伴随常压—低幅超压—常压的压力旋回相应地发生过2幕原油和1幕天然气充注。其中发淡黄色—蓝白色荧光油充注代表了第1幕油充注,形成早期油藏,晚期深部原油裂解气再次充注并对早期油藏施加了调整改造之影响,以至最终形成了现今的凝析油藏(第2幕蓝色荧光油)。丰深1井深层油气成藏特点决定该区构造高部位以油藏、深部以原油裂解气藏、中部以凝析油气藏为特征的分布格局。这种深层油气成藏模式对中国东部其他断陷盆地深层的油气勘探具有一定的指导意义。

Characteristics of high temperature and high pressure in a deeply buried reservoir of basins determine the complicacy of petroleum migration and accumulation.Based on the petrologic sequence of host minerals in fluid inclusions,fluorescence spectrum analysis of hydrocarbon-bearing fluid inclusions,microthermometry and thermodynamic modeling of petroleum inclusions and integrated with basin modeling,natural gas carbon isotopic geochemistry and kinetics of crude oil cracking,we discussed the pressure-volume-temperature-composition-time（PVTx-t）evolutionary history of deeply buried condensate accumulation of Well Fengshen1 in the northern Dongying depression.The result showed that accompanied by a pressure evolutionary cycle of normal pressure to lower overpressure and then to normal pressure again,there occurred accordingly two oil-charging episodes and one gas-charging episode in the lower sub-member of Member 4 of Shahejie Formation（Es4x）of Well Fengshen1 in the northern Dongying depression.The first episode oil featured by yellow to blue-white florescence color contributed to the early oil accumulation,and the present gas condensate pool with the second episode oil featured by blue florescence color,was formed due to the late recharging of deep oil cracking gas and the alteration of the former oil pool.Characteristics of deeply buried oil-gas accumulation in Well Fengshen1 determined the distribution pattern of hydrocarbons in the study area,which shows the oil reservoir in the structural high,the oil-cracking-gas reservoir in deeply buried formations,and the gas condensate reservoir between them.This hydrocarbon accumulation pattern in deeply buried formations in Minfeng sag is of a certain instructive significance in petroleum exploration of deeply buried formations in other rift basins in eastern China.