北部湾盆地福山凹陷原油充注方向及成藏特征

利用油藏地球化学方法研究了北部湾盆地福山凹陷花场油气田流沙港组(E₂l)油气运移和充注方向,分析了流沙港组三段上部与下部油气成藏特征的差异。结果表明花场油气田流沙港组三段上部(E₂l₃1)原油主要来自花场次凸北东方向的白莲次凹,油气沿流二段和流三段之间的不整合面、流三段扇三角洲前缘砂体和断层构成的输导体系运移至花场次凸有利圈闭中聚集成藏。造成流沙港组三段中下部(E₂l₃2—E₂l₃3)相对上部油气藏原油密度略高、成熟度稍低、CO₂气含量高、油气产量低的原因在于:受下部反向正断层的控制,流三段中下部原油可能主要来自花场次凸原地流三段烃源岩的贡献。该烃源岩成熟度和生烃潜力明显低于白莲次凹,输导条件也如上部油气藏优越,断穿流三段并切到基岩的深大断裂可能作为火山—幔源成因CO₂充注的通道。油藏地球化学为判识油气运移充注方向和成藏特征研究提供了直接有力的证据。 

OIL CHARGING ORIENTION AND ACCUMULATION CHARACTERISTICS OF OIL RESERVOIRS IN THE FUSHAN SAG,BEIBUWAN BASIN

By using reservoir geochemical approach,this paper mainly studies on the hydrocarbon migration and charging orientation of Eocene Liushagang Formation(E2l) oil reservoirs in the Fushan Sag,Beibuwan Basin.Combined with the petroleum geological background,the reason that caused the difference between oil pools in upper(E2l13) and mid-lower parts(E2l23-E2l33)of Liushagang Formation has also been discussed.It shows that the oils in E2l13 horizon in Huachang oil and gas field are mainly sourced from the Bailian sub-Sag.The unconformity between E2l2 and E2l3,the sandstone of fan delta front and the faults are good carrier beds for these oils.Comparison with the E2l13,the oils in E2l23-E2l33 horizons have relatively higher density,lower maturity,high content of CO2 and lower oil and gas yields.All these characteristics are determined by the special fault systems and specific geological background.The oils in E2l23-E2l33 horizons are mainly derived from the source rock of the third member of the Liushagang Formation in Huachang area,which have relatively lower thermal maturity and limited hydrocarbon generation potential.Controlled by the giant faults that cut through the E2l3 stratum and terminated in the basement,the volcanic-mantle derived CO2 can migrate through these faults and charge in E2l23-E2l33 traps.The geochemical research provides direct evidence for hydrocarbon charging orientation and pathways.