秦南凹陷陡坡带Q29构造含CO_2凝析气藏储层特征及成因

The Genesis and Characteristics of CO_2-bearing Condensate Gas Reservoir in Q29 Structure in the Actic Area,Qinnan Depression,Bohai Bay Basin

秦南凹陷陡坡带Q29构造含CO_2凝析气藏,片钠铝石不发育,物性好,与传统含CO_2储层有较大差别。通过偏光显微镜、扫描电镜、X射线衍射、同位素分析等,明确了CO_2成因,含CO_2储层特征及储层高孔渗成因。研究区CO_2质量分数为25%~59%,δ^(13)C(CO2)(值为-5.2‰^-6.4‰(PDB),R/Ra为3.9~4.4,具有明显的岩浆-幔源特征;CO_2热流体侵位后成岩共生组合为次生加大石英+自生石英+自生高岭石;CO_2热流体侵入后加剧了溶蚀作用,含CO_2储层段次生孔隙比例较高;与同成岩阶段不合CO_2的储层相比,自生高岭石相对含量高,伊利石相对含量低;CO_2热流体对碳酸盐胶结物溶蚀并重新分配,有利于主储层段物性改善;由于受多期酸性流体侵位影响,储层中片钠铝石含量低、结晶差,对储层物性影响小。上述原因是含CO_2储层高孔渗的主要原因。

CO2-bearing condensate gas reservoir in Q29 Structure in Qinnan depression, is characterized by good physical property, low level of dawsonite, which is different from most of CO2-bearing reservoir. Through analysis with polarizing microscope, scan- ning electron microscope, X-ray diffraction and isotope analysis, etc, the genesis of CO2 and origin of CO2-bearing high-quality reservoir have been made clear. In the study area, the content of CO2 ranges from 25% to 59%, the value of 613C CO2 is from -5.2%0 to -6.4‰（PDB） and the R/Ra is from 3.9 to 4.4, all of which are the obvious features of mantle origin magma. The diagenesis para- genetic association are composed of overgrowth quartz, authigenic quartz and authigenic kaolinite after the incursion of the thermal fluid of CO2, which increased reservoir dissolution. Therefore, the secondary pores are well developed in CO2-bearing reservoir. Compared with the reservoir without bearing CO2 developed at the same diagenetic stage, the relative content of authigenic kaolinite is higher and the content of illite is lower in CO2-bearing reservoir. The dissolution and redistribution of carbonate cementation made by the thermal fluid of CO： are favorable for the improvement of physical properties of main reservoir. For multiperiod acidic fluid invasion, the content of dawsonite cementation is low and poorly crystallization, which has little influence on reservoir. All of above are the main reasons for the higher porosity and high permeability in CO2-bearing reservoir.