生物降解作用对储层抽提物中多甲基取代萘分布的影响

对辽河盆地冷东油田冷43块沙三段油藏3口取心井岩心抽提物进行了详细的地球化学分析, 族组成和饱和烃生物标志物分布显示油藏遭受了不同程度生物降解作用的影响, 降解程度由油柱顶部向底部增大, 呈良好梯度变化特征.对比不同降解程度原油样品中三甲基萘、四甲基萘和五甲基萘含量和分布可以发现生物降解的明显控制作用, 根据甲基取代萘异构体在生物降解过程中相对含量的变化初步确定了三甲基萘、四甲基萘和五甲基萘单个异构体的生物降解顺序, 结果表明那些热力学稳定性高的异构体容易遭受微生物的攻击, 而热力学稳定性低的异构体却在生物降解过程中相对富集, 表明生物降解作用完全不同于热力学作用过程, 当原油遭受中等程度生物降解作用影响后, 根据热力学稳定性提出的成熟度参数不再能提供有效的成熟度信息, 易降解和难降解异构体间的比值却是衡量原油遭受生物降解作用程度的地球化学新指标. 

Biodegradation Effect on Distributions of Multiple Methylated Naphthalenes in Reservoir Extracts

Detailed geochemical analysis has been carried out on reservoir extracts from the Es 3 reservoir of the Leng 43 block of the Lengdong oilfield, Liaohe basin. Bulk compositions and aliphatic biomarker parameters indicate that these residual oils from three different oil columns are biodegraded at varying degrees. The biodegradation degree increases from the top of oil columns to the bottom of oil columns with excellent gredient variations. Comparison of the distributions of trimethylnaphthalenes (TMNs), tetramethylnaphthalenes (TeMNs) and pentamethylnaphthalenes (PMNs) at various biodegradation levels indicate that biodegradation controls their occurrence and distribution. The susceptibility of individual isomer of TMNs, TeMNs and PMNs to biodegradation has been determined on its relative abundance variation during biodegradation. The results show that these thermal dynamic stable structures are more susceptible to bacterial attack than these thermal unstable structures, suggesting biodegradation completely differs from thermal dynamic process. This study reveals that after moderate biodegradation these maturity parameters based on thermal stability of isomers are invalid and the ratios between easily biodegraded and refractory structures, in turn, can be used as new geochemical indicators to assess the degree of biodegradation.