断层对烃类微渗漏主控作用及异常分布影响的实验模拟研究

在油气化探中,传统观点认为断层是优势通道,烃类沿断层渗漏形成的化探异常将偏离实际油气藏位置在近地表的垂向投影,这引起了地质界对化探技术预测地下油气藏的质疑.针对上述质疑,以断块油气藏的简化地质模型为基础,研制实验装置,开展断块油气藏烃类通过盖层及上覆地层垂向微渗漏模拟实验,研究了地下断层对烃类垂向微渗漏的影响.结果表明,受断层控制的油气藏,断层不是烃类微渗漏的唯一优势通道,油藏上覆盖层及地层中广泛发育的裂隙或微裂隙系统等都是决定地表化探异常分布的重要因素,烃类垂向微渗漏是客观存的;断层是否是微渗漏的优势通道,取决于断层的封闭性;另外实验结果也证实了圈定油气靶区的最好采样方法是高密度的网格采样.

Experimental simulation of the effect of faults on vertical hydrocarbon microseepage

Hydrocarbons in the oil/gas accumulations can seep vertically along the pores,joints,microfractures,fractures,and faults to the surface and form geochemical anomalies,which is the theoretical basis of surface geochemical exploration technique.Most of faults underground have big inclination angle,and are not vertically distributed.It is thought that faults are the dominant pathways for microseepage,the geochemical anomalies formed through faults may deviate from the vertical projection of actual hydrocarbon accumulation on the surface.Such a point of view will arouse doubt among geologists about the role of surface geochemistry exploration technique in predicting hydrocarbon accumulations underground.Based on a theoretical model of fault block hydrocarbon accumulation,the authors developed an experimental apparatus to simulate the phenomena of hydrocarbon microseepage of the fault block hydrocarbon accumulations.The effect of faults on vertical hydrocarbon microseepage was studied.The results of the simulation experiments show that faults are not the only dominant pathways of hydrocarbon microseepage from the fault block hydrocarbon accumulations,the fractures and micro-fractures system developed widely in the strata are also the important factors to decide the distribution of surface geochemical anomalies,and vertical hydrocarbon microseepage exists objectively.Whether faults are the dominant pathways of hydrocarbon microseepage or not depends on the sealing capability of faults.The study also shows that the sampling method which is most suitable for delineating the oil and gas target is the highest density grid.