【摘要】 常规测井资料识别天然气主要依据三孔隙度测井曲线。理论认为当储层中存在着天然气时,会导致纵波时差增大,横波时差不变,密度测井值减小,中子孔隙度减小。根据这些测井响应特征,发展了一系列识别天然气的有效方法。比较常用的是密度—中子曲线重叠法。但是由于密度测井受井眼影响较大,导致在井眼条件较差的储层段采用密度—中子曲线重叠法不能很好地指示天然气的存在,高估或低估了气层。针对这一问题,本文提出了密度—中子孔隙度重叠法的一种改进方法———视水层中子孔隙度测井值法,同时给出了合成纵波时差以及纵横波时差比值法。通过实际应用证实,这些方法能很好地指示天然气的存在。更多还原

【Abstract】 Identifying natural gas with conventional log data mainly is based on three porosity log curves.Theoretically,when gas exists in reservoir,longitudinal wave offset time will increase and transverse wave offset time will not change and density will decrease and neutron will decrease,too.By this responding feature,many effective methods have been established to identify natural gas.Density—neutron overlapping is quite familiar.But density is much sensitive to borehole condition,which make it vitiated.Consider this condition,this paper proposes a reformed method of density—neutron overlapping——the method of apparent water layer neutron porosity.And it proposes synthetic longitudinal wave offset time,the ratio of longitudinal wave offset time and transverse wave offset time.The practical application of these methods show that they can indicate the existence of natural gas.更多还原