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致密砂岩气层在孔隙度测井曲线上有明显的反映，与含水及含油地层的测井曲线相比较，气层的声波孔隙度、密度孔隙度增大，中子孔隙度减小，用曲线重叠或交会图的方法容易将其识别。当中子孔隙度与密度孔隙度曲线重叠时，会有密度孔隙度远高于中子孔隙度的特征；在中子－密度交会图上，气层的资料点将出现在图的左上方而形成所谓的气层影响区。但是，对埋藏较深的气层而言，由于其孔隙度曲线特征并不明显，故用常规方法识别十分困难，

RECOGNITION METHOD OF TIGHT SAND GAS BEARING BED

Obviously reflected by porosity log, tight sand gas bearing bed with bigger acoustic porosity,density porosity and smaller neutron porosity when comparing with the logs of water bearing and oil bearing beds is easily recognized by the method of log superposition or crossplot.When superposing neutron porosity log with density porosity log,density porosity is far higher than neutron porosity.In neutron-density crossplot,the datapoint of gas bearing bed will come out on right-upper to form"influence area"of gas bearing bed. But it will fail to recognize the gas bearing bed buried deeper by the two methods as its porosity log feature is not obvious,especially when density porosity is lower than neutron porosity.So,a new oil-gas corrective method, progressively correcting the influence of oil-gas on neutron density log by superposition and calculating out oil-gas density and neutron porosity to form crossplot.The various districts of oil,gas and water bearing beds appear in the crossplot to get a good recognition result.