METHOD AND APPARATUS FOR PRODUCING A POROSITY LOG OF A SUBSURFACE FORMATION

摘要

A borehole logging tool (10) is lowered into a borehole tra- versing a subsurface formation and a neutron detector (19) mea- sures the die-away of nuclear radiation in the formation. Intensity signals are produced representing the die-away of nuclear radiation as the logging tool (10) traverses the borehole. A signal processor (17), employing as least one neural network, processes the intensity signals and produces a standoff corrected epithermal neutron life- time signal to correct for standoff from the borehole wall (24) en- countered by the detector (19) as the logging tool (10) traverses the borehole. The signal processor further generates a porosity signal from the standoff corrected epithermal neutron lifetime signal de- rived from measurements in borehole models at known porosities and conditions of detector (19) standoff. A log is generated of such porosity signal versus depth as the logging tool (10) traverses the borehole.