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

摘要

A borehole logging tool (10) is lowered into a borehole traversing a subsurface formation and a neutron detector (19) measures 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 lifetime signal to correct for standoff from the borehole wall (24) encountered 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 derived 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.