Abstract: A method, of logging a borehole, for use in a cased oil well for detecting the gas/oil or water/oil contact in a hydrocarbon reservoir, using a neutron capture technique to detect one or more properties of fluid includes comparing the count rates from two or more radiation detectors spaced at respective first and second distances from an isotopic source of continuous neutron radiation. The contact detection criteria are arranged to be substantially independent of borehole fluid characteristics.

Abstract: A well logging device of compact reduced diameter compared to the prior art, such well logging device having both short spaced and long spaced types of gamma ray crystal detectors installed in a measurements skid that comprises a relatively small diameter device constructed to withstand high temperatures and pressures, this device comprising a continuous stainless steel tube which provides pressure resistance and also allows low energy gamma ray transparency via large and small windows. This elongate type of stainless steel skid tube is furthermore internally supported by an internal tungsten tube placed therewithin, while the skid design also includes means for pressing the skid tube against a borehole wall so as to obtain more accurate formation density measurements downhole.