Abstract: A method of method of logging an invaded geological formation comprises the steps of: (i) operating plural receivers in order to receive signals generated by one or more transmitters and thereby create logs of overlapping lengths of a bore formed in the said geological formation, the respective said receivers logging distinct depths of penetration, as previously defined, of the geological formation measured with respect to the bore; (ii) recording the resultant values in a two-dimensional plot one of whose axes represents the respective depth of penetration of the said formation to which each said log corresponds; (iii) establishing whether the resulting plot appears to approach an asymptote; and if so (iv) determining the value of the asymptote.

Abstract: A method of compensating a density log comprises the step of compensating the far density by adding a correction at a given point in the density log wherein: (a) the correction comprises at least a first correction function and optionally a second correction function; (b) when the correction includes both the first and second correction functions they respectively are corrections for “slow-moving” and “fast-moving” perturbations at the said given point; and (c) regardless of whether the correction includes the second correction function the first correction is filtered by a long filter.

Abstract: A method of well logging in which the logging tool is delivered to the bottom of the well within a drill pipe and then the well is logged by withdrawing the drill pipe with the sensor portion of the logging tool protruding from the drill pipe. Following the logging operation, the logging tool is returned to the surface by reverse circulation.

Abstract: A self contained logging tool comprising electronic apparatus for logging a well is disclosed. This tool includes a normally open fluid flow valve structure being activated to operation by differential movement of drill pipe in which the logging tool resides. The valve structure operates to gradually close and thereby restrict the flow of fluid through the valve, which in turn restricts the flow of fluid within the drill pipe. This flow restriction results in increasing the back pressure within drill pipe to provide an indication at the surface that the logging tool is struck.

Abstract: A well logging method and apparatus is described, which enables well logging to be conducted while still allowing passage of fluid mud within the well to maintain well control.

Abstract: A small diameter tool for measurement of resistivity of geological rock formations, including a complex auxiliary electrode structure which is adjustable in electrode length between deep and shallow mode measurement operations.

Abstract: A method of well logging in which the logging tool is delivered to the bottom of the well within a drill pipe and then the well is logged by withdrawing the drill pipe with the sensor portion of the logging tool protruding from the drill pipe. Following the logging operation, the logging tool is returned to the surface by reverse circulation.

Abstract: The well logging tool comprises differential valve means allowing passage of fluid through said tool during logging operations on when the tool becomes jammed inside a drillpipe.