Abstract: In a method of processing resistivity log data, two or more resistivity log measurements of differing depths of penetration of an invaded formation are generated. The deepest and shallowest of the resistivity log measurements are combined in accordance with a non-linear combination algorithm that is modulated by a parameter. The value of the parameter used varies in dependence on a comparison between deep and shallow log measurements. The results of the comparison are forward modelled from sample data. A modified log output is generated as a result of combining the deepest and shallowest of the resistivity log measurements in accordance with the non-linear combination algorithm.

Abstract: A method of improving geological log data obtained from use of one or more logging tools, the method including the steps of (i) from raw log data recorded by the said one or more logging tools, respectively deriving according to differing first and second derivation methods a first log data set and a corresponding second log data set having the same vertical response attribute, (ii) mixing, to form resulting log curves, the first and second log data sets, the extent of mixing varying from one logged depth to another in relation to a function of (a) the semblance between the recorded log data and reference log data of a differing kind from the recorded log data and (b) the activity of one of the said first and second log data sets at each logged depth; and (iii) displaying transmitting, saving, outputting or processing one or more resulting improved log curves.

Abstract: A method of improving geological log data obtained from use of one or more logging tools, the method including the steps of (i) from raw log data recorded by the said one or more logging tools, respectively deriving according to differing first and second derivation methods a first log data set and a corresponding second log data set having the same vertical response attribute, (ii) mixing, to form resulting log curves, the first and second log data sets, the extent of mixing varying from one logged depth to another in relation to a function of (a) the semblance between the recorded log data and reference log data of a differing kind from the recorded log data and (b) the activity of one of the said first and second log data sets at each logged depth; and (iii) displaying transmitting, saving, outputting or processing one or more resulting improved log curves.

Abstract: A logging method includes carrying out respective density logs, using gamma detectors, along a length of borehole. The density log is corrected for the dimensions and properties of the borehole tubing, the method comprising correcting and combing the plurality of density logs obtained using a gamma ray source inside the tubing and relating to a length of well including the non-fixed tubing.

Abstract: A method is disclosed of enhancing one or more attributes of a log, of a geological formation, including data generated in plural measurement channels corresponding to plural measurement devices, the method including the steps of: selecting data corresponding to a single said channel and deconvolving it; and seeking to impose one or more attributes of the resulting deconvolved data onto convolved log data of plural said channels in order to create an enhanced log.

Abstract: A method of processing geological log data obtained from use of one or more logging tools and including at least a first log having a relatively poor attribute and a corresponding, second log having a relatively good said attribute comprises the step of incorporating into the first log characteristics of the second log that confer improvements in the said attribute, characterised in that the incorporating step includes modulating the extent of incorporation into the first said log of the said characteristics without distorting geologically significant information in the first log.

Abstract: In a method of processing resistivity log data, two or more resistivity log measurements of differing depths of penetration of an invaded formation are generated. The deepest and shallowest of the resistivity log measurements are combined in accordance with a non-linear combination algorithm that is modulated by a parameter. The value of the parameter used varies in dependence on a comparison between deep and shallow log measurements. The results of the comparison are forward modelled from sample data. A modified log output is generated as a result of combining the deepest and shallowest of the resistivity log measurements in accordance with the non-linear combination algorithm.

Abstract: In a method of logging a geological formation, a neutron generator is pulsed to generate a series of neutron bursts that irradiate the formation. Mutually spaced radiation detectors are operated without counting or detecting individual pulses stimulated by a burst from the neutron generator. The detectors are located to detect neutrons that have traversed the formation and to generate respective current outputs indicative of the neutron detection at the respective detectors. The current outputs of the detectors are integrated to generate respective analog waveforms characteristic of the count rates at the detectors. Each of the analog waveforms is converted to digital form, and the respective digital waveforms are compared to establish a ratio of radiation detector count rates corresponding to the outputs of the respective radiation detectors. From the resulting ratio, a compensated measure of the neutron-based porosity of the formation is established.

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 is disclosed of enhancing one or more attributes of a log, of a geological formation, including data generated in plural measurement channels corresponding to plural measurement devices, the method comprising the steps of: selecting data corresponding to a single said channel and deconvolving it; and seeking to impose one or more attributes of the resulting deconvolved data onto convolved log data of plural said channels in order to create an enhanced log.

Abstract: A method and apparatus for processing neutron log data having the steps of a) deriving from the near-spaced neutron count of a neutron logging tool an approximate, unfiltered, lithology-related characteristic of a formation; b) deriving a correction that is essentially independent of the lithology; c) long filtering the correction; and d) adding the resulting, long-filtered correction to the approximate, unfiltered characteristic resulting from step a. in order to derive a compensated characteristic. The method provides statistically good, compensated logs while permitting the use of low activity neutron sources.

Abstract: A method of processing geological log data obtained from use of one or more logging tools and including at least a first log having a relatively poor attribute and a corresponding, second log having a relatively good said attribute comprises the step of incorporating into the first log characteristics of the second log that confer improvements in the said attribute, characterised in that the incorporating step includes modulating the extent of incorporation into the first said log of the said characteristics without distorting geologically significant information in the first log.

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 gas detection method includes carrying out respective neutron and density logs, using neutron and density detectors, along a length of well. The density log is corrected for the dimensions and properties of the well casing. The corrected density log is then combined with the neutron log to compensate for regions of artificially high density outside the casing. The compensated density log is continuously calibrated against the neutron log. The dynamically calibrated density and neutron logs are inspected for crossovers that signify the presence of gas in a formation.

Abstract: In the field of wellbore data logging it is known to use isotopic neutron sources in a neutron capture logging technique. However, continuous isotopic sources are unpopular for regulatory and safety reasons. Attempts to employ neutron generator tubes to generate neutron bursts for use in the neutron capture technique have encountered various difficulties in areas connected with signal identification and processing. The disclosure relates to a method of data logging in which a low burst rate neutron generator tube is pulsed at comparatively low rates to generate neutron bursts that are captured in atomic nuclei in a proximal formation. The gamma radiation arising from the neutron capture is detected over a gating intervals defined by temporally distinct points. The gamma detector output is integrated over the gating interval to provide a measure of the decay rate that is independent of the pulse rate. Consequently the signal processing problems do not arise.

Abstract: A gas detection method includes carrying out respective neutron and density logs, using neutron and density detectors, along a length of well. The density log is corrected for the dimensions and properties of the well casing. The corrected density log is then combined with the neutron log to compensate for regions of artificially high density outside the casing. The compensated density log is continuously calibrated against the neutron log. The dynamically calibrated density and neutron logs are inspected for crossovers that signify the presence of gas in a formation.

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. Apparatus (10) for carrying out the method includes a logging tool (10) having an isotopic source (16) and two spaced detectors (17,18).

Abstract: In the field of through-casing gas detection related to oil production there is a need to identify the presence of gas in a formation.

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.