Abstract: A method of processing borehole log data to create one or more image logs involve modeling the log data as components of an image in the form i(x, y)=l(x, y)×r(x, y) (1), in which i(x, y) is an image representative of the log data, l(x, y) denotes an illumination value of the image at two-dimensional spatial co-ordinates x, y, and r(x, y) denotes a surface reflectance value at the co-ordinates x, y. Equation (1) is transformed to a logarithmic domain, and a Fourier transform is obtained of the resulting logarithmic domain expression to obtain a Fourier domain expression. The Fourier domain expression is high-pass filtered, and an inverse Fourier transform is obtained of the resulting filtered Fourier domain expression. An exponential operation is performed on the result of inverse Fourier transform to obtain a filtered image model expression. Values of the filtered image model expression are mapped to respective color values across the range of the filtered image model expression values.

Abstract: A logging tool, toolstring (10), or element (19) comprises a stabilizer including a pair of moveable, rigid, main stabilizer arms (23, 24) that each is pivotably secured adjacent to one another at one end to the logging tool or toolstring. As a result the arms (23, 24) are moveable between a relatively retracted position on the one hand and a relatively advanced position on the other in which the main stabilizer arms diverge from one another and protrude from the logging tool so as to present a pair of main arm free ends (29, 31) that are spaced from an outer surface of the tool and are engageable with a borehole surface. The logging tool (10) or element (19) includes a mechanism for effecting coordinated, powered, linked movement of the main stabilizer arms (23, 24) between the retracted and advanced positions.

Abstract: A shock absorber (29) for downhole use comprises an elongate, hollow member defined by a series of mutually aligned, plastically deformable perforated members (38) having aligned perforations that define the hollowness of the elongate, hollow member that are spaced from one another in the direction of elongation by respective relatively rigid spacer members (39) that are secured to the perforated members. The elements of each pair of perforated members (38) of the series are so spaced from one another by one or more of the spacer members (39) such that on compression of the shock absorber (29) the perforated members (38) deform plastically to a lesser extent in regions at which the spacer members (39) are secured than at other regions. The arrangement of the perforated members (38) and the spacer members (39) causes compression to occur substantially parallel to the length of the shock absorber (29).

Abstract: A method of detecting an edge of a geological characteristic in a borehole comprises, in respect of an image log of a length of a borehole, carrying out the steps of a gradient-based edge detection method, a phase congruence-based edge detection method or a combination of such methods as preliminary, pre-processing stages. Subsequent steps of the method may include operating a relatively computationally simple process to identify sinusoids among detected edge features; and a relatively computationally complex process for parameterizing the thus-identified sinusoids.

Abstract: A method of detecting an edge of a geological characteristic in a borehole comprises, in respect of an image log of a length of a borehole, carrying out the steps of a gradient-based edge detection method, a phase congruence-based edge detection method or a combination of such methods as preliminary, pre-processing stages. Subsequent steps of the method may include operating a relatively computationally simple process to identify sinusoids among detected edge features; and a relatively computationally complex process for parameterizing the thus-identified sinusoids.

Abstract: A downhole tool coupling (10) comprises first (11) and second (12) downhole tool elements that are securable one to the other in a releasably locking manner by moving the tool elements from a longitudinally relatively less proximate, especially overlapping position into longitudinally relatively more overlap with one another. The first downhole tool element (11) supports a first inductive, capacitative and/or magnetic energy coupler (23) and the second downhole tool element (12) supports a second inductive, capacitative and/or magnetic energy coupler (24). The first and second energy couplers (23, 24) are movable from an energetically uncoupled position when the tool elements (11, 12) are in the longitudinally relatively less overlapping position to an energetically coupled position when the first and second downhole tool elements (11, 12) overlap relatively more.

Abstract: Inverting nuclear log data for a geological formation surrounding a borehole involves acquiring nuclear log data for a borehole portion using a moveable nuclear logging tool and acquiring additional log data for the borehole portion using another logging device with superior resolution. Boundaries between adjacent zones are identified that exhibit an attribute of the geological formation to a detectably contrasting degree. From pre-acquired data describing one or more characteristics of the nuclear logging tool, a modeled log of the attributes is generated over the borehole portion, and a zone response is calculated from the pre-acquired data for each zone by using the boundaries to define an initial measure of the depth of each zone and ascribing a value of the attribute in dependence on the depth of each zone.

Abstract: A method of calculating the unconfined compressive strength (UCS) of subterranean rock having a borehole formed or being formed therein comprises the steps of: (a) establishing or accessing a set of input variables pertaining to characteristics of the rock and the geographical region in which the rock exists; (b) allocating to each of a plurality of mnemonic types each representing a respective UCS calculation expression and contained within a database of UCS calculation curves up to one said input variable in the form of a data element or up to one series of said input variables in the form of a data curve the allocation taking place on the basis of identity of each said input variable or data curve, as applicable, to which a said UCS calculation curve is allocated to a variable of a said UCS calculation curve (herein “curve variables”); (c) dividing the set of allocated UCS calculation curves according to one or more respective zones of the rock to which they pertain and calculating a resultant curve; (d

Abstract: Disclosed herein is method of computing formation attributes from acoustic measurements in a borehole. The acoustic measurements can be made by operating an acoustic source at multiple frequencies to excite the formation and operating receivers at multiple, longitudinally spaced receiver stations to receive acoustic energy from the formation. The method can include: deriving phase data from the spectrum of received acoustic signals; unwrapping phase information of the phase spectrum data; determining two or more values of difference of phase between acoustic signals at each of a range of frequencies each based on a single generated signal received at two or more pairs of adjacent said receiver stations; generating a value of slope of phase difference values; and in any case of slope ambiguity, unwrapping phase difference information and deriving a dominant slope, at each frequency, from which slowness of the acoustic signal in the formation can be derived.

Abstract: A shock absorber (29) for downhole use comprises an elongate, hollow member defined by a series of mutually aligned, plastically deformable perforated members (38) having aligned perforations that define the hollowness of the elongate, hollow member that are spaced from one another in the direction of elongation by respective relatively rigid spacer members (39) that are secured to the perforated members. The elements of each pair of perforated members (38) of the series are so spaced from one another by one or more of the spacer members (39) such that on compression of the shock absorber (29) the perforated members (38) deform plastically to a lesser extent in regions at which the spacer members (39) are secured than at other regions. The arrangement of the perforated members (38) and the spacer members (39) causes compression to occur substantially parallel to the length of the shock absorber (29).

Abstract: A method of processing borehole log data to create one or more image logs involve modeling the log data as components of an image in the form i(x, y)=l(x, y)×r(x, y) (1), in which i(x, y) is an image representative of the log data, l(x, y) denotes an illumination value of the image at two-dimensional spatial co-ordinates x, y, and r(x, y) denotes a surface reflectance value at the co-ordinates x, y. Equation (1) is transformed to a logarithmic domain, and a Fourier transform is obtained of the resulting logarithmic domain expression to obtain a Fourier domain expression. The Fourier domain expression is high-pass filtered, and an inverse Fourier transform is obtained of the resulting filtered Fourier domain expression. An exponential operation is performed on the result of inverse Fourier transform to obtain a filtered image model expression. Values of the filtered image model expression are mapped to respective color values across the range of the filtered image model expression values.

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 downhole seal element (10) comprises a cup portion (11) formed of or including a resiliently deformable material. The cup portion (11) extends between on the one hand a nose part (12) comprising an annulus intended for sealingly mounting the seal element on a mandrel (22) and on the other hand a skirt (13), the seal element flaring in shape between the nose part (12) and the skirt (13). The skirt includes extending therefrom away from the nose part (12) a plurality of elongate, flexible limbs (18) that are spaced at intervals about the skirt (13).

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 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 valve assembly (10) comprises a drillpipe (11) defining a hollow, generally cylindrical interior having secured therein a valve member (12) that is moveable between an open position, permitting passage of an object through the valve (10), and a closed position preventing passage of fluids along the drillpipe (11). A resiliently contractile arm (17) interconnects the valve member (12) and the drillpipe (11) so as to urge the valve member (12) towards the closed position and such that when an object passes along the drillpipe (11) and engages the valve member (12) or the arm (17) the valve member (12) occupies the open position.

Abstract: An acoustic isolator section for an acoustic well logging tool, the isolator section comprising: an isolator comprising: (i) an isolator body; (ii) a mass; (iii) a resiliently deformable portion formed integrally with the isolator body; (iv) a movement limiter.

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 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.