Schlumberger Technology Corporation

Japan National Oil Corporation

Jacques M Holenka

Michael Lynn Evans

William R Sloan

Philip Lawrence Kurkoski

W Robert Sloan

David L Best

Kenneth Edward Stephenson

Bradley Albert Roscoe

Keith A Moriarty

Benoit Couet

Wolfgang P Ziegler

Paul Albats, Jr

William A Loomis

Erik Rhein-Knudsen

Jerome A Truax

Philip L Kurkoski

S Zema Chowdhuri

Apparatus for determining the density of underground formations surrounding a borehole, such as a wireline logging tool or a logging-while-drilling tool, includes a neutron source for irradiating the formations from within the borehole and at least one detector which detects neutrons and gamma rays in the borehole resulting from the irradiation of the formations with neutrons. Multiple detectors can also be used to separately detect neutrons and gamma rays. Detected neutron and gamma ray signals are each analyzed and combined to determine the density of an earth formation.

Method for determining density of an earth formation

A method and apparatus is disclosed for suppressing microphonic noise in proportional counter neutron detection in borehole logging-while-drilling measurements. Noise is reduced by (1) applying the outputs of two detectors respectively to positive and negative inputs of a differential amplifier; (2) generating output pulses by applying the output of the differential amplifier to positive and negative comparators to produce first and second output pulses; (3) counting output pulses as neutron counts only if the first or second output pulses have time lengths less than a predetermined time length; and (4) rejecting the output pulses in the count of pulses as neutron counts if first and second output pulses coincide in time.

Apparatus and method for the suppression of microphonic noise in

Measurement-while-drilling apparatus includes a 14 MeV neutron accelerator, a near-spaced neutron detector which primarily senses source neutrons and whose output is proportional to source strength, one or more intermediately-spaced epithermal neutron detectors eccentered against the drill collar wall and primarily responsive to formation hydrogen concentration, and a third far-spaced radiation detector, either gamma ray or neutron, primarily responsive to formation density. The intermediately-spaced and far-spaced detector outputs, normalized by the near-spaced detector output, are combined to provide measurements of porosity, density and lithology and to detect gas. A thermal neutron detector and/or a gamma ray detector may also be provided at intermediate spacings to provide additional information of interest, such as standoff measurements and spectral analysis of formation composition. Tool outputs are related to the angular or azimuthal orientation of the measurement apparatus in the borehole.

Accelerator-based methods and apparatus for measurement-while-drilling

A method and apparatus for measuring formation characteristics as a function of angular distance segments about the borehole is disclosed. The measurement apparatus includes a logging while drilling tool which turns in the borehole while drilling. Such characteristics as bulk density, photoelectric effect (PEF), neutron porosity and ultrasonic standoff are all measured as a function of such angular distance segments where one of such segments is defined to include that portion of a 'down' or earth's gravity vector which is in a radial cross sectional plane of the tool. The measurement is accomplished with either a generally cylindrical tool which generally touches a down or bottom portion of the borehole while the tool rotates in an inclined borehole or with a tool centered by stabilizer blades in the borehole.

Logging while drilling method and apparatus for measuring standoff as a

Logging while drilling method and apparatus for measuring formation

Apparatus and method for measuring density, porosity and other formation characteristics while drilling is disclosed. The apparatus, preferably housed in a drill collar and placed within a drill string, includes a source of neutrons and a source of gamma rays placed within a tubular body which is adapted to provide for the flow of drilling through it. Two sets of stabilizer blades are provided. One set, associated with the neutron source, includes secondary radiation detectors that are placed radially beyond the nominal outer radius of the body. Formation porosity measurement accuracy is substantially enhanced since the standoff of the detectors from the formation is substantially decreased. Another set, associated with the gamma ray source, includes one or more gamma ray detection assemblies in a single blade. Each of the gamma ray detector assemblies is also placed radially beyond the nominal outer radius of the tubular wall. Formation density or absorption coefficient accuracy is substantially enhanced since the standoff between the detection assembly and the borehole wall is decreased. In a particularly preferred embodiment, ultrasonic sensors incorporated either or both sets of blades provide a measurement of the borehole diameter and/or standoff of the detectors from the borehole. The bulk density measurement and neutron porosity measurement data can be corrected with information derived from the standoff or borehole diameter.

Stand-off compensated formation measurements apparatus and method

Nuclear spectroscopy method and apparatus for the stabilization of an energy spectrum, made from a signal, emitted by a radiation detector, and containing nuclear events, represented by pulses, whose amplitude is a measure of the energy of the particles, such as gamma rays, collected by the detector, the spectrum including at least a first reference energy peak coming from an ancillary nuclear source, wherein the method comprises: detecting the radiation under analysis by two detectors between which is placed the ancillary source; establishing at least one coincident spectrum corresponding to pairs of events simultaneously detected in both detectors and originating from the ancillary source; and stabilizing the coincident spectrum by using one energy peak of said spectrum as said first reference energy peak.

Nuclear spectroscopy signal stabilization and calibration method and

A well logging sonde is disclosed which includes a collimating window design for the accurate detection of gamma rays of low and high energy which are back-scattered from a region near a source of gamma rays emitted into the formation. The sonde includes a tungsten support inner tube or shell surrounded by a length of 'U' shaped steel. A conduit is formed in the wall of the shell at an angle with respect to its axis and is oriented symmetrically toward the opening of the 'U' shaped steel support member. A closing member of a thin layer of titanium is welded to the open ends of the 'U' shaped steel member. An arcuate tungsten pad is secured about the titanium closing member and partially about the exterior of the open ends of the 'U' shaped steel support member. A conduit in the pad is aligned with the conduit of the inner shell to form a collimating window. A gamma ray detector of a length shorter than the 'U' shaped steel section is mounted within the inner tube in the path of the collimating window.

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Missouri City, TX, United States of America

Jacques M Holenka