Schlumberger Technology Corporation

Weatherford Technology Holdings, LLC

Donald C McKeon

Christian Stoller

Peter D Wraight

Bradley Albert Roscoe

Richard R Pemper

Bronislaw Seeman

Dominique Benimeli

Cyrille Levesque

Nihal I Wijeyesekera

Jean-Remy Olesen

Urmi DasGupta

Hugh D Scott

Systems and methods for determining the composition of an earth formation are disclosed. One or more spectra that correspond to gamma radiation that is detected at each of multiple depths in a wellbore are generated, the contributions of each of multiple detection elements to the one or more spectra are determined, and the weight fractions of each of multiple compounds that are associated with the detection elements are calculated. The weight fraction calculations are based on a number density ratio value for the compound's associated detection element, which allows the weight fraction to be calculated directly from the contribution of the compound's associated detection element without a normalization factor.

Techniques for determining formation composition from measured nuclear spectra

Body () for measuring the resistivity of a formation () surrounding a well () equipped with a lining (), comprising: a body () of a probe (), a set of three primary voltage measurement electrodes (ea, eb, ec), an upper electrode (ea) and a lower electrode (ec) and a central electrode (eb), two electrodes (In, In), an upper current injection electrode (In) and a lower current injection electrode (In) arranged on each side of the set of primary electrodes, characterized in that it also comprises, two secondary voltage measurement electrodes () arranged on each side of the set of primary electrodes (ea, eb, ec), and between the two current injection electrodes (In, In), the spacing between a secondary electrode () and the closest primary end electrode (ea, ec) being more than 1.5 times the spacing between the primary electrodes (ea, eb, ec).

Device and process for determination of the resistivity of a formation surrounding a cased borehole

This invention makes an NMR measurement at extended depths into the formation using the earth's magnet field to generate an NMR measurement and using a magnet field from a permanent magnetic to suppress the NMR signal in the borehole and shallow formation. The magnetic field from a permanent magnet increases the Larmor frequency in the borehole and the shallow earth formation. An oscillator applies an RF magnetic field to the formation for a period of time in order to align nuclei spins approximately perpendicular to the earth's magnetic field. At the end of this period, the field is turned off rapidly. Since the spins are unable to follow this sudden change, they are left aligned perpendicular to the earth's field. These nuclei precess about the earth's field at the approximate Larmor frequency of the earth's field. The RF receiver detects the RF signals in the approximate frequency range of the Larmor frequency. Borehole and shallow formation protons precessing at the high frequencies resulting from the permanent magnet are not detected by the receiver. Therefore, the receiver only detects signals from greater depths in the earth's formation.

Method and apparatus for evaluating an earth formation using nuclear

The present invention is an improved method and tool for determining formation density by using an array of gamma-ray detectors. This invention can correct for large standoffs encountered in abnormally shaped boreholes and in particular for the increased standoffs typically encountered by mandrel tools. In this invention, the collimated detectors have varying depths of investigation into the formation. At small standoffs a short spaced (SS) detector investigates mainly the mud and mudcake and a shallow layer of the formation. Unlike the SS, a mid spaced (MS) detector has a deeper depth of investigation and is sensitive to borehole and formation even at increased standoffs. A long spaced (LS) detector is mainly sensitive to the formation density and its density reading is corrected by using the standoff information from the MS and SS detectors. In addition to measuring density, this invention can measure the photo-electric factor (PEF) of the formation. Because photo-electric absorption preferentially removes low energy gamma-rays, the tool housing needs to allow passage of low energy gamma-rays. This can be accomplished through the use of a window of a material with a low atomic number (Z) or through the use of a low-Z housing material like titanium. Typical window materials are beryllium and titanium. Housing materials can be titanium or for lower pressure requirements graphite or high-strength carbon compounds.

Method and apparatus for measuring formation density and the formation

A method and apparatus for detecting natural gamma-ray signals of an earth formation and correcting these gamma-ray signals for effects from borehole gamma-rays. Gamma-ray signals are detected at two detector locations in the borehole. The borehole effects are derived from the differences between the detected signals. After the borehole effects are determined, the detected gamma-ray signal is corrected for these effects and measurements of the formation elements are derived. A differential signal between the two detectors is created by excluding a small volume of borehole fluid from one of the detectors from the borehole fluid, before detecting gamma-rays at both detectors. The excluder displaces a known volume of borehole fluid equal to the volume of the excluder. Both detectors record gamma-ray generated from the formation and borehole. The additional volume of borehole fluid at one detector causes the detected signals to be different. This difference in signals is caused by the detection of the gamma-rays from the extra volume of fluid by the exposed detector. From this differential signal, correction parameters are derived to correct the signal for borehole effects caused by potassium in the borehole fluid, and thereby leave a signal indicative of natural gamma-rays from the earth formation.

Method and apparatus for correcting natural gamma ray measurements for

A nuclear spectroscopy method and apparatus for obtaining qualitative and quantitative information related to water flow, comprising the steps of:

Nuclear oxygen activation method and apparatus for detecting and

Method and apparatus for identifying and determining the concentrations of subsurface formation elements next to a borehole, by detecting and counting the gamma rays resulting from the activation of Al atoms by neutrons emitted by a high energy source. The total count rates from Al are corrected for Si interference by (1) calculating the ratio of the count rates of gamma rays from Si activation to the count rates of the gamma rays resulting from the inelastic collisions of neutrons with Si atoms, thus providing a reference ratio independent of environmental parameters; (2) detecting and counting the gamma rays resulting from the Si inelastic collisions; (3) determining from the count rates of silicon inelastic gamma rays and from said ratio, the count rates of Si activation gamma rays; and (4) subtracting, from the total count rates of activation gamma rays, the count rates of Si activation gamma rays. The method comprises also detecting and counting the gamma rays resulting from the capture of said neutrons by atoms of a plurality of elements.

Logging apparatus and method for determining concentrations of

A nuclear spectroscopic method and apparatus for determining hydrocarbon saturation or water saturation of a formation adjacent a well bore is disclosed. Near and far inelastic gamma ray spectra are detected in response to pulses of fast neutrons irradiating the formation and materials in the borehole. Near and far carbon/oxygen (C/O) ratios are extracted from each spectra using predetermined spectra of postulated elements. The near and far C/O ratios are combined to determine a representation of formation hydrocarbon saturation substantially corrected for borehole gamma rays produced by inelastic reaction of fast neutrons and hydrocarbons in the well bore. Shielding of near and far detectors is provided to make the near detector more sensitive to gamma rays emanating from borehole gamma rays and to make the far detector less sensitive to borehole gamma rays and more sensitive to formation gamma rays.

Growing community of inventors

Houston, TX, United States of America

Donald C McKeon