Abstract: A downhole tool and apparatus is described for logging and/or remedial operations in a wellbore in a hydrocarbon reservoir. The tool comprises an autonomous unit (1) for measuring downhole conditions, preferably flow conditions. The autonomous unit comprises locomotion means (12) for providing a motion along said wellbore; means (14) for detecting said downhole conditions; and logic means (113) for controlling said unit, said logic means being capable of making decisions based on at least two input parameters. It can be separately attached to a wireline unit (22) connected to the surface or launched from the surface. The connection system (31, 32) between both units can be repeatedly operated under down hole conditions and preferably includes an active component for closing and/or breaking the connection.

Abstract: The invention relates to a method of characterizing an oil borehole effluent, formed by a multiphase fluid mixture typically containing water, oil, and gas. According to the invention, a gadolinium 153 source is used to emit gamma rays at a first energy level of about 100 keV and at a second energy level of about 40 keV, and the attenuation of the gamma rays at these two energy levels is measured after the rays have passed through the effluent.

Abstract: A method and system is provided for perforating a casing in a hydrocarbon well so as to avoid perforating in a direction where a cable resides. A mass of metallic material is clamped to the casing at a predetermined offset angle with respect to the cable. The angular position of the metallic mass is detected using a detector placed inside the casing. Then, a perforating gun is oriented based on the detected angular position of the metallic mass and the predetermined offset angle. Finally, the casing is perforated so as to avoid damage to the cable. The cable comprises a number of electrical conductors and is used to communicate with permanent sensors located on the cable in the vicinity of the casing to be perforated.

Abstract: A method for determining a pore characteristic of a substance includes the following steps: subjecting the substance to a substantially uniform static magnetic field; applying a magnetic pulse sequence to the substance, the pulse sequence being selected to produce nuclear magnetic resonance signals that are responsive to internal magnetic field inhomogeneities in the pore structure of the substance, and detecting, as measurement signals, nuclear magnetic resonance signals from the substance; applying a reference magnetic pulse sequence to the substance, the reference pulse sequence being selected to produce nuclear magnetic resonance signals that are substantially unresponsive to internal magnetic field inhomogeneities in the pore structure of the substance, and detecting, as reference measurement signals, nuclear magnetic resonance signals from the substance; and determining a pore characteristic of the substance from the measurement signals and the reference measurement signals.

Abstract: Methods and apparatus for seismic data compression are described, making use of a local discrete sine/cosine transform of the type IV applied to a data set which is limited by a stationary window function which reduces the overlap to the adjoining windows.

Abstract: A method of measuring the resistivity of drilling mud in a borehole passing through a terrestrial formation includes the steps of a) inserting a sonde into the borehole, the sonde having an elongate body provided with at least one annular current electrode (A0, A′0) and at least two annular guard electrodes (A, A′, A1, A′1, A2, A′2) situated on either side of the annular current electrode; b) performing computed focusing to simulate an operating mode in which at least one current I0 is emitted into the surrounding formation from the annular current electrode, the current I0 being focused in the formation by emitting two currents I1 and I′1 from the two annular guard electrodes situated on either side of the annular current electrode; and c) producing a signal representative of the resistivity Rm of the drilling mud from the simulated operating mode.

Abstract: A method for the determining a nuclear magnetic resonance characteristic of earth formations surrounding a borehole, includes the following steps: providing a logging device that is movable through the borehole, the logging device having a longitudinal axis; providing a first coil, in the logging device, for generating a magnetic field in the formations; providing a second coil in the logging device; applying a polarizing signal to the first coil; detecting, with the second coil, magnetic resonance of spins in the formations that are precessing around earth's magnetic field; and providing a third coil in the logging device, the third coil being operative to produce a further magnetic field in the borehole that reduces the contribution of spins in the borehole to the magnetic resonance detected by the second coil.

Abstract: Methods for enhancing dynamic range, sensitivity, accuracy, and resolution in fiber optic sensors include manipulating the polarization characteristics of the light entering a fiber optic sensor and/or manipulating the polarization characteristics of the light exiting the sensor before it enters the light detection system. An apparatus according to the invention includes a fiber optic core having one or more gratings written onto it, a light source and a detection system for detecting light transmitted through the grating or reflected by the grating. The light source and the spectral demodulation system may be coupled to opposite ends of the fiber optic (transmission mode) or may be coupled to the same end of the fiber optic through the use of a beam splitter and terminators (reflection mode). Apparatus according to the invention include a polarizer and controller located either between the light source and the fiber or between the fiber and the detection system.

Abstract: A method for determining unknown stress parameters in earth formation measures velocities in four sonic transmissions modes (compression, fast shear, slow shear and Stoneley) at a series of depths. Relationships between measured velocities and other measured values, two independent linear constants, and three nonlinear constants associated with equations of motion for pre-stressed isotropic materials are expressed in a set of four or five velocity difference equations derived from non-linear continuum mechanics. The velocity difference equations are solved using inversion for useful stress parameters, including maximum horizontal stress, minimum horizontal stress, pore pressure, and change in pore pressure over time.

Abstract: A method and apparatus is provided for determining a quality of downhole fluid. A series of measurements are taken of at least one parameter of borehole fluid that is indicative of OBM filtrate contamination. By curve-fitting, the series of the measured parameter values are used to create an asymptotic curve indicative of the quality of the downhole fluid. One embodiment determines OBM filtrate fraction in a borehole fluid sample. One embodiment is used when there is significant difference between the coloration of formation fluid and the coloration of OBM filtrate. Another is used when there is little or no difference between the coloration of formation fluid and the coloration of OBM filtrate. Another determines GOR of formation fluid corrected for OBM filtrate contamination. Another determines OD of formation fluid corrected for OBM filtrate contamination. Another determines conditions that would render optical density measurements invalid and sample capture premature.

Abstract: The invention relates to a method of surveying the resistivity of a geological formation through which a borehole provided with metal casing passes, in which method a leakage current is caused to leak into the formation outside the casing, and the leakage current is determined on a casing section at a certain level, the leakage current being indicative of the resistivity of the formation. According to a characteristic of the invention, the resistivity is determined on the basis of the leakage current by applying a factor that depends on the distance z between the level and the surface.

Abstract: Magnetic resonance techniques, e.g., nuclear magnetic resonance (NMR) and electron spin resonance (ESR), are used in a fluid sampling tool that extracts a fluid from subsurface earth formations into a flow channel within the tool. The magnetic resonance techniques involve applying a static magnetic field and an oscillating magnetic field to the fluid in the flow channel, and magnetic resonance signals are detected from the fluid and analyzed to extract information about the fluid such as composition, viscosity, etc.

Abstract: Methods and apparatus for measuring differential pressure with fiber optic sensor systems are disclosed. The apparatus of the present invention include both monopolar and bipolar sensors, sensors incorporating side-hole fibers, sensors incorporating fibers without side holes, FBGs subjected to transverse strain, and FBGs subjected to longitudinal strain. All of the embodiments utilize FBGs. Two embodiments utilize a piston having oppositely extending rods, each of which is exposed to a different pressure. Seven embodiments utilize one or more silica diaphragms coupled to a silica body and exposed to two pressures. In each of these embodiments, pressure is converted into movement of the piston or diaphragm which is then used to strain the FBG(s). When each FBG is interrogated, the spectral information is indicative of the strain exerted by the piston or diaphragm on the FBG and thus the difference between the two pressures.

Abstract: A method and apparatus is provided for determining OBM filtrate fraction in a downhole fluid sample. One embodiment of the method is used when there is significant difference between the coloration of formation fluid and the coloration of OBM filtrate. Another is used when there is little or no difference between the coloration of formation fluid and the coloration of OBM filtrate. Another determines GOR of formation fluid corrected for OBM filtrate contamination. Another determines OD of formation fluid corrected for OBM filtrate contamination. Another determines conditions that would render optical density measurements invalid and sample capture premature. Another predicts the reduction of filtrate fraction for a specific extended pumping time. Another initiates sample capture when computed contamination fraction exhibits stable asymptotic convergence.

Abstract: A morphological survey of geological formations traversed by a borehole includes constructing, from an initial image of the wall of the borehole representative of variations in a physical parameter of the formation in the longitudinal direction of the borehole (“depth”), and in the peripheral direction of the borehole wall (laterally), a “crossing-component image.” The cross-component image includes only those components of the parameter that extend all the way across the initial image from one side of the image to the other. The survey includes determining variations in one or more attributes relating to the parameter in the crossing-component image as a function of depth. The variations providing information relating to morphology to indicate solid zones, bedded zones, or different types of heterogeneous zones, for example.

Abstract: Methods and apparatuses for investigating formations surrounding a borehole involve acquiring a fluorescent signal over a portion of the borehole and analyzing the signal to detect the presence of crude oil. Analyzing the signal to detect the presence of crude oil may involve distinguishing mineral fluorescence from oil fluorescence. The signal may be analyzed further to distinguish characteristics of the crude oil, such as its grade (light, medium or heavy), and to indicate a physical property correlated with the fluorescence, such as the presence of laminations or formation permeability. In some embodiments, fluorescence signals from illuminating the portion of the borehole with at least two different wavelengths of light are analyzed.

Abstract: The invention relates to a flow section for measurements concerning oil well effluent, the section comprising a pipe in parallel with a pipe connected to the well head. The flow section includes elements of material having low attenuation for gamma rays fixed in recesses formed in the wall of the pipe on its inside, and protection members disposed in housings connecting said recesses respectively to the outside, said housings being suitable for receiving gamma ray attenuation measuring means after the protection members have been removed.

Abstract: There is provided downhole power generation apparatus with a first electrode, a second electrode and an electrolyte, wherein the first electrode comprises a casing within a borehole. The first electrode and the second electrode are formed from dissimilar metals and by appropriate selection of the two dissimilar metals, the casing functions as the cathode. Typically the first electrode is formed from a steel casing and the second electrode is of zinc. The second electrode is provided on an insulated connector joining at least two sections of casing. Power is extracted in an electrical load connected between the casing and the second electrode. Where a cement holds the casing in place within the borehole, it serves as the electrolyte. The cement is provided with additives to improve its conductivity. The first electrode is provided with oxide coatings, such as iron (III) oxide, to mediate the electrolytic reaction at the cathode.

Abstract: An optical fiber is provided with a Bragg grating formed along a portion of its core and a mechanical structure arranged adjacent to the Bragg grating for amplifying longitudinal strain on the fiber in the vicinity of the grating. The mechanical structure is designed to convert ambient pressure into longitudinal strain on the fiber in the vicinity of the grating and to allow the fiber to pass through the structure so that several pressure measuring apparatus may be arranged along a single optical fiber. An intermediate structure is provided between the fiber and the mechanical structure for minimizing buckling of the fiber. The methods of the invention include converting pressure into longitudinal strain on an optical fiber, amplifying the effect of pressure on the longitudinal strain, measuring pressure by determining the spectral location related to peaks (or minimums) of light reflected from an optical grating subjected to longitudinal strain.

Abstract: The methods and apparatus of the invention include installing sensors in one or more of the many hole sections which are abandoned before the holes are sealed with cement. According to the invention, a sensor array is attached to the cement delivery device which is used to seal a hole which would otherwise be abandoned. The preferred apparatus for cement delivery is a “coiled tubing”. Preferably, the sensor array is passed through the center of the tubing so that it is protected from damage or snagging while being delivered to its deployment position. The coiled tubing may be withdrawn or left in place after the cement is delivered into the hole. When the cement cures, the sensor array is centered in the cement plug which seals the reservoir. According to the invention, the sensor array may be placed in any well which is to be abandoned.