Abstract: The invention relates to a method of obtaining a developed two-dimensional image of the wall of a borehole. The method comprises the steps consisting in: measuring a primary physical magnitude in said borehole as a function both of depth and of azimuth; measuring a secondary physical magnitude in said borehole as a function of depth; establishing a relationship (ƒ) between said primary physical magnitude and said secondary physical magnitude; and deducing from said relationship values for said secondary physical magnitude as a function both of depth and of azimuth, which method makes it possible to reconstruct a two-dimensional image developed over the wall of a borehole concerning a secondary physical magnitude which is measured in said borehole as a function of depth only. The invention is particularly applicable to density imaging.

Abstract: The invention relates to a method and apparatus for studying the resistivity of a geological formation around a borehole fitted with metal casing. An electric current is applied to the casing so as to cause current to leak into said formation at a given level, and said current is shunted by a feedback circuit in contact with the casing on either side of the measurement level, said circuit being organized to ensure that the current flowing along the casing at said level is less compared with the shunt current, the difference between the voltage drops on the adjacent sections of casing situated on either side of the measurement level is determined, and the leakage current (Ifor) is deduced therefrom.

Abstract: In order to ensure that at least some of the tools (12-1) to 12-4) in a string of tools that is permanently installed in an oil well (10) are kept in operation even in the event of a localized fault, the link (18) interconnecting the tools and a surface installation (16) is subdivided into segments by switch members (20). More precisely, a switch member is associated with each tool. In addition, the link (18) forms a loop with both ends thereof being connected to the surface installation (16).

Abstract: For various reasons it may be desirable to change the way a sonde is programmed to behave and respond to the data it receives and operates on, and at present each time this must be done it has been necessary to lift the sonde out of the borehole and then disassemble it to permit the removal of the old ROM and its replacement with a new ROM storing the new program. The operability and efficiency of such an arrangement is poor. To deal with this, the present invention proposes that the sonde also includes: signal processing means for processing a sampled detection signal according to a predetermined signal processing program; first memory means for storing that signal processing program; and second memory means storing a writing program for writing the signal processing program in the first memory means according to a command from the ground surface processing apparatus.

Abstract: 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 high energy neutron source for irradiating the formations from within the borehole and a detector which detects gamma rays in the borehole resulting from the irradiation of the formations with high energy neutrons. The detected gamma rays are analyzed to determine the density of the formations.

Abstract: The invention relates to a method of determining the resistivity of a geological formation through which a metal-cased borehole passes, by means of at least three electrodes in contact with the casing and spaced apart in the longitudinal direction of the borehole. In order to eliminate the effect of any differences between the two sections of casing delimited by the electrodes, a circuit connected to the electrodes and forming a Wheatstone bridge is balanced, with said sections of casing constituting two of the resistances in said Wheatstone bridge circuit.

Abstract: A borehole logging tool includes a particle accelerator including a Cockcroft-Walton voltage multiplier that provides linear axial and radial fields. The Cockcroft-Walton voltage multiplier includes capacitors that are arranged radially relative to one another, such that a linear voltage increase occurs between the capacitors. The particle accelerator is made by placing conductive foils on an insulating sheet, connecting the foils as a Cockcroft-Walton voltage multiplier, and rolling the insulating sheet with the foils into a cylinder to form the radially arranged capacitors.

Abstract: A method for determining the porosity of an underground formation includes the steps of irradiating the formation with neutrons, detecting and measuring gamma rays resulting from irradiation of the formation, discriminating between gamma rays from the formation and gamma rays from the tool, and using a measurement of the gamma rays from the tool to determine the formation porosity. A suitable logging tool includes a neutron source, a gamma ray detector, means for discriminating between gamma rays from the formation and gamma rays from the tool, and means for relating the gamma rays from the tool to the formation porosity.

Abstract: The invention concerns a method of and apparatus for measuring the flow rate of a continuous phase in a flowing multiphase fluid. It includes the steps of measuring a velocity of the fluid with a thermal anemometer at a location in the flow and simultaneously measuring the passage of a discontinuous phase at the same location with a local probe system capable of measuring the passage of a discontinuous phase, and then using the measurement of the discontinuous phase to correct the measurement of the continuous phase so as to derive the flow rate thereof.

Abstract: A method of performing small scale micro hydraulic fracturing in which fluid is pumped into the test interval until the initiation of a fracture is indicated, immediately after which fluid is pumped out of the interval so as to prevent propagation of the fracture and allow closure thereof, the portion then being repressurized by pumping fluid back in. By pumping out when the fracture is initiated, propagation is substantially prevented allowing estimation of the fracture length and toughness to be obtained and the time taken for the measurement reduced.

Abstract: A downhole penetrometer comprising a body which can be lowered into a borehole and including a tooth and an associated actuator for moving the tooth radially outwardly from the body so as to penetrate the wall of the borehole, a sensing arrangement being provided for determining the force applied to the tooth and the extent of penetration of the tooth into the borehole wall. A motor and pump arrangement is included to power the actuator, power typically being provided by a wireline which can also be used to communicate readings to the surface. A pair of inflatable packer modules are situated above and below the tooth to isolate an interval of the borehole in which a measurement is being made.

Abstract: The invention relates to a method of monitoring the drilling of a borehole through an earth formation with a rotating drill bit fixed at the lower end of a drillstring. At least one physical quantity associated with the vibrations resulting from the interaction of the rotating drill bit with the earth formation is detected and an oscillatory signal is generated in response thereto. Filter coefficients a.sub.k of an auto-regressive filter model are determined by fitting the filter output signal with the oscillatory signal. The reflection coefficients of the vibrations propagating along the drill string and being reflected by a mis-match of impedance of two successive elements of the system earth formation/drillstring are derived from the filter coefficients. Finally, the hardness of the formation being drilled, the contact of the drillstring with the borehole and the vibration level of the vibration along the drillstring are determined from the reflection coefficients.

Abstract: In the rotary drilling of oil wells a drilling mud is used both to transport the cuttings up to the surface and to impose an hydrostatic pressure on the walls of the borehole. For these functions the mud must for example have an acceptable viscosity and density. It is therefore important to monitor the characteristics of the mud, and to keep them within certain limits. Only recently, however, has drilling practice recognized the importance of monitoring the mud's ionic composition. The various techniques proposed involve separation of the mud into liquid and solid portions, and analysis of these. Though they have proven useful, yet there are a number of problems. For example, the separation has not always been easy, and the available techniques often may not satisfactorily remove the fines.

Abstract: A method for the estimation of pore pressure within a subterranean formation containing fluid during the drilling of a bore hole. The bore hole is drilled using a drill string consisting of a drill bit fitted to its lower end, and using drilling mud pumped from the surface through the drill string and finally evacuated.

Abstract: A method of real time analysis and control of a fluid influx from an underground formation into a wellbore being drilled with a drill string, a drilling and circulating from the surface down to the bottomhole into the drill string and flowing back to the surface in the annulus defined between the wall of the wellbore and the drill string, the method comprising the steps of shutting-in the well, when the influx is detected; measuring the inlet pressure P.sub.i or outlet pressure P.sub.o of the drilling mud as a function of time at the surface; determining, from the increase of the mud pressure measurement, the time t.sub.c corresponding to the minimum gradient in the increase of the mud pressure and controlling the well from the time t.sub.c.

Abstract: The invention relates to a method of analyzing fluid influxes into an oil well from an underground formation. During a drilling mud transient flow state, the successive values of the rate Q.sub.i or pressure p.sub.r of injection of the drilling mud into the well and the successive values of the rate Q.sub.r or pressure p.sub.r of return of the drilling mud to the surface are measured. The changing values of the rate or pressure of injection are compared with the changing values of the return rate or pressure. From this comparison the nature and volume of the fluids that have penetrated into the well are determined.

Abstract: A method for determining at least one dynamic flow characteristic of a multiphase flow circulating in a pipe, the flow being composed of a lighter dispersed-phase and a heavier continuous-phase. A tracer is discharged (or activated) into the flow at a chosen first location in the pipe by mixing (or activating) a portion of the tracer with the continuous-phase therein. The tracer concentration at a chosen second location in the pipe is measured with a detector as a function of time t, so as to obtain a signal S(t). Then a relationship is fitted to the signal S(t) so as to derive the values of the velocity U of the continuous phase and/or of a dispersion coefficient k. The slip velocity v.sub.s of the dispersed phase relative to the velocity of the continuous phase is also advantageously determined. From the values of velocities U and v.sub.s and from the volume fraction y.sub.

Abstract: The method comprises during a drilling operation wherein the drilling fluid is set moving and the drill string is stationary, monitoring the pressure of the drilling fluid pumped into the drill string depending on the volume of liquid pumped in the drill string and determining, from the pressure curve, a physical property linked to the thixotropy of the drilling fluid. An advantage of the invention is that the highest point of the pressure curve indicating the start of the fluid flow into the well is easily visible, and its maximum value can be measured to find the gel strength specific value.

Abstract: An apparatus for use in the capacitive measurement of the void fraction in a flowing liquid. An assembly of at least two electrodes is spaced apart around the exterior of the body defining a flow passage such that the capacitance of the electrode assembly is a function of the dielectric constant of material within the passageway. The radial thickness of the body is substantial such that the passageway occupies a portion of the electrostatic field of the electrode assembly which is relatively uniform. The dielectric constant of the body may be substantially equal to the expected dielectric constant of the said liquid. The body may be tubular with the electrode assembly directly supported on the radially outer surface of the tube.