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: 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: 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: 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.

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 density and viscosity. It is therefore important to monitor the characteristics of the mud, and to keep them within certain limits. The technique proposed involves the use of an ion selective/reference electrode pair to measure in the mud the potential of the selected ion (as a potential difference), and thus allow a determination of that ion's concentration. Thus, it is a method in which, using a selective/reference electrode pair where the reference electrode is of the type having a liquid junction via an aperture within the reference electrode containment vessel, there is determined the potential difference generated by, and thus the concentration of, the ion in the mud.

Abstract: The invention relates to a method of determining the porosity of an undergound formation being drilled by a rotating drill bit mounted at the lower end of a drill string. The torque (TOR) and the weight (WOB) applied on the bit when drilling the underground formation are measured; the effect of the geometry of the drill bit on the torque and weight on bit response is determined; the porosity (phi) of the formation being drilled is derived from the measured TOR and WOB taking into account the effect of the geometry of the drill bit. Preferentially, the porosity phi is determined from the following equation:TOR=(k.sub.1 +k.sub.2.phi)WOB.sup.awhere k.sub.1, k.sub.2 and a are parameters characteristic of the geometry of the drill bit.

Abstract: The logging tool comprises a gas void fraction measurement section (37) consisting of a first set (37) of eight longitudinal electrodes (38) extending parallel to the longitudinal axis of the tool and positioned and regularly spaced around said longitudinal axis, a sleeve (40) made of dielectric material and located in contact and around the electrodes for obtaining an electric field pattern distributed essentially radially between the electrodes and the wall (12) of the borehole facing the electrodes (38), a centralizer (32) for substantially centralizing the tool in the borehole, and a circuit means (69-115) for measuring sequentially the capacitance between two adjacent electrodes for each pair of electrodes, said capacitance being characteristic of the gas void fraction of the fluid flowing in the wellbore. The logging tool comprises in addition a cross correlation gas velocity measurement section (28) which includes a second (48) and a third (50) set of electrodes.

Abstract: It is often desirable to meter multiphase fluid flow in pipes (e.g. bore holes). In order to obtain reliable/accurate flow rate measurements it is known to incorporate obstructions in the flow path to cause homogenization. A non-obstructive method of homogenizing the flow of a multiphase mixture of fluids in a bore hole comprises providing in the bore hole a pipe section which has an internal surface with a step discontinuity, whereby when fluid flows through the pipe section, turbulent stresses are caused by the discontinuity, leading to homogenization by turbulent mixing. There is disclosed a flow meter which comprises a pipe length with a first section having a step change in cross-section for homogenizing fluid flow therethrough, in series with a venturi flow meter in which a differential pressure can be measured in a second pipe section having a smooth change in cross-section.

Abstract: A method is provided for determining the state of wear of a multicone drill bit. Vibrations generated by the working drill bit are detected and converted into a time oscillatory signal from which a frequency spectrum is derived. The periodicity of the frequency spectrum is extracted. The rate of rotation of at least one cone is determined from the periodicity and the state of wear of the drill bit is derived from the rate of cone rotation. The oscillatory signal represents the variation in amplitude of the vertical or torsional force applied to the drill bit. To extract periodicity, a set of harmonics in the frequency spectrum is given prominence by computing the cepstrum of the frequency spectrum or by obtaining an harmonic-enhanced spectrum. The fundamental frequency in the set of harmonics is determined and the rate of cone rotation is derived from the fundamental frequency.