Abstract: Methods and apparatus are described for identifying and removing noise from borehole telemetry signals. A spectrum of the signal and of an approximated noise-free spectrum of the signals are generated and compared so as to identify frequencies at which noise occurs. The approximated spectrum is preferably generated by an averaging or integrating process which essentially results in a smoothened variant of the signal spectrum. The comparison includes dividing the signal spectrum by the approximated spectrum, and setting a threshold in the resulting dimensionless peak spectrum. The remaining parts of the peak spectrum are identified as noise. The dimensionless spectrum is found to have major advantages when having to identify noise frequencies.

Abstract: A method and apparatus of raising or lowering an oil drilling rig mounted on a platform is provided. The rig is mounted on the platform hull, which is supported by a plurality of legs. Each leg has a plurality of jacking chords. The legs are raised or lowered relative to the hull to lower or raise the rig. The elevation of each chord of a leg is measured during the raising or lowering action, and the measured elevations are used to determine the deformation of the leg. In this manner, a corrective action is instituted according to the determined deformation by acting individually on each chord of the leg.

Abstract: A method for filtering noise from discrete noisy seismic signals in a time interval ([1, . . . , T]) is provided. The method comprising the steps of using the noisy seismic signals for determining at least one reference channel (x(t)) for the time interval as an estimate of the noise; determining coefficients for M temporally local filters (w(i, t)), the filters forming a filter bank, and M being a number equal to or larger than two, by minimizing a cost function (J(t)) representing a measure of the error of the output of the filter bank, and applying the filter bank to at least one estimate (x(t)) to determine M filtered estimates of the noise. The filtered estimates are multipled with temporal windows (h(i, t)).

Abstract: Methods and apparatus are described for recognizing wellbore telemetry signals, wherein a received analog telemetry signal is compared to a number of possible analog signals. The probability of representing the received signal is determined for each of the possible analog signals. By selecting the signal with the highest probability, the received signal is demodulated. For calculating the probability, Bayes' method or any equivalent thereof is used. In variants, this probabilistic method is used to determine the synchronization point of the telemetry signal and for controlling the noise removal therefrom. The method and apparatus show increased accuracy in recognizing and demodulating the received signals.

Abstract: This invention describes methods and apparatus for identifying potentially hazardous events during the drilling or production of hydrocarbon reservoirs where such events include kick detection in a well, fluid influx from a drilled formation, sticking pipe in a borehole, pipe washouts or formation fracture generation, according to measurements made by instruments such as flowmeter paddles, electro-chemical transducers or MWD parameter sensors. Measured signals are compared to a number of possible signals and the probability for said measured signals representing such an event are determined.

Abstract: A cross correlation fluid flow meter including a body having first and second sensor devices positioned such that in use they are spaced apart a known distance in the direction of fluid flow, each sensor device having a signal transmitter and a signal receiver. According to one embodiment of the flow meter, the signal transmitter of the first sensor device is operable to transmit signals at a first frequency and the signal receiver of the first sensor device is arranged to receive signals at the first frequency. The signal transmitter of the second sensor device is operable to transmit a second signal at a second frequency and the signal receiver of the second device is operable to receive signals at the second frequency, the first and second frequencies being different from one another. The first sensor is non-responsive to the second frequency and the second sensor is non-responsive to the first frequency. Cross correlation of the received signals provides an indication of the fluid flow rate.

Abstract: Methods and apparatus are described for compressing seismic data. The data compression is achieved by splitting the data into subsets and applying requantization levels to those subsets which depend on a number representing the subset and on time. Further error criteria ensure that the error introduced by the data compression does not affect the data in a time window representing the listening time. The compression ratio can be improved by applying data encoding techniques to the subsets.

Abstract: A cross correlation fluid flow meter including a body having first and second sensor devices positioned such that in use they are spaced apart a known distance in the direction of fluid flow, each sensor device having a signal transmitter and a signal receiver. According to one embodiment of the flow meter, the signal transmitter of the first sensor device is operable to transmit signals at first phase of a first frequency and the signal receiver of the first sensor device is arranged to receive signals at the first phase of the first frequency. The signal transmitter of the second sensor device is operable to transmit a second signal at a second phase of the first frequency and the signal receiver of the second device is operable to receive signals at the second phase of the first frequency, the first and second phases being out of phase with one another. The first sensor is non-responsive to the second phase and the second sensor is non-responsive to the first phase.

Abstract: After an oil well has been drilled, lined and cased, and is producing, it may be desirable in situ (either at the wellhead or downhole) to measure, and log (record), the rate at which fluid, and its several distinct components, is flowing out of the geological formations through which the bore has been drilled and is passing into and up the casing. A useful type of detector system for this purpose is an optical probe (31), and the invention proposes a novel design of probe which has a doubly-angled tip, there being measured the light totally internally reflected at the interface (37), which depends on the ratio of the refractive indices of the probe tip and fluid component in which it is immersed.

Abstract: A seismic processing method relating finely sampled data of earth formations, such as that obtained from borehole measurements, to substantially longer wavelength seismic data, such as that obtained from surface seismic surveys or the like, while improving the ease of manipulation and processing speed of seismic processing. In a preferred embodiment, a fine layer model having n layers is defined, with the properties of each fine layer corresponding to the properties of each of n sampling points. An equivalent model is constructed by defining m equivalent layers, where m is substantially smaller than n and the thickness of the thickest of the equivalent layers is substantially smaller than a predetermined dominant wavelength of a seismic signal. Equivalent formation properties are generated for each equivalent layer by combining the sampled formation properties of the fine layers within the respective equivalent layer, preferably in accordance with the equivalent medium theory.

Abstract: A method of locating hydrocarbon reserves comprising: selecting on the basis of a hydrocarbon hypothesis from a region of interest below the surface of the earth patches having probabilities of containing hydrocarbon reserves greater than a predetermined probability; defining from structural data a respective structural closure for each of the patches, each structural closure comprising an area capable of enclosing a hydrocarbon reserve and having a perimeter of constant depth substantially equal to the deepest point of the patch; determining a measure of the geometrical match between each patch and the respective structural closure; and selecting each patch having a measure of the geometrical match exceeding a predetermined measure. Particular geometrical matching methods include those relating to the height, area, volume and perimeter outline of the potential reserves.

Abstract: A method of determining the rate of penetration .DELTA.d of a drill bit at the end of a drill string while drilling a well, comprising:(a) measuring the vertical displacement S of the drill string at the surface,(b) determining a state space description of S comprising a state space measurement equation: ##EQU1## and a state evolution equation: ##EQU2## wherein S and .DELTA.d are as previously defined, .DELTA. is the difference operator for time .tau. between adjacent samples k and k+1, .LAMBDA. is the drill string compliance, .rho. is the noise term associated with the surface displacement measurement, r is the noise term associated with fluctuations in the state, and h is the hookload, and(c) applying a Kalman filter to said equations to obtain an estimate of the state parameters including .DELTA.d.

Abstract: The present invention provides a bottom hole assembly (BHA) for connection to a drillstring for use in directing the path of a drill bit while rotary drilling, the BHA comprising an apparatus for providing a modified cutting action of the bit in a predetermined portion of the hole, a stabilizer, and a flexible member interposed between the bit and the stabilizer. By "flexible" member is meant a member made from a material having a lower Young's modulus than steel and/or a member with a smaller wall thickness than the remainder of the BHA. In the case where the BHA is formed from steel pipe, a flexible member might be provided by an aluminum drill collar or a composite material drill collar. Alternatively or additionally, the wall thickness of the material from which the collar is formed can be made less than the remainder of the BHA.

Abstract: A method of analyzing a drilling fluid comprising subjecting a sample of the fluid to an XRF analysis technique and comparing the results obtained with a calibration model to determine the amount of one or more components of the fluid present in the sample. The method is particularly useful for determining solids in the fluid such as barite and can be combined with an FTIR technique which is sensitive to other components of the fluid. A PLS algorithm is used to construct the model from the spectra.

Abstract: A method of analysing the major and/or minor phase composition of a cement comprising a) preparing a calibration model from samples for which the phase composition has been determined and for which infra red spectra, typically Fourier transform infrared spectra, obtained by a diffuse reflectance technique, have been obtained so as to relate differences between spectra of the samples to differences in clinker phase composition of the samples; and b) obtaining the infra red spectrum of a sample of unknown phase composition and determining the phase composition of the sample from the calibration model typically using a multivariate statistical method.

Abstract: An NMR pulse sequence for use in the borehole environment is provided which combines a modified fast inversion recovery (FIR) pulse sequence with a series of more than ten, and typically hundreds, of CPMG pulses according to[W.sub.i -180-.tau..sub.i -90-(t.sub.cp -180-t.sub.cp -echo).sub.j ].sub.iwhere j is the index of the CPMG echoes gathered, i is the index of the wait times in the pulse sequence, W.sub.i are the wait times, i are the recovery times before the CPMG pulses, and tcp is the Carr-Purcell spacing. Measurements are made of the signals induced in the formation as a result of the magnetic fields. Determinations of M.sub.o and/or T1 are then made from the measurements according to relationships which relate Mp.sub.o, T1 and T2 to the signal magnitude. Other relationships which provide stretched exponentials or multiple exponentials can also be used. From the M.sub.

Abstract: Method and apparatus for applying the measuring pads of a logging sonde against the walls of a borehole. Dip measurements and geological investigation of earth formations traversed by a deviated borehole require that the measuring pads be pressed against the borehole walls by means of articulated arms which maintain the pads symmetrical and parallel with respect to the sonde. In the preferred embodiment, two independent resilient forces are applied to the pads. The first resilient force is substantially constant at all extensions of the arms in the borehole, while the second resilient force is adjustable to suit local parameters. The second resilient force is preferably adjustable from surface instrumentation while the sonde is making measurements in the borehole. The first resilient force is provided by independent leaf springs acting on each of the pads, while the second resilient force is preferably provided by a coil spring acting on each of the pairs of opposing arms.

Abstract: A filter removes certain noise-induced artifacts from a two-dimensional image of a bore-hole wall, this image being formed by signals from a two-dimensional array of staggered electrodes pulled along the bore-hole wall. The noise artifacts are due to a type of noise which varies as a function of depth of the array, but which is substantially the same at all electrodes at any given time. The artifacts appear in the image in the form of a "footprint" of the electrode array, as an unintended result of a depth-adjustment process in which the original frames of samples of the signals at the electrodes of the staggered array, all taken essentially at the same time, are later resampled to produce frames of samples each corresponding to the same depth in said bore-hole. The filter makes use of the fact that the configuration of the artifact in the image is known, and that the true signal values do not change much between azimuthally adjacent electrodes.

Abstract: A borehole apparatus for analyzing the composition of a formation fluid is disclosed and generally comprises a testing chamber, a means for directing a sample of fluid into the chamber, a light source which emits at least near infrared rays, a spectral detector, a data base means, and a processing means. The light source is preferably an incandescent lamp and the testing chamber includes a window which is substantially optically transparent to at least one near infrared light, and preferably also the near ultraviolet and visible light of the source. The light source is directed at least partly towards the window in the chamber either via collimation or fiber optics. The spectral detector means is preferably a spectrometer which detects and measures the spectra of the light which has been transmitted through and the light which is backscattered by the fluid sample. The preferred data base means stores the spectra at different pressures and temperatures of water, gas, and a plurality of oils.

Abstract: A sonde for aquiring seismic signals in a borehole, the sonde comprising: a detector module (30) enclosing at least one seismic sensor (G); an elongate body (21) having a lateral cavity (22) suitable for receiving the detector module (30); a resilient suspension (40, 50) connecting said module to said body; and an anchor member (12, 13) disposed on the opposite side of said body to the side in which said cavity is disposed. The sonde is characterized by the fact that the resilient suspension exerts a force on said module suitable for displacing it out from the cavity and for pressing it against the wall of the borehole so as to couple it to said wall, together with means (41, 43, 51, 53, 60) which are provided to retract the module into said cavity against the force exerted by the resilient suspension.