Abstract: This invention relates to a method for analyzing data from a measurement-while-drilling (MWD) formation evaluation logging tool which compensates for rotations of the logging tool (along with the rest of the drillstring) during measurement periods. In accordance with this method, the received signal is broken down into a plurality of sections. In a preferred embodiment, the present invention calls for the breaking of the signal from the formation into four different sections: top, bottom, right, left. As the tool rotates, it will quickly pass through these four quadrants. Each time it passes a boundary, a counter is incremented, pointing to the next quadrant. This will allow for dividing the data into four spectra for each detector. Each of these four spectra will be obtained for 1/4th of the total acquisition time. The relative error is minimized by comparing the relative error in each spectrum and selecting a specific spectrum or by combining at least two spectra.

Abstract: A method and apparatus for nuclear logging, and in particular, neutron porosity logging is presented. In accordance with the present invention, a novel programmable gain amplifier circuit and a novel peak detector circuit are used in conjunction with other electronic circuitry to provide borehole formation logs in a nuclear logging tool.

Abstract: A downhole motor includes a bearing assembly for allowing rotational and bidirectional axial movement of a drive shaft in a housing. The bearing assembly includes a stationary race member, a displaceable race member, ball bearings disposed between the race members, and resilient load carrying members for distributing axial thrust loading from the drive shaft to the displaceable race member when the drive shaft is axially displaced in a first direction. The bearing assembly further includes resilient preload members for maintaining the ball bearings in contact with the race members in the absence of axial loading and when the drive shaft is axially displaced in a second direction. The downhole motor of the present invention provides a high axial thrust load capacity, prevents shock loading on the bearing assembly during sudden changes in the direction of axial loading on the bearing assembly and exhibits improved durability during cyclic bidirectional axial thrust loading.

Abstract: A simplified ananlog circuit is presented for controlling electromechanical transducer pairs in an acoustic telemetry system. The analog circuit of this invention comprises a single electrical resistor which replaces all of the digital components in a known digital circuit. In accordance with this invention, a first transducer in a transducer pair of array is driven in series with the resistor. The voltage drop across this resistor is then amplified and used to drive the second transducer. The voltage drop across the resistor is proportional and in phase with the current to the transducer. This current is approximately 90 degrees out of phase with the driving voltage to the transducer. This phase shift replaces the digital delay required by the digital control circuit of the prior art.

Abstract: The present invention comprises a method and apparatus for estimating and identifying the channel filter characteristics of the drilling fluid communictions channel (e.g. standpipe) based on surface decoding of the MWD data signal. The channel filter characteristics can be mathematically defined by the transfer function of the channel. The transfer function is a mathematical model defining the input-output relationship of a physical system. The present invention may also characterize the channel filter defined by the drilling mud in the annulus between the borehole and the drillstring.

Abstract: A method of acoustically trasmitting data signals over a drillstring is presented. In accordance with the present invention, acoustic data is transmitted only during preselected short time intervals thereby avoiding destructive interference caused by the signal being reflected back and forth from the ends of the drillstring. The present invention makes use of the fact that the first reflective wave has to travel three times the length of the drillstring before it can interfere with the original data signal. For example, the time for the first wave to travel three times the length of the drillstring can be in the order of one second. Therefore, if the data content of the transmission signal is confined to the first one second or so of transmission, then a transmission channel relatively free of interference is available for data transfer.

Abstract: A method and apparatus for establishing a remote communications link from the rig floor to the downhole MWD system is presented. In accordance with the present invention, the state of a physical condition downhole is changed in a predetermined timed sequence. This state change is controlled on the surface at the drilling platform and detected downhole by the MWD system. The desired operating mode of the MWD system is then determined based on the detected time sequence of the state changes. Preferred embodiments of the present invention utilize two different state changes which are detectable downhole and which can be controlled at the surface. In a first embodiment, the state changes comprise a preselected timed sequence of powering the MWD system up or down. This power cycling is accomplished by operating the mud pump in an ON/OFF sequence which will cause the MWD turbine to similarly be powered up or down.

Abstract: Downhole measurements are made for accurately determining whether or not a core barrel contains an appropriate amount of core sample before retrieval of the coring tool is attempted. This is accomplished by using a known apparatus for measuring downhole weight on bit (WOB) at the beginning of a coring run to make a first measurement corresponding to the weight of all drillstring components suspended below the measurement point at a selected depth. Thereafter, the coring tool drills down the length of the core barrel. When sufficient drilling takes place to obtain a core, the drillstring is pulled up to the same depth as the measurement and a second measurement is taken. After correcting the data for temperature changes, the difference in between the first and second measurements is obtained and compared to a calculated weight for a full core.

Abstract: A method and apparatus is presented for measuring the azimuth angle of a borehole being drilled, the data for determining the azimuth angle being obtained while the drillstring is rotating.

Abstract: A phase and amplitude calibration system for an electromagnetic propagation based earth formation evaluation tool is presented. In accordance with the present invention, improved phase and amplitude logs of a borehole section are provided by an automatic calibration system which compensates for errors caused by temperature and pressure variations in the borehole. This improvement is accomplished by applying in-phase, equal-amplitude reference signals to both measurement channels of a two channel system to thereby characterize system errors for correction of data used for logging. The reference signals are applied by tightly coupling a calibration signal to each receiving antenna. In a first embodiment, this is accomplished by adding a second antenna (a calibration antenna) to each of the two spaced receiving antennas.

Abstract: A method and apparatus for remote signal entry of control or data information from an equipment operator into an MWD system is presented. In accordance with an important feature of the present invention, the magnetometer, which is typically present in commercial MWD systems, is used as a communications channel for remote (e.g. wireless) transfer of data and/or control commands into the MWD tool. The present invention functions by replacing the direct electrical RS232 coupling with a wireless magnetic link. The invention uses the RS232 output of the operator's computer to drive its power amplifier which in turn drives the field coils in a transmitter. The axis of the field coils must be aligned with one of the sensitive axes of the magnetometer which, as mentioned, is a pre-exisitng part of the directional measurement system of the MWD apparatus. Thus, the present invention overcomes the necessity in the prior art for a direct RS232 link up between the surface computer and the computer on the MWD tool.

Abstract: A flexible coupling for use in a down-hole motor assembly such as a positive displacement moineau motor is presented. The flexible coupling includes two sets of flexible joints. Each joint consists of two cylindrically shaped slipper couplings angularly offset by 90 degrees. Each slipper coupling is comprised of mating male and female members which are joined together by ball bearings positioned in arcuate grooves located along the cylindrical mating surface.

Abstract: A method for determining the free point of a stuck drillstring is disclosed. The method includes determining the hookload on the stuck drillstring, comparing the hookload on the stuck drillstring with the most recent hookload prior to drillstring sticking to determine the depth of the free point.

Abstract: Apparatus is presented for measuring weight, torque and side force (bending) on a drill bit for oil and gas well drilling. This apparatus includes radial holes which do not pass completely through the wall of the drill collar sub, but instead, pass only partially through the wall of the drill collar sub. Strain gages are located in the partial radial openings. These strain gages measure each of the three parameters of weight, torque and bending. Each partially formed hole is sealed by a plug and retained in place by a retaining ring. For torque and bending measurements, the strain gages are arranged with symmetry of position between diametrically opposed holes. The strain gages are positioned in an array which departs from symmetry of position to minimize errors in the weight measurement caused by pressure changes in the drilling fluid.

Abstract: The filtering technique of the present invention cancels or minimizes noise in data signals found to be caused by dynamic variations in the drilling process. It has been discovered that the measurement of surface vibrations in the drill string and their effects on certain drilling equipment such as rotary table torque contains information that can be used to remove some or all of the pressure disturbance caused by these dynamic variations (vibrations). The result of removing some or all of the dynamic variation induced noise from the measurment-while-drilling (MWD) data signal yields a better signal to noise ratio (SNR) and therefore improves decoding of the MWD signal. In accordance with another important feature of the present invention, it has been found that improved SNR results from taking the first derivative with respect to time of the torque measurement. This first derivative measurement more closely resembles the actual disturbance in the standpipe pressure (SPP).

Abstract: A near bit offset stabilizer for use with a bent sub or bent motor housing is presented wherein a mechanism is provided to correctly orient and lock the stabilizer in a desired position in alignment with the bend angle in the bent sub or bent motor housing. This alignment and locking mechanism comprises a ring nut having a series of radial slots on its lower end; and the provision of a series of corresponding radial slots on the upper end of the stabilizer. The corresponding slots permit mutual interlocking between the ring nut and stabilizer for locking the stabilizer in any one of a plurality of radial positions. A scribe line or other indicia on the stabilizer permits visual alignment with the bend in the bent sub or bent motor housing in the drill string above. Finally, a second nut locks the stabilizer in the selected radial position.

Abstract: A debris catcher comprising a conical screen (filter) in a drill string which defines an annular accumulation space between the screen and the inner wall of the drill string is presented. The central portion of the screen is open to establish an unimpeded flow path. A centrifugal deflector, impeller or similar device above (upstream from) the screen establishes a helical flow pattern in the drilling mud whereby debris entrained in the mud is forced outwardly by centrifugal action. The debris is then caught in the annular accumulation space between the screen and the drill string wall when the mud flows through the screen. If the accumulator fills or the screen becomes clogged, mud will still flow through the center flow passage. The debris catcher of the present invention is preferably positioned within a drill string upstream of a mud powered turbine or other device in the mud stream, the operation of which may be jeopardized by debris in the mud stream.

Abstract: A system for determining kelly-to-riser position on floating drilling platforms is presented. The system removes (e.g. filters) uncompensated heave from surface sensor measurements so that bit depth can be accurately calculated. During operation, surface sensors on the drilling platform measure heave compensator action and kelly movements. Each heave sensor reading is then added to a kelly sensor reading in order to obtain a value termed kelly-to-riser. Each kelly-to-riser value is fed (inputted) into the system of the present invention and a filtered reading is returned for use in calculating bit depth and rate of penetration (ROP). The filtering system is termed a linear extrapolative filter (LEF). The LEF generates filtered readings by performing a linear regression on measurements taken over its pre-specified filter interval. It then predicts the current kelly-to-riser position from the resultant trend line.

Abstract: A cable tensiometer (referred to herein as a weight beam) is presented for measuring line tension in a wire rope. The cable tensiometer is characterized by a beam section, a load cell mounted on the beam section and configured so as to measure variable forces in tension, rather than in compression, and clamping of the cable at a single central point at the load cell, with all other cable contacts being free floating.

Abstract: Apparatus is presented for measuring weight, torque and side force (bending) on a drill bit for oil and gas well drilling. Strain gages are located in radial holes in the wall of a drill collar sub for measuring each of the three parameters of weight, torque and bending. The holes are sealed by inner and outer plugs and a ring and bolt structure retains the plugs in place. For torque and bending measurements, the strain gages are arranged with symmetry of position beteween diametrically opposed holes. The strain gages are positioned in a novel array which departs from symmetry of position to minimized errors in the weight measurement caused by pressure changes in the drilling fluid.