Abstract: Fluid influx in a borehole is determined by examining and monitoring the computed transfer function in the signal channel defined by the annulus between the borehole and a drillstring in the borehole.

Abstract: In accordance with the present invention, several methods are presented for the detection of gas into an offshore marine riser (e.g., riser gas). In a first embodiment of this invention, an acoustic transmitter is positioned on or nearby the subsea blowout preventor stack and imparts continuous low frequency waves into the annular fluid in the marine riser. These imparted waves define pressure perturbations which are received by a pressure transducer positioned on the riser at a location above the acoustic transmitter. Gas detection in the riser is then indicated by determining the rate of change of certain characteristics of the output. The output characteristics are preferably the moduli and phase angles of the acoustic fundamentals and their harmonics.

Abstract: An apparatus and method for selecting a passband frequency for acoustically transmitting signals over a drillstring is presented. In accordance with the present invention, a series of electrical signals, each progressively increasing in frequency over a predetermined range, excite an acoustic transmitter producing an acoustic signal in the drillstring. The power spectral density of this signal is measured and correlated to a modeled power spectral density for the drillstring. A passband frequency having the strongest correlation ratio between the measured and modeled power spectral density is selected as the frequency for acoustical communication in the drillstring.

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: 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 device for detecting and sensing the boundaries between differing rock strata is provided. This device utilizes electrical conductivity or resistivity to detect and measure the boundary layer. The device of the present invention may be used with a "measurement-while-drilling" (MWD) tool, using either wire-line or wireless data communication with a surface receiver. Moreover, the resistivity or conductivity detection device of the present invention may also be used alone or in conjunction with gamma radiation sensors. The present invention utilizes at least a pair of electrodes which occupy a small area and are located on one side of the tool aligned with the longitudinal axis thereof. Thus, in drilling a well along a specific formation stratum (which may be horizontal or inclined), the present invention will act to indicate to the driller whether the drill bit is approaching a stratum boundary, and in which direction that boundary lies.

Abstract: The infusion of fluid from the formation being drilled into a borehole is detected in an MWD system by modulating the drilling fluid stream in the drill pipe and detecting pressure variations commensurate with the modulation at the surface in the annulus between the drill pipe and wall of the well. Modulation to generate the pressure variations in the annulus is accomplished by the same pressure generating element used to generate pressure signals in the mud column for MWD measurements. The detected pressure variations are compared in phase and/or amplitude with their own near term past history or with the drilling fluid pressure variations in the drill pipe resulting from the modulation. Variations in phase or amplitude which can not be attributed to changes in the drilling operation will be indicative of fluid infusion.

Abstract: The infusion of fluid from the formation being drilled into a borehole is detected by modulating the drilling fluid stream in the drill pipe and detecting pressure variations commensurate with the modulation at the surface in the annulus between the drill pipe and wall of the well. The detected pressure variations are compared in phase and/or amplitude with their own near term past history or with the drilling fluid pressure variations in the drill pipe resulting from the modulation. Variations in phase or amplitude which can not be attributed to changes in the drilling operation will be indicative of fluid infusion.

Abstract: An explosion and flame proof electrical connector protective assembly is presented which comprises an explosion proof cylindrical housing threadably connected at each end to explosion proof gland members. A pair of disconnectable conventional, i.e. non-explosion proof, connector elements, each leading from ends of respective cables, are disposed and connected within the housing and gland members. Both gland members are tightly sealed to the respective cables forming a protective explosion proof environment within the housing for the attached connector elements. The protective assembly of the present invention is especially well suited for use in extremely hazardous environments such as Class 1, Division 1 hazardous areas as defined by the National Electric Code (NEC) and which are associated with oil rigs and the like.

Abstract: An insulating and electrode structure for a drill string is presented. The drill string includes a drill string segment having a recess along an axial length thereof. The recess has a band of elastomeric nonconductive material therein which receives electrodes comprised of rings of conductive elastomeric material.

Abstract: An array of electrodes is presented for accurate and improved measurement of borehole resistivity. The electrode array comprises five electrodes mounted on a relatively short insulated segment of a drill string. Current flows from the first electrode to the second electrode and is sensed by third and fourth electrodes. Any leakage current from the first electrode is collected by a fifth electrode and is kept isolated from the current flowing between the first and second electrodes thus insuring accurate determination of apparent formation resistivity. A current source, preferably a constant current source is used to determine the current in the circuit of the first and fifth electrodes.

Abstract: A borehole sensor is presented including a three axis gimbal device for determining (1) a vertical plane, using the force of gravity as a reference, (2) a horizontal plane, using the force of gravity as a reference, and (3) the north direction, using the earth's magnetic field as a reference. A motor drive system drives parts of the mechanism to desired positions about the three axes, and error transducers determine the deviation from desired positions about the axes and provide feedback to the motor drive system to eliminate the error.

Abstract: A rotation sensor and output signal processing apparatus is presented. The rotation sensor is a ring core flux gate magnetometer whose output varies as a function of the earth's magnetic field. The phase angle of the second harmonic of the magnetometer output is sensed to provide an indication of the state of rotation of the magnetometer. When a state of no rotation is sensed, actuating signals are delivered to a control system to sense borehole parameters and telemeter the parameters to the top of the borehole.

Abstract: A control system is presented for controlling the operation of a borehole sensor. The borehole sensor includes a three axis gimbal device for determining (1) a vertical plane, (2) a horizontal plane, and (3) the north direction. Upon receipt of an initiation signal, the control causes a motor drive associated with each gimbal to drive error transducers on each gimbal to desired "home" positions about the three axes and error transducers determine the deviation from desired positions about the axes and provide feedback to the motor drive system to eliminate error. A home signal is generated when each error transducer reaches its home position. When home signals are received from all error transducers, the control system then senses the sign and magnitude of the error output from each error transducer and operates the motor drive system to drive the gimbals in directions to reduce the error. When each error transducer reaches its null position, the control terminates operation of its associated motor drive.