Abstract: An apparatus and method are disclosed for eliminating a noise signal from at least one source during an acoustic measurement of a subsurface geological formation or borehole. The apparatus includes a longitudinal body for positioning in the borehole and a transmitter supported by the body for transmitting acoustic signals into the formation and borehole. A sensor, substantially isolated within the body, is used to detect one or more noise signals and a receiver is carried by the body for receiving acoustic signals traversing the formation and borehole, and for receiving one or more noise signals. A processor is connected to the sensor and receiver for processing the acoustic signals and noise signals coupled from the receiver and the noise signal coupled from the sensor into a preferred formation or borehole signal by determining the noise signal received at the receiver using the noise signal received in the sensor and a propagation factor for the noise signal between the sensor and receiver.

Abstract: A method is disclosed for correcting for the distorting effect of cross-axial magnetic interference on the readings of a well survey tool using a reduced number of measurements and measuring locations. A well survey tool connected to a drill string assembly measures the gravitational and distorted terrestrial magnetic fields at two or more axially displaced locations in an axially extending well bore. The measurements are made from two or more different orientations (tool faces) of the tool about the well axis. Initial values for the tool inclination, azimuth and tool face angle are first determined without correction for the cross-axial magnetic interference introduced by the drill string assembly and the survey tool. Measurements made at each location and tool face are referred to the toots coordinate system and variations introduced by the different tool face angles are used to estimate the cross-axial interference. The estimated interference is used to improve the estimate of the azimuth.

Abstract: Bit instrumentation and method for controlling drilling are disclosed that include multiple resistivity sensors 5B and accelerometer sensors 4 disposed within an insert portion 1B of the drill bit 1. The resistivity sensors have a beveled portion to provide an interference fit with a cavity formed within the insert portion 1B of the drill bit. Resistivity sensors 5B may be used to determine the motion of the bit 1 within the wellbore 106 including unstable bit operation such as bit whirling and bit tilting. As well, accelerometer sensors 4 may also be provided in conjunction with the resistivity sensors 5B to provide information concerning motion, accelerations and stresses applied to or within the drill bit 1.

Abstract: A sacrificial anode sub and method are disclosed which provide a lower voltage at the proximately located bit than at the sacrificial anode disposed on sub to thereby deter bit balling. An electromotive force (emf) dynamo is built into the sacrificial anode sub to provide a direct current voltage source for this purpose. Annular insulator electrically insulates sacrificial anode from tubular body. An electrical connection to drill bit is made through threaded lower connector with bit. Impeller rotates in response to drilling fluid flow to rotate the rotor assembly of dynamo.

Abstract: Methods and apparatus for detecting the approach of a boundary stratum while drilling in a substantially horizontal subsurface zone using sensor tools having sensors with different depths of investigation. The two depths of investigation signals are used to reduce spurious signals. In some cases, dips or angles of the boundary strat with the borehole may be determined. In alternative embodiments, one or more electromagnetic energy transmitters are used with a single receiver pair to generate a characteristic signature of approaching boundary stratum.

Abstract: An electromagnetic wave propagation well logging system for measuring dielectric constant and/or formation resistivity (conductivity) includes three transmitters and a pair of receivers. The receiver pair is connected to circuitry that measures the amplitude ratio between the receivers, as well as the phase angle difference between the receivers. Signals representative of the detected amplitude ratio and of the detected phase angle difference are combined in such a manner as to make the depth of investigation controllable. Methods are also disclosed for maintaining a common depth of investigation as the well logging instrument traverses the earth borehole.

Abstract: Various steel, downhole tools and components of a drill string, including, as examples, a PDC drill bit, a rotary rock bit, a cross-over sub, a stabilizer, a reamer, a hole enlarger and a coring bit, are selectively treated to cause certain of their parts to be electro-negative with respect to steel, and certain other parts to either have the same electro-negativity as steel, or to be treated to be electro-positive with respect to steel.

Abstract: An apparatus and method for determining formation resistivity at a plurality of radial distances from an earth borehole uses a single receiver pair and a plurality of electromagnetic energy transmitters sequentially spaced along the apparatus from the receiver pair, such transmitters being sequentially pulsed at approximately 1-2 MHz each to provide time separation between the pulsing of the plurality of transmitters. The closest spaced transmitter is spaced a predetermined distance from the closer receiver to make the depth of investigation of the closest transmitter essentially independent of formation resistivity. Alternatively, a single transmitter is spaced a predetermined distance from the closer receiver to make the depth of investigation of such transmitter essentially independent of formation resistivity.

Abstract: The present invention is directed to a system, apparatus and methods for determining influx of formation fluids into a well borehole during drilling. The methods of the present invention comprise determining the dielectric constant and/or conductivity of the fluid in the annulus about a drill pipe in a well borehole, comparing the determined dielectric constant and/or conductivity to a reference value and inferring that influx has occurred when the difference between the dielectric constant and/or conductivity and the reference value is greater than a predetermined limit.

Abstract: A conventional electromagnetic logging device, having both MWD and wire line embodiments, and having a pair of cutouts spaced along the length of the tool mandrel, each cutout having a length of greater than 4.0 inches as measured along the longitudinal axis of the tool, is modified by adding a pair of full metal jackets around the pair of cutouts. The first metal jacket placed around the first cutout in the mandrel has an additional cutout therein having a length in the range of 1.0 to 4.0 inches and a depth in the range of 0.25 to 1.0 inch. A transmitting antenna is placed in the cutout in the first metal jacket. The second metal jacket placed around the second cutout of the tool mandrel has a pair of spaced cutouts therein, each having a length in the range of 1.0 to 4.0 inches and a depth in the range of 0.25 to 1.0 inch. First and second electromagnetic receiving antennas are placed in the first and second cutouts in the second metal jacket, respectively.

Abstract: Two downhole measurement-while-drilling tools, at least one of which is borehole sensitive, are used to make standard measurements of borehole conditions while drilling. From these measurements, and with some prior knowledge of the lithology, the caliber of the borehole is determined by iteration. The preferred tools are a neutron porosity and a density tool with lithology having been determined by prior seismic survey techniques.

Abstract: A bucket brigade filter is disclosed having a feedback loop resulting in a tight comb structure filter response whereby a periodic noise and all its harmonics may be removed from a signal. Scalers featuring selectively variable scaler parameters permit prompt adaptation to changes in the noise period, rapid initialization of the filter to an operating condition and adjustable stopband widths of the filter frequency response. Sampling of the input data signal may be synchronized to the periodic variations of the noise to be eliminated from the signal.

Abstract: The present invention relates to an apparatus and method for calipering a borehole using acoustic measurements within the borehole. These acoustic measurements are useful for measuring the reflectivity of the side walls of a borehole and for calipering a borehole in a wireline or measurement while drilling configuration. The apparatus comprises at least one acoustic transceiver disposed on a calipering tool, together with a second acoustic receiver disposed longitudinally a selected distance from the first receiver. Further, a second acoustic transceiver is disposed on the caliper tool azimuthally from the first transceiver. Measurement of the travel times of acoustic pulses reflected from the borehole walls by the transceivers and receivers of this device, together with other known data, permits an accurate caliper of the borehole to be produced.

Abstract: An electronic noise filtration system for use in improving the signal to noise ratio of acoustic data transmitted from a downhole transducer in a measurement while drilling system. Signals from a pair of receiving acoustic transducers located in the mud flow path directed downhole are input to a differencing amplifier. The RMS output of the amplifier is converted from an analog to a digital signal and then processed by a computer programmed with a least mean squares technique for minimizing the signal. The input from one receiving transducer is routed through a delay line wherein a programmable clock controls the timing of the signal delay. The delay time is controlled and adjusted by the computer's calculation of the frequency with which the clock should drive the delay line to minimize the difference between the two received transducer signals. This function minimizes ambient noise in the acoustic transmission line formed by the column of drilling fluids when no data transmissions are being made.