Abstract: Three-axis vertical seismic profile measurements are analyzed to derive values for the velocity v.sub.p and angel of incidence .PSI..sub.p of a plane compressional wave at the borehole and for the shear wave velocity v.sub.s and angle of incidence .PSI..sub.s of a plane shear wave at the borehole. In the described embodiment this is accomplished by finding values for these parameters which maximize the expression.SIGMA..sub..omega. .vertline.(a.sub.p +a.sub.s).sup.H u(.omega.).vertline..sup.2 /.parallel.a.sub.p +a.sub.5 .parallel..sup.2 +.vertline.(a.sub.p -a.sub.s).sup.H u(.omega.).vertline..sup.2 /.parallel.a.sub.p -a.sub.s .parallel..sup.2where.omega. is angular frequency;a.sub.p and a.sub.s are column vectors representing compressional and shear wave particle motions at frequency .omega. at a multiplicity of locations in the borehole;u(.omega.) represents components in a plane of waveform measurements obtained at these locations;.parallel. .parallel.

Abstract: A method and apparatus for determining the vertical location of a logging tool in a wellbore is disclosed. An electrical signal is transmitted through a conductor in a well logging cable and a second conductor in the surface. Change in length of the well logging cable is determined by monitoring phase changes in the signals from the first and second conductors.

Abstract: For seismic exploration, a method and apparatus are set forth wherein geophones, preferably arranged in XYZ relationship to one another fixedly within a hermetically sealed housing, are located in a deviated well. The position of the housing with respect to a reference such as the earth's north axis is determined. This reference enables determination of the geophone location and the direction of propagation of seismic impulse.

Abstract: Using waveforms or travel time acquired by multitransmitter and/or borehole sonic tools, acoustic velocity (or slowness) is computed for compressional, shear, and Stoneley waves using direct phase determination (DPD), the slowness time coherence (STC) method, and multiple shot processing (MSP). There is a nonzero difference between transmitter and receiver delta-t's (slownesses) when the sonic tool is in the vicinity of a borehole feature, such as a fracture or a borehole enlargement. The amount of the difference, T/R delta-t, for compressional, shear and Stoneley waves depends on the size and nature of the fracture(s). It is possible to determine the height, width, and dip angle of the fracture when the T/R delta-t's are used in conjunction with other model data. It is also possible to distinguish between borehole enlargements and fractures with the method of this invention.

Abstract: A well logging tool employing at least one transmitter and at least one receiver is incrementally advanced through a borehole. A plurality of recorded well log traces from successive ones of the incremental depth points for a single transmitter-receiver pair are correlated to identify a moveout trend for the recorded waveforms about the measured arrival time of the waveform on the center trace of such plurality of traces. A second correlation of the center trace of the plurality of traces with the next successive depth trace is carried out in accordance with the identified moveout trend to determine the arrival time of the acoustic waveform on such next successive depth trace with respect to the measured arrival time of the center trace.

Abstract: A video system measures the position of the traveling block of a drilling rig to determine borehole depth and the rate of drill bit penetration. A television camera is arranged to track the vertical movement of the traveling block of a drilling rig between its uppermost and lowermost positional limits. An encoding unit is connected to the television camera. The output of the encoder indicates the block's position along its vertical path of movement. The output signal is processed to provide information such as borehole depth and drill bit penetration rate. The output may be in the form of an analog output to a dial indicator, a chart recorder or the like. The system is not subject to fouling or mechanical failure and the system, including the input sensor, may be located in its entirety remotely from the drilling rig.

Abstract: A method and apparatus using a multiple transducer acoustic logging tool to detect fractures surrounding a borehole, particularly fractures that do not intersect the borehole wall. The transducers are actuated to produce broad band width pulses and signal enhancement techniques are used to determine fracture width, orientation and distance from the borehole wall.

Abstract: Method for generating a composite logging data base from two separate historical data bases in a form suitable for further on-site computerized analysis and processing. A generalized system is provided for automatically producing, as a function of a plurality of elected options, an output which is either a merger of logging curves from the two data bases, a replacement of one or more logging curves or portions thereof from one data base with those of a correlative curve or curves from the second data base, or a splice of one or more logging curves from one data base derived over one borehole increment with a curve or curves from the second data base derived over a different borehole increment, with further provision for automated renaming and reordering of curves as they appear in the output as well as compatibility checks between the two data bases thus being combined in terms of logging parameters and borehole increments as a function of the elected option.

Abstract: The present invention relates to the acquisition of seismic signals at different levels in a borehole, in response to the generation of seismic waves by a source placed on the surface or in the vicinity of the surface. The acquisition is carried out by means of a sonde suspended in the borehole from a cable and equipped with an anchoring pad. At each acquisition level, the pad is anchored in the borehole wall to couple the sonde to the formation, and then the pad is released from the wall once the acquisition is over. The signals acquired are then sent to the surface by means of the cable. The force with which the pad is anchored in the wall is controlled by means of a feedback arrangement which includes a sensor arranged in the pad itself. During the sonde movements from one level to another, the pad is kept in contact with the wall.

Abstract: The present invention relates to the acquisition of seismic signals at different levels in a borehole, in response to the generation of seismic waves by a source placed on the surface or in the vicinity of the surface. The acquisition is carried out by means of a sonde suspended in the borehole from a cable and equipped with an anchoring pad. At each acquisition level, the pad is anchored in the borehole wall to couple the sonde to the formation, and then the pad is released from the wall once the acquisition is over. The signals acquired are then sent to the surface by means of the cable. The force with which the pad is anchored in the wall is controlled by means of a feedback arrangement which includes a sensor arranged in the pad itself. During the sonde movements from one level to another, the pad is kept in contact with the wall.

Abstract: An improved well logging technique is provided for more accurately deriving and correlating a plurality of measurements made during a single traversal of a logging instrument through subsurface formations. In one exemplary embodiment, methods and apparatus are provided for deriving a more accurate and precise measurement of depth at which real-time logging measurements are made, and in particular for correcting anomalies occurring in the depth indication from cable stretch, yo-yo of the sonde in the borehole and the like. The more accurate and precise depth measurement is then utilized for generating well logging measurements on a depth-dependent basis, deriving at least some of such measurements in digital form and alternately transmitting to the surface digital and analog representations of such measurements.

Abstract: A method and apparatus for measuring an earth formation characteristic from inside a borehole penetrating earth formations is described. A tool carrying a sonic transmitter and an array of receivers is moved along the borehole and waveform signals from the receiver array are generated from repetetive operations of the transmitter. Sub-arrays of particularly related waveform signals relevant to a selected depth interval that is less in length than the aperture of the array are identified. Each sub-array of signals is then converted to a domain of signals composed of values of a coherence as a function of a range of values of a characteristic such as slowness. The converted signals are then combined so as to provide combined coherence values as a function of different values of the characteristic. One or several peaks of the combined coherence values are detected and determine the value of the characteristic for the selected depth interval. Similar processing is continued for other depth intervals.

Abstract: Acoustic signals are transmitted in a direction substantially perpendicular to the borehole axis, from different levels of at least three determined generatrices of the borehole wall. Reflected acoustic signals are received from the same direction at different levels of these generatrices. A train of signals is derived from each reflected acoustic signal and at least a group of significant elements of this signal train is selected. The groups of significant elements of the signals obtained for the different generatrices are correlated. The interval between signal trains corresponding to the maximum correlation corresponds to one and the same geological formation and is representative of the dip angle of this formation.

Abstract: The specification discloses a method and system for determining the position of a drill bit in the earth without interrupting the drilling operations. In operation, rotation of the drill bit against the formation being drilled generates coherent acoustical signals which are recorded at the surface of the earth by a plurality of spaced detectors. The signals recorded at each of the different detectors are time shifted relative to each other. These time shifts correspond to possible locations of the drill bit within the earth and are controlled to some degree by the length of drill pipe in the borehole. After the acoustic signals are shifted in time their coherency is determined. This procedure is repeated for a number of assumed locations of the drill bit. The drill bit position is determined to be at the location having the highest coherency value.

Abstract: Apparatus and method for recording seismic signals on a logging chart as a function of the depth of a logging sonde within a well bore includes apparatus for analyzing the seismic signals. The method utilizes the recording of information relating to the slope of a seismic signal received from the sonde. A recording trace is made using successive horizontal sweeps with no vertical deflection, and presence of a mark on the recording can indicate a positive slope for the seismic signal, and the absence of a mark can indicate a negative slope. An apparatus of the present invention utilizes this method to record well logging information obtained from seismic signals.

Abstract: Disclosed is a well logging system using the output of a dipmeter tool, preferably a three or more trace tool, to produce a map showing at least one or more of the following characteristics of the earth formations surrounding a borehole: the location of a depth zone in which the formation dips are mutually consistent within defined criteria, the structural dip within a zone, the formation dips within a zone rotated to account for the shown structural dip of the zone, the confidence limits of the magnitude and azimuth of a shown structural dip and an azimuth frequency polar histogram of the dips within a zone. In addition, the system identifies sedimentary patterns within a zone, such as blue and red patterns and shows their nature and characteristics.

Abstract: In a representative embodiment of the invention described herein, a well logging system for investigating subsurface formations is controlled by a general purpose computer programmed for real-time operation. The system is cooperatively arranged to provide for all aspects of a well logging operation, such as data acquisition and processing, tool control, information or data storage, and data presentation as a well logging tool is moved through a wellbore. The computer controlling the system is programmed to provide for data acquisition and tool control commands in direct response to asynchronous real-time external events. Such real-time external events may occur, for example, as a result of movement of the logging tool over a selected depth interval, or in response to requests or commands directed to the system by the well logging engineer by means of keyboard input.

Abstract: A logging tool recording system counts and converts depth pulses into a digital coded format. Such digital coded format is converted to a serial digital word for recording on an analog recorder. During playback the digital serial word is converted back into a digital coded format for reproduction by means of a visual digital display.

Abstract: Methods and apparatus, for processing signals derived along portions of the length of a borehole to determine the relative position of geological formation characteristics, effect the correlation of pairs of signals using substantially overlapping correlation intervals to obtain cross-correlation functions for each pair of signals. These cross-correlation functions are then displayed as a function of borehole depth for each pair of curves such that discontinuities in the cross-correlation functions are rendered obvious. From such discontinuities, zoning of the data is enabled through determination of the position of significant continuous intervals. Sequences of cross-correlation functions which belong to one of these intervals may then be used to directly determine the corresponding relative position of a formation characteristic. When applied to dipmeter signals, the method produces more accurate and geologically consistent dip and azimuth values for subsurface formations.

Abstract: In depth correlation of logs according to the subject invention, the starting data is an array of correlograms on a depth v. shift coordinate system. Unreliable correlation coefficients are eliminated to leave only valid ones, then valid clusters of correlation coefficients are examined to find reliable indications of trends in shift and in changes in shift. These indications are used to compute the shift and the corresponding depth which would result in a corrected correlation between the two logs from which the correlograms are derived.

Abstract: An illustrative embodiment described herein discloses an automatic method of determining correlations between characteristic signal elements corresponding to common recognizable features represented by sampled signals. Specific types of characteristic elements are detected and their boundary positions and characteristic parameters recorded. These records are sorted according to predefined procedures employing relative positions of the boundaries. Efficient references are generated to provide search bounds and elements located above and below each boundary.Specified types of elements are selected in a given order to provide a desired type of correlation. Compatible types of elements occurring within predefined search bounds are located and compared to determine corresponding elements. The comparison employs the use of the previously recorded characteristic parameters. As the correspondents are found, the search bounds are modified accordingly to guide the procedure in location of subsequent elements.