Abstract: The invention relates to a nondestructive downhole seismic source capable of generating S.sub.V -waves, S.sub.H -waves, and P-waves alone or in combination to determine information about a surrounding geologic formation. The invention also includes processes of performing crosswell tomography and reverse vertical seismic profiling. The invention also includes a means and process to carry out in hole seismic logging operations.

Abstract: The present invention relates to an economical, high resolution non-destructive method to remotely image rock mass and subsoil features. More specifically, the invention relates to a method measuring the properties of subsoil structure by first creating at least two boreholes in the area to be examined. At least one electromagnetic radiation transmitter is placed in one borehole and at least one receiver is placed in a second at least one other borehole. The transmitter produces a continuous constant signal of about 100 Hz or greater, which traverses the plane between the transmitter and receiver. After measuring simultaneously both the amplitude and phase of the received electromagnetic signal, the signal information is processed using a linear approximation algorithm. Upon comparison of the processed data, with standard data for nearby geological formations, it is possible to accurately determine both the dielectric constant and the conductivity of the subsoil in the plane.

Abstract: The present invention is a downhole seismic source capable of generating seismic forces in excess of 1000 newtons. The source produces seismic waves for seismic applications, particularly cross borehole measurements and vertical seismic profiling. Coupled with motion sensing devices, the present invention also performs as a seismic logging tool. The source is comprised of an outer housing, a means for clamping the source securely to the wellbore, and a linear electromagnetic actuator which utilizes permanent magnetic material having remanent magnetic field exceeding about 0.9 T such as rare earth permanent magnetics. The source has a diameter of about 12.5 cm to fit within a typical wellbore and the acuator has a length of about 1 meter.

Abstract: In a process for obtaining seismic data relating to an exploratory well, a seismic wave transmitter and a seismic wave receiver are provided, one arranged on the surface adjacent the well and the other at a plurality of measurement points down the well, and the output of the receiver is processed in a processing installation. The measurement points are divided into at least two groups, each of which comprises a plurality of measurement points spaced apart in a distance (D.sub.z) which is less than a predetermined limit distance so as to avoid aliasing, and the groups of measurement points are separated from each other by a distance (D) greater than the limit distance. In the processing installation separation of the down-going waves from the up-going waves belonging to the same group is carried out before coherence filtration of the separated waves.

Abstract: A method for determining the position of a subterranean plane reflector relative to a known location on the earth surface from unprocessed seismic data received at a number of colinear acoustic receiver locations. A traveltime curve associated with the reflector is identified from the seismic data. From two points on the traveltime curve, a signal indicative of the reflector's dip angle is generated. Using the dip angle signal, signals indicative of the position of each imaged point of the reflector are generated. The inventive method assumes knowledge of the average velocity of seismic waves in the subterranean formation above the reflector, and that such formation region can adequately be considered to have constant velocity equal to such average velocity. The method may be applied to process raw data generated during a vertical seismic profiling operation.

Abstract: A borehole logging tool includes at least one acoustic energy transmitter and at least one spaced apart acoustic energy receiver. Acoustic energy signals travel from the transmitter to the receiver directly through the subsurface formation adjacent the borehole and indirectly through reflections from subsurface formation changes below the bottom of the borehole. The difference in travel times of the directly arriving and indirectly arriving signals are determined for like acoustic waveforms as a measure of the depth of the subsurface reflecting formations below the borehole.

Abstract: A method and apparatus are disclosed for selectively reinforcing an acoustic wave traveling in a first predetermined direction in a body of water while attenuating an acoustic wave traveling in a second opposite direction. The output signals from vertically spaced receivers are appropriately delayed and summed to reinforce a wave traveling in the first direction and attenuate the wave traveling in the opposite direction. The invention is particularly useful for reinforcing desirably detected ascending acoustic waves and attenuating undesirably detected surface reflected descending waves.

Abstract: A method of processing seismic data enables correlation of P and S-wave seismic traces. First, P and S-waves are transmitted into the subsurface. The two-way vertical travel times are then measured for each wave to different depths so as to yield two sets of time-depths pairs. Mathematical functions relating two-way vertical travel time, T.sub.s or T.sub.p, and depth are fitted to each set of time-depth pairs. These functions are combined to yield an expression relating T.sub.s and T.sub.p. This expression may be utilized to rescale one of the traces to yield correlated P and S-wave traces.

Abstract: In vertical seismic profiling (VSP), VSP seismic data is transformed into surface seismic data by mapping segments of the VSP seismic data into surface seismic data time. The transformation results in data which is more easily interpreted with respect to determining subsurface structure because the data is stacked and because the data is in a more conventional form.

Abstract: A logging sonde has directivity control of multiple sources and receivers in linear arrays. Each of the sources produces acoustic pulses which are delayed by a time delay between the sources to direct acoustic energy at an angle such that the resulting acoustic wave strikes a vertical formation orthogonally. The reflections of the acoustic pulses are detected with a linear array of receivers. The acoustic pulse detected by each receiver is delayed by an amount such that the total differential moveout for a reflected directional wave is zero.

Abstract: A seismic wave generator and method of using it, which comprises a vertical array of sources at known spacings, for detonation in a seismic wave propagating medium of known seismic velocity; means to initiate the sources in time sequence in a selected series of known different time intervals and recording the seismic waves at a distant location to provide a first electrical signal; and correlating the first electrical signal with a second electrical signal derived from the pattern of initiation, as modified by the travel times of the waves between the several separate charges.

Abstract: A method of seismic surveying which provides a horizontal profile of reflector surfaces located between two spaced apart drillholes which profile appears similar to that of a marine type seismic reflection profile. The method comprising raising and lowering a seismic source and receiver in adjacent drillholes to provide a profile of reflectors which are located between the drillholes.

Abstract: Seismic sources and detectors are each positioned in a series of shotholes along a course to be explored. The sources in the shotholes are activated in a sequence along the course and caused to emit seismic waves. The detectors remaining along the course sense or detect the seismic waves which are then recorded. Since the detector at each shothole has performed its function, that of sensing signals from earlier shots in the sequence, its disposal by destruction when the source in the shothole with it is activated does not impair further surveying efforts.

Abstract: A novel array of vertically and horizontally spaced hydrophones is shown which is capable of high ratio of desired signal to noise because of good directional sensitivity when used with any seismic source. Alternatively, a novel directionally sensitive array of vertically and horizontally spaced seismic sources is disclosed for use in seismic surveying with any spread of hydrophones or geophones, again attaining a high ratio of desired signal to noise. A reception pattern (in the first case) and a radiation pattern (in the second place) is produced which essentially eliminates reception or radiation at all frequencies except for waves within a predetermined angle with respect to the array. The sensitivity is essentially constant within such angle for all frequencies and essentially zero outside it.

Abstract: A method of and apparatus for determining the precise position of the drill bit on the bottom of a long drill string in a deep borehole in the earth, during a drilling operation. The method comprises placing a plurality of geophones in a three-dimensional array near the surface of the earth, above the expected position of the drill bit in the earth, causing at least a low energy seismic source to be initiated near the drill bit in the earth, repeating the source a number of times, and determining at the surface of the earth the times of initiation of each of the seismic waves. Responsive to the known times of initiation, stacking each of the repeated geophone signals from each of the geophones, for each of the repetitions of the source, whereby each of the stacked signals will be in-phase with those that resulted from earlier and later repetitions of the source. Several embodiments of an improved downhole seismic source are described, and an improved type of three-dimensional array.

Abstract: Data for use in producing a tomograph of subsoil structure between boreholes is derived by placing spaced geophones in one borehole, and if desired also on the earth surface, and by producing a sequence of shots at spaced apart locations in the other borehole. The signals, detected by each of the geophones from the various shots, are processed either on a time of arrival basis, or on the basis of signal amplitude, to provide information of the characteristics of a large number of incremental areas (pixels) between the boreholes. Such information is useable to produce a tomograph of the subsoil structure between the boreholes. By processing signals of relatively high frequencies, e.g., up to 1000 Hz, and by closely spacing the geophones, a high resolution tomograph can be produced.