Exxon Production Research Company

James A Rice

Graham A Winbow

Sen-Tsuen Chen

Louis M Houston

Arthur H Thompson

Grant A Gist

Roel Arevalo

Dennis E Willen

Christine E Krohn

A method of seismic prospecting using electromagnetic grounded antennas to detect electromagnetic waves that are produced from acoustic waves in the earth's formation. Seismic waves reflected by a formation in the earth are converted into electromagnetic waves in the vicinity of the antenna according to the streaming potential theory. The antenna has two electrodes which detect the horizontal component of the electromagnetic waves, thus providing additional seismic information that is not readily available using standard geophones. Antennas are also not subject to coupling problems and thus provide more accurate information than traditional geophones. For example, using multicomponent detection, all three components of the seismic pressure gradient can be detected. In addition, using geophones and antennas directly provides a method of separating source and receiver-generated static corrections for more effective stacking of seismic data and allows computation of seismic signal velocity through the low-velocity layer.

Method for using electromagnetic grounded antennas as directional

A marine geophysical prospecting system employs a hydrophone streamer cable containing electromagnetic field sensors, modified to be towed at a preselected distance above the sea floor by a first marine vessel senses electromagnetic energy from selected substrata beneath bodies of water. The voltage between sensors may be amplified by amplifiers in the cable or by amplifiers aboard the towing vessel. Optionally, a second similarly modified cable is preferably located above the near-bottom cable. Both cables may also contain hydrophones and/or accelerometers, as well as depth and position sensors. Optionally, a second vessel tows at least one conventional seismic source to create compressional energy which propagates downwardly through the water into the substrata beneath the body of water. At appropriate porous subsurface formations, the acoustic energy is converted to electromagnetic energy. This electromagnetic energy propagates upwardly and is detected by the electromagnetic sensors in the near-bottom cable; the second cable provides a reference array to suppress electromagnetic noise. Alternatively, the electromagnetic sensors in the near-bottom cable and a power source on the towing vessel may create an alternating or pulsed electromagnetic field in the sea floor. This electromagnetic field travels into the substrata beneath the water body and via conversion of the electromagnetic waves into seismic pressure waves at other appropriate porous subsea earth formations, generates a seismic wave. The resulting seismic wave is detected by the hydrophones and/or accelerometers in the cables.

Marine geophysical prospecting system

A data collection and transmission system for gathering high count vertical seismic data is disclosed using a sequence of vertically aligned seismic receivers, the analog outputs from which are sequentially analog sampled and time multiplexed onto a common pair of data conductors in the support and transmission cable. The data is time demultiplexed at the surface and appears substantially as digital data because of the relatively short sampling times. Such data is converted into analog data with conventional digital-to-analog converter means. A clock signal activates counters for establishing non-overlapping data gates in the respective sondes, the operation of the gates supplying the cable with the respective receiver analog signals in a sequence from bottom to top, simultaneously switching off previously gated signals until a clock reset pulse resets the entire sonde string. Borehole engaging means are locally powered at each sonde and are controlled for engagement and disengagement from above using appropriate control signals therefor. The appropriate coupling by the engagement means at each sonde is monitored by examining the change in motor voltage reflected on the data lines. Alternatively, a shaker may be employed for generating geophone receiver signals for comparison purposes with an appropriate standard.

High count seismic data collection and transmission through analog time

A geophone configuration is disclosed that includes an elongated extension or spike that couples with the soil in the hole made by the spike in the region near the end of the spike without hard or firm coupling with the soil above that region. A bow spring or drill bit larger in diameter than the diameter of the spike can be used for achieving predominant contact for the coupled region compared to soil opposite the remainder of the spike. Alternately, a weighted tip can be employed to achieve relative superior coupling by weight compared with the less heavy region of the spike above such weighted tip.

Geophone with depth sensitive spikes

Method and system for creating a vertical seismic profile (VSP) whereby the spacing interval between units, either seismic sources or receivers, in a borehole increase exponentially as their distance from the surface increases, and the spacing interval between units, either seismic sources or receivers, along the surface of the earth decreases exponentially as their distance from the surface intercept of the wellbore increases. In a preferred embodiment of this invention, the common depth point (CDP) fold of the data gathered is substantially flattened across the reflectors surveyed.

Method for positioning seismic sources to flatten CDP fold in VSP surveys

A method for high-resolution seismic recording with increased bandwidth using detectors planted at shallow depths below the earth's surface. In one embodiment, an optimum depth where the amplitudes of high frequency signals increase relative to that of the noise during high-resolution recording is determined, geophones are then planted at that optimum depth and signals are recorded at that depth. To find this optimum depth, detectors are planted at various depths below the earth's surface in order to record the signals at those various depths. The frequency spectra for each detected signal is generated and a velocity profile of the depths covered by the detectors is also generated from the signals. The bandwidth of the frequency spectra and the velocity profile are used to determine a depth for planting the detectors that is closer to the earth's surface than the depths previously considered.

Method for high-resolution seismic recording using detectors planted at

The quadrupole shear wave logging device of this invention includes a logging sonde, means for generating a quadrupole shear wave in the earth formation surrounding a borehole containing fluid, and means for detecting in the fluid the refraction of the quadrupole shear wave. In the preferred embodiment, the generating means comprises four similar sectors of a hollow piezoelectric cylinder. The four cylinders are polarized radially. The four sectors are so connected to the sonde that they are in the form of a split cylinder coaxial with the sonde axis. Electrical pulses of similar waveforms are applied across the inner and outer cylindrical surfaces of each sector to vibrate the four sectors. The electrical pulses are of such polarities that, during their initial motions of vibration, two oppositely situated sectors are caused to move outward and the remaining two oppositely situated sectors to move inward substantially simultaneously. Thus, the oppositely situated sectors will vibrate in phase whereas adjacent sectors will vibrate substantially opposite in phase. The vibrations of the four sectors generate four pressure waves: two positive pressure aves and two negative pressure waves. The four pressure waves generatred will interfere and produce a quadrupole shear wave in the formation. The pressure wave in the fluid caused by refraction of such quadrupole shear wave is detected by the detecting means comprising two detectors in the fluid spaced apart longitudinally from each other and from the generating means. Shear wave velocity of the formation may be determined from the time interval between the detections of the refraction of the quadrupole shear wave by the two detectors.

Acoustic quadrupole shear wave logging device

The quadrupole shear wave logging device of this invention includes a logging sonde, means for generating a quadrupole shear wave in the earth formation surrounding a borehole containing fluid, and means for detecting in the fluid the refraction of the quadrupole shear wave. In the preferred embodiment, the generating means comprises four similar sectors of a hollow piezoelectric cylinder. The four cylinders are polarized radially. The four sectors are so connected to the sonde that they are in the form of a split cylinder coaxial with the sonde axis. Electrical pulses of similar waveforms are applied across the inner and outer cylindrical surfaces of each sector to vibrate the four sectors. The electrical pulses are of such polarities that, during their initial motions of vibration, two oppositely situated sectors are caused to move outward and the remaining two oppositely situated sectors to move inward substantially simultaneously. Thus, the oppositely situated sectors will vibrate in phase whereas adjacent sectors will vibrate substantially opposite in phase. The vibrations of the four sectors generate four pressure waves: two positive pressure waves and two negative pressure waves. The four pressure waves generated will interfere and produce a quadrupole shear wave in the formation. The pressure wave in the fluid caused by refraction of such quadrupole shear wave is detected by the detecting means comprising two detectors in the fluid spaced apart longitudinally from each other and from the generating means. Shear velocity of the formation may be determined from the time interval between the detections of the refraction of the quadrupole shear wave by the two detectors.

The multipole shear wave logging device of this invention includes a logging sonde, means for generating a 2.sup.n -pole shear wave in an earth formation surrounding a borehole containing liquid where n is an integer greater than 2, and means for detecting in the liquid the refraction of the 2.sup.n -pole shear wave. In the preferred embodiment the generating means comprises six similar sectors of a hollow piezoelectric cylinder. The six sectors are polarized radially and are so connected to the sonde that they are in the form of a split cylinder coaxial with the sonde axis. Electrical pulses of similar wave forms are applied across the inner and outer cylindrical surfaces of each sector. The electrical pulses are of such polarities that adjacent sectors vibrate radially in substantially opposite phase. Circumferentially polarized sectors may also be used in the place of radially polarized sectors. The vibrations of the six sectors will generate compressional waves in the liquid which will interfere to produce an octopole shear wave in the formation. The compressional wave in the liquid caused by refraction of such octopole shear wave is detected by detecting means. The detecting means comprises two detectors in the liquid spaced apart longitudinally from each other and from the generating means. The shear wave velocity of the formation is determined from the time interval between detections of the refraction of the octopole shear wave by the two detectors.

Shear wave logging using acoustic multipole devices

A seismic exploration method and system employing a streamer that houses at least one pair of orthogonally mounted hydrophones. The streamer may be operated downhole in a well, or may be towed in a body of water by a marine vessel. In the downhole embodiment, the invention permits detection of seismic signals of interest with suppression of noise due to tube waves and (dipole and monopole) modal waves propagating in and along the well, and without the need for locking the seismic detectors to the wall of the well. In the marine embodiment, the invention permits selective detection of waves incident from any incidence direction of interest (including the horizontal and vertical directions). In all embodiments, the incidence angle of the detected seismic wave is determined. The amplitude of the detected wave may also be determined from the incidence angle and the amplitude components detected at each hydrophone.

Method and system for seismic exploration employing a dual-dipole

The shear wave velocity of the formation is determined by logging the fastest component of the guided wave generated by the generating means. This method is advantageous for logging the shear wave velocities of soft formations. If the generating means of a multipole acoustic logging device radiates at frequencies including a critical frequency, the fastest component of the guided wave generated by the generating means will have substantially the same velocity as a shear wave traveling in the earth formation. By logging the velocity of this fastest component, the shear wave velocity of the earth formation is determined.

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Houston, TX, United States of America

James A Rice