SE430544B - SEISMIC INVESTIGATION PROCEDURE AND DEVICE - Google Patents

Abstract

A long, flexible cable is drawn over the surface of the earth. This cable has liquid-filled detectors which are constructed as geophones (10) and are mounted on the cable at suitable spacings. The seismic cable receives the individual output signals of the geophone. Each geophone supplies an electrical output signal having a polarity which corresponds to the direction of the movement of the earth. Their output signals are transmitted to a processing device, and then it is moved into a different position and the measurement operation is repeated. The geophones have a cylindrical, hollow housing (12) with a chamber (34) in the interior. A liquid (36) of high density, e.g. mercury, mostly fills the chamber (34). The chamber has a flexible base plate (22) which forms a force-measuring or pressure-measuring transducer (27). In addition to the flexible base plate (22), the chamber (34) has a further flexible base plate (22') on the upper side, which likewise forms a measuring transducer (27'). The geophone supplies at its output terminals (56, 58) electrical signals corresponding to the seismic signals.

Description

The geophones commercially used in practice constitute an electromagnetic circuit which includes a coil and a magnetically movable relative thereto. An ordinary geophone responds essentially only to such movements of the earth which have a force component along its axis and produces in use an electrical output signal which has a polarity which depends on the direction of such a force.

During normal seismic exploration, the geophones are placed manually erected on the earth's surface with their axes substantially in line with the vertical direction. When a geophone is temporarily or otherwise applied to the earth's surface in such a way that its axis deviates significantly from the vertical direction, or in the extreme case when the geophone is completely on its side (90 ° from the vertical direction), it becomes completely for all practical purposes idle. Even when a geophone is temporarily placed upside down (180 ° from the vertical direction), it will produce a signal with a polarity opposite to the polarity of the signal produced when the geophone is upright. In both cases, the lack of an output signal or the generation of a signal of opposite polarity will adversely affect the records produced by the seismic exploration. To overcome these problems when such an upright position is impractical, the geophones are mounted on orientation means which are trained to continuously maintain the geophones in an upright position. A very common orientation means is provided by a gimbal suspension. Recently, attempts have been made to place the geophone on a flat and flexible conveyor-type belt which is pulled or towed by a vessel. The strap is intended to keep the geophones essentially upright. The tightening of such belts has in many cases not produced the expected results and therefore seismic crews have continued to manually spread the geophones in upright positions, but this is time consuming and expensive.

As the search for hydrocarbons is increasingly extended to comparatively inaccessible areas, the need to place the geophones upright on the earth's surface, or the use of self-orienting bodies, such as gimbal suspensions, has placed a heavy burden on seismic crews. This burden has plagued the seismic industry for many years despite the continuous efforts to provide geophones that can be towed or towed and do not need to be mounted upright on the earth's surface, as described.

After long experimentation, a new liquid-filled geophone has been produced which can effectively replace ordinary geophones, especially those of the electromagnetic type which have hitherto been used almost exclusively commercially.

Accelerometers using liquids have been described in U.S. Pat. Nos. 3,270,565, 3,555,5U3,171,676 of July 26, 1965.

However, such liquid-filled devices produce a gene and Russian inventor's certificate response with the same polarities for all influences, regardless of direction, or they are not able to meet the specific requirements that occur in seismic exploration.

The new geophone is comparatively light, cheap to manufacture, able to withstand the usual stresses in the field and, above all, does not need to be applied to the earth's surface with any particular orientation. The new and improved geophone therefore does not require self-orienting devices, which are expensive and often become faulty due to the usual stresses in the field. The polarity of the output signal produced by this new geophone can be made to be independent of the inclination that the axis of the geophone occupies in relation to the vertical direction.

For upward and downward movements of the earth, this geophone will generate electrical signals of opposite polarities, as required by seismic exploration.

The method of the present invention in a preferred embodiment comprises towing a long flexible element over the earth's surface, and the element has liquid-filled geophones arranged or connected thereto at suitable intervals, and a seismic cable has been arranged to receive the individual output signals of the geophones. Each liquid-filled geophone produces an electrical output signal with properties corresponding to the direction of the earth's motion. The motion of the earth can be produced by a seismic energy source, which supplies the earth with energy to produce reflected seismic signals therein from the underlying layers thereof.

When using the preferred form of the geophone, the polarity of the electrical signals detected by the geophones and transmitted via the seismic cable to a utilization device is substantially independent of the orientation of the flexible element relative to the ground surface and the orientation. the axes of the geophones in relation to the vertical direction. In another embodiment of the method according to the invention, the geophones are placed on the surface of the earth in a predetermined pattern, and their output signals are transmitted to the utilization device, and then the geophones are moved to another location and the process is repeated. In a simplified embodiment of an apparatus, the geophone comprises a hollow, cylindrical housing which defines a chamber therein. A suitable liquid, preferably a high density one, essentially fills the chambers. The chamber has a flexible bottom wall which constitutes a power or pressure converter.

The converter produces an electrical signal with properties in terms of amplitude and polarity that correspond to the size and direction that the bending of the wall shows. In a preferred embodiment of the geophone, in addition to the flexible bottom serving as a transducer, the chamber also has a transducer at the flexible top wall. When the axis of the geophone is substantially vertical in an upright position, the liquid in the chamber will only hit the bottom transducer, while for most slopes of the geophone the liquid hits both the bending transducers of the bottom and top walls. When the geophone is up and down, the liquid will only hit the top converter. The geophone produces electrical signals at its connections which correspond to the output signals of the converter pair.

When using a pair of transducers, these must be placed opposite. In this context, the phrase "oppositely arranged" is intended to mean that the transducers in each pair are separated by at least a substantial portion of the liquid at at least certain orientations of the housing. A pair of transducers can be oppositely mounted in separate liquid parts. This can conveniently be done by using two separate housings, each of which has a part of the liquid associated with a single transducer.

In any case, it is preferable to have the plane of sensitivity of each transducer parallel to each other and, in a preferred embodiment, to have these planes perpendicular to a line joining the transducers.

The transducers generate output signals in response to pressure exerted on them by the interaction between the liquid mass and the transducers caused by effects on the earth's surface through reflected seismic signals. In particular, the geophone is primarily sensitive to accelerations at the earth's surface. 9 10 15 20 25 30 35 H0 7803556-5 Such accelerations are typically in the range 10 to 1000 Hz and are of the order of less than 3 percent of the acceleration due to gravity. The effects on the ground surface to which the device is sensitive can be considered to have both vertical and horizontal components. The sensitivity of a geophone to vertical and horizontal components can be regulated by the way in which the output signals from the individual converters in a pair are combined.

The geophones can be made sensitive to primarily the vertical components by combining the individual converter output signals by addition. The polarity of the sum will then indicate the direction of the vertical component without regard to the orientation of the geophone in relation to the vertical direction. This means that positive polarity can be used to indicate vertical components that are directed towards the center of the earth and negative polarity to indicate vertical components that are directed away from the center or center of the earth.

If the dimensions of the chamber and the part of the chamber filled with the liquid are carefully selected, the amplitude of the sum can be made constant for a given vertical component regardless of the orientation of the housing. The components of the output signals from each converter generated in response to horizontal components are of opposite polarity to each other and have equal sizes. They will therefore cancel each other out when combined by addition. On the other hand, the outputs of the converters in each pair are possible to combine by subtraction. If the geophones are placed approximately on their sides, the signal resulting from subtraction is then proportional to only the horizontal components. All signals representing vertical components will be canceled by the subtraction because in this orientation the output signals from each converter generated in response to vertical components will be of equal size and be of the same polarity.

It is therefore particularly convenient to place the geophones approximately on their sides and to record separately the output signals from each converter in a pair. The signals can then be combined by addition and by subtraction to determine both horizontal and vertical components without the geophones having to be reoriented. Additional pairs of oppositely arranged flexible transducers may be added to increase the accuracy and amplitude of the resulting outputs.

The output signals from the converters in each pair can be combined by addition and / or subtraction, in parallel or in series, with the signals from the converters in other pairs or can be transmitted separately according to the need in a particular situation.

In order that the invention may be better understood, the same will be described in more detail with reference to the accompanying drawings.

Pig. 1 is a side sectional view of a preferred embodiment of a geophone according to the present invention.

Pig. 2 shows the operation of the geophone for slopes of the same extending from upright to upside down for upward movements of the earth.

Pig. Fig. 3 is a similar representation as in Fig. 2 but for downward movements of the earth. _ Pig. 4 shows the installation of the geophone according to the invention in a towed seismic cable.

Pig. 5 shows a preferred method of seismic exploration according to the invention.

Pig. 6 is a view reminiscent of FIG. 1 of a simplified embodiment of the geophone.

Pig. Fig. 7 shows a view reminiscent of Fig. 2 of the geophone embodiment shown in Fig. 6.

Pig. 8 is a perspective view of a housing for the geophone.

Pig. Fig. 9 shows the connection of geophone housings, shown in Fig. 8, to a seismic spreading cable and the use of the spreading cable for the seismic exploration shown in Fig. 5. 10 is a sectional view showing a geophone having a rectangular cross section.

Pig. 11 is a view reminiscent of FIG. 10 of an elliptical cross-sectional geophone.

The preferred embodiment of the liquid geophone, designated 10 in its entirety, comprises a metal housing 12 of cylindrical cross-section (Fig. 1). The housing 12 may also have a rectangular cross-section (Fig. 10), an elliptical cross-section (Fig. 11) or variations thereof depending on the desired sensitivity in terms of the geophone response.

In Fig. 1, the housing 12 has bottom and top caps 14 and 16 and these hermetically close the inner cylindrical cavity 18. A cut ring 20 rests on the bottom cover 1U and provides a support for a circular conductive wall 22, on the lower side of which has been attached a crystal 24 with a silver electrode 26. In the description and to the extent possible, similar parts have been denoted by the same reference numeral followed by a prime sign ('). A cut ring 20 'abuts against the top cover 16 and forms a support for a circular conductive wall 22', on the upper side of which a crystal 2H 'with a silver electrode 26' has been attached. The housing 12 is lined with a plastic cover 30 (Figs. 1, 10, 11), which extends between the bottom and top caps 1H, 16. The walls 22, 22 'abut against O-rings 32, 32' located on resp. shoulders 33, 33 'formed in the housing 30. The walls 22, 22' are attached to the shoulders 33, 33 'by resp. rings 20, 20 '.

The walls 22, 22 'are flexible and their bends are sensed by means of their resp. crystals ZH, 24 '. The flexible wall and the crystal mounted thereon constitute an ordinary pressure or force converter. The transducers formed by the walls 22, 22 'and their resp. crystals 2H, 24 'have in their entirety been denoted by 27 resp. 27 '.

In the present description, the transducers 27 and 27 'are assumed to be positioned so that they will generate signals of the same polarity, when a force or pressure causes them to bend outwardly away from the liquid 36. Additional pairs of oppositely arranged flexible transducers (not shown ) can be added to increase the accuracy and amplitude of the resulting outputs.

The housing 12 can also be made of non-metallic material, for example plastic, thereby eliminating the need for the tubular plastic housing 30. The walls 22 and 22 'need not be made of conductive material except to the extent required to provide an electrical connection. to the crystals 24 and 2U '.

The output signals from the pressure transducer 27 are passed through a pair of wires 51, 52 and the output signals from the pressure transducer 27 'are passed through a pair of wires 51', 52 '. The wires 51, 52 pass through a slot 53 in the ring 20, a longitudinal groove in the outer wall of the housing 30 and further through a slot 53 'in the ring 20'. The output signals passing through the wires 51, 52, 51 ', 52' can be added either in series or in parallel at a pair of the geophone's terminals 56, 58 extending through the top cover 16. On the other hand, the wires 51, 52 , 51 ', 52' are connected to four terminals (not shown).

When the wires are connected to four terminals, the output signals from each converter in the pair can be recorded or otherwise used separately. Addition and / or subtraction can then be achieved during the recording or afterwards. As another alternative, the output signals present on the wires 51, 52 and 51 ', 52' can be subtracted from each other, either in series or in parallel, at the terminals 56 and 58.

The internal space enclosed between the transducers and the inner cylindrical wall of the housing 30 forms a chamber BH, which is substantially but not completely filled with a liquid 36, which serves as the inert mass of the geophone 10. It is therefore desirable that the liquid 36 have a high density, and a suitable such liquid is mercury. In the preferred embodiment, the liquid 36 fills approximately 90% of the space in the chamber 34 and leaves approximately 10% of the available space for the expansion of the liquid due to temperature changes within the operating temperature range of the geophone.

By the terms "substantially" and "substantially filled", when used to denote the degree to which the chamber is filled with liquid, is meant all degrees of such filling in addition to 50% filling where the upper transducer is at least - stone partially relaxed from the liquid, when the geophone is in an upright position. The term "liquid" has been used herein to include other media, for example, powdered metals, which are suitable for use as inert masses in geophones of the type described herein. Z The action of the sluggish liquid 36 on the pressure transducers 27, 27 'will now be elucidated with reference to Figs. 2 and 3, where only the active parts of the geophone are shown, i.e. the housing 30 and the associated bottom and top transducers 27, 27 '. The solid lines show the flexible walls 22, 22 ', positions when the transducers are at rest and the dashed lines show their deflected positions generated by pressure from the inert mass or liquid which reacts for the motion of the earth.

In Fig. 2, the geophone 10 has been shown located above the earth's surface H0 with different slopes from an upright position A to an inverted position E, which is up and down. The earth is assumed to undergo upward movements and these are represented by the arrows H2, and the said movements are transmitted to the sluggish liquid 36, which in turn produces a force or a pressure outwards relative to the axis 30 of the housing 30. Thus, in position A, the transducer 27 will be bent outwards towards the cover 14 and the transducer 27 'will not be bent either outwards or inwards, since it is disconnected from the inert mass 36.

In position B with a slope of H50 from the vertical direction, the transducer 27 will bend outwards towards the cover 1ß and the transducer 27 'will bend outwards towards the cover 16. The same applies to the position C, which corresponds to a slope of 90 °, so that the geophone lies completely on its side, and for the position D, which corresponds to a slope of 1350. In the completely upside down position E, which corresponds to a slope of 1800, the transducer 27 'will bend outwards towards the lid. 16 and the transducer 27 will not bend either inwardly or outwardly because in this position it is disconnected from the liquid 36.

For all positions from 0 ° to 1000 ° in relation to the upright position A, either one or both of the pressure transducers 27, 27 'will undergo an outward deflection. The transducers 27, 27 'will therefore produce electrical signals H3 of the same polarity for all outward elevations.

As the degree or level at which the chamber 34 is filled with liquid 36 increases, another effect becomes noticeable. At sufficiently high degrees of filling, the upper transducer in the vertical position will no longer be completely disconnected, even if the liquid 36 does not in fact collide with this transducer. This means that the transducer 27 'in the position A and the transducer 27 in the position E can each have a tendency to move inwards in response to upward movements of the earth, as indicated by the arrows H2. In such situations, this upper converter will generate an output signal of opposite polarity to the output signal from the other converter in the pair. The amplitude of this output signal of opposite polarity will always not be greater than the output signal from the lower converter. The geophone output signal # 3, which is the sum of the outputs from the transducers 27 and 27 ', will therefore always have the same polarity for all vertical components in the same direction without regard to the orientation of the geophone in relation to the vertical direction.

The degree of filling of the chamber 3H has a different effect on the amplitude of the geophone output signal H3 in position A or E than it has on the amplitude of the signal 43 in positions B, C or D. The magnitude of the variation in the signal 43 amplitude for the same accelerations in different geophone orientations may therefore to a certain extent regulated or controlled by changing the degree of filling of the chamber 34. The amplitude of the output signal from a transducer in response to a particular influence amplitude is controlled primarily by the liquid level above the transducers at this particular orientation.

The partial decoupling of a transducer in certain orientations can be used to indicate such a configuration for a geophone that the sensitivity, i.e. the ratio between the amplitude of the output signal and the amplitude of the detected component is not affected by the orientation of the geophone in relation to the vertical direction.

In the preferred embodiment, the ratio between the diameter and height of the enclosed liquid column 36 has been chosen such that the amplitude of the signal 43 remains substantially constant for all positions A to E of the geophone, i.e. from the same upright to upside down positions.

The geophone 10 can therefore be used in geophysical surveys to detect seismic reflections without any precise positioning. This means that a series of such geophones can be placed with random orientations but nevertheless generate output signals that have correct amplitudes and polarities to represent vertical components of the earth's acceleration.

In fact, the geophone 10 can be made actuable by exclusively vertical components. This means that horizontal components cause the converters 27 and 27 'to react in such a way that the effects of such horizontal components are canceled by the addition of the output signals from the converters to form signals H3.

For illustrative purposes, the effects of a horizontal component will be described assuming acceleration from left to right. The effects of the horizontal components in each direction can thereby be understood. In position A, the horizontal components have no effect on any of the transducers because the acceleration is parallel to the surface of the transducers. In position B, the transducer 27 'will be deflected inwards and the transducer 27 will be deflected outwards. The same applies to positions C and D. In position E, no net effect will occur, as previously stated.

In position C, the magnitude of the deflection and therefore the amplitudes of the outputs of the transducers 27 and 27 'will be equal. In positions B and D, the ratio of diameter to height of the enclosed pillar (seen in position A) can be selected, and the degree of filling of the chamber 34 with the liquid 36 is adjusted so that the amplitudes of the output signals from the transducers 27 and 27 'are approximately equal. Since these signals have opposite polarities, they will cancel each other out when the outputs of the transducers 27 and 27 'are added to produce the signal H3. It is clear that in this way the geophone 10 can be made to be sensitive only to vertical components but not to horizontal components. This means that the effective sensitive axis of the geophone 10 automatically remains oriented to the vertical direction without regard to the actual orientation of the device.

As already stated, in position C the amplitudes of the output signals derived from horizontal components will be equal in terms of the amplitudes but opposite in terms of the polarities. When combined by subtraction, these signals will not cancel each other out but will amplify each other. The signal H3 formed in this way will therefore be proportional to the effects of the horizontal components. Furthermore, the output signals generated by vertical components generated by the transducers 27 and 27 'in the position C will be equal in terms of the amplitudes and have the same polarity. A combination by subtraction will therefore result in a cancellation. When the output signals from the transducers 27 and 27 'in position C are combined by subtraction, the resulting geophone output signal 43 will contain the effects of horizontal components but not of vertical components.

When the orientation of the geophone 10 changes from the position C to the position B or D, the amplitude of the geophone output signal H3, which is formed by subtraction, will decrease as a function of the cosine of the orientation angle relative to the horizontal direction. When position A or E is reached, the output signals 43 are not at all representative of the horizontal components.

It is therefore particularly convenient to use a plurality of geophones 10 in substantially horizontal positions to detect reflected seismic signals. The output signals from individual converters 27 and 27 'in each pair can then be separately transmitted to the utilization device for combination by addition and subtraction in the utilization device or for recording and later combination, so that both vertical and horizontal components can be determined for the same location on the earth surface by one of the geophones without relocation.

The description of Fig. 3 is similar to that of Fig. 2 except that the movements of the earth, represented by the arrows 42 ', are now assumed to be directed downwards and cause inward bends, which arise by winding the static pressure of the sluggish liquid and the spring action of the flexible walls 22, 22 '.

As shown in Fig. 3, for all geophone positions from the upright position A to the upside down position E y, the transducers 27, 27 'will be bent inwards, i.e. away from their resp. covers 14, 16. The transducers 27, 27 'will therefore generate electrical signals 43' having a polarity opposite to the polarity of the electrical signals H3 generated by the transducers 27, 27 'in response to the upward movements of the earth, as shown in FIG. 2.

The construction of the geophone 10 makes it comparatively easy to maintain the desired ratio between the mass of the sluggish liquid 36 and the remaining components of the geophone including the housing 12 being larger than one. Such a relationship is favorable for seismic exploration, as set forth in U.S. Patent No. 3,067,404. According to the prior art, where self-adjusting means, for example gimbal rings, have been used to orient the geophone. , the large mass by which said means shows that it is practically impossible to achieve the said desirable condition.

Fig. 6 shows a less desirable embodiment of the geophone and the same has been designated in its entirety by 10 '.

In the geophone 10 'only a single bottom converter 27 has been used, and a rigid wall 80 has replaced the pressure converter 27'. In all other important respects, the geophones 10 and 10 'are identical.

In Fig. 7, different gradients A to E of the geophone 10 'have been shown, and the said slopes are equal to the slopes A to E shown for the geophone 10 in Fig. 2. It is to be noted that when the geophone 10 'is in the upright position A, its output signal S1 will be identical in amplitude and polarity with the output signal H3 of the geophone 10 for the upright position for upward movements 42a of the earth. When the geophone 10 'takes successive slopes towards the upside-down position E, the amplitude of the output of the geophone will decrease, as shown by the reduced amplitudes of the signals S2, S3, Su produced by the geophone in its positions B and . C and D. The output signal S5 is substantially zero when the geophone 10 'is upside down. It should be noted, however, that the polarities of the signals S1 - S4 are the same as the polarity of the signal 43 shown in Fig. 2. However, these comparisons with the output signal 43 from the geophone 10 do not take into account the effects of the output signal of opposite polarity from the upper transducer, as previously discussed.

The geophone 10 or 10 'can be accommodated in a suitable housing 60 (Fig. U), which is protected by an elastic sleeve, the ends of which by means of a strip 65 are suitably fastened to the outer sleeve of a towable seismic cable 62. A pair of wires 66, 67 connects the geophone terminals to a pair of conductors in the seismic cable 62. If sensitivity to both vertical and horizontal components is desired, an additional pair of wires, not shown, will be required to connect the geophone to an additional pair of conductors. not even shown, in the seismic cable 62. 10 15 20 25 30 7805556-5 1H The cable 62 may be associated with and connected to a plurality of suitably spaced geophones. In accordance with a very important aspect of the present invention, each geophone may be on its side, as shown in Fig. 4, but nevertheless be fully effective and responsive, as shown in Figs. 2C, SC and 7C, for up and down - to directed movements of the earth and represented by resp. arrows H2 and 42 '.

According to an embodiment of the method according to the invention, the seismic cable 62 is towed by means of a seismic truck 72, which has a utilization device, for example a recording device 73, which receives and records the signals from the carbide 62. The cable 62 can be wound on and off a rotatably arranged coil 70 and the seismic energy required for the seismic survey can be supplied to the earth from a suitable 7% seismic energy source.

In an alternative embodiment of the method according to the invention, each geophone 10 is housed in a housing 90 (Fig. 8) and the connections of the geophone are connected to a short input cable 81, which extends from a spreading cable 93. The seismic crew places the cable 93 on the ground surface 40 with the housings 90 arranged in a desired detection pattern, but the housings 90 need not be oriented in any particular direction relative to the vertical direction. However, if the housings 90 contain geophones 10 ', the housings should not be placed on the ground surface 40 in an upside down position to prevent decoupling of the sluggish liquid 36 from the wall 22 of the single transducer 27, as shown in Fig. 7E.

Instead of using 2%, 24 'crystal pressure sensors, which are typically made of piezoceramic material, other pressure sensors may just as well be used, as will be apparent to one skilled in the art.

Claims (21)

10 15 20 25 30 35 7803556-5 15 PATENT CLAIMS 1. A method of seismic survey, characterized in that it comprises the steps of placing a plurality of seismic detectors, which are substantially but not completely filled with fluid masses, in random orientations on the earth's surface, and measuring the pressures of the masses. exerts as a result of effects on the earth's surface caused by reflected seismic signals by means of a pair of oppositely arranged pressure transducers in each detector, and on the other hand combines the output signals produced by each transducer in a pair to determine components of the influences. A method according to claim 1, in that it includes the step of combining the output signals by the feature of addition to determine only the vertical components. 3. A method according to claim 2, characterized in that it includes the step of setting the degree of filling in the detector so that the sensitivity of the detector to vertical components is the same in all orientations. 4. A method according to claim 1, characterized in that the detectors are placed in horizontal orientations and that the combining step includes combining the output signals by subtraction to determine only the horizontal components of the influences. 5. A method according to claim 1, characterized in that the combining step includes the steps of combining the output signals by addition and subtraction to separately determine the vertical and horizontal components of the effects. A seismic detector device for practicing the method according to any one of the preceding claims and comprising a plurality of seismic detectors, each comprising a housing (12) with an inner chamber (34), a pair of pressure transducers (27, 27 ') and a fluid mass (36) is arranged in the chamber, characterized in that the fluid mass (36) substantially but not completely fills the chamber (34), the transducers (27, 27 ') being arranged opposite each other so that a transducer (27') ) is at least partially disconnected from the fluid mass (36) in certain orientations, as well as by means for combining the output signals generated by each of the transducers (27, 27) mounted in pairs. ') for the determination of components of the effects of the earth's surface caused by reflected seismic signals. Device according to claim 6, characterized in that the means arranged to combine the output signals from each converter (27, 27 ') are adder, so that the polarity of the output sum represents the direction for vertical components of the seismic signals regardless of the orientation of the house with respect to it. Device according to claim 7, characterized in that the size of the output sum represents the size of the vertical components independently of the orientation of the housing (12) with respect to the surface. Device according to claim 7, characterized in that horizontal components are effectively canceled by output signals from each transducer (27, 27 ') by the combination by addition independent of the orientation of the housing (12) with respect to the vertical direction. Device according to claim 9, characterized in that the amplitude of the sum of the outputs of the transducers (27, 27 ') is substantially the same for vertical components of equal size regardless of the orientation of the housing (12) with respect thereto. Device according to claim 9, characterized in that the dimensions of the part of the chamber (34) which is filled with the fluid mass (36) are selected so that the detector is equally sensitive to vertical components regardless of the orientation of the housing (12). ) in that regard. Device according to claim 9, characterized in that the degree of filling of the chamber (34) with the fluid mass (36) is chosen such that the amplitude of the sum of the converter output signals is substantially the same for equal vertical components for each orientation of the house (12). Device according to claim 6, characterized in that the means arranged for combining output signals from each converter (27, 27 ') are subtractors, so that the result thereof represents the horizontal components of seismic signals, when the detector is oriented so that a line 10 15 20 25 7803556-5 17 drawn between the transducers is substantially horizontal. Device according to claim 13, characterized in that the sensitivity of the detector is a function of the cosine of the angle between the line and the horizontal direction. Device according to claim 6, characterized in that the fluid mass (36) is substantially contained between the transducers (27, 27 '). Device according to claim 6, characterized in that the sensitivity planes of each of the two transducers (27, 27 ') are parallel. 17. Device according to claim 16, characterized in that the plane is perpendicular to a line drawn between the transducers (27, 27 '). Device according to claim 6, characterized in that each transducer comprises a flexible wall (22, 22 ') which forms part of the inner chamber (34) and that means (24, 24') are arranged to detect deflections of k ä nne - the flexible wall. Device according to claim 18, characterized in that the deflection detecting means is a piezoelectric crystal (24, 24 '). Device according to claim 19, characterized in that the inner chamber (34) is a straight circular center cylinder and that the flexible walls (22, 22 ') form the circular ends thereof. 21. A device according to claim 6, characterized in that the inner chamber includes two separate sensor parts, each of which includes a part of the fluid mass and an associated transducer.