WO1988006739A1

WO1988006739A1 - Process and device for establishing the cohesion curve of an ocean floor at great depth

Info

Publication number: WO1988006739A1
Application number: PCT/FR1987/000300
Authority: WO
Inventors: Pierre Guevel; Odile Fanton D'andon; Jean-Luc Viaud; François VACHERAND
Original assignee: Principia Recherche Developpement S.A.; Commissariat A L'energie Atomique
Priority date: 1987-03-04
Filing date: 1987-07-29
Publication date: 1988-09-07
Also published as: EP0304434A1; FR2611922A1; FR2611922B1

Abstract

Process for establishing the cohesion curve of an ocean floor at great depth, characterized in that it consists in releasing from the surface a missile (1) of optimal shape for reaching the bottom at a speed sufficient to penetrate the floor for a considerable distance, and in equipping this missile with sensors (modules 3, 4 and 5) which transform the various resistances encountered by the missile as it penetrates the floor into electric signals. The signals are processed successively by electronic and data processing means (9) located within the misille itself so that the required information concerning the nature of the layers of the floor traversed are transmitted directly to the surface.

Description

PROCESS AND DEVICE FOR ESTABLISHING THE COHESION CURVE OF A GREAT DEPTH OF MARINE SOIL.

The present invention relates to a method for establishing the physical profile of soil layers, and in particular the property of soils designated by

"cohesion", as well as a machine adapted to the implementation of this process.

It is well known in the techniques of soil recognition, and more particularly underwater soils, used in particular by oil prospecting companies, that the methods currently used, although using very elaborate and expensive means, are not practically not applicable to very great sea depths for example in the area reaching 6000m.

Indeed, these current processes are essentially based on the technique of "coring" consisting in taking a vertical cylindrical sample from the ground, with a diameter of the order of a few tens of centimeters and several meters high, so as to carry out the study of the soil directly on this sample. If this technique is conceivable for low or medium depths, ranging from a few hundred meters to 2 or 3000 meters-s, it becomes inapplicable when it leads to submerging heavy equipment to thousands of meters deep. There are many techniques similar to those used for electrical prospecting, but they give only insufficient information, when we try to establish the cohesion curve of a soil on

5 a thickness of several tens of meters at depths of several thousand meters.

The present invention achieves this result in conditions of speed and precision that no other technique can fulfill. lu The method according to the invention, for establishing the cohesion curve of an underwater soil in particular but not exclusively at great depth, consists in dropping from the surface a machine whose shape is optimized so as to reach by reaching basically

T5 a sufficiently high descent speed to then penetrate into a significant thickness of the ground, and to provide this machine with sensors transforming the various resistances encountered by the machine by crossing the ground into electrical signals which are 0 processed as and when required by electronic means and IT contained in the machine itself, so as to transmit directly to the surface the information sought on the nature of the soil layers crossed.

To obtain the said information in a way

25 complete, the method according to the invention consists in capturing with the same machine on the one hand the forces resulting from the resistance encountered by the latter when penetrating into the ground and on the other hand the lateral forces resulting from friction between the machine and the ground.

The invention also relates to a machine adapted to the implementation of this method, this machine being characterized, first of all, in that it has an optimized shape to take, during its descent from the surface to the bottom , the maximum acceleration, and meet the bottom with the maximum speed, so as to penetrate the ground to the maximum depth, secondly in that it is equipped with stress sensors continuously measuring the bonding forces between the body of the machine and its tip and its rear and the lateral stresses resulting from the friction of the machine on the successive layers of the ground, and thirdly in that it constitutes at the same time a hyperbar container in which are housed a conditioner of the signals delivered by the sensors, an amplifier of these signals and a system for storing these signals, itself consisting of a microcomputer and a converter performing the sampling of these signals according to their frequencies uences.

Such a device is connected to the surface by any means allowing the permanent transmission of the signals thus processed, so that the soil cohesion curve can be established instantly with each release. of the craft. An electrical conductor is obviously suitable for this purpose, but it is also possible to use other means such as optical fibers.

According to another characteristic of the invention, each of said sensors comprises means for guiding by elastic blades, which do not introduce any stiffness and which, moreover, are perforated, which allows the passage of water, so that in principle, the hydrostatic pressure being exerted on the two sides of these blades, it is not likely to distort the measurement.

In this regard, it should be noted that each sensor is completely autonomous and independent at the mechanical level, which makes it easy to exchange and individually calibrate them in the laboratory.

According to another characteristic of the invention, the machine also comprises a control rod, mounted in said machine at a point where the temperature and the pressure are the same as those which are transmitted to the bars supporting the strain gauges, so to compensate for the hydrostatic component and the thermal drift which would risk distorting the measurements of said gauges if they were not constantly taken into account.

Like this witness rod, which therefore ensures the consistency of the measurement results with respect to variations in temperature and pressure, provision is made, -.

REPLACEMENT SHEET according to the invention, that the machine comprises a three-dimensional accelerometer, providing information on the inertia effects and therefore also ensuring the consistency of the measurement results with respect to these inertia effects.

Finally, the invention relates to a particular and original embodiment of the parietal sensor intended for measuring the lateral forces undergone by the machine and resulting from friction between said machine and the ground. According to the invention, such a parietal sensor is characterized in that it comprises an element sensitive to external lateral friction, connected to a base secured to the machine by elastic blades, and whose displacements relative to said base are transmitted to a measurement gauge through the deformations of a measurement element such as a rod embedded in the fixed base at one of its two ends, and positioning the movable sensitive element longitudinally relative to this fixed base. The interest of the invention is multiple. It makes it possible to establish over a very large thickness the cohesion curves of soils located at considerable depths, with light and inexpensive equipment, compared to coring equipment.

In addition, the operation is very rapid, asking for a few minutes. For example, a device according to the invention takes two minutes to reach a bottom of 6000 meters, then 1 second to sink 40 meters. In addition, the results are instantaneous and do not require an analysis as is the case for carrots.

By way of example, a machine will be described constructed in accordance with the invention, with reference to the appended drawing, in which: FIG. 1 is a very schematic view in axial section of the machine,

FIG. 2 is an axial section of the front of the machine,

FIG. 3 is an axial section of the device mounted at the rear of the machine,

FIG. 4 is a very schematic axial section of a wall sensor according to the invention, illustrating the principle of its operation,

FIG. 5 is a view similar to FIG. 4, illustrating in more detail the practical embodiment of a wall sensor,

FIG. 6 is a top view of the sensor of FIG. 5, and

Figure 7 is a section along VII-VII of Figure 6.

As we see first of all in Figure 1,

REPLACEMENT SHEET the machine consists of an envelope or body 1 whose overall profile is optimized as described in French patent No. 85.09355 of the applicant. It is thanks to this optimized profile that the machine, dropped vertically from a surface structure, very quickly takes a very high speed, ensuring its maximum penetration into the ground when it reaches the bottom.

Behind the head or cone of penetration 2, 0 is mounted in the machine an apparatus or module 3 for measuring the forces resulting from the resistance encountered by the machine during its penetration into the ground. This module 3 is described in more detail below with reference to FIG. 2. 5 Towards the rear of the machine is similarly mounted an apparatus or module 4 for measuring the connection forces between the rear of the 'machine and body 1. This module 4 is described in more detail below with reference to Figure 3.' - ⁾ Finally on the side of the machine is mounted an apparatus or module 5 for measuring the lateral forces resulting friction between the machine and the ground. This module 5 is described in more detail below with reference to FIGS. 4 to 7.

These three modules 3,4 and 5 are connected by connections 6, 7 and 8 to a processing unit 9, housed in the heart of the craft, and which is itself connected by a suitable connection 10 to the surface structure.

If we refer more particularly to Figure 2, we see that the module 3 consists of an outer cage 11 in which are mounted two elastic diaphragms 12 and 13, for the lateral guidance of a bar 14, arranged in the axis of the machine by resting on the bottom of the cage and carrying gauges 14 '. The penetration cone 2 transmits the forces encountered by the machine to these gauges by means of a threaded mounting sleeve 15 which leaves a clearance 16, allowing the passage of water inside the cage 11 Referring now to FIG. 3, it can be seen that the rear module 4 also consists of a cage 17 in which are mounted two elastic blades 18 and 19 serving for the lateral guidance of a bar 20, arranged in the axis of the machine carrying gauges 20 '. A plate 21 is used for fixing the module 4 to the body 1, so that the gauges 20 ′ allow the connection forces between this body 1 and a rear plate 22 fixed to the bar 20 to be measured.

If we now refer again to FIG. 2, we see that there is shown a witness rod 30 free at one of its ends 30 ′ and subjected to the

REPLACEMENT SHEET hydrostatic component of the forces undergone by the sensor, since the blades 12 and 13 are perforated to allow the passage of water and brought to the temperature of the machine. Knowledge of the measurements of gauge 30 therefore provides the means of compensating for the hydrostatic component and the thermal drift which would risk distorting the measurements if they were not taken into account. The gauge 30 is sufficient for the calculation of the measurements carried out by all. the sensors of the machine. If we now refer to Figure 4, we see the principle of the parietal sensor designated by 5 in Figure 1: In a recess 40 in the side wall of the machine 41 is housed a base 42 on which is adapted an outer plate 43..through two elastic blades 44 and 45, and which is kept at constant distance from the base 42 by a bar 48 working in bending. The internal end 48 ′ of the bar 48 is embedded in the base 42, while its external head 48 ″ has the shape of a ball joint housed in a recess 60 in the plate 43, so as to freely follow the movements of this plate 43 parallel to the direction XX ′. This bar 48 carries strain gauges 46 and 47, arranged on either side. The external wall 43 can thus move parallel to the axis of the machine, by relative to the body 41 of the machine, the operation of the device is the following: the machine 41 moving in the direction X'X, within an environment such as loose ground, the friction which it undergoes on the part of this ground determine braking, and consequently a displacement of the plate 43, in the direction XX 'relative to the machine 41. This displacement results in a deformation of the element 48, which is measured by. the gauges 46-47 and this measurement is taken as an element of appreciation of said friction, and integrated with the other measurements transmitted by the head and tail sensors of the machine in the study of said earth -

The practical implementation of such a sensor is illustrated in the detailed views in FIGS. 5-6-7, where the corresponding elements have been designated by the same reference numerals, assigned with a "" sign.

We thus find the sensitive element constituted by the outer plate 43 ', movable relative to the base 42' fixed in a housing 40 'of the machine 41', by four screws 51, this sensitive element 43 'being mounted on two elastic blades 44 'and 45' and connected to the base 42 'by the measuring element 48', with which it is secured by two adjustable screws 54 and 55.

The measuring element 48 'has the form of a plate 50 fixed on the base of four screws 52, and extending towards the plate 43' by a rod 53 on the end part of which act the screws 54-55. The gauges 49 'are placed on this rod. Any movement of the sensitive plate 43 'within the limits of the travel e.' induced by the longitudinal friction of the machine on the medium traversed results in a deformation of the rod 48 ', measured by the gauges 49', the signals of which are transmitted, like those of the head and tail gauges, to the system 9 amplification and storage of these signals, then their sampling, and their retransmission by any means appropriate to the surface structure. Of course, the parietal sensor which has just been described operates regardless of the medium in which the machine 41 (or 41 ′) moves, so that the application of the invention is not limited to the penetrants intended to the study of marine soils, but can extend to the study of all other environments, loose or fluid.

As indicated at the beginning, a three-dimensional accelerometer 61 is also housed in the sealed enclosure of the machine, in order to allow corrections to be made to the measurements required by the existence of the inertia effects.

It is moreover precisely in the case of applications of the devices according to the invention in other environments that the wall sensors which have just been described take on all their importance. Indeed, it is in this case that the gauges react in a significant way to the inertia effects, which must be subtracted, which is possible, since they are known.

REPLACEMENT SHEET by the accelerometer, so as to have a measurement only friction. However as long as these frictions are weak, they have little importance, while in other environments, they can become predominant, which thus justifies the presence of the parietal sensors.

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Claims

1. A method for establishing the cohesive curve of a sea floor at great depth, characterized in that it consists in dropping from the surface a machine whose forum is optimized so as to reach, by reaching fo a speed of Descent high enough to penetrate into a large thickness of the ground, and to equip this machine with sensors transforming the different resistances encountered by the machine by crossing the ground into electrical signals which are processed as required by electronic and computer means contained in the 'eng itself, so as to transmit directly to the surface the information sought on the nature of the soil layers crossed.

2. Method according to claim 1, characterized in that it consists in capturing with the same device on the one hand the forces resulting from the resistance encountered by it- penetrating into the ground and on the other hand the lateral forces resulting from friction between the machine and the ground.

3. Machine for implementing the method according to claims 1 and 2, characterized in that it has an optimized shape to take, during its descent from the surface to the bottom, the maximum acceleration, to meet the bottom with maximum speed, so as to penetrate the ground to the maximum depth, and in that it is equipped with stress sensors measuring continuously

REPLACEMENT SHEET the connection forces between the body of the machine and its tip and its rear and the lateral stresses resulting from the friction of the machine on the successive layers of the ground, and in that it constitutes at the same time a hyperbar container in which are housed a conditioner of the signals delivered by the. sensors, an amplifier of these signals and a system for storing these signals, itself consisting of a microcomputer and a converter sampling these signals according to their

ÎO frequencies.

4. Engine. According to claim 3, characterized in that each sensor consists of a bar equipped with strain gauges, and comprising guide means parallel to the axis of the machine by elastic perforated blades,

T5 does not introduce any stiffness and allows the passage of water so that the same hydrostatic pressure is exerted on both sides of these blades.

5. Machine according to claims 3 and 4, characterized in that it further comprises a witness rod having 0 one of its free ends, and equipped with a strain gauge, mounted at a point of said machine where the temperature and the pressures are the same as those transmitted to the gauge support bars, so as to compensate for the hydrostatic component and any thermal drift. 5

6. Machine according to claims 3 and 5, characterized e that, the parietal sensor, intended for the measurement of the lateral forces undergone by the machine, consists of a sensitive element to external lateral friction, connected to a base secured to the machine by elastic blades, and whose displacements with respect to said base are transmitted to at least one measurement gauge by means of deformations of a measurement element such that a bar embedded in the fixed base at one of its ends e longitudinally positioning the movable sensitive element pa relative to this fixed base.

7. Machine according to claim 6, characterized in that said rod is a rod perpendicular to the lateral fac of the machine, embedded at one of its ends dan a fixed base and whose other end is pinched between two organs screwed into a movable outer plate constituting the movable element.

8. Machine according to any one of the preceding claims, characterized in that it comprises in its sealed enclosure a three-dimensional accelerometer ensuring the consistency of the measurements with respect to the effects of inertia.

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