A device for measuring deformations in boreholes

Abstract

A measuring device (10) for measuring deformation suitable for placement in a borehole (2), comprising: a hollow elastic shell (11) having a diameter compatible with the borehole into which it is to be inserted; a pressurizing system (12) for pressurizing the hollow elastic shell; and a uniaxial sensor (13) for measuring the elongation of the hollow elastic shell in at least six different directions.

Description

[Technical field]

[0001] The present invention relates to a device for measuring deformations in a borehole. The invention also relates to a drilling rig comprising said device and to a measurement method implemented by said device. [Background technology]

[0002] All devices for measuring deformation in the borehole are installed vertically during drilling and mechanically fixed with concrete in the casing.

[0003] Some of these devices measure only the horizontal volume component, while others measure only the deformation component in the horizontal plane, of which there are three.

[0004] Furthermore, there are no devices that can measure all six deformation components.

[0005] Finally, existing devices do not allow for in-situ measurement of the mechanical properties of the drilled material and surrounding rock. Summary of the Invention

[0006] One object of the present invention is, inter alia, to remedy all or some of the above mentioned drawbacks.

[0007] To this end, according to a first aspect of the invention, a device for measuring deformations is proposed, suitable to be placed in a borehole, said device comprising a hollow elastic shell having a diameter matching the borehole into which it is to be inserted, a system for pressurizing said hollow elastic shell, and a uniaxial sensor arranged inside the hollow elastic shell for measuring the elongation of said hollow elastic shell in at least six different directions.

[0008] The single-axis sensor may have an end that is secured within the hollow elastomeric shell.

[0009] The hollow elastomeric shell may be spherical in shape.

[0010] Advantageously, the hollow elastic shell may have uniform elastic properties and a moderate coefficient of thermal expansion.

[0011] For example, the hollow resilient shell may be made of fiber reinforced concrete or polycarbonate. Preferably, the hollow resilient shell is made of a single material.

[0012] According to one embodiment, the pressurization system includes a tube extending from the surface of the wellbore to the interior of the hollow elastomeric shell.

[0013] The single-axis sensor can be formed from a deformable system, the ends of which are mounted (glued or bonded) onto a hollow elastic shell to ensure a secure connection.

[0014] The deformable system may be a displacement amplifier, with two opposing vertices of the deformable system located on the long axis of a parallelogram and attached to the hollow elastic shell.

[0015] Advantageously, the long axis of the uniaxial system is parallel to the edges of the tetrahedron.

[0016] The device according to the first aspect of the invention may further comprise a non-contact measurement device arranged to measure the refractive index of the environment.

[0017] The non-contact measuring device may be capacitive or optical.

[0018] The device according to the first aspect of the invention may further comprise a communications device arranged to transmit measurements from the non-contact measuring device to the borehole surface.

[0019] According to a second aspect of the invention, there is proposed a drilling rig comprising a measuring device according to the first aspect of the invention, or one or more of its improvements.

[0020] According to a third aspect of the present invention, a method for measuring deformation in a borehole is proposed, the method being implemented in a drilling rig according to the second aspect of the present invention, comprising an initial step of pressurizing an elastic shell and a step of measuring the change in elongation of each of the uniaxial sensors of a measuring device of the drilling rig relative to a reference elongation measured during a calibration step.

[0021] The method according to the third aspect of the invention may include a calibration step, during which a reference elongation may be measured for each of the uniaxial sensors.

[0022] The method may further include determining a change in mechanical properties in the borehole by measuring the change in elongation of each of the single-axis sensors after increasing the pressure inside the hollow elastic shell with a system for pressurizing the hollow elastic shell and then comparing it to isotropy. [Brief description of the drawings]

[0023] Other advantages and particularities of the invention will become apparent upon reading the detailed description of embodiments and implementations, which is by no means exhaustive, with reference to the attached drawings, in which: [Figure 1] 1 shows a schematic cross-sectional view of an embodiment of a drilling rig according to the present invention; [Diagram 2] 2 shows a schematic cross-sectional view of an embodiment of a measuring device according to the invention equipping the drilling rig shown in FIG. 1; [Diagram 3] 2 shows a perspective view of a second embodiment of a measuring device according to the invention equipped with the drilling rig shown in FIG. 1; [Figure 4] 2 shows a schematic cross-sectional view of a third embodiment of a measuring device according to the invention equipping the drilling rig shown in FIG. 1; [Diagram 5] FIG. 3 shows a schematic diagram of a deformable system implemented in the device shown in FIG. 2. [Figure 6] 2 illustrates an embodiment of a method for measuring deformation in a borehole implemented in the drilling rig shown in FIG. 1 . [Figure 7] A method for determining the configuration of the resolved tetrahedrons is described. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The embodiments described below are in no way limiting, and therefore it is possible to consider a variant of the invention that includes only a selection of the described features and then separates them from the other features described, provided that this selection of features provides a technical advantage or is sufficient to distinguish the invention from the prior art. This selection includes at least one feature, preferably functional, and does not include structural details, or includes only a portion of the structural details, if only a portion of the structural details provides a technical advantage or is sufficient to distinguish the invention from the prior art.

[0025] In the figures, elements that appear in several figures are labeled with the same reference numerals.

[0026] 1, a schematic cross-sectional view of a drilling rig 1 according to an embodiment of the present invention is shown. The cross-section is made along a horizontal axis X and a vertical axis Z.

[0027] The drilling rig 1 comprises in particular a borehole 2 made in a casing 3 and extending from a surface 4 along a vertical axis Z. The borehole 2 must be filled with a rigid, slightly compressible object. It may be, for example, concrete or it may be filled with glass or silica beads having a diameter of millimetres.

[0028] The drilling rig 1 is equipped with a measuring device 10 according to the invention.

[0029] The measuring device 10 preferably comprises a hollow elastic shell 11 of the spherical type, the hollow elastic shell 11 having a diameter that matches the borehole 2 into which it is to be inserted. Alternatively, the hollow elastic shell may be of the elliptical or cylindrical type.

[0030] The outer diameter of the hollow elastic shell has a value in the range of 15 cm to 30 cm.

[0031] The hollow elastic shell may have an elastic inner wall, the thickness of the wall being determined to allow for measurable deformation in response to the force exerted by the casing 3. The inner wall may be on the order of 1-2 cm thick.

[0032] The hollow elastic shell may have isotropic or substantially isotropic mechanical properties.

[0033] More precisely, the elastomeric inner wall is formed from polystyrene which immediately surrounds the interior volume of the hollow elastomeric shell.

[0034] The second elastic annular thickness, which may be made of metal, preferably low-shrinkage fiber-reinforced concrete, or polycarbonate, forms another part of the hollow elastic shell by surrounding the elastic inner wall. More generally, the second elastic annular thickness may be made of any resistive material (e.g. concrete) with uniform elastic properties and a moderate coefficient of thermal expansion. The hollow elastic shell may therefore be made of a single material.

[0035] The thermal expansion coefficient is 10 -5 C° -1 It may be less than.

[0036] The measuring device 10 further comprises a system 12 for pressurizing the hollow elastic shell 11 .

[0037] The pressurization device 12 has several functions. In the laboratory, transient pressurization makes it possible to calibrate the six uniaxial sensors, to verify the deformation isotropy of the sphere and to calculate its elastic properties. In excavation, the transient pressurization and the response of the six sensors make it possible to evaluate the elastic properties of the surrounding medium. At depth, continuous pressurization makes it possible to compensate the weight of the soil and to hold the hollow spherical shell with respect to elastic deformations.

[0038] The pressurization system 12 may, for example, comprise a metal tube 121 extending from the surface 4 into the hollow spherical shell 11. At the surface side 4, the metal tube may, for example, be connected to a pressurization cylinder equipped with a pressure gauge and a control valve (not shown).

[0039] The measuring device 10 further comprises a uniaxial sensor 13 for measuring the elongation of the sphere in six different directions. More precisely, the deformation measurements can be performed by a Fabry-Perot nanometer resolution optical fiber end interferometer.

[0040] As shown in Fig. 2, the single-axis sensor 13 can be formed from a deformable system with flexible joints c1, c2, c3, c4, c5, c6 attached at the ends to the sphere 11. In the illustrated embodiment, the deformable system with flexible joints c1, c2, c3, c4, c5, c6 measures the extensions d1, d2, d3, d4, d5, d6, respectively. Rigid systems for optical or capacitive measurements can also be used to measure the change in deformation. These deformable systems are called flexure hinges in the scientific literature and can result in structures with flexible joints.

[0041] The deformation of the hollow elastic shell 11 is determined from the measurements of the lateral stretches d1, d2, d3, d4, d5, d6 from equations corresponding to the inversion of a 6x6 linear system. This system contains as data the orientation vectors of the uniaxial sensors and the longitudinal stretches of the detectors, and as unknowns a six-component strain tensor. It is possible to add redundancy by adding additional uniaxial sensors. The measurements of the lateral stretches make it possible to first calculate the longitudinal stretches and then the six components of the strain tensor of the hollow elastic shell.

[0042] In the illustrated example, the deformable systems c1, c2, c3, c4, c5, c6 are deformation amplifiers, the two opposite vertices of which are located on the long axis and are attached to the sphere at points P1, P2, P3 and P4, which in the given example form a regular tetrahedron of the sphere 11, whose faces P1, P2 and P3 are inscribed in the plane XY and whose bases X, Y, Z are directly orthogonal. The deformable systems make it possible to amplify in the transverse direction the longitudinal displacements applied at the ends, which increases the resolution of the measurements.

[0043] The spherical shape allows for optimal orientation of the uniaxial sensor, for example the orientation of the edge of a regular tetrahedron, allowing for sampling three-dimensional deformations of small volumes in an optimal way.

[0044] The choice of material used for the amplifier is important, since any deformation of the sphere, whether of thermal or mechanical origin, is amplified by a factor of 10 to 30 before being measured by the optical system.

[0045] It is therefore very beneficial to have a material that expands as little as possible so that the measurements only take into account deformations of mechanical origin.

[0046] The expansion coefficients of materials that can be used to fabricate the amplifier are as follows: Aluminum: 26×10 -6 K -1 Steel: 11×10 -6 K -1 Invar: 1.0 x 10 -6 K -1 Borosilicate glass: 3.3 x 10 -6 K -1 Silica glass: 0.6 x 10 -6 K -1 "Zerodur" glass-ceramic: 0.02 x 10 -6 K -1

[0047] The first laboratory amplifier was machined from aluminum, since glass and ceramics are difficult to machine due to their brittleness, therefore the use of Zerodur, an ultra-stable material on a thermal plane (1300 times less expansive than aluminum), seems particularly beneficial.

[0048] In the illustrated embodiment, the major axes of the sensors are paired to form an arccosine angle (1 / 3), i.e., 70.529 degrees. The amplification factor between the longitudinal deformation imposed by the sphere and the measured lateral deformation can vary between 10 and 30 depending on the device used.

[0049] 2, each of the parallelograms of the deformable systems c1, c2, and c6 has a vertex attached to a point P1, each of the parallelograms of the deformable systems c2, c3, and c4 has a vertex attached to a point P2, and each of the parallelograms of the deformable systems c4, c5, and c6 has a vertex attached to a point P3. The vertex of the parallelograms of the deformable systems c1, c3, and c5 opposite points P1, P2, and P3 is attached to point P4.

[0050] As can be seen in FIG. 2, points P1, P2, and P3 are provided with ends secured within hollow elastic shell 11.

[0051] Figure 3 shows another arrangement of deformable systems in a hollow elastic shell 11, where the deformable systems c1, c2, c3, c4, c5 and c6 are arranged differently on the exploded tetrahedron, which requires 12 fixation points instead of four, respectively P1 and P1', P2 and P2', P3 and P3', P4 and P4', P5 and P5', P6 and P6'. Again, the edges c1 and c4, c2 and c5, c3 and c6, are pairwise orthogonal. With reference to Figure 7, a method for determining the shape of the exploded tetrahedron will be described.

[0052] Fig. 4 shows yet another embodiment, where a deformable system, for example system c1, comprises a pressure-deformable bar b around which an optical fiber fo is wound in a number of turns. The deformation of the sphere 11 produces a change in length between the fixation points P1, P1', which causes a tension / compression of the fiber that can be measured by interferometry. To calculate the deformation tensor associated with the sphere, at least six systems of this type must be placed in a direction parallel to the direction of the edges of the regular tetrahedron.

[0053] The measuring device 10 further comprises a non-contact measuring device 14 arranged to measure the variation of the optical path in the absence of stretching. This optical measuring device makes it possible to correct the measurements of the variation of the lateral distances d1, d2, d3, d4, d5, d6 of the variation of the refractive index.

[0054] As shown in Fig. 5, the non-contact measuring device 14 associated with the system c1 has a topology based on a symmetrical structure with five rigid bars bh, b1, b1', b1s, b1's for the amplification of the displacement, and a flexible mechanism is implemented for the amplifier. In the literature, this type of mechanical amplifier is called a compliant mechanical amplifier or CMA. The non-contact measuring device 14 can reach large amplification ratios and high natural frequencies compared to other topologies.

[0055] The circles represent flexible joints and the bars represent rigid parts. Application of an axial compression / tension input at the fixation points P1, P1' (horizontal arrows on the outside of the device) produces a lateral deformation at the output (vertical arrows) that is proportional to the input deformation but amplified.

[0056] The non-contact measuring device 14 also conventionally comprises a collimator connected to an optical fiber and oriented to measure the change in distance at its output, the output being disposed at one end of the output space, at the center of the bar bh, between an angle mirror disposed in the optical path of the collimator, and a plane mirror disposed at the other end of the output space in the optical path of the collimator.

[0057] The measuring device 10 further comprises a communication device 15 provided for communicating measurements of the non-contact measuring device to the surface of the borehole. The communication device 15 comprises, for example, a sealed data acquisition cable 151 extending from the surface 4 into the sphere 11 and connected to the measuring device 10 at the sphere 11.

[0058] FIG. 6 shows an embodiment of a method P for measuring deformations in a borehole, implemented in a drilling rig 1 according to the invention.

[0059] The measurement method P includes the following steps.

[0060] Initial step Ei of pressurizing the sphere of the measuring device.

[0061] A calibration step Ec of measuring the elongation of each of the uniaxial sensors of the measuring device 10 of the drilling rig 1, during which a reference elongation is measured for each of the uniaxial sensors.

[0062] One or more steps Emi of measuring the amount of change in elongation of each of the uniaxial sensors relative to a reference elongation measured during a calibration step.

[0063] The measuring device according to the invention makes it possible to measure the strain tensor in a borehole with an accuracy of the order of 10^-9 (1 nanometer / meter), which is useful for geophysical applications in the fields of geological reservoirs, volcanoes, faults, and in civil engineering.

[0064] The invention further proposes an active method for determining in situ the properties of the assembly formed by the sphere, the borehole filled with concrete and the casing. In fact, the borehole strain sensor must make it possible to measure the "ideal" deformations that the Earth's crust undergoes in the absence of disturbances such as deformations of the borehole in which the measuring device is located. This is not directly possible.

[0065] To access this information, a correction term must be subtracted from the measurements, which is a deformation model that represents the heterogeneity of the subsoil.

[0066] Typically, this is done by using an idealized geophysical model linked to the surface tides, and by comparing this idealized model over several days with measurements that give rise to a number of problems related to the inaccuracies of the geophysical model, which are affected by topography, ocean tides, and pressure variations, it is possible to determine the correction terms.

[0067] The present invention proposes a direct and accurate measurement method for in situ determination of the change in mechanical properties in a borehole by measuring the change in elongation of each of the uniaxial sensors (13) after increasing the pressure inside the sphere of the measuring device by the pressurization system of said sphere, and then comparing it with isotropy. In fact, if the sphere, the concrete filling of the borehole and the casing rock formed a homogeneous medium, the expansion measured by the six uniaxial sensors in response to overpressure should be isotropic. The deviation from isotropy is related to the contrast in elastic properties between the filling of the borehole and the casing. Using the six elongation measurements, the contrast can be accurately estimated by a finite element mechanical model. This model makes it possible to determine the ratio of the elastic properties between the filling of the borehole and the casing, taking into account the exact geometry of the borehole and the sphere. Once the contrast in properties has been determined, it is possible to return from the actual measurements to the ideal measurements of deformation in a homogeneous medium.

[0068] Furthermore, measurements after increased pressure make it possible to estimate the slow variations in the properties of the concrete fill of the borehole, which is essential for accurately estimating crustal deformation over long periods of time, months or years.

[0069] FIG. 7 illustrates the method for determining the configuration of the decomposed tetrahedron. Step S1 includes information about the variable length L of the six bars. Step S2 initializes the inter-bar distance variable Dib to 0: Dib=0

[0070] Then a loop over variable i, from i=1 to i=N, for example, N=1000000, begins with this loop.

[0071] Step S3i performs a random selection of six positions on the osculating circle (0 to 2pi), where the osculating circle is defined as the location of contact between the sphere and the segment of fixed orientation. The contact points are defined, for example, by selecting a random angle (0 to 2pi) on the osculating circle for each of the six segments.

[0072] Step S4i calculates the minimum of the 15 distances between the bars, and this minimum is stored in the variable Dmin.

[0073] In step S5i, if the variable Dmin is greater than the variable Dib, the variable Div stores the value of the variable Dmin: if Dmin>Dib, then Dib=Dmin

[0074] End of the loop Step S6 proposes to write the optimal configuration, i.e. the configuration that corresponds to the maximum distance between the bars. The distance between two bars is defined as the minimum of the distance between two points of the two bars.

[0075] Of course, the invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. Moreover, the different features, forms, variants and embodiments of the invention can be associated with one another in various combinations, unless they are mutually incompatible or exclusive.

Claims

1. A device (10) for measuring deformation, suitable for being disposed within a drilled hole (2), comprising: A hollow elastic shell (11) having a diameter compatible with the drilled hole, the hollow elastic shell being inserted into the drilled hole; A system (12) for pressurizing the hollow elastic shell; A uniaxial sensor (13) disposed within the hollow elastic shell for measuring the elongation of the hollow elastic shell in at least six different directions; The measuring device (10) comprising the above.

2. The measuring device according to claim 1, wherein the uniaxial sensor is provided with an end fixed within the hollow elastic shell (11).

3. The measuring device according to claim 1, wherein the hollow elastic shell (11) is spherical in shape.

4. The measuring device according to claim 1, wherein the hollow elastic shell (11) has uniform elastic properties and a suitable coefficient of thermal expansion.

5. The measuring device according to claim 4, wherein the hollow elastic shell is made of fiber-reinforced concrete or polycarbonate.

6. The measuring device according to claim 1, wherein the hollow elastic shell is made of a single material.

7. The measuring device according to claim 1, wherein the system (12) for pressurizing comprises a pipe portion (121) extending from the surface (4) of the drilled hole (2) to the interior of the hollow elastic shell (11).

8. A deformable system (c1, c2, c3, c4, c5, c6) is a displacement amplifier, and two opposing vertices of the deformable system are located on the major axis of a parallelogram and are attached to the hollow elastic shell (11). The measuring device according to claim 7.

9. The measuring device according to claim 1, wherein the uniaxial sensor is parallel to the edges of a regular tetrahedron.

10. The measuring device according to claim 1, further comprising a non-contact measuring device (14) arranged to measure the refractive index of the environment.

11. The measuring device according to claim 10, wherein the non-contact measuring device is capacitive or optical.

12. The measuring device according to claim 10, further comprising a communication device (15) provided to communicate measurement values from the non-contact measuring device to the surface of the drilled hole.

13. A drilling rig (1) comprising the measuring device (10) according to any one of claims 1 to 12.

14. A method (P) for measuring deformation in a borehole, implemented in a drilling rig (1) according to claim 13, comprising: An initial step (Ei) of pressurizing the hollow elastic shell; A step (Emi) of measuring the amount of change in the elongation of each of the uniaxial sensors (13) of the measuring device (10) of the drilling rig with respect to a reference elongation measured during a calibration step (Ec); A method (P) for measuring deformation, comprising:

15. The method for measuring deformation according to claim 14, comprising a calibration step (Ec) of measuring the reference elongation for each of the uniaxial sensors (13).

16. The method for measuring deformation according to claim 14, comprising the step of increasing the pressure inside the hollow elastic shell of the measuring device by a system for pressurizing the hollow elastic shell, then measuring the amount of change in the elongation of each of the uniaxial sensors (13), and then determining a change in mechanical properties in the borehole by comparing with isotropy.

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