EP1977048B1 - Pressure meter probe and pressure meter - Google Patents

Abstract

The pressure meter has a down hole tool (1) e.g. probe, introduced in a boring (F), and a reservoir (4) carried by the down hole tool and containing a liquid (L) and a pressurized gas (G) such as pressurized nitrogen. A gas source (21) delivers the pressurized gas to the reservoir. A volume sensor comprises a liquid level detector (61) housed in the reservoir. A connection unit includes a transmission line (30) connecting the liquid level detector and a surface equipment (2).

Description

The invention relates generally to logging techniques.

More specifically, the invention relates to a pressuremeter for the evaluation of a geotechnical property of the subsoil, the pressuremeter comprising, as subassemblies, a downhole tool intended to be introduced into a borehole, equipment surface, and connecting means at least adapted to connect the tool to the equipment, these subassemblies themselves comprising at least a first inflatable sleeve carried by the bottom tool, a substantially indeformable reservoir containing volumes. complementary gas and liquid, a source of gas under pressure, a first conduit connecting the gas source to the gas volume of the reservoir, a second conduit connecting the liquid volume of the reservoir to the first inflatable sleeve, flow control means interposed on the first conduit, a pressure sensor adapted to provide a signal related to the pressure of the liquid in the reservoir, and a volume sensor adapted to provide a signal al related to the volume of the liquid in the tank.

Devices of this type are very well known to those skilled in the art since their invention by L. Ménard in 1955. They are described in particular in the patent. FR 1.117.983 . The document US 4,598,591 discloses a probe according to the preamble of claim 1.

The pressuremeter makes it possible to evaluate the mechanical parameters of the soil in situ.

Once the bottom tool, or "probe", introduced into a borehole, each inflatable sleeve is subjected to increasing pressure in stages, in number from six to fourteen, for example, and following an arithmetic progression.

At each stage, the volume of liquid introduced into the first sleeve from the reservoir is measured, typically 15 seconds, 30 seconds and one minute after the end of pressurization.

The result of these measurements is expressed by two loading graphs, or pressuremeter curves, one of which gives the variation of volume, measured at one minute, as a function of the pressure, and the other of which corresponds to the volume variations between 30 seconds and a minute, depending on the pressure.

Existing pressuremeters suffer from several defects that seriously limit the accuracy of the results they provide.

The invention, which is part of this context, is precisely intended to overcome these imperfections and to propose a precision pressuremeter.

To this end, the pressuremeter of the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the reservoir is carried by the bottom tool, in that the sensor volume detector comprises a liquid level detector housed in the reservoir, and in that the connection means comprise a transmission link connecting the level detector to the surface equipment.

Thanks to this arrangement, the volume is measured simply and reliably without the measurement obtained being disturbed by various artefacts, such as the weight of the liquid column between the surface and the bottom, the deformation of the liquid conduit which, in the existing pressuremeters, generally connects the first sleeve to the reservoir disposed on the surface, or the inertia that opposes this conduit to the flow of liquid between the surface and the bottom.

In operational configuration of the downhole tool in a borehole, the reservoir is advantageously arranged above the first inflatable sleeve, that is to say closer to the surface of the ground than this first sleeve.

Preferably, the volume signal is electrical in nature, the transmission link then comprising a power line.

In the preferred embodiment of the invention, it is provided that the liquid has a relatively low electrical resistivity, that the level detector comprises at least one resistive element connected to a generator of electrical energy and partially immersed in the liquid, that the resistive element has an elongated shape according to the height of the reservoir and a relatively high electrical resistivity, and that the liquid and the resistive element partially shunted by the liquid form for the generator a resistive load having a resistance depending on the level of this liquid in the tank.

Moreover, the electrical energy generator preferably delivers an alternating current to avoid parasitic polarizations.

To simplify the measurement and its interpretation, the reservoir may be of cylindrical shape, the resistive element may itself extend along the central axis of the reservoir.

As in the case of known pressuremeters, the bottom tool of the pressuremeter of the invention may further comprise second and third inflatable sleeves, and a third conduit connecting the volume of gas from the reservoir to these second and third sleeves.

To further increase the accuracy of the pressuremeter of the invention, it is possible to provide that the flow control means comprise a nozzle and a valve, the surface equipment further comprises pressure control means in which are stored a plurality of increasing pressure setpoints, a successive application program in the time of these instructions, and a correspondence law connecting at least these instructions at corresponding respective time intervals, and that these pressure control means are designed to selectively open the valve, for the purpose of applying each new setpoint pressure in accordance with the program, during the time interval corresponding to this setpoint.

Thanks to this arrangement, the pressure of the liquid is rigorously controlled, without human intervention, and without undergoing the influence of the gas flow on the measurement of the pressure, or that of the pressure setting delay in The reservoir.

Preferably, the pressure control means are connected to the pressure sensor and are furthermore designed to open the valve during a predefined time interval in response to a deficit of the pressure signal with respect to a set pressure, when this deficit appears during a plateau at this set pressure and when it exceeds a predetermined threshold.

The pressure control means comprise, for example, a control unit actuating the valve and a computer in which the pressure instructions, the program and the correspondence law are stored, this computer being connected to the control unit and controlling it. .

In an easy embodiment of the invention, the flow control means may comprise a solenoid valve carrying both the nozzle and the valve.

In another embodiment, the gas supply duct is connected, in the tank, firstly to a first valve, for example via a first duct or channel, allowing admission of the gas into the tank, and secondly to a second valve, for example via a second conduit or channel, allowing the escape of the gas out of the tank.

It can be envisaged that the first and second valves are arranged on a single conduit or channel.

The valve can be chosen from any type of valve, including a ball valve, ball, valve, piston or disc.

It is advantageous to use a valve comprising a valve body, in particular tubular, provided with two threaded zones separated by an abutment, the valve body being extended by a thinner tubular element than the valve body, in particular of diameter less than the diameter of the valve. valve body when the latter is tubular, and comprising a gas outlet port covered with a cylindrical elastic envelope.

The elastic cylinder casing may be chosen from any type of elastic and waterproof material, in particular rubber.

• la figure 1 est une vue schématique en coupe verticale d'un pressiomètre conforme à l'invention et en cours d'utilisation;
• la figure 2 est une vue schématique en coupe verticale d'un détail fonctionnel de ce pressiomètre ;
• la figure 3 est une vue schématique d'un détail du pressiomètre selon un mode de réalisation ;
• la figure 4 est une vue schématique d'un clapet utilisable dans le pressiomètre selon ce mode de réalisation.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

• the figure 1 is a schematic view in vertical section of a pressuremeter according to the invention and in use;
• the figure 2 is a schematic view in vertical section of a functional detail of this pressiometer;
• the figure 3 is a schematic view of a detail of the pressuremeter according to one embodiment;
• the figure 4 is a schematic view of a valve used in the pressuremeter according to this embodiment.

As previously announced, the invention relates to a pressuremeter for the evaluation of a geotechnical property of the subsoil.

Such an apparatus comprises, as subassemblies, a bottom tool 1 intended to be introduced into a borehole F, a surface equipment 2, and connection means, such as 30 to 33, making it possible in particular to connect the tool 1 to equipment 2.

The bottom tool 1 generally comprises three inflatable sleeves, namely a main and central sleeve 11, and two auxiliary sleeves 12 and 13, adjacent to the central sleeve 11 and located on either side of the latter.

The main sleeve 11 is essentially formed by an annular elastic membrane that can be inflated by injection of a liquid L under pressure, for example water, coming from a tank 4 and conveyed by a duct 32.

The reservoir 4 is for example made in a metal cylinder substantially indeformable at the pressures considered, so that the variation in the volume of liquid in the reservoir 4 is solely due to the deformation of the central sleeve 11. The reservoir 4 contains, above the liquid L, a propellant gas G such as pressurized nitrogen, the liquid and the gas occupying respective and complementary volumes Vl and Vg of this tank 4.

The surface equipment 2 typically comprises a source 21 of clean gas for delivering the gas G under pressure and connected to the volume of gas Vg of the tank 4 by a supply duct 31.

The surface equipment 2 also comprises flow control means, such as 220-222, which are interposed on the conduit 31 and which make it possible to control the passage of the gas G from the source 21 to the tank 4, thus the passage of the liquid L of the reservoir 4 towards the sleeve 11 through the conduit 32.

The pressuremeter of the invention further comprises, in a conventional manner, a pressure sensor 5 and a sensor of volume 6, the pressure sensor 5 being designed to provide a signal Sp related to the pressure of the liquid L in the tank 4, and the volume sensor 6 being designed to provide a signal Sv related to the volume Vl of the liquid in the tank 4.

According to the invention, the volume sensor 6 comprises a detector 61 of liquid level housed in the tank 4, this tank being carried by the bottom tool 1 and for example disposed above the central inflatable sleeve 11 when the bottom tool 1 is in place in a drill F.

A transmission link 30 is then provided to connect the level detector 61 to the surface equipment 2, this link being constituted for example by an electric line in the advantageous case where the volume signal Sv is of an electrical nature.

In an efficient embodiment of the invention, the level detector 61 is of the resistive type.

To do this, the liquid L is chosen to have a relatively low electrical resistivity. It is particularly possible to use, as liquid L, ionized water by the presence of impurities, salt or, more preferably, antifreeze.

The level detector 61 is composed of, for example, a resistive element 610 and a pure conductor such as a copper bar, the resistive element and the conductor being connected to an electrical energy generator 60 and partially immersed in the liquid L of the tank 4.

The generator delivers for example an alternating current of constant amplitude and frequency equal to 270 Hz.

The resistive element 610 has an elongated shape along the height of the tank 4 and, by definition, a relatively strong electrical resistivity that is to say at least a hundred times greater than that of the liquid L.

The resistive element 610 is for example wound around the conductive bar 611 without being in direct galvanic contact with this bar.

Under these conditions, the resistive element 610 and the conductive bar 611 are galvanically connected to each other by the liquid L in the immediate vicinity of the level of this liquid in the tank, the resistive element 610 being shunted by the liquid over its entire submerged length.

In other words, the liquid L, the resistive element 610, and incidentally the conductive bar 611, form for the current generator 60 a resistive load CR whose electrical resistance depends on the level of this liquid in the tank 4, therefore the volume of liquid L in this tank.

The volume signal Sv can thus be represented by the output signal of a phase detection voltmeter 62 installed in parallel on the current generator 60.

Alternatively, the wall of the tank 4, also supposed to be conductive, can be used in place of the conductive bar 611 to close the current loop.

Level detectors of this type are for example described in the patent US 4,188,826 .

As shown in figure 1 , the pressure sensor can be placed in the gas phase of the contents of the tank 4, and in particular in the conduit 31 for supplying gas G.

As shown again figure 1 , the auxiliary inflatable sleeves 12 and 13 are selectively inflated by the gas G, and for this purpose connected, via a conduit 33, to the volume Vg of gas G of the reservoir 4.

The accuracy of the pressuremeter of the invention can be further increased by equipping the surface equipment with pressure control means, and providing that the flow control means comprise a nozzle 221 and a valve 222, for example integrated with a solenoid valve 220.

In the illustrated embodiment, the pressure control means comprise a control unit 7 adapted to actuate the valve 222, and a computer 8 connected to the control unit 7 and the driver.

The computer 8 is provided with a memory in which are stored a plurality of pressure instructions of increasing values Kpi, a program PROG of successive application in time of these instructions Kpi, and a correspondence law CORR for determining, at least on the basis of Kpi instructions, corresponding respective time intervals Tpi.

The purpose of the PROG program is to determine at which instants the different pressure levels should be applied, the Kpi instructions defining the values of the different pressures that will have to be reached and maintained during these different pressure levels.

The correspondence law CORR is defined so that at each new pressure level, that is to say when applying each new pressure setpoint Kpi according to the program PROG, this pressure setpoint can be reached by the opening of the valve 222, by the means 7 and 8 of pressure control, during the time interval Tpi corresponding to this setpoint Kpi.

In practice, since the gas G is admitted into the tank G through the nozzle 221, it flows laminarly.

The mass of gas G admitted into the reservoir during a determined period of time is therefore, in accordance with Poiseuille's law, essentially represented by a linear function of this duration, the minor incidence of variations in the difference between the pressures existing upstream and downstream. downstream of the nozzle may further be taken into account and corrected thanks to the prior knowledge of the pressure upstream of the nozzle 221 and the setpoint Kpi to achieve.

Alternatively, or cumulatively, the correspondence law CORR can be determined or refined experimentally by preliminary calibration.

The CORR law can finally be stored in the form of a mathematical relationship, or more simply in the form of one or more charts.

Once a new pressure level has been reached in the manner indicated above, the pressure in the reservoir 4 should be maintained at the value of the set pressure of that stage until the instant when another pressure level should be reached.

As, however, the sleeve 11 may, during the duration of a pressure bearing, radially push back the wall of the borehole F and thus increase in volume, the pressure in the tank 4 may decrease during this period and must therefore be compensated.

To do this, the computer 8 receives the pressure signal Sp from the pressure sensor 5 to which it is connected and compares this pressure signal Sp, permanently or periodically at high frequency, to the reference pressure Kpi which must be maintained during the current pressure level.

In the case where the pressure signal Sp has, relative to this set pressure Kpi, a deficit greater than a predetermined tolerance threshold, the computer 8 transmits to the control unit 7 the order to open the valve 222 during a predefined time interval T0.

In practice, the time interval T0 is chosen so that the mass of gas passing through the nozzle 221 during this time interval is at least slightly greater than the mass of gas required, in the worst case. case, to compensate for the pressure deficit corresponding to the tolerance threshold.

In the case where the desired precision on maintaining the pressure during a step is high, that is to say in the case where the value given at the tolerance threshold is low, the time interval T0 will take therefore itself a low value, the adequate compensation of the pressure deficit during a pressure bearing being achieved by automatically adjusting the opening frequency of the valve 222 as a function of the speed of the pressure drop in the reservoir 4.

Finally, the computer 8, which receives the volume signal Sv, also records this signal Sv and the pressure signal Sp in a time-correlated manner, with a view to the subsequent processing of these signals.

The figure 3 schematically illustrates the top of the tank 4 according to one embodiment of the pressuremeter according to the invention.

According to this embodiment, the conduit 33 for supplying gas G is connected, in the volume of gas Vg of the tank 4, to a first valve 40 via a first channel 331, and secondly to a second valve 41 , via a second channel 332. The valve 40 is arranged to allow the admission of the gas G from the gas source 21 in the tank 4, while the valve 41 is arranged to allow the escape of the gas G from the tank 4 to the conduit 33. The valves 40 and 41 are arranged using support members 48 and 49.

Thus, when gas G is injected from the gas source 21 to the probe 1, to carry out the pressuremeter tests, the gas G is admitted into the tank via the valve 40. When the tests have been completed and it is desired to evacuate the gas G from the tank 4 by decreasing the gas pressure, the gas G escapes from the tank 4 via the valve 41. Thanks to the presence of two valves 40, 41, the liquid L present in the tank 4 can not escape the tank 4, both during the pressuremeter tests and during the handling of the probe 1 at the surface. The probe 1 can thus be transported horizontally, or even vertically upside down, the tank 4 being positioned below the three sleeves 11, 12, 13, without the liquid L escaping from the tank 4.

This embodiment thus allows improved operation of the probe 1, since the routing / escape of the gas G in the probe 1 as well as the manipulations of the probe 1 are made without the liquid L can leave the tank 4. thus avoids losses of liquid L and therefore frequent refilling of the tank 4.

A valve 40, 41 particularly adapted to the pressuremeter according to the invention is illustrated in FIG. figure 4 . The valve 40, 41 comprises a valve body 42. The valve body 42 is tubular and comprises two threaded zones 43, 44 separated by an abutment 45. The valve body 42 is extended by a tubular element 46 of diameter less than the diameter. valve body 42 and comprising a gas outlet port covered with a resilient cylindrical envelope 47 made of rubber.

Referring to the figure 3 , the valve 40 is screwed using the threaded zone 44 in a threaded zone of the support element 48, the tubular element 46 being positioned outside the support element 48, so as to allow the admission of the gas G to the tank 4. Conversely, the valve 41 is screwed using the threaded zone 43, so as to prevent the admission of the gas into the tank 4 via the channel 332 and to allow the escape of the gas G from the tank 4 to the conduit 33.

During the admission of the gas G, the gas G enters the channel 331 and then into the inlet valve 40, successively in the valve body 42 and in the tubular element 46. The end of the valve body 42 being closed, the gas G then arrives at the outlet orifice and presses and deform the cylindrical elastic envelope 47. When the deformation of the elastic cylindrical envelope 47 is sufficient, the gas G reaches the tank 4. Conversely, during the exhaust, the gas pressure is eliminated in the pipe 31, and the gas G can be escape from the tank 4 via the exhaust valve 41 and the tube 332.

Thus, if the probe 1 is positioned upside down during transport, with the tank 4 below the sleeves 11, 12, 13, the liquid L will be in contact with the valves 40, 41. The elastic cylindrical envelope 47 of the inlet valve 40 is pressed against the valve body 42, thus preventing the liquid L from entering the pipe 33. On the exhaust valve 41 side, the water enters the valve body 42 and arrives bearing on the inner face of the elastic envelope 47 of the exhaust valve 41. The mass of the liquid L pressing on the envelope 47 is not sufficient to deform the membrane 47, and the liquid can not penetrate either. the conduit 33. Thus, the liquid L can not leave the tank 4.

The invention as described therefore also includes all the steps of implementation of the pressuremeter as just described.

Claims (13)

1. Probe for pressure meter (1), comprising a central inflatable sleeve (11), two inflatable sleeves (12, 13) adjacent to the central sleeve (11) and situated on either side of the latter, a liquid supply duct (32) connected to the central sleeve (11), a gas supply duct (33) connected to the adjacent sleeves (12, 13), characterised in that the probe (1) further comprises a reservoir (4) intended to contain additional volumes (Vg, Vl) of gas (G) and of liquid (L), the liquid volume (Vl) of the reservoir (4) being in communication with the central sleeve (11) via the liquid supply duct (32), the gas volume (Vg) of the reservoir (4) being connected to the gas supply duct (33).
2. Probe (1) set forth in claim 1, characterised in that the reservoir (4) comprises a volume sensor (6) able to provide a signal (Sv) linked to the volume (Vl) of the liquid (L) in the reservoir (4).
3. Probe (1) set forth in claim 2, characterised in that the volume sensor (6) comprises a liquid level detector (61).
4. Probe (1) set forth in claim 3, characterised in that the liquid level detector (61) comprises at least one resistive element (610) intended to be immersed, at least partially, in the liquid volume (Vl) of the reservoir (4), the resistive element (610) being arranged substantially in parallel to the axis of the reservoir (4).
5. Probe according to one of claims 1 to 4, characterised in that the reservoir (4), in operational configuration of the probe (l), is arranged above the three inflatable sleeves (11, 12, 13).
6. Probe (1) according to one of claims 1 to 5, characterised in that the reservoir (4) is cylindrical.
7. Probe (1) according to one of claims 1 to 6, characterised in that the gas supply duct (33) is connected, in the reservoir (4), on the one hand to a first valve (40) allowing for the intake of the gas (G) in the reservoir (4), and on the other hand to a second valve, (41) allowing for the exhaust of the gas (G) outside of the reservoir (4).
8. Probe (1) set forth in claim 7, characterised in that the valves (40, 41) include a valve body (42) provided with two threaded zones (43, 44) separated by a thrust bearing (45), the valve body (42) being extended by a tubular element (46) that is thinner than the valve body (42) and comprising a gas outlet orifice covered with an elastic cylindrical envelope (47).
9. Pressure meter, characterised in that it comprises:

   - a probe (1) according to one of claims 1 to 8,

   - a piece of surface equipment (2) comprising a pressurised gas source (21), a duct (31) connecting the gas source (21) to the reservoir (4) of the probe (1), a pressure sensor (5) able to provide a signal (Sp) linked to the pressure in the reservoir (4) of the probe (1), and

   - means for connecting (30-33) the probe (1) to the piece of surface equipment (2).
10. Pressure meter set forth in claim 9, characterised in that the piece of surface equipment (2) further comprises flow control means (220-222) comprising a nozzle (221) and a valve (222), said flow control means (220-222) being interposed on the duct (31) connecting the gas source (21) to the reservoir (4) of the probe (1), as well as pressure control means (7, 8) connected to the flow control means (220-222), and wherein is memorised a plurality of setpoint pressures (Kpi) of increasing values according to a programme (PROG) of successive applications over time of these setpoints.
11. Pressure meter set forth in claim 10, characterised in that the pressure control means (7, 8) are furthermore connected to the pressure sensor (5) and are designed to open the valve (222) during a predefined period of time when the difference between the pressure signal (Sp) and the setpoint pressure (Kpi) exceeds a predetermined value.
12. Pressure meter set forth in claim 10 or 11, characterised in that the pressure control means (7, 8) include a control unit (7) able to actuate the valve (222) and which is connected to a computer (8) wherein are memorised the pressure setpoints (Kpi) and the programme (PROG) of successive applications over time of these setpoints (Kpi).
13. Pressure meter according to one of claims 10 to 12, characterised in that the flow control means (220-222) include a solenoid valve (220) supporting the nozzle (221) as well as the valve (222).

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