EP1977049B1 - Automated-precision pressure meter - Google Patents

Abstract

The pressure meter has a reservoir (4) carried by a down hole tool (1) e.g. probe, and a pressurized gas whose flow is controlled by a nozzle (221) and a valve (222). A pressure control unit includes a computer (8) and a control unit (7) for selectively opening the valve for application of new pressure set points (Kpi) conforming to an application program (PROG) during time intervals (Tpi) corresponding to the set points.

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. The document FR 2,512,860 discloses a pressuremeter 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 conformity 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 means flow control apparatus comprises a nozzle and a valve, in that the surface equipment further comprises pressure control means in which a plurality of increasing pressure setpoints are stored, 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 in that these pressure control means are designed to selectively open the valve, for the application of each new pressure set according to 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 period of time. predefined time in response to a deficit of the pressure signal relative 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.

To further increase the precision of the pressuremeter of the invention, it is possible to provide that the volume sensor comprises a liquid level detector housed in the reservoir, and that the connection means comprise a transmission link connecting the level detector. to 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 disposed above the first inflatable sleeve, that is to say closer to the surface of the ground than the 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.

• la figure 1 est une vue schématique en coupe verticale d'un pressiomètre conforme à l'invention et en cours d'utilisation; et
• la figure 2 est une vue schématique en coupe verticale d'un détail fonctionnel de ce pressiomètre.

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; and
• the figure 2 is a schematic view in vertical section of a functional detail of this pressuremeter.

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, for example made in a metal cylinder substantially indeformable at the pressures considered, 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 volume sensor 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 tank 4 is 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 bore F.

The surface equipment 2 further comprises pressure control means, and 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 can also 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, with respect to this reference 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 for 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, to compensate for the deficit of pressure 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.

On the other hand, 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.

To further increase the accuracy of the pressuremeter of the invention, it is possible to provide that the volume sensor 6 comprises a liquid level detector 61 housed in the tank 4.

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 in particular it is 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 5 can in turn be arranged 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 invention as described therefore also includes all the steps of implementation of the pressuremeter as just described.

Claims (11)

1. Pressure meter intended to allow for the evaluation of a geotechnical property of the subsoil, this pressure meter comprising, as subunits, a bottom tool (1) intended to be introduced into a drill hole (F), a piece of surface equipment (2), and means (30-33) of connecting at least able to connect the tool to the equipment, these subunits themselves comprising at least one first inflatable sleeve (11) supported by the bottom tool (1), a substantially non-deformable reservoir (4) containing additional volumes (Vg, Vl) of gas (G) and of liquid (L), a pressurised-gas source (21), a first duct (31) connecting the gas source (21) to the gas volume (Vg) of the reservoir (4), a second duct (32) connecting the liquid volume (Vl) of the reservoir (4) to the first inflatable sleeve (11), flow control means (220-222) interposed on the first duct (31), and comprising a nozzle (221) and a valve (222), a pressure sensor (5) able to provide a signal (Sp) linked to the pressure of the liquid in the reservoir (4), and a volume sensor (6) able to provide a signal (Sv) linked to the liquid volume (Vl) in the reservoir (4), characterised in that the reservoir (4) is supported by the bottom tool (1), in that the piece of surface equipment (2) further comprises pressure control means (7, 8) wherein are memorised a plurality of pressure setpoints (Kpi) of increasing values, a programme (PROG) for the successive application over time of these setpoints (Kpi), and a correspondence law (CORR) connecting at least these setpoints (Kpi) to corresponding respective time period (Tpi), and in that these pressure control means (7, 8) are designed to selectively open the valve (222), in order to apply each new pressure setpoint (Kpi) in accordance with the programme (PROG), during the time period (Tpi) corresponding to this setpoint.
2. Pressure meter according to claim 1, characterised in that the pressure control means (7, 8) are connected to the pressure sensor (5) and in that they are furthermore designed to open the valve (222) during a redefined time period (T0) in response to a deficit in the pressure signal (Sp) in relation to a setpoint pressure (Kpi), when this deficit appears during a level at this setpoint pressure (Kpi) and when it exceeds a predetermined threshold.
3. Pressure meter according to claim 1 or 2, characterised in that the pressure control means (7, 8) comprises a control unit (7) actuating the valve (222) and a computer (8) wherein are memorised the setpoint pressures (Kpi), the programme (PROG), and the correspondence law (CORR), this computer (8) being connected to the control unit (7) and controlling it.
4. Pressure meter as claimed in any of the preceding claims, characterised in that the flow control means (220-222) comprise a solenoid valve (220) supporting the nozzle (221) as well as the valve (222).
5. Pressure meter as claimed in any of the preceding claims, characterised in that the volume sensor (6) comprises a liquid level detector (61) housed in the reservoir (4), and in that the means of connecting (30-33) include a transmission link (30) connecting the level detector (61) to the piece of surface equipment (2).
6. Pressure meter as claimed in any of the preceding claims, characterised in that the reservoir (4), in operational configuration of the bottom tool (1) in a drill hole (F), is arranged above the first inflatable sleeve (11).
7. Pressure meter as claimed in any of the preceding claims combined with claim 5, characterised in that the volume signal (Sv) is of an electric nature and in that the transmission link (30) comprises an electrical line.
8. Pressure meter as claimed in any of the preceding claims, characterised in that the reservoir (4) is cylindrical.
9. Pressure meter as claimed in any of claims 6-8 combined with claim 5, characterised in that the liquid (L) has a relatively low electrical resistance, in that the level detector (61) comprises at least one resistive element (610) connected to an electrical energy generator (60) and partially immersed in the liquid (L), in that the resistive element (610) has an extended form according to the height of the reservoir (4) and a relatively high electrical resistance, and in that the liquid (L) and the resistive element (610) partially shunted by the liquid (L) form for the generator (60) a resistive charge (CR) with a resistance that depends on the level of this liquid in the reservoir (4).
10. Pressure meter according to claim 9, characterised in that the electrical energy generator (60) delivers alternating current.
11. Pressure meter as claimed in any of the preceding claims, characterised in that the bottom tool (1) further comprises second and third inflatable sleeves (12, 13), and a third duct (33) connecting the gas volume (Vg) of the reservoir (4) to the second and third sleeves (12, 13).

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